A method for improving the light intensity distribution in dental light-curing units.

PubMed

Arikawa, Hiroyuki; Takahashi, Hideo; Minesaki, Yoshito; Muraguchi, Kouichi; Matsuyama, Takashi; Kanie, Takahito; Ban, Seiji

2011-01-01

A method for improving the uniformity of the radiation light from dental light-curing units (LCUs), and the effect on the polymerization of light-activated composite resin are investigated. Quartz-tungsten halogen, plasma-arc, and light-emitting diode LCUs were used, and additional optical elements such as a mixing tube and diffusing screen were employed to reduce the inhomogeneity of the radiation light. The distribution of the light intensity from the light guide tip was measured across the guide tip, as well as the distribution of the surface hardness of the light-activated resin emitted with the LCUs. Although the additional optical elements caused 13.2-25.9% attenuation of the light intensity, the uniformity of the light intensity of the LCUs was significantly improved in the modified LCUs, and the uniformity of the surface hardness of the resin was also improved. Our results indicate that the addition of optical elements to the LCU may be a simple and effective method for reducing inhomogeneity in radiation light from the LCUs.

Mechanical and Thermal Properties of Dental Composites Cured with CAD/CAM Assisted Solid-State Laser

PubMed Central

De Santis, Roberto; Gloria, Antonio; Maietta, Saverio; Martorelli, Massimo; De Luca, Alessandro; Spagnuolo, Gianrico; Riccitiello, Francesco; Rengo, Sandro

2018-01-01

Over the last three decades, it has been frequently reported that the properties of dental restorative composites cured with argon laser are similar or superior to those achieved with conventional halogen and light emitting diode (LED) curing units. Whereas laser curing is not dependent on the distance between the curing unit and the material, such distance represents a drawback for conventional curing units. However, a widespread clinical application of this kind of laser remains difficult due to cost, heavy weight, and bulky size. Recently, with regard to the radiation in the blue region of the spectrum, powerful solid-state lasers have been commercialized. In the current research, CAD (computer-aided design)/CAM (computer-aided manufacturing) assisted solid-state lasers were employed for curing of different dental restorative composites consisting of micro- and nanoparticle-reinforced materials based on acrylic resins. Commercial LED curing units were used as a control. Temperature rise during the photopolymerisation process and bending properties were measured. By providing similar light energy dose, no significant difference in temperature rise was observed when the two light sources provided similar intensity. In addition, after 7 days since curing, bending properties of composites cured with laser and LED were similar. The results suggested that this kind of laser would be suitable for curing dental composites, and the curing process does not suffer from the tip-to-tooth distance. PMID:29584683

Odontological light-emitting diode light-curing unit beam quality.

PubMed

de Magalhães Filho, Thales Ribeiro; Weig, Karin de Mello; Werneck, Marcelo Martins; da Costa Neto, Célio Albano; da Costa, Marysilvia Ferreira

2015-05-01

The distribution of light intensity of three light-curing units (LCUs) to cure the resin-based composite for dental fillings was analyzed, and a homogeneity index [flat-top factor (FTF)] was calculated. The index is based on the M2 index, which is used for laser beams. An optical spectrum analyzer was used with an optical fiber to produce an x-y power profile of each LCU light guide. The FTF-calculated values were 0.51 for LCU1 and 0.55 for LCU2, which was the best FTF, although it still differed greatly from the perfect FTF = 1, and 0.27 for LCU3, which was the poorest value and even lower than the Gaussian FTF = 0.5. All LCUs presented notably heterogeneous light distribution, which can lead professionals and researchers to produce samples with irregular polymerization and poor mechanical properties.

Odontological light-emitting diode light-curing unit beam quality

NASA Astrophysics Data System (ADS)

de Magalhães Filho, Thales Ribeiro; Weig, Karin de Mello; Werneck, Marcelo Martins; da Costa Neto, Célio Albano; da Costa, Marysilvia Ferreira

2015-05-01

The distribution of light intensity of three light-curing units (LCUs) to cure the resin-based composite for dental fillings was analyzed, and a homogeneity index [flat-top factor (FTF)] was calculated. The index is based on the M2 index, which is used for laser beams. An optical spectrum analyzer was used with an optical fiber to produce an x-y power profile of each LCU light guide. The FTF-calculated values were 0.51 for LCU1 and 0.55 for LCU2, which was the best FTF, although it still differed greatly from the perfect FTF=1, and 0.27 for LCU3, which was the poorest value and even lower than the Gaussian FTF=0.5. All LCUs presented notably heterogeneous light distribution, which can lead professionals and researchers to produce samples with irregular polymerization and poor mechanical properties.

Halogen and LED light curing of composite: temperature increase and Knoop hardness.

PubMed

Schneider, L F; Consani, S; Correr-Sobrinho, L; Correr, A B; Sinhoreti, M A

2006-03-01

This study assessed the Knoop hardness and temperature increase provided by three light curing units when using (1) the manufacturers' recommended times of photo-activation and (2) standardizing total energy density. One halogen--XL2500 (3M/ESPE)--and two light-emitting diode (LED) curing units--Freelight (3M/ESPE) and Ultrablue IS (DMC)--were used. A type-K thermocouple registered the temperature change produced by the composite photo-activation in a mold. Twenty-four hours after the photo-activation procedures, the composite specimens were submitted to a hardness test. Both temperature increase and hardness data were submitted to ANOVA and Tukey's test (5% significance). Using the first set of photo-activation conditions, the halogen unit produced a statistically higher temperature increase than did both LED units, and the Freelight LED resulted in a lower hardness than did the other curing units. When applying the second set of photo-activation conditions, the two LED units produced statistically greater temperature increase than did the halogen unit, whereas there were no statistical differences in hardness among the curing units.

Evaluation of light intensity output of QTH and LED curing devices in various governmental health institutions.

PubMed

Al Shaafi, Mm; Maawadh, Am; Al Qahtani, Mq

2011-01-01

The purpose of this study was to evaluate the light intensity output of quartz-tungsten-halogen (QTH) and light emitting diode (LED) curing devices located at governmental health institutions in Riyadh, Saudi Arabia.Eight governmental institutions were involved in the study. The total number of evaluated curing devices was 210 (120 were QTH and 90 were LED). The reading of the light intensity output for each curing unit was achieved using a digital spectrometer; (Model USB4000 Spectrometer, Ocean Optics Inc, Dunedin, FL, USA). The reading procedure was performed by a single investigator; any recording of light intensity below 300 mW/cm2 was considered unsatisfactory.The result found that the recorded mean values of light intensity output for QTH and LED devices were 260 mW/cm2 and 598 mW/cm2, respectively. The percentage of QTH devices and LED devices considered unsatisfactory was 67.5% and 15.6%, respectively. Overall, the regular assessment of light curing devices using light meters is recommended to assure adequate output for clinical use.

Effects of blue diode laser (445 nm) and LED (430-480 nm) radiant heat treatments on dental glass ionomer restoratives

NASA Astrophysics Data System (ADS)

Dionysopoulos, Dimitrios; Tolidis, Kosmas; Strakas, Dimitrios; Gerasimou, Paris; Sfeikos, Thrasyvoulos; Gutknecht, Norbert

2018-02-01

The purpose of this in vitro study was to evaluate the effect of two radiant heat treatments on water sorption, solubility and surface roughness of three conventional glass ionomer cements by using a blue diode laser (445 nm) and a light emitting diode (LED) unit (430-480 nm). Thirty disk-shaped specimens were prepared for each tested GIC (Equia Fil, Ketac Universal Aplicap and Riva Self Cure). The experimental groups (n = 10) of the study were as follows: Group 1 was the control group, in Group 2 the specimens were irradiated for 60 s at the top surface using a LED light-curing unit and in Group 3 the specimens were irradiated for 60 s at the top surface using a blue light diode laser. Statistical analysis was performed using one-way ANOVA and Tukey post hoc tests at a level of significance of a = 0.05. Radiant heat treatments with both laser and LED devices significantly decreased water sorption and solubility (p < 0.05) of most of the tested GICs. Blue diode laser treatment was seemed to be more effective compared to LED treatment for some of the tested materials. There were no changes in surface roughness of the GICs after the treatments (p > 0.05). Among the tested materials there were differences in water sorption and solubility (p < 0.05) but not in surface roughness (p > 0.05). The use of the blue diode laser for this radiant heat treatment was harmless for the surface of the tested GICs and may be advantageous for the longevity of their restorations.

Evaluation of Vickers hardness and depth of cure of six composite resins photo-activated with different polymerization modes.

PubMed

Poggio, C; Lombardini, M; Gaviati, S; Chiesa, M

2012-07-01

The current in vitro study evaluated Vickers hardness (VK) and depth of cure (hardness ratio) of six resin composites, polymerized with a light-emitting diode (LED) curing unit by different polymerization modes: Standard 20 s, Standard 40 s, Soft-start 40 s. SIX RESIN COMPOSITES WERE SELECTED FOR THE PRESENT STUDY: three microhybrid (Esthet.X HD, Amaris, Filtek Silorane), two nanohybrid (Grandio, Ceram.X mono) and one nanofilled (Filtek Supreme XT). The VK of the surface was determined with a microhardness tester using a Vickers diamond indenter and a 200 g load applied for 15 seconds. The mean VK and hardness ratio of the specimens were calculated using the formula: hardness ratio = VK of bottom surface / VK of top surface. For all the materials tested and with all the polymerization modes, hardness ratio was higher than the minimum value indicated in literature in order to consider the bottom surface as adequately cured (0.80). Curing time did not affect hardness ratio values for Filtek Silorane, Grandio and Filtek Supreme XT. The effectiveness of cure at the top and bottom surface was not affected by Soft-start polymerization mode.

Clinical effect of reducing curing times with high-intensity LED lights

PubMed Central

Ward, Justin D.; Wolf, Bethany J.; Leite, Luis P.; Zhou, Jing

2016-01-01

Objective To evaluate the clinical performance of brackets cured with a high-intensity, light-emitting diode (LED) with a shorter curing time. Materials and Methods Thirty-four patients and a total of 680 brackets were examined using a randomized split-mouth design. The maxillary right and mandibular left quadrants were cured for 6 seconds with a high-intensity LED light (3200 mW/cm2) and the maxillary left and mandibular right quadrants were cured for 20 seconds with a standard-intensity LED light (1200 mW/cm2). Alternating patients had the quadrants inverted for the curing protocol. The number and date of each first-time bracket failure was recorded from 199 to 585 days posttreatment. Results The bracket failure rate was 1.18% for both curing methods. The proportion of bracket failure was not significantly different between curing methods (P = 1.000), genders (P = 1.000), jaws (P = .725), sides (P = .725), or quadrants (P = .547). Posterior teeth exhibited a greater proportion of failures (2.21%) relative to anterior teeth (0.49%), although the difference was not statistically significant (P = .065). Conclusions No difference was found in bond failure rates between the two curing methods. Both methods showed bond failure rates low enough to be considered clinically sufficient. The high-intensity LED light used with a shorter curing time may be considered an advantage due to the reduced chair time. PMID:25760887

Comparison of hardness of three temporary filling materials cured by two light-curing devices.

PubMed

Bodrumlu, E; Koçak, M M; Hazar Bodrumlu, E; Ozcan, S; Koçak, S

2014-01-01

Polymerization ability of light-curing devices can affect the light-cured material hardness. The purpose of the present study was to evaluate and compare the hardness of three temporary filling materials that had been light-cured by either a light emitting diode (LED) or a halogen light-curing unit. The temporary filling materials, First Fill, Voco Clip and Bioplic, were placed in wells in a Teflon plate. The 24 specimens of each material were divided into two groups (N.=12/group) for photo-activation by either of the two light-curing units. The LED or halogen device was applied for 40s to the top surface of each specimen. A Knoop hardness test was performed on the top and bottom surface of each specimen, with five measurements per specimen. The highest hardness values for both the LED and halogen treated groups were observed for First Fill and the lowest values were for Voco Clip in top and bottom surfaces. The hardness obtained for the three materials with the halogen unit were significantly higher than the values obtained with the LED unit in both surfaces (P<0.05). First Fill light-cured temporary material exhibited the highest hardness values on the top and bottom surfaces than Voco Clip and Bioplic temporary materials. The hardness of light-cured temporary filling materials can be affected by the type of light-curing unit.

Combinational light emitting diode-high frequency focused ultrasound treatment for HeLa cell.

PubMed

Choe, Se-Woon; Park, Kitae; Park, Chulwoo; Ryu, Jaemyung; Choi, Hojong

2017-12-01

Light sources such as laser and light emitting diode or ultrasound devices have been widely used for cancer therapy and regenerative medicines, since they are more cost-effective and less harmful than radiation therapy, chemotherapy or magnetic treatment. Compared to laser and low intensity ultrasound techniques, light emitting diode and high frequency focused ultrasound shows enhanced therapeutic effects, especially for small tumors. We propose combinational light emitting diode-high frequency focused ultrasound treatment for human cervical cancer HeLa cells. Individual red, green, and blue light emitting diode light only, high frequency focused ultrasound only, or light emitting diode light combined with high frequency focused ultrasound treatments were applied in order to characterize the responses of HeLa cells. Cell density exposed by blue light emitting diode light combined with high frequency focused ultrasound (2.19 ± 0.58%) was much lower than that of cells exposed by red and green light emitting diode lights (81.71 ± 9.92% and 61.81 ± 4.09%), blue light emitting diode light (11.19 ± 2.51%) or high frequency focused ultrasound only (9.72 ± 1.04%). We believe that the proposed combinational blue light emitting diode-high frequency focused ultrasound treatment could have therapeutic benefits to alleviate cancer cell proliferation.

Residual HEMA and TEGDMA Release and Cytotoxicity Evaluation of Resin-Modified Glass Ionomer Cement and Compomers Cured with Different Light Sources

PubMed Central

Botsali, Murat Selim; Kuşgöz, Adem; Altintaş, Subutay Han; Ülker, Hayriye Esra; Kiliç, Serdar; Başak, Feridun; Ülker, Mustafa

2014-01-01

The purpose of this study was first to evaluate the elution of 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) monomers from resin-modified glass ionomer cement (RMGIC) and compomers cured with halogen and light-emitting diode (LED) light-curing units (LCUs). The effect of cured materials on the viability of L929 fibroblast cells was also evaluated. One RMGIC (Ketac N100) and two compomers (Dyract Extra and Twinkystar) were tested. Materials were prepared in teflon disks and light-cured with LED or halogen LCUs. The residual monomers of resin materials in solution were identified using high-performance liquid chromatography. The fibroblast cells' viability was analyzed using MTT assay. The type of LCU did not have a significant effect on the elution of HEMA and TEGDMA. A greater amount of HEMA than TEGMDA was eluted. The amount of TEGDMA eluted from Twinkystar was greater than Dyract Extra (P < 0.05) when cured with a halogen LCU. All material-LCU combinations decreased the fibroblast cells' viability more than the control group (P < 0.01), except for Dyract Extra cured with a halogen LCU (P > 0.05). Curing with the LED LCU decreased the cells' viability more than curing with the halogen LCU for compomers. For Ketac N100, the halogen LCU decreased the cells' viability more than the LED LCU. PMID:24592149

Comparison of the heat generation of light curing units.

PubMed

Bagis, Bora; Bagis, Yildirim; Ertas, Ertan; Ustaomer, Seda

2008-02-01

The aim of this study was to evaluate the heat generation of three different types of light curing units. Temperature increases were recorded from a distance of 1 mm from a thermocouple to the tip of three different types of light curing units including one quartz-tungsten halogen (QTH), one plasma arc (PAC), and one light emitting diode (LED) unit. An experimental model was designed to fix the 1 mm distance between the tip of the light curing units and the thermocouple wire. Temperature changes were recorded in 10 second intervals up to 40 seconds. (10, 20, 30, and 40 seconds). Temperature measurements were repeated three times for every light curing unit after a one hour standby period. Statistical analysis of the results was performed using the analysis of variance (ANOVA) and the Bonferroni Test. The highest temperature rises (54.4+/-1.65 degrees C) occurred during activation of a PAC light curing unit for every test period (p<.05). The least temperature increase (11.8+/-1.3 degrees C) occurred with a LED curing unit for each tested period except for the measurement of the temperature rise using the QTH curing unit at the tenth second interval (p<.05). These results indicate the choice of light activation unit and curing time is important when polymerizing light activated resin based restorations to avoid any thermal damage to the pulp.

A comparative evaluation of effect of modern-curing lights and curing modes on conventional and novel-resin monomers

PubMed Central

Roy, Konda Karthik; Kumar, Kanumuru Pavan; John, Gijo; Sooraparaju, Sujatha Gopal; Nujella, Surya Kumari; Sowmya, Kyatham

2018-01-01

Aim: The aim of this study is to compare and to evaluate effect of curing light and curing modes on the nanohybrid composite resins with conventional Bis-GMA and novel tricyclodecane (TCD) monomers. Methodology: Two nanohybrid composites, IPS empress direct and charisma diamond were used in this study. Light-emitting diode (LED)-curing unit and quartz-tungsten-halogen (QTH)-curing unit which were operated into two different modes: continuous and soft start. Based on the composite resin, curing lights, and mode of curing used, the samples were divided into 8 groups. After polymerization, the samples were stored for 48 h in complete darkness at 37°C and 100% humidity. The Vickers hardness (VK) of the surface was determined with Vickers indenter by the application of 200 g for 15 s. Three VK readings were recorded for each sample surface both on top and bottom surfaces. For all the specimens, the three hardness values for each surface were averaged and reported as a single value. The mean VK and hardness ratio were calculated. The depth of cure was assessed based on the hardness ratio. Results: Comparison of mean hardness values and hardness ratios was done using ANOVA with post hoc Tukey's test. Conclusion: Both QTH- and LED-curing units had shown the adequate depth of cure. Soft-start-curing mode in both QTH- and LED-curing lights had effectively increased microhardness than the continuous mode of curing. TCD monomer had shown higher hardness values compared with conventional Bis-GMA-containing resin. PMID:29628651

Efficient and bright organic light-emitting diodes on single-layer graphene electrodes

NASA Astrophysics Data System (ADS)

Li, Ning; Oida, Satoshi; Tulevski, George S.; Han, Shu-Jen; Hannon, James B.; Sadana, Devendra K.; Chen, Tze-Chiang

2013-08-01

Organic light-emitting diodes are emerging as leading technologies for both high quality display and lighting. However, the transparent conductive electrode used in the current organic light-emitting diode technologies increases the overall cost and has limited bendability for future flexible applications. Here we use single-layer graphene as an alternative flexible transparent conductor, yielding white organic light-emitting diodes with brightness and efficiency sufficient for general lighting. The performance improvement is attributed to the device structure, which allows direct hole injection from the single-layer graphene anode into the light-emitting layers, reducing carrier trapping induced efficiency roll-off. By employing a light out-coupling structure, phosphorescent green organic light-emitting diodes exhibit external quantum efficiency >60%, while phosphorescent white organic light-emitting diodes exhibit external quantum efficiency >45% at 10,000 cd m-2 with colour rendering index of 85. The power efficiency of white organic light-emitting diodes reaches 80 lm W-1 at 3,000 cd m-2, comparable to the most efficient lighting technologies.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement.

PubMed

Komori, Paula Carolina de Paiva; de Paula, Andréia Bolzan; Martin, Airton Abrāo; Tango, Rubens Nisie; Sinhoreti, Mario Alexandre Coelho; Correr-Sobrinho, Lourenço

2010-01-01

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm x 5 mm) and covered with a Mylar strip. The tip of the light-curing unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37 degrees C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (alpha = 0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the light-curing unit and by its light energy density.

Effects of various light curing methods on the leachability of uncured substances and hardness of a composite resin.

PubMed

Moon, H-J; Lee, Y-K; Lim, B-S; Kim, C-W

2004-03-01

The purpose of this study was to evaluate the effect of the various light curing units (plasma arc, halogen and light-emitting diodes) and irradiation methods (one-step, two-step and pulse) using different light energy densities on the leachability of unreacted monomers (Bis-GMA and UDMA) and the surface hardness of a composite resin (Z250, 3M). Leachability of the specimens immersed for 7 days in ethanol was analysed by HPLC. Vicker's hardness number (VHN) was measured immediately after curing (IC) and after immersion in ethanol for 7 days. Various irradiation methods with three curing units resulted in differences in the amount of leached monomers and VHN of IC when light energy density was lower than 17.0 J cm(-2) (P = 0.05). However, regardless of curing units and irradiation methods, these results were not different when the time or light energy density increased. When similar light energy density was irradiated (15.6-17.7 J cm(-2)), the efficiency of irradiation methods was different by the following order: one-step > or = two-step > pulse. These results suggest that the amount of leached monomers and VHN were influenced by forming polymer structure in activation and initiation stages of polymerization process with different light source energies and curing times.

The effects of light curing units and environmental temperatures on C 000000000000 000000000000 000000000000 111111111111 000000000000 111111111111 000000000000 000000000000 000000000000 C conversion of commercial and experimental bonding agents.

PubMed

Jafarzadeh-Kashi, Tahereh Sadat; Erfan, Mohmmad; Kalbasi, Salmeh; Ghadiri, Malihe; Rakhshan, Vahid

2014-10-01

Polymerization of bonding agents (BA) is a critical factor in determining the success of bonded restorations. We aimed to assess the effects of two light curing units and two temperatures on the extent of polymerization (EP) of a commercial BA and an experimental BA. Forty BA specimens were randomly divided into 8 subgroups of n = 5 to compare the polymerization of two BAs (experimental/Scotchbond) based on the variables: temperature (23/37 °C) and light-curing unit (quartz-tungsten-halogen/light-emitting diode). The EP (%) was measured using differential scanning calorimetry, and analyzed using the t-test, two- and three-way analyses of variance (ANOVA), and the Bonferroni test (α = 0.05). There were significant differences between the EP results between the two BAs (P = 0.012) and due to the different temperatures (P = 0.001), but not between the different light-curing units (P = 0.548). The interaction between BA and temperature was significant (P < 0.001). The other interactions were nonsignificant. The two light-curing units had similar effects on the EP. The EP values were better when curing was performed at human body temperature.

Super-Lattice Light Emitting Diodes (SLEDS) on GaAs

DTIC Science & Technology

2016-03-31

Super-Lattice Light Emitting Diodes (SLEDS) on GaAs Kassem Nabha1, Russel Ricker2, Rodney McGee1, Nick Waite1, John Prineas2, Sydney Provence2...infrared light emitting diodes (LEDs). Typically, the LED arrays are mated with CMOS read-in integrated circuit (RIIC) chips using flip-chip bonding. In...circuit (RIIC) chips using flip-chip bonding. This established technology is called Hybrid-super-lattice light emitting diodes (Hybrid- SLEDS). In

Means for phase locking the outputs of a surface emitting laser diode array

NASA Technical Reports Server (NTRS)

Lesh, James R. (Inventor)

1987-01-01

An array of diode lasers, either a two-dimensional array of surface emitting lasers, or a linear array of stripe lasers, is phase locked by a diode laser through a hologram which focuses the output of the diode laser into a set of distinct, spatially separated beams, each one focused onto the back facet of a separate diode laser of the array. The outputs of the diode lasers thus form an emitted coherent beam out of the front of the array.

Lifetime Improvement of Organic Light Emitting Diodes using LiF Thin Film and UV Glue Encapsulation

NASA Astrophysics Data System (ADS)

Huang, Jian-Ji; Su, Yan-Kuin; Chang, Ming-Hua; Hsieh, Tsung-Eong; Huang, Bohr-Ran; Wang, Shun-Hsi; Chen, Wen-Ray; Tsai, Yu-Sheng; Hsieh, Huai-En; Liu, Mark O.; Juang, Fuh-Shyang

2008-07-01

This work demonstrates the use of lithium fluoride (LiF) as a passivation layer and a newly developed UV glue for encapsulation on the LiF passivation layer to enhance the stability of organic light-emitting devices (OLEDs). Devices with double protective layers showed a 25-fold increase in operational lifetime compared to those without any packaging layers. LiF has a low melting point and insulating characteristics and it can be adapted as both a protective layer and pre-encapsulation film. The newly developed UV glue has a fast curing time of only 6 s and can be directly spin-coated onto the surface of the LiF passivation layer. The LiF thin film plus spin-coated UV glue is a simple packaging method that reduces the fabrication costs of OLEDs.

Effect of the insertion and polymerization technique in composite resin restorations: analysis of marginal gap by atomic force microscopy.

PubMed

da Silva, Marcos Aurélio Bomfim; de Oliveira, Guilherme José Pimentel Lopes; Tonholo, Josealdo; Júnior, José Ginaldo da Silva; Santos, Lucineide de Melo; Dos Reis, José Ivo Limeira

2010-12-01

This in vitro study evaluated the marginal gap at the composite tooth/resin interface in class V cavities under the influence of two insertion techniques and a curing system by means of atomic force microscopy (AFM). Forty enamel and dentin cavities were prepared on the buccal surface in bovine teeth with quadratic forms measuring 2 mm × 2 mm and depth of 1.5 mm. The teeth were then divided into four groups: group A, 10 cavities were restored in one increment, light cured by halogen light; group B, 10 cavities filled with bulk filling, light cured by the light emitting diodes (LED); group C, 10 cavities were restored by the incremental technique, light cured by halogen light; group D, 10 cavities were restored by the incremental technique, light cured by the LED. The teeth underwent the polishing procedure and were analyzed by AFM for tooth/restoration interface evaluation. The data were compared between groups using the nonparametric Kruskall-Wallis and Mann-Whitney tests (p < 0.05). The results showed a statistically significant difference between groups A and B and groups A and C. It was concluded that no insertion and polymerization technique was able to completely seal the cavity.

Characterization of curing behavior of UV-curable LSR for LED embedded injection mold

NASA Astrophysics Data System (ADS)

Tae, Joon-Sung; Yim, Kyung-Gyu; Rhee, Byung-Ohk; Kwak, Jae B.

2016-11-01

For many applications, liquid silicone rubber (LSR) injection molding is widely used for their great design flexibility and high productivity. In particular, a sealing part for a mobile device such as smartphone and watch has been produced by injection molding. While thermally curable LSR causes deformation problem due to a high mold temperature, UV-curable LSR can be molded at room temperature, which has advantages for over-molding with inserts of temperature-sensitive materials. Ultraviolet light-emitting diodes (UV LEDs) have advantages such as a longer service life, a lower heat dissipation, and smaller size to equip into the mold than conventional halogen or mercury UV lamps. In this work, rheological behavior of UV-curable LSR during curing process was analyzed by UV LEDs available in the market. UV-LEDs of various wave lengths and intensities were tested. The steady shear test was applied to find the starting time of curing and the SAOS was applied to find the ending time of curing to estimate processing time. In addition, the hardness change with irradiation energy was compared with the rheological data to confirm the reliability of the rheological test.

Design Considerations for a Water Treatment System Utilizing Ultra-Violet Light Emitting Diodes

DTIC Science & Technology

2014-03-27

DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING DIODES...the United States. ii AFIT-ENV-14-M-58 DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING DIODES...DISTRIBUTION UNLIMITED. iii AFIT-ENV-14-M-58 DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING

Bactericidal effects of a high-power, red light-emitting diode on two periodontopathic bacteria in antimicrobial photodynamic therapy in vitro.

PubMed

Umeda, Makoto; Tsuno, Akiko; Okagami, Yoshihide; Tsuchiya, Fumito; Izumi, Yuichi; Ishikawa, Isao

2011-11-01

  Light-emitting diodes have been investigated as new light activators for photodynamic therapy. We investigated the bactericidal effects of high-power, red light-emitting diodes on two periodontopathic bacteria in vitro.   A light-emitting diode (intensity: 1100 mW/cm(2) , peak wavelength: 650 nm) was used to irradiate a bacterial solution for either 10 or 20 s. Bacterial solutions (Porphyromonas gingivalis or Aggregatibacter actinomycetemcomitans) at a concentration of 2.5 × 10(6) c.f.u./mL were mixed with an equal volume of either methylene blue or toluidine blue O (0-20 μg/mL) and added to titer plate wells. The plate wells were irradiated with red light-emitting diode light from a distance of 22 or 40 mm. The contents were diluted, and 50 μL was smeared onto blood agar plates. After 1 week of culturing, bacterial c.f.u. were counted.   The light-emitting diode energy density was estimated to be approximately 4 and 8 J/cm(2) after 10 and 20 s of irradiation, respectively. Red light-emitting diode irradiation for 10 s from a distance of 22 mm, combined with methylene blue at concentrations >10 μg/mL, completely killed Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans.   High-power, red light-emitting diode irradiation with a low concentration of dye showed effective bactericidal effects against two periodontopathic bacteria. © 2011 Blackwell Publishing Asia Pty Ltd.

Effect of Thickness on Light Transmission and Vickers Hardness of Five Bulk-fill Resin-based Composites Using Polywave and Single-peak Light-emitting Diode Curing Lights.

PubMed

Maghaireh, G A; Price, R B; Abdo, N; Taha, N A; Alzraikat, H

2018-06-28

This study compared light transmission through different thicknesses of bulk-fill resin-based composites (RBCs) using a polywave and a single-peak light-emitting diode light-curing unit (LCU). The effect on the surface hardness was also evaluated. Five bulk-fill RBCs were tested. Specimens (n=5) of 1-, 2-, 4-, or 6-mm thickness were photopolymerized for 10 seconds from the top using a polywave (Bluephase Style) or single-peak (Elipar S10) LCU, while a spectrophotometer monitored in real time the transmitted irradiance and radiant exposure reaching the bottom of the specimen. After 24 hours of storage in distilled water at 37°C, the Vickers microhardness (VH) was measured at top and bottom. Results were analyzed using multiple-way analysis of variance, Tukey post hoc tests, and multivariate analysis (α=0.05). The choice of LCU had no significant effect on the total amount of light transmitted through the five bulk-fill RBCs at each thickness. There was a significant decrease in the amount of light transmitted as the thickness increased for all RBCs tested with both LCUs ( p<0.001). Effect of LCU on VH was minimal (η p 2 =0.010). The 1-, 2-, and 4-mm-thick specimens of SDR, X-tra Fill, and Filtek Bulk Restorative achieved a VH bottom/top ratio of approximately 80% when either LCU was used. The total amount of light transmitted through the five bulk-fill RBCs was similar at the different thicknesses using either LCU. The polywave LCU used in this study did not enhance the polymerization of the tested bulk-fill RBCs when compared with the single-peak LCU.

Compact 2100 nm laser diode module for next-generation DIRCM

NASA Astrophysics Data System (ADS)

Dvinelis, Edgaras; Greibus, Mindaugas; TrinkÅ«nas, Augustinas; NaujokaitÄ--, Greta; Vizbaras, Augustinas; Vizbaras, Dominykas; Vizbaras, Kristijonas

2017-10-01

Compact high-power 2100 nm laser diode module for next-generation directional infrared countermeasure (DIRCM) systems is presented. Next-generation DIRCM systems require compact, light-weight and robust laser modules which could provide intense IR light emission capable of disrupting the tracking sensor of heat-seeking missile. Currently used solid-state and fiber laser solutions for mid-IR band are bulky and heavy making them difficult to implement in smaller form-factor DIRCM systems. Recent development of GaSb laser diode technology greatly improved optical output powers and efficiencies of laser diodes working in 1900 - 2450 nm band [1] while also maintaining very attractive size, weight, power consumption and cost characteristics. 2100 nm laser diode module presented in this work performance is based on high-efficiency broad emitting area GaSb laser diode technology. Each laser diode emitter is able to provide 1 W of CW output optical power with working point efficiency up to 20% at temperature of 20 °C. For output beam collimation custom designed fast-axis collimator and slow-axis collimator lenses were used. These lenses were actively aligned and attached using UV epoxy curing. Total 2 emitters stacked vertically were used in 2100 nm laser diode module. Final optical output power of the module goes up to 2 W at temperature of 20 °C. Total dimensions of the laser diode module are 35 x 25 x 16 mm (L x W x H) with a weight of 28 grams. Finally output beam is bore-sighted to mechanical axes of the module housing allowing for easy integration into next-generation DIRCM systems.

Evaluation of microleakage of class II dental composite resin restorations cured with LED or QTH dental curing light; Blind, Cluster Randomized, In vitro cross sectional study

PubMed Central

2014-01-01

Background The aim of this study is to compare the microleakage of Class II dental composite resin restorations which have been cured by three different LED (light emitting diode) light curing modes compared to control samples cured by QTH (quartz tungsten halogen) light curing units (LCUs), to determine the most effective light curing unit and mode of curing. Results In this experimental study, class II cavities were prepared on 100 sound human premolars which have been extracted for orthodontic treatment. The teeth were randomly divided into four groups; three experimental and one control group of 25 teeth each. Experimental groups were cured by either conventional, pulse-delay, or ramped curing modes of LED. The control group was cured for 20 seconds by QTH. The restorations were thermocycled (1000 times, between 5 and 55°C, for 5 seconds dwell time), dyed, sectioned mesio-distally and viewed under stereo-microscope (40×) magnification. Teeth were then scored on a 0 to 4 scale based on the amount of microleakage. The data were analyzed by Chi-square test. No significant difference was demonstrated between the different LCUs (light curing units), or modes of curing, at the enamel side (p > 0.05). At the dentin side, all modes of LED curing could significantly reduce microleakage (p < 0.05). The results suggest that slow start curing improves marginal integrity and seal. High intense curing endangers those aims. Conclusions Comparison between the three LED mode cured composite resin restorations and QTH curing showed LED curing in all modes is more effective than QTH for reducing microleakage. Both LED and QTH almost completely eliminate the microleakage on the enamel side, however none of them absolutely eliminated microleakage on the dentin side. PMID:24990296

77 FR 75446 - Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-20

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-784] Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant the Joint Motion To Terminate the... sale within the United States after importation of certain light-emitting diodes and products...

Spin-polarized light-emitting diodes based on organic bipolar spin valves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vardeny, Zeev Valentine; Nguyen, Tho Duc; Ehrenfreund, Eitan Avraham

Spin-polarized organic light-emitting diodes are provided. Such spin-polarized organic light-emitting diodes incorporate ferromagnetic electrodes and show considerable spin-valve magneto-electroluminescence and magneto-conductivity responses, with voltage and temperature dependencies that originate from the bipolar spin-polarized space charge limited current.

Effect of Shade and Light Curing Mode on the Degree of Conversion of Silorane-Based and Methacrylate-Based Resin Composites.

PubMed

Sm, Mousavinasab; M, Atai; N, Salehi; A, Salehi

2016-12-01

The degree of conversion depends on the material composition, light source properties, distance from light source, light intensity, curing time, and other factors such as shade and translucency. In the present study, we evaluated the effects of different light-curing modes and shades of methacrylate and silorane-based resin composites on the degree of conversion of resin composites (DC). The methacrylate-based (Filtek Z250, 3M, ESPE) and low-shrinkage silorane-based (Filtek P90, 3M, ESPE) resin composites were used in three groups as follows: group 1-Filtek Z250 (shade A3), group 2-Filtek Z250 (shade B2), and group 3-Filtek P90 (shade A3). We used a light-emitting diode (LED) curing unit for photopolymerization. 10 samples were prepared in each group to evaluate the degree of conversion; 5 samples were cured using soft-start curing mode, and the other 5 were cured using standard curing mode. The DC of the resin composites was measured using Fourier Transform Infrared Spectroscopy (FTIR). The data were analyzed using Kruskal Wallis and one-way ANOVA statistical tests. The degree of conversion of silorane-based resin composite was 70 - 75.8% and that of methacrylate-based resin composites was 60.2 - 68.2% (p = 0.009). The degree of conversion of the composite with brighter colour (B2) was statistically more than the darker composite (A3). Higher degree of conversion was achieved applying the standard curing mode. The results of the study showed that the colour and type of the resin composite and also the curing mode influence the degree of conversion of resin composites.

Evaluation of shear bond strength of orthodontic brackets using trans-illumination technique with different curing profiles of LED light-curing unit in posterior teeth.

PubMed

Heravi, Farzin; Moazzami, Saied Mostafa; Ghaffari, Negin; Jalayer, Javad; Bozorgnia, Yasaman

2013-11-21

Although using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. Limited access and poor direct sight may be a problem in the posterior teeth. Meanwhile, effectiveness of the trans-illumination technique is questionable due to increased bucco-lingual thickness of the posterior teeth. Light-emitting diode (LED) light-curing units cause less temperature rise and lower risk to the pulpal tissue. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit. Sixty premolars were randomly divided into six groups. Bonding of brackets was done with 40- and 80-s light curing from the buccal or lingual aspect with different intensities. Shear bond strengths of brackets were measured using a universal testing machine. Data were analyzed by one-way analysis of variance test and Duncan's post hoc test. The highest shear bond belonged to group 2 (high intensity, 40 s, buccal) and the lowest belonged to group 3 (low intensity, 40 s, lingual). Bond strength means in control groups were significantly higher than those in experimental groups. In all experimental groups except group 6 (80 s, high intensity, lingual), shear bond strength was below the clinically accepted values. In clinical limitations where light curing from the same side of the bracket is not possible, doubling the curing time and increasing the light intensity during trans-illumination are recommended for achieving acceptable bond strengths.

InGaN/GaN dot-in-nanowire monolithic LEDs and lasers on (001) silicon

NASA Astrophysics Data System (ADS)

Bhattacharya, P.; Hazari, A.; Jahangir, S.

2017-02-01

GaN-based nanowire arrays have been grown on (001)Si substrate by plasma-assisted molecular beam epitaxy and their structural and optical properties have been determined. InxGa1-xN disks inserted in the nanowires behave as quantum dots with emission ranging from visible to near-infrared. We have exploited these nanowire heterostructure arrays to realize light-emitting diodes and diode lasers in which the quantum dots form the active light emitting media. The fabrication and characteristics of 630nm light-emitting diodes and 1.3μm edge-emitting diode lasers are described.

Effect of Dental Chair Light on Enamel Bonding of Orthodontic Brackets Using Light Cure Based Adhesive System: An In-Vitro Study

PubMed Central

Tiwari, Anil; Shyagali, Tarulatha; Kohli, Sarvraj; Joshi, Rishi; Gupta, Abhishek; Tiwari, Rana

2016-01-01

Aim: The aim of this in vitro study was to evaluate the influence of the Dental chair light on the bond strength of light cured composite resin. Materials and Methods: Sixty therapeutically extracted human premolar teeth were randomly allocated to two groups of 30 specimens each. In both groups light cured composite resin (Transbond XT) and MBT premolar metal brackets (3M Unitek) was used to bond brackets. In group I and II light curing was done using Light-emitting diode light curing units without and with the dental chair light respectively. After bonding, all samples were stored in distilled water at room temperature for 24 hours and subsequently tested for shear bond strength and Adhesive Remnant Index (ARI) scores. Data was subjected to Mann Whitney U statistical test. Results: Results indicated that there was significantly higher shear bond strength (7.71 ± 1.90) for the Group II (composite cured with LED and dental chair light) compared with Group I (composite cured with LED LCU only) (5.74 ± 1.13).the obtained difference was statistically significant. There was no statistical significant difference between ARI scores in between the groups. Conclusions: light cure bonding with dental chair light switched on will produce greater bond strength than the conventional bonding. However, the ARI score were similar to both the groups. It is advised that the inexperienced orthodontist should always switch off the dental chair light while bonding for enough working time during the bracket placement. PMID:28077886

Photobiomodulation partially rescues visual cortical neurons from cyanide-induced apoptosis.

PubMed

Liang, H L; Whelan, H T; Eells, J T; Meng, H; Buchmann, E; Lerch-Gaggl, A; Wong-Riley, M

2006-05-12

Near-infrared light via light-emitting diode treatment has documented therapeutic effects on neurons functionally inactivated by tetrodotoxin or methanol intoxication. Light-emitting diode pretreatment also reduced potassium cyanide-induced cell death, but the mode of death via the apoptotic or necrotic pathway was unclear. The current study tested our hypothesis that light-emitting diode rescues neurons from apoptotic cell death. Primary neuronal cultures from postnatal rat visual cortex were pretreated with light-emitting diode for 10 min at a total energy density of 30 J/cm2 before exposing to potassium cyanide for 28 h. With 100 or 300 microM potassium cyanide, neurons died mainly via the apoptotic pathway, as confirmed by electron microscopy, Hoechst 33258, single-stranded DNA, Bax, and active caspase-3. In the presence of caspase inhibitor I, the percentage of apoptotic cells in 300microM potassium cyanide was significantly decreased. Light-emitting diode pretreatment reduced apoptosis from 36% to 17.9% (100 microM potassium cyanide) and from 58.9% to 39.6% (300 microM potassium cyanide), representing a 50.3% and 32.8% reduction, respectively. Light-emitting diode pretreatment significantly decreased the expression of caspase-3 elicited by potassium cyanide. It also reversed the potassium cyanide-induced increased expression of Bax and decreased expression of Bcl-2 to control levels. Moreover, light-emitting diode decreased the intensity of 5-(and -6) chloromethy-2', 7-dichlorodihydrofluorescein diacetate acetyl ester, a marker of reactive oxygen species, in neurons exposed to 300 microM potassium cyanide. These results indicate that light-emitting diode pretreatment partially protects neurons against cyanide-induced caspase-mediated apoptosis, most likely by decreasing reactive oxygen species production, down-regulating pro-apoptotic proteins and activating anti-apoptotic proteins, as well as increasing energy metabolism in neurons as reported previously.

New yellow Ba 0.93Eu 0.07Al 2O 4 phosphor for warm-white light-emitting diodes through single-emitting-center conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xufan; Budai, John D.; Liu, Feng

2013-01-01

Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature <4000 K) with good color rendition (i.e., color rendering index >80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba 0.93Eu 0.07Al 2O 4 phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80more » were readily achieved when combining the Ba 0.93Eu 0.07Al 2O 4 phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index >80) can be achieved based on single-phosphor, single-emitting-center conversion.« less

Nanoparticle embedded p-type electrodes for GaN-based flip-chip light emitting diodes.

PubMed

Kwak, Joon Seop; Song, J O; Seong, T Y; Kim, B I; Cho, J; Sone, C; Park, Y

2006-11-01

We have investigated high-quality ohmic contacts for flip-chip light emitting diodes using Zn-Ni nanoparticles/Ag schemes. The Zn-Ni nanoparticles/Ag contacts produce specific contact resistances of 10(-5)-10(-6) omegacm2 when annealed at temperatures of 330-530 degrees C for 1 min in air ambient, which are much better than those obtained from the Ag contacts. It is shown that blue InGaN/GaN multi-quantum well light emitting diodes fabricated with the annealed Zn-Ni nanoparticles/Ag contacts give much lower forward-bias voltages at 20 mA compared with those of the multi-quantum well light emitting diodes made with the as-deposited Ag contacts. It is further presented that the multi-quantum well light emitting diodes made with the Zn-Ni nanoparticles/Ag contacts show similar output power compared to those fabricated with the Ag contact layers.

Investigating Bandgap Energies, Materials, and Design of Light-Emitting Diodes

ERIC Educational Resources Information Center

Wagner, Eugene P., II

2016-01-01

A student laboratory experiment to investigate the intrinsic and extrinsic bandgaps, dopant materials, and diode design in light-emitting diodes (LEDs) is presented. The LED intrinsic bandgap is determined by passing a small constant current through the diode and recording the junction voltage variation with temperature. A second visible…

High efficiency light source using solid-state emitter and down-conversion material

DOEpatents

Narendran, Nadarajah; Gu, Yimin; Freyssinier, Jean Paul

2010-10-26

A light emitting apparatus includes a source of light for emitting light; a down conversion material receiving the emitted light, and converting the emitted light into transmitted light and backward transmitted light; and an optic device configured to receive the backward transmitted light and transfer the backward transmitted light outside of the optic device. The source of light is a semiconductor light emitting diode, a laser diode (LD), or a resonant cavity light emitting diode (RCLED). The down conversion material includes one of phosphor or other material for absorbing light in one spectral region and emitting light in another spectral region. The optic device, or lens, includes light transmissive material.

Degree of conversion of two lingual retainer adhesives cured with different light sources.

PubMed

Usümez, Serdar; Büyükyilmaz, Tamer; Karaman, Ali Ihya; Gündüz, Beniz

2005-04-01

The aim of this study was to evaluate the degree of conversion (DC) of two lingual retainer adhesives, Transbond Lingual Retainer (TLR) and Light Cure Retainer (LCR), cured with a fast halogen light, a plasma arc light and a light-emitting diode (LED) at various curing times. A conventional halogen light served as the control. One hundred adhesive samples (five per group) were cured for 5, 10 or 15 seconds with an Optilux 501 (fast halogen light), for 3, 6 or 9 seconds with a Power Pac (plasma arc light), or for 10, 20 or 40 seconds with an Elipar Freelight (LED). Samples cured for 40 seconds with the conventional halogen lamp were used as the controls. Absorbance peaks were recorded using Fourier transform infrared (FT-IR) spectroscopy. DC values were calculated. Data were analysed using Kruskal-Wallis and Mann-Whitney U-tests. For the TLR, the highest DC values were achieved in 6 and 9 seconds with the plasma arc light. Curing with the fast halogen light for 15 seconds and with the LED for 40 seconds produced statistically similar DC values, but these were lower than those with the plasma arc light. All of these light exposures yielded a statistically significantly higher DC than 40 seconds of conventional halogen light curing. The highest DC value for the LCR was achieved in 15 seconds with the fast halogen light, then the plasma arc light curing for 6 seconds. These two combinations produced a statistically significantly higher DC when compared with the 40 seconds of conventional halogen light curing. The lowest DC for the LCR was achieved with 10 seconds of LED curing. The overall DC of the LCR was significantly higher than that of the TLR. The results suggest that a similar or higher DC than the control values could be achieved in 6-9 seconds by plasma arc curing, in 10-15 seconds by fast halogen curing or in 20 seconds by LED curing.

An intraocular micro light-emitting diode device for endo-illumination during pars plana vitrectomy.

PubMed

Koelbl, Philipp S; Lingenfelder, Christian; Spraul, Christoph W; Kampmeier, Juergen; Koch, Frank Hj; Kim, Yong Keun; Hessling, Martin

2018-03-01

Development of a new, fiber-free, single-use endo-illuminator for pars plana vitrectomy as a replacement for fiber-based systems with external light sources. The hand-guided intraocularly placed white micro light-emitting diode is evaluated for its illumination properties and potential photochemical and thermal hazards. A micro light-emitting diode was used to develop a single-use intraocular illumination system. The light-source-on-tip device was implemented in a prototype with 23G trocar compatible outer diameter of 0.6 mm. The experimental testing was performed on porcine eyes. All calculations of possible photochemical and thermal hazards during the application of the intraocular micro light-emitting diode were calculated according to DIN EN ISO 15007-2: 2014. The endo-illuminator generated a homogeneous and bright illumination of the intraocular space. The color impression was physiologic and natural. Contrary to initial apprehension, the possible risk caused by inserting a light-emitting diode into the intraocular vitreous was much smaller when compared to conventional fiber-based illumination systems. The photochemical and thermal hazards allowed a continuous exposure time to the retina of at least 4.7 h. This first intraocular light source showed that a light-emitting diode can be introduced into the eye. The system can be built as single-use illumination system. This light-source-on-tip light-emitting diode-endo-illumination combines a chandelier wide-angle illumination with an adjustable endo-illuminator.

Strain tunable light emitting diodes with germanium P-I-N heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lagally, Max G; Sanchez Perez, Jose Roberto

Tunable p-i-n diodes comprising Ge heterojunction structures are provided. Also provided are methods for making and using the tunable p-i-n diodes. Tunability is provided by adjusting the tensile strain in the p-i-n heterojunction structure, which enables the diodes to emit radiation over a range of wavelengths.

Effect of light-curing units, post-cured time and shade of resin cement on knoop hardness.

PubMed

Reges, Rogério Vieira; Costa, Ana Rosa; Correr, Américo Bortolazzo; Piva, Evandro; Puppin-Rontani, Regina Maria; Sinhoreti, Mário Alexandre Coelho; Correr-Sobrinho, Lourenço

2009-01-01

The aim of this study was to evaluate the Knoop hardness after 15 min and 24 h of different shades of a dual-cured resin-based cement after indirect photoactivation (ceramic restoration) with 2 light-curing units (LCUs). The resin cement Variolink II (Ivoclar Vivadent) shade XL, A2, A3 and opaque were mixed with the catalyst paste and inserted into a black Teflon mold (5 mm diameter x 1 mm high). A transparent strip was placed over the mold and a ceramic disc (Duceram Plus, shade A3) was positioned over the resin cement. Light-activation was performed through the ceramic for 40 s using quartz-tungsten-halogen (QTH) (XL 2500; 3M ESPE) or light-emitting diode (LED) (Ultrablue Is, DMC) LCUs with power density of 615 and 610 mW/cm(2), respectively. The Koop hardness was measured using a microhardness tester HMV 2 (Shimadzu) after 15 min or 24 h. Four indentations were made in each specimen. Data were subjected to ANOVA and Tukey's test (alpha=0.05). The QTH LCU provided significantly higher (p<0.05) KHN values than the LED LCU. When the post-cure times were compared for the same shade, QTH and LED at 24 h provided significantly higher (p<0.05) KHN values than at 15 min. It may be concluded that the Knoop hardness was generally dependent on the LCU and post-cure time. The opaque shade of the resin cement showed lower Knoop hardness than the other shades for both LCUs and post-cure times.

Site-controlled InGaN/GaN single-photon-emitting diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Lei; Deng, Hui, E-mail: dengh@umich.edu; Teng, Chu-Hsiang

2016-04-11

We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots. The device is fabricated from a planar light-emitting diode structure containing a single InGaN quantum well, using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

High yield and ultrafast sources of electrically triggered entangled-photon pairs based on strain-tunable quantum dots.

PubMed

Zhang, Jiaxiang; Wildmann, Johannes S; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G

2015-12-01

Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10(-2)). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications.

Aluminum-nanodisc-induced collective lattice resonances: Controlling the light extraction in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Auer-Berger, Manuel; Tretnak, Veronika; Wenzl, Franz-Peter; Krenn, Joachim R.; List-Kratochvil, Emil J. W.

2017-10-01

We examine aluminum-nanodisc-induced collective lattice resonances as a means to enhance the efficiency of organic light emitting diodes. Thus, nanodisc arrays were embedded in the hole transporting layer of a solution-processed phosphorescent organic blue-light emitting diode. Through extinction spectroscopy, we confirm the emergence of array-induced collective lattice resonances within the organic light emitting diode. Through finite-difference time domain simulations, we show that the collective lattice resonances yield an enhancement of the electric field intensity within the emissive layer. The effectiveness for improving the light generation and light outcoupling is demonstrated by electro-optical characterization, realizing a gain in a current efficiency of 35%.

Perovskite Materials for Light-Emitting Diodes and Lasers.

PubMed

Veldhuis, Sjoerd A; Boix, Pablo P; Yantara, Natalia; Li, Mingjie; Sum, Tze Chien; Mathews, Nripan; Mhaisalkar, Subodh G

2016-08-01

Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic light emitting diode with surface modification layer

DOEpatents

Basil, John D.; Bhandari, Abhinav; Buhay, Harry; Arbab, Mehran; Marietti, Gary J.

2017-09-12

An organic light emitting diode (10) includes a substrate (12) having a first surface (14) and a second surface (16), a first electrode (32), and a second electrode (38). An emissive layer (36) is located between the first electrode (32) and the second electrode (38). The organic light emitting diode (10) further includes a surface modification layer (18). The surface modification layer (18) includes a non-planar surface (30, 52).

Phototoxic action of light emitting diode in the in vitro viability of Trichophyton rubrum.

PubMed

Amorim, José Cláudio Faria; Soares, Betania Maria; Alves, Orley Araújo; Ferreira, Marcus Vinícius Lucas; Sousa, Gerdal Roberto; Silveira, Lívio de Barros; Piancastelli, André Costa Cruz; Pinotti, Marcos

2012-01-01

Trichophyton rubrum is the most common agent of superficial mycosis of the skin and nails causing long lasting infections and high recurrence rates. Current treatment drawbacks involve topical medications not being able to reach the nail bed at therapeutic concentrations, systemic antifungal drugs failing to eradicate the fungus before the nails are renewed, severe side effects and selection of resistant fungal isolates. Photodynamic therapy (PDT) has been a promising alternative to conventional treatments. This study evaluated the in vitro effectiveness of toluidine blue O (TBO) irradiated by Light emitting diode (LED) in the reduction of T. rubrum viability. The fungal inoculums' was prepared and exposed to different TBO concentrations and energy densities of Light emitting diode for evaluate the T. rubrum sensibility to PDT and production effect fungicidal after photodynamic treatment. In addition, the profiles of the area and volume of the irradiated fungal suspensions were also investigated. A small reduction, in vitro, of fungal cells was observed after exposition to 100 µM toluidine blue O irradiated by 18 J/cm² Light emitting diode. Fungicidal effect occurred after 25 µM toluidine blue O irradiation by Light emitting diode with energy density of 72 J/cm². The analysis showed that the area and volume irradiated by the Light emitting diode were 52.2 mm² and 413.70 mm³, respectively. The results allowed to conclude that Photodynamic therapy using Light emitting diode under these experimental conditions is a possible alternative approach to inhibit in vitro T. rubrum and may be a promising new treatment for dermatophytosis caused by this fungus.

Top-emitting organic light-emitting diodes.

PubMed

Hofmann, Simone; Thomschke, Michael; Lüssem, Björn; Leo, Karl

2011-11-07

We review top-emitting organic light-emitting diodes (OLEDs), which are beneficial for lighting and display applications, where non-transparent substrates are used. The optical effects of the microcavity structure as well as the loss mechanisms are discussed. Outcoupling techniques and the work on white top-emitting OLEDs are summarized. We discuss the power dissipation spectra for a monochrome and a white top-emitting OLED and give quantitative reports on the loss channels. Furthermore, the development of inverted top-emitting OLEDs is described.

Optogenetic Stimulation of Peripheral Vagus Nerves using Flexible OLED Display Technology to Treat Chronic Inflammatory Disease and Mental Health Disorders

DTIC Science & Technology

2016-03-31

transcutaneously via the outer ear using a high-resolution, addressable array of organic light emitting diodes (OLEDs) manufactured on a flexible...therapeutic optical stimulation in optogenetically modified neural tissue. Keywords: Optogenetics; neuromodulation; organic light emitting diode ...the outer ear using a high-resolution, two-dimensional (2-D), addressable array of red organic light - emitting diodes (OLEDs) manufactured on a thin

Direct Bandgap Group IV Materials

DTIC Science & Technology

2016-01-21

devices. In this project, we have accomplished (a) direct bandgap group IV materials of GeSn, (b) GeSn-based planar light - emitting diode operated at near...devices of planar light emitting diode , detector and laser ” 6/12/2015 PI and Co-PI information: - Name of Principal Investigators: Prof. H. H. Cheng...IV materials of GeSn, (b) GeSn-based planar light - emitting diode operated at near infrared with direct emission, and (c) the first planar

Combatant Eye Protection: An Introduction to the Blue Light Hazard

DTIC Science & Technology

2015-12-01

visible solar radiation (i.e., blue light ), as well as from light - emitting diode (LED)-generated radiant energy remains a questionable factor under...Garcia, M., Picaud, S., Attia D. 2011. Light - emitting diodes (LED) for domestic lighting : Any risks for the eye?. Progress in retinal and eye research...C., Sliney, D. H., Rollag, M., D., Hanifin, J. P., and Brainard, G. C. 2011. Blue light from light - emitting diodes elicits a dose-dependent

Phosphor suspended in silicone, molded/formed and used in a remote phosphor configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolodin, Boris; Deshpande, Anirudha R

A light emitting package comprising a support hosting at least one light emitting diode. A light transmissive dome comprised of a silicone including a phosphor material positioned to receive light emitted by the diode. A glass cap overlies said dome.

Effect of light dispersion of LED curing lights on resin composite polymerization.

PubMed

Vandewalle, Kraig S; Roberts, Howard W; Andrus, Jeffrey L; Dunn, William J

2005-01-01

This study evaluated the effect of light dispersion of halogen and LED curing lights on resin composite polymerization. One halogen (Optilux 501, SDS/Kerr, Orange, CA, USA) and five light-emitting diode (LED) curing lights (SmartLite iQ, Dentsply Caulk, Milford, DE, USA; LEDemetron 1, SDS/Kerr; FLASHlite 1001, Discus Dental, Culver City, CA, USA; UltraLume LED 5, Ultradent Products, South Jordan, UT, USA; Allegro, Den-Mat, Santa Maria, CA, USA) were used in this study. Specimens (8 mm diameter by 2 mm thick) were made in polytetrafluoroethylene molds using hybrid (Z100, 3M ESPE, St. Paul, MN, USA) and microfill (A110, 3M ESPE) composite resins. The top surface was polymerized for 5 seconds with the curing light guide tip positioned at a distance of 1 and 5 mm. Degree of conversion (DC) of the composite specimens was analyzed on the bottom surface using micro-Fourier Transform Infrared (FTIR) spectroscopy (Perkin-Elmer FTIR Spectrometer, Wellesley, PA, USA) 10 minutes after light activation. DC at the bottom of the 2 mm specimen was expressed as a percentage of the mean maximum DC. Five specimens were created per curing light and composite type (n=5). Percent mean DC ratios and SDs were calculated for each light under each testing condition. Data were analyzed by analysis of variance (ANOVA)/Tukey's test (alpha = .05). A beam analyzer (LBA-700, Spiricon, Logan, UT, USA) was used to record the emitted light from the curing lights at 0 and 5 mm distances (n=5). A Top Hat factor was used to compare the quality of the emitted beam profile (LBA/PC, Spiricon). The divergence angle from vertical was also determined in the x- and y-axes (LBA/PC). Mean values and SDs were calculated for each light under each testing condition (0 and 5 mm, x- and y-axes) and analyzed by a two-way ANOVA/Tukey's test (alpha = .05). For DC ratios, significant differences were found based on curing light and curing distance (p < .05). At 1 mm, Optilux 501 and FLASHlite 1001 produced significantly higher DC ratios with the hybrid resin composite. No differences were found among lights with the microfill at 1 mm. At 5 mm, SmartLite iQ, FLASHlite 1001, LEDemetron 1, and UltraLume LED 5 produced significantly higher DC ratios with the hybrid resin composite, whereas LEDemetron 1 and SmartLite iQ produced significantly higher DC ratios with the microfill resin composite. The UltraLume LED 5, Allegro, and Optilux 501 had significant reductions in mean DC ratios at curing distances of 1 and 5 mm with both resin composite types. For dispersion of light, significant differences were found in Top Hat factor and divergence angle (p < .001). SmartLite iQ had overall the highest Top Hat factor and lowest divergence angle of tested lights. A linear regression analysis relating pooled DC with pooled Top Hat factors and divergence angles found a very good correlation (r2 = .86) between dispersion of light over distance and the ability to polymerize resin composite. The latest generation of LED curing lights provides DC ratios similar to or better than the halogen curing light at a curing distance of 5 mm. Dispersion of light plays a significant role in the DC of resin composite. To maximize curing effectiveness, light guides should be maintained in close proximity to the surface of the light-activated restorative material.

Demonstrating the Light-Emitting Diode.

ERIC Educational Resources Information Center

Johnson, David A.

1995-01-01

Describes a simple inexpensive circuit which can be used to quickly demonstrate the basic function and versatility of the solid state diode. Can be used to demonstrate the light-emitting diode (LED) as a light emitter, temperature sensor, light detector with both a linear and logarithmic response, and charge storage device. (JRH)

Study of phase-locked diode laser array and DFB/DBR surface emitting laser diode

NASA Astrophysics Data System (ADS)

Hsin, Wei

New types of phased-array and surface-emitting lasers are designed. The importance and approaches (or structures) of different phased array and surface emitting laser diodes are reviewed. The following are described: (1) a large optical cavity channel substrate planar laser array with layer thickness chirping; (2) a vertical cavity surface emitter with distributed feedback (DFB) optical cavity and a transverse junction buried heterostructure; (3) a microcavity distributed Bragg reflector (DBR) surface emitter; and (4) two surface emitting laser structures which utilized lateral current injection schemes to overcome the problems occurring in the vertical injection scheme.

Light curing through glass ceramics: effect of curing mode on micromechanical properties of dual-curing resin cements.

PubMed

Flury, Simon; Lussi, Adrian; Hickel, Reinhard; Ilie, Nicoleta

2014-04-01

The aim of this study was to investigate micromechanical properties of five dual-curing resin cements after different curing modes including light curing through glass ceramic materials. Vickers hardness (VH) and indentation modulus (Y HU) of Panavia F2.0, RelyX Unicem 2 Automix, SpeedCEM, BisCem, and BeautiCem SA were measured after 1 week of storage (37 °C, 100 % humidity). The resin cements were tested following self-curing or light curing with the second-generation light-emitting diode (LED) curing unit Elipar FreeLight 2 in Standard Mode (1,545 mW/cm(2)) or with the third-generation LED curing unit VALO in High Power Mode (1,869 mW/cm(2)) or in XtraPower Mode (3,505 mW/cm(2)). Light curing was performed directly or through glass ceramic discs of 1.5 or 3 mm thickness of IPS Empress CAD or IPS e.max CAD. VH and Y HU were analysed with Kruskal-Wallis tests followed by pairwise Wilcoxon rank sum tests (α = 0.05). RelyX Unicem 2 Automix resulted in the highest VH and Y HU followed by BeautiCem SA, BisCem, SpeedCEM, and finally Panavia F2.0. Self-curing of RelyX Unicem 2 Automix and SpeedCEM lowered VH and Y HU compared to light curing whereas self-curing of Panavia F2.0, BisCem, and BeautiCem SA led to similar or significantly higher VH and Y HU compared to light curing. Generally, direct light curing resulted in similar or lower VH and Y HU compared to light curing through 1.5-mm-thick ceramic discs. Light curing through 3-mm-thick discs of IPS e.max CAD generally reduced VH and Y HU for all resin cements except SpeedCEM, which was the least affected by light curing through ceramic discs. The resin cements responded heterogeneously to changes in curing mode. The applied irradiances and light curing times adequately cured the resin cements even through 1.5-mm-thick ceramic discs. When light curing resin cements through thick glass ceramic restorations, clinicians should consider to prolong the light curing times even with LED curing units providing high irradiances.

Organic light emitting diode with light extracting electrode

DOEpatents

Bhandari, Abhinav; Buhay, Harry

2017-04-18

An organic light emitting diode (10) includes a substrate (20), a first electrode (12), an emissive active stack (14), and a second electrode (18). At least one of the first and second electrodes (12, 18) is a light extracting electrode (26) having a metallic layer (28). The metallic layer (28) includes light scattering features (29) on and/or in the metallic layer (28). The light extracting features (29) increase light extraction from the organic light emitting diode (10).

Synthesis and luminescent properties of Tb3Al5O12:Ce3+ phosphors for warm white light emitting diodes

NASA Astrophysics Data System (ADS)

Meng, Qinghuan; Liu, Ying; Fu, Yujie; Zu, Yuangang; Zhou, Zhenbao

2018-01-01

A series of Tb3Al5O12:Ce3+ phosphors were successfully synthesized by a precipitation method. The pure Tb3Al5O12 phase was obtained in the synthesized Tb3Al5O12:Ce3+ phosphors after heat treatments at 500 °C in air for 3 h. The excitation spectra of Tb3Al5O12:Ce3+ phosphors include excitation bands corresponding to Tb3+ and Ce3+ ions. Under the excitation at 455 nm, Tb3Al5O12:Ce3+ phosphors show emission band at around 553 nm. The critical doping concentration of Ce3+ in Tb3Al5O12 is 6mol%, which shows the highest emission intensity. White light-emitting diodes were fabricated by combining InGaN-based blue light-emitting diodes with Tb3Al5O12:Ce3+ and Y3Al5O12:Ce3+ phosphors. The Tb3Al5O12:Ce3+ based white light-emitting diode shows a lower color temperature than that of Y3Al5O12:Ce3+ based white light-emitting diode. The experimental results clearly indicate that the prepared Tb3Al5O12:Ce3+ has potential applications in white light emitting diodes.

Efficiency and droop improvement in a blue InGaN-based light emitting diode with a p-InGaN layer inserted in the GaN barriers

NASA Astrophysics Data System (ADS)

Wang, Xing-Fu; Tong, Jin-Hui; Zhao, Bi-Jun; Chen, Xin; Ren, Zhi-Wei; Li, Dan-Wei; Zhuo, Xiang-Jing; Zhang, Jun; Yi, Han-Xiang; Li, Shu-Ti

2013-09-01

The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells.

Organic electrophosphorescence device having interfacial layers

DOEpatents

Choulis, Stelios A.; Mathai, Mathew; Choong, Vi-En; So, Franky

2010-08-10

Techniques are described for forming an organic light emitting diode device with improved device efficiency. Materials having at least one energy level that is similar to those of a phosphorescent light emitting material in the diode are incorporated into the device to directly inject holes or electrons to the light emitting material.

Long Persistent Light Emitting Diode Indicators

ERIC Educational Resources Information Center

Jia, Dongdong; Ma, Yiwei; Hunter, D. N.

2007-01-01

An undergraduate laboratory was designed for undergraduate students to make long persistent light emitting diode (LED) indicators using phosphors. Blue LEDs, which emit at 465 nm, were characterized and used as an excitation source. Long persistent phosphors, SrAl[subscript 2]O[subscript 4]:Eu[superscript 2+],Dy[superscript 3+] (green) and…

Temperature rise during polymerization of different cavity liners and composite resins

PubMed Central

Karatas, Ozcan; Turel, Verda; Bayindir, Yusuf Ziya

2015-01-01

Objective: The purpose of this study was to evaluate the thermal insulating properties of different light curing cavity liners and composite resins during light emitting diode (LED) curing. Materials and Methods: Sixty-four dentin discs, 1 mm thick and 8 mm in diameter, were prepared. Specimens were divided into four groups. Calcium hydroxide (Ca[OH]2), resin-modified glass ionomer cement, flowable composite and adhesive systems were applied to dentin discs according to the manufacturers’ instructions. The rise in temperature during polymerization with a LED curing unit (LCU) was measured using a K-type thermocouple connected to a data logger. Subsequently, all specimens were randomly divided into one of two groups. A silorane-based composite resin and a methacrylate-based composite resin were applied to the specimens. Temperature rise during polymerization of composite resins with LCU were then measured again. Data were analyzed using one-way ANOVA and post hoc Tukey analyses. Results: There were significant differences in temperature rise among the liners, adhesives, and composite resins (P < 0.05). Silorane-based composite resin exhibited significantly greater temperature rises than methacrylate-based resin (P < 0.05). The smallest temperature rises were observed in Ca(OH)2 specimens. Conclusion: Thermal insulating properties of different restorative materials are important factors in pulp health. Bonding agents alone are not sufficient to protect pulp from thermal stimuli throughout curing. PMID:26751112

Influence of light curing and sample thickness on microhardness of a composite resin

PubMed Central

Aguiar, Flávio HB; Andrade, Kelly RM; Leite Lima, Débora AN; Ambrosano, Gláucia MB; Lovadino, José R

2009-01-01

The aim of this in vitro study was to evaluate the influence of light-curing units and different sample thicknesses on the microhardness of a composite resin. Composite resin specimens were randomly prepared and assigned to nine experimental groups (n = 5): considering three light-curing units (conventional quartz tungsten halogen [QTH]: 550 mW/cm2 – 20 s; high irradiance QTH: 1160 mW/cm2 – 10 s; and light-emitting diode [LED]: 360 mW/cm2 – 40 s) and three sample thicknesses (0.5 mm, 1 mm, and 2 mm). All samples were polymerized with the light tip 8 mm away from the specimen. Knoop microhardness was then measured on the top and bottom surfaces of each sample. The top surfaces, with some exceptions, were almost similar; however, in relation to the bottom surfaces, statistical differences were found between curing units and thicknesses. In all experimental groups, the 0.5-mm-thick increments showed microhardness values statistically higher than those observed for 1- and -2-mm increments. The conventional and LED units showed higher hardness mean values and were statistically different from the high irradiance unit. In all experimental groups, microhardness mean values obtained for the top surface were higher than those observed for the bottom surface. In conclusion, higher levels of irradiance or thinner increments would help improve hybrid composite resin polymerization. PMID:23674901

Influence of curing mode with a LED unit on polymerization contraction kinetics and degree of conversion of dental resin-based materials.

PubMed

Mortier, Eric; Simon, Yorick; Dahoun, Abdelsellam; Gerdolle, David

2009-01-01

The purpose of this study was to evaluate the influence of photopolymerization mode with a light emitting diode (LED) lamp on the curing contraction kinetics and degree of conversion of 3 resin-based restorative materials. The curing contraction kinetics of Admira (ADM), Filtek P60 (P60), and Filtek Flow (FLO) were measured by the glass slide method. The materials were exposed to light from a 1,000 mW/cm-(2) power LED lamp (Elipar Freelight 2) in 3 modes: 2 continuous modes of 20 and 40 seconds (C20 and C40), and 1 exponential mode (E20; 5 seconds of exponential power increase followed by 15 seconds of maximum intensity). The degree of conversion (DC) was measured for each of the materials, and each of the modes by Fourier transformed infra-red spectrometry. P60 had the significantly lowest final contraction and FLO the highest among all light exposure modes. The C20 and C40 modes did not produce any difference in contraction or degree of conversion. The E20 mode led to a significant slowing of contraction speed combined with greater final contraction. Use of a LED lamp (1,000 mW/cm2) in continuous mode reduces the exposure time by half for identical curing shrinkage and degree of conversion.

Innovative Facet Passivation for High-Brightness Laser Diodes

DTIC Science & Technology

2016-02-05

and anti-reflection (AR) coatings are deposited after cleaving. Edge- emitting laser diodes emit very high optical powers from small emission areas, as...SECURITY CLASSIFICATION OF: The objective of this effort is to increase the power of low fill-factor (20%) laser diode (LD) bars from the present...2012 16-Nov-2015 Approved for Public Release; Distribution Unlimited Final Report: Innovative Facet Passivation for High-Brightness Laser Diodes The

Photoluminescence of Copper-Doped Lithium Niobate Crystals

NASA Astrophysics Data System (ADS)

Gorelik, V. S.; Pyatyshev, A. Yu.; Sidorov, N. V.

2018-05-01

The photoluminescence (PL) of copper-doped lithium niobate single crystals is studied using different UV-Vis light-emitting diodes and a pulse-periodic laser with a wavelength of 266 nm as excitation radiation sources. With the resonance excitation from a 527-nm light-emitting diode, the intensity of PL increases sharply (by two orders of magnitude). When using a 467-nm light-emitting diode for excitation, the PL spectrum is characterized by the presence of multiphonon lines in the range of 520-620 nm.

Light curing through glass ceramics with a second- and a third-generation LED curing unit: effect of curing mode on the degree of conversion of dual-curing resin cements.

PubMed

Flury, Simon; Lussi, Adrian; Hickel, Reinhard; Ilie, Nicoleta

2013-12-01

The aim of this study was to measure the degree of conversion (DC) of five dual-curing resin cements after different curing modes with a second- and a third-generation light-emitting diode (LED) curing unit. Additionally, irradiance of both light curing units was measured at increasing distances and through discs of two glass ceramics for computer-aided design/manufacturing (CAD/CAM). Irradiance and spectra of the Elipar FreeLight 2 (Standard Mode (SM)) and of the VALO light curing unit (High Power Mode (HPM) and Xtra Power Mode (XPM)) were measured with a MARC radiometer. Irradiance was measured at increasing distances (control) and through discs (1.5 to 6 mm thickness) of IPS Empress CAD and IPS e.max CAD. DC of Panavia F2.0, RelyX Unicem 2 Automix, SpeedCEM, BisCem, and BeautiCem SA was measured with an attenuated total reflectance-Fourier transform infrared spectrometer when self-cured (negative control) or light cured in SM for 40 s, HPM for 32 s, or XPM for 18 s. Light curing was performed directly (positive control) or through discs of either 1.5- or 3-mm thickness of IPS Empress CAD or IPS e.max CAD. DC was analysed with Kruskal-Wallis tests followed by pairwise Wilcoxon rank sum tests (α = 0.05). Maximum irradiances were 1,545 mW/cm(2) (SM), 2,179 mW/cm(2) (HPM), and 4,156 mW/cm(2) (XPM), and all irradiances decreased by >80 % through discs of 1.5 mm, ≥95 % through 3 mm, and up to >99 % through 6 mm. Generally, self-curing resulted in the lowest DC. For some cements, direct light curing did not result in higher DC compared to when light cured through ceramic discs. For other cements, light curing through ceramic discs of 3 mm generally reduced DC. Light curing was favourable for dual-curing cements. Some cements were more susceptible to variations in curing mode than others. When light curing a given cement, the higher irradiances of the third-generation LED curing unit resulted in similar DC compared to the second-generation one, though at shorter light curing times.

Enhanced Optical and Electrical Properties of Polymer-Assisted All-Inorganic Perovskites for Light-Emitting Diodes.

PubMed

Ling, Yichuan; Tian, Yu; Wang, Xi; Wang, Jamie C; Knox, Javon M; Perez-Orive, Fernando; Du, Yijun; Tan, Lei; Hanson, Kenneth; Ma, Biwu; Gao, Hanwei

2016-10-01

Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr 3 ) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr 3 films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m -2 and 4%: a new benchmark of device performance for all-inorganic PeLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Operation of AC Adapters Visualized Using Light-Emitting Diodes

ERIC Educational Resources Information Center

Regester, Jeffrey

2016-01-01

A bridge rectifier is a diamond-shaped configuration of diodes that serves to convert alternating current(AC) into direct current (DC). In our world of AC outlets and DC electronics, they are ubiquitous. Of course, most bridge rectifiers are built with regular diodes, not the light-emitting variety, because LEDs have a number of disadvantages. For…

Reshaping Light-Emitting Diodes To Increase External Efficiency

NASA Technical Reports Server (NTRS)

Rogowski, Robert; Egalon, Claudio

1995-01-01

Light-emitting diodes (LEDs) reshaped, according to proposal, increasing amount of light emitted by decreasing fraction of light trapped via total internal reflection. Results in greater luminous output power for same electrical input power; greater external efficiency. Furthermore, light emitted by reshaped LEDs more nearly collimated (less diffuse). Concept potentially advantageous for conventional red-emitting LEDs. More advantageous for new "blue" LEDs, because luminous outputs and efficiencies of these devices very low. Another advantage, proposed conical shapes achieved relatively easily by chemical etching of semiconductor surfaces.

Heat transfer properties and thermal cure of glass-ionomer dental cements.

PubMed

Gavic, Lidia; Gorseta, Kristina; Glavina, Domagoj; Czarnecka, Beata; Nicholson, John W

2015-10-01

Under clinical conditions, conventional glass-ionomer dental cements can be cured by application of heat from dental cure lamps, which causes acceleration in the setting. In order for this to be successful, such heat must be able to spread sufficiently through the cement to enhance cure, but not transmit heat so effectively that the underlying dental pulp of the tooth is damaged. The current study was aimed at measuring heat transfer properties of modern restorative glass-ionomers to determine the extent to which they meet these twin requirements. Three commercial glass ionomer cements (Ionofil Molar, Ketac Molar and Equia™ Fill) were used in association with three different light emitting diode cure lamps designed for clinical use. In addition, for each cement, one set of specimens was allowed to cure without application of a lamp. Temperature changes were measured at three different depths (2, 3 and 4 mm) after cure times of 20, 40 and 60 s. The difference among the tested groups was evaluated by ANOVA (P < 0.05) and post hoc Newman-Keuls test. All brands of glass-ionomer showed a small inherent setting exotherm in the absence of heat irradiation, but much greater temperature increases when exposed to the cure lamp. However, temperature rises did not exceed 12.9 °C. Application of the cure lamp led to the establishment of a temperature gradient throughout each specimen. Differences were typically significant (P < 0.05) and did not reflect the nominal power of the lamps, because those lamps have variable cooling systems, and are designed to optimize light output, not heating effect. Because the thermal conductivity of glass-ionomers is low, temperature rises at 4 mm depths were much lower than at 2 mm. At no time did the temperature rise sufficiently to cause concern about potential damage to the pulp.

Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes.

PubMed

Liu, Xiao-Ke; Chen, Zhan; Zheng, Cai-Jun; Liu, Chuan-Lin; Lee, Chun-Sing; Li, Fan; Ou, Xue-Mei; Zhang, Xiao-Hong

2015-04-08

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

PubMed

Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

2014-06-11

Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

Optical Experiments Using Mini-Torches with Red, Green and Blue Light Emitting Diodes

ERIC Educational Resources Information Center

Kamata, Masahiro; Matsunaga, Ai

2007-01-01

We have developed two kinds of optical experiments: color mixture and fluorescence, using mini-torches with light emitting diodes (LEDs) that emit three primary colors. Since the tools used in the experiments are simple and inexpensive, students can easily retry and develop the experiments by themselves. As well as giving an introduction to basic…

Evaluation of light-emitting diode beacon light fixtures.

DOT National Transportation Integrated Search

2009-12-01

Rotating beacons containing filament light sources have long been used on highway maintenance trucks : to indicate the presence of the truck to other drivers. Because of advances in light-emitting diode (LED) : technologies, flashing lights containin...

76 FR 43722 - Notice of Receipt of Complaint; Solicitation of Comments Relating to the Public Interest

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-21

... Certain Light- Emitting Diodes and Products Containing Same, DN 2831; the Commission is soliciting... United States after importation of certain light-emitting diodes and products containing same. The...

76 FR 46323 - Notice of Receipt of Complaint; Solicitation of Comments Relating to the Public Interest

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-02

... Certain Light- Emitting Diodes and Products Containing Same, DN 2837; the Commission is soliciting... the United States after importation of certain light-emitting diodes and products containing same. The...

76 FR 33780 - Notice of Receipt of Complaint; Solicitation of Comments Relating to the Public Interest

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-09

... Certain Light- Emitting Diodes and Products Containing the Same, DN 2812; the Commission is soliciting... light- emitting diodes and products containing the same. The complaint names as respondents LG...

Assessment of the performance of light-emitting diode roadway lighting technology.

DOT National Transportation Integrated Search

2015-10-01

This study, championed by the Virginia Department of Transportation (VDOT) Traffic Engineering : Division, involved a thorough investigation of light-emitting diode (LED) roadway lighting technology by : testing six types of roadway luminaires (inclu...

Electroplex as a New Concept of Universal Host for Improved Efficiency and Lifetime in Red, Yellow, Green, and Blue Phosphorescent Organic Light‐Emitting Diodes

PubMed Central

Song, Wook; Cho, Yong Joo; Yu, Hyeonghwa; Aziz, Hany; Lee, Kang Mun

2017-01-01

Abstract A new concept of host, electroplex host, is developed for high efficiency and long lifetime phosphorescent organic light‐emitting diodes by mixing two host materials generating an electroplex under an electric field. A carbazole‐type host and a triazine‐type host are selected as the host materials to form the electroplex host. The electroplex host is found to induce light emission through an energy transfer process rather than charge trapping, and universally improves the lifetime of red, yellow, green, and blue phosphorescent organic light‐emitting diodes by more than four times. Furthermore, the electroplex host shows much longer lifetime than a common exciplex host. This is the first demonstration of using the electroplex as the host of high efficiency and long lifetime phosphorescent organic light‐emitting diodes. PMID:29610726

Light transmittance of zirconia as a function of thickness and microhardness of resin cements under different thicknesses of zirconia

PubMed Central

Egilmez, Ferhan; Ergun, Gulfem; Kaya, Bekir M.

2013-01-01

Objective: The objective of this study was to compare microhardness of resin cements under different thicknesses of zirconia and the light transmittance of zirconia as a function of thickness. Study design: A total of 126 disc-shaped specimens (2 mm in height and 5 mm in diameter) were prepared from dual-cured resin cements (RelyX Unicem, Panavia F and Clearfil SA cement). Photoactivation was performed by using quartz tungsten halogen and light emitting diode light curing units under different thicknesses of zirconia. Then the specimens (n=7/per group) were stored in dry conditions in total dark at 37°C for 24 h. The Vicker’s hardness test was performed on the resin cement layer with a microhardness tester. Statistical significance was determined using multifactorial analysis of variance (ANOVA) (alpha=.05). Light transmittance of different thicknesses of zirconia (0.3, 0.5 and 0.8 mm) was measured using a hand-held radiometer (Demetron, Kerr). Data were analyzed using one-way ANOVA test (alpha=.05). Results: ANOVA revealed that resin cement and light curing unit had significant effects on microhardness (p < 0.001). Additionally, greater zirconia thickness resulted in lower transmittance. There was no correlation between the amount of light transmitted and microhardness of dual-cured resin cements (r = 0.073, p = 0.295). Conclusion: Although different zirconia thicknesses might result in insufficient light transmission, dual-cured resin cements under zirconia restorations could have adequate microhardness. Key words:Zirconia, microhardness, light transmittance, resin cement. PMID:23385497

Using light emitting diodes in traffic signals : final report.

DOT National Transportation Integrated Search

1998-07-01

In 1993, the Oregon Department of Transportation (ODOT) began testing red light emitting diodes (LED's) as a replacement to the incandescent lamps in vehicular and pedestrian signals. Field performance was found to be reliable and subsequently ODOT b...

Evaluation of light-emitting diode beacon light fixtures : final report.

DOT National Transportation Integrated Search

2009-12-01

Rotating beacons containing filament light sources have long been used on highway maintenance trucks : to indicate the presence of the truck to other drivers. Because of advances in light-emitting diode (LED) : technologies, flashing lights containin...

Determining Planck's Constant Using a Light-emitting Diode.

ERIC Educational Resources Information Center

Sievers, Dennis; Wilson, Alan

1989-01-01

Describes a method for making a simple, inexpensive apparatus which can be used to determine Planck's constant. Provides illustrations of a circuit diagram using one or more light-emitting diodes and a BASIC computer program for simplifying calculations. (RT)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vashchenko, A. A.; Goriachiy, D. O., E-mail: goryachii@phystech.edu; Vitukhnovsky, A. G.

Experimental samples of organic light-emitting diodes with transport layers based on polythienothiophenes and using CdSe/CdS/ZnS semiconductor quantum dots with an internal quantum efficiency up to 85% in the emitting layer are investigated. It is shown that solubility and film-forming properties are key for using polythienothiophenes in light-emitting diodes. The most promising polythienothiophenes are identified on the basis of the results obtained.

Semi-transparent all-oxide ultraviolet light-emitting diodes based on ZnO/NiO-core/shell nanowires

NASA Astrophysics Data System (ADS)

Shi, Zhi-Feng; Xu, Ting-Ting; Wu, Di; Zhang, Yuan-Tao; Zhang, Bao-Lin; Tian, Yong-Tao; Li, Xin-Jian; Du, Guo-Tong

2016-05-01

Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores.Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07236k

LED intense headband light source for fingerprint analysis

DOEpatents

Villa-Aleman, Eliel

2005-03-08

A portable, lightweight and high-intensity light source for detecting and analyzing fingerprints during field investigation. On-site field analysis requires long hours of mobile analysis. In one embodiment, the present invention comprises a plurality of light emitting diodes; a power source; and a personal attachment means; wherein the light emitting diodes are powered by the power source, and wherein the power source and the light emitting diodes are attached to the personal attachment means to produce a personal light source for on-site analysis of latent fingerprints. The present invention is available for other applications as well.

Workshop on Compound Semiconductor Devices and Integrated Circuits held in Europe (24th) on May 29 - Jun 2, 2000 in Aegean Sea, Greece

DTIC Science & Technology

2000-06-02

Telecomunicazioni, Torino. Italy 1.30pm XIV.4 "The Reliability of AlGalnP Visible Light Emitting Diodes " D.V. MORGAN and I. Al-Ofi Cardiff University...XV.5 "Green SQW InGaN light - emitting diodes on Si( 111) by metalorganic vapor phase epitaxy" E. Feltin, S. Dalmasso, H. Lareche, B. Beaumont, P. de...effect on GaN-based high efficiency light emitting diodes of a surprisingly high density of TDs has led to considerable interest in determining their

Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.

PubMed

Sun, Liangfeng; Choi, Joshua J; Stachnik, David; Bartnik, Adam C; Hyun, Byung-Ryool; Malliaras, George G; Hanrath, Tobias; Wise, Frank W

2012-05-06

Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr(-1) m(-2)) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH(2) groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

PubMed Central

Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

2017-01-01

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date. PMID:28589960

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

2017-06-01

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m-2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

n-ZnO/p-GaN heterojunction light-emitting diodes featuring a buried polarization-induced tunneling junction

NASA Astrophysics Data System (ADS)

Li, Ling; Zhang, Yuantao; Yan, Long; Jiang, Junyan; Han, Xu; Deng, Gaoqiang; Chi, Chen; Song, Junfeng

2016-12-01

n-ZnO/p-GaN heterojunction light-emitting diodes with a p-GaN/Al0.1Ga0.9N/n+-GaN polarization-induced tunneling junction (PITJ) were fabricated by metal-organic chemical vapor deposition. An intense and sharp ultraviolet emission centered at ˜396 nm was observed under forward bias. Compared with the n-ZnO/p-GaN reference diode without PITJ, the light intensity of the proposed diode is increased by ˜1.4-folds due to the improved current spreading. More importantly, the studied diode operates continuously for eight hours with the decay of only ˜3.5% under 20 mA, suggesting a remarkable operating stability. The results demonstrate the feasibility of using PITJ as hole injection layer for high-performance ZnO-based light-emitting devices.

Development of 1300 nm GaAs-Based Microcavity Light-Emitting Diodes

DTIC Science & Technology

2001-06-01

vertical - cavity surface emitting lasers ( VCSEL ) and micro- cavity light- emitting diodes (MC-LED) for short-to-medium... epitaxial growth run [1 ]. Self-organized In(Ga)As quantum dot (QD) heterostructures grown by molecular beam epitaxy ( MBE ) are promising candidates as...successfully grown by molecular beam epitaxy on GaAs substrates without the need to rely on any in-situ calibration technique. Fabricated

Safety Evaluation of Converting Traffic Signals From Incandescent to Light-emitting Diodes : Summary Report

DOT National Transportation Integrated Search

2013-08-01

Across the Nation, many agencies have been replacing conventional incandescent light bulbs in traffic signals with light-emitting diodes (LED) (see figure 1 and figure 2). LEDs are primarily installed to reduce energy consumption and decrease mainten...

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Deng, Lingling; Zhou, Hongwei; Chen, Shufen; Shi, Hongying; Liu, Bin; Wang, Lianhui; Huang, Wei

2015-02-01

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the use of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Lingling; Zhou, Hongwei; Chen, Shufen, E-mail: iamsfchen@njupt.edu.cn

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the usemore » of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.« less

405 nm diode laser, halogen lamp and LED device comparison in dental composites cure: an "in vitro" experimental trial.

PubMed

Fornaini, C; Lagori, G; Merigo, E; Rocca, J-P; Chiusano, M; Cucinotta, A

2015-12-30

A 405 nm diode laser is indicated for composite materials polymerizing, thanks to the recent evolution in their compositions, absorbing in blue part of the spectrum. The purpose of this research was to evaluate its performance on two different kinds of composite resins. Two different composites were polymerized with a traditional halogen lamp, a LED device and a 405 nm diode laser. The depth of the cure, the volumetric shrinkage, and the degree of the conversion (DC%) of the double bond during the curing process were measured. One-way ANOVA test, Kruskal-Wallis tests, and Dunn comparison tests were used for statistic analysis. Regarding the depth of polymerization, the laser had the worst performance on one composite while on the other, no significant difference with the other devices was observed. The volumetric shrinkage showed that laser produced the lowest change in both of the composites. The DC% measure confirmed these findings. Based on the results of this preliminary study, it is not possible to recommend the 405 nm diode laser for the polymerization of dental composites.

Measurement of the water content in oil and oil products using IR light-emitting diode-photodiode optrons

NASA Astrophysics Data System (ADS)

Bogdanovich, M. V.; Kabanau, D. M.; Lebiadok, Y. V.; Shpak, P. V.; Ryabtsev, A. G.; Ryabtsev, G. I.; Shchemelev, M. A.; Andreev, I. A.; Kunitsyna, E. V.; Ivanov, E. V.; Yakovlev, Yu. P.

2017-02-01

The feasibility of using light-emitting devices, the radiation spectrum of which has maxima at wavelengths of 1.7, 1.9, and 2.2 μm for determining the water concentration in oil and oil products (gasoline, kerosene, diesel fuel) has been demonstrated. It has been found that the measurement error can be lowered if (i) the temperature of the light-emitting diode is maintained accurate to 0.5-1.0°C, (ii) by using a cell through which a permanently stirred analyte is pumped, and (iii) by selecting the repetition rate of radiation pulses from the light-emitting diodes according to the averaging time. A meter of water content in oil and oil products has been developed that is built around IR light-emitting device-photodiode optrons. This device provides water content on-line monitoring accurate to 1.5%.

Broadband mid-infrared superlattice light-emitting diodes

NASA Astrophysics Data System (ADS)

Ricker, R. J.; Provence, S. R.; Norton, D. T.; Boggess, T. F.; Prineas, J. P.

2017-05-01

InAs/GaSb type-II superlattice light-emitting diodes were fabricated to form a device that provides emission over the entire 3-5 μm mid-infrared transmission window. Variable bandgap emission regions were coupled together using tunnel junctions to emit at peak wavelengths of 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.4 μm, 4.7 μm, and 5.0 μm. Cascading the structure recycles the electrons in each emission region to emit several wavelengths simultaneously. At high current densities, the light-emitting diode spectra broadened into a continuous, broadband spectrum that covered the entire mid-infrared band. When cooled to 77 K, radiances of over 1 W/cm2 sr were achieved, demonstrating apparent temperatures above 1000 K over the 3-5 μm band. InAs/GaSb type-II superlattices are capable of emitting from 3 μm to 30 μm, and the device design can be expanded to include longer emission wavelengths.

Best practices : bus signage for persons with visual impairments : light-emitting diode (LED) signs

DOT National Transportation Integrated Search

2004-01-01

This best-practices report provides key information regarding the use of Light-Emitting Diode (LED) sign technologies to present destination and route information on transit vehicles. It will assist managers and engineers in the acquisition and use o...

Experimental effective intensity of steady and flashing light emitting diodes for aircraft anti-collision lighting.

DOT National Transportation Integrated Search

2013-08-01

Research was conducted to determine the effective intensity of flashing lights that incorporate light-emitting diodes (LEDs). LEDs require less power and have the ability to flash without the addition of moving parts. Compared with incandescent bulbs...

High-efficiency electroluminescence and amplified spontaneous emission from a thermally activated delayed fluorescent near-infrared emitter

NASA Astrophysics Data System (ADS)

Kim, Dae-Hyeon; D'Aléo, Anthony; Chen, Xian-Kai; Sandanayaka, Atula D. S.; Yao, Dandan; Zhao, Li; Komino, Takeshi; Zaborova, Elena; Canard, Gabriel; Tsuchiya, Youichi; Choi, Eunyoung; Wu, Jeong Weon; Fages, Frédéric; Brédas, Jean-Luc; Ribierre, Jean-Charles; Adachi, Chihaya

2018-02-01

Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.

Doping concentration effect on performance of single QW double-heterostructure InGaN/AlGaN light emitting diode

NASA Astrophysics Data System (ADS)

Halim, N. Syafira Abdul; Wahid, M. Halim A.; Hambali, N. Azura M. Ahmad; Rashid, Shanise; Shahimin, Mukhzeer M.

2017-11-01

Light emitting diode (LED) employed a numerous applications such as displaying information, communication, sensing, illumination and lighting. In this paper, InGaN/AlGaN based on one quantum well (1QW) light emitting diode (LED) is modeled and studied numerically by using COMSOL Multiphysics 5.1 version. We have selected In0.06Ga0.94N as the active layer with thickness 50nm sandwiched between 0.15μm thick layers of p and n-type Al0.15Ga0.85N of cladding layers. We investigated an effect of doping concentration on InGaN/AlGaN double heterostructure of light-emitting diode (LED). Thus, energy levels, carrier concentration, electron concentration and forward voltage (IV) are extracted from the simulation results. As the doping concentration is increasing, the performance of threshold voltage, Vth on one quantum well (1QW) is also increases from 2.8V to 3.1V.

Manipulating Ion Migration for Highly Stable Light-Emitting Diodes with Single-Crystalline Organometal Halide Perovskite Microplatelets.

PubMed

Chen, Mingming; Shan, Xin; Geske, Thomas; Li, Junqiang; Yu, Zhibin

2017-06-27

Ion migration has been commonly observed as a detrimental phenomenon in organometal halide perovskite semiconductors, causing the measurement hysteresis in solar cells and ultrashort operation lifetimes in light-emitting diodes. In this work, ion migration is utilized for the formation of a p-i-n junction at ambient temperature in single-crystalline organometal halide perovskites. The junction is subsequently stabilized by quenching the ionic movement at a low temperature. Such a strategy of manipulating the ion migration has led to efficient single-crystalline light-emitting diodes that emit 2.3 eV photons starting at 1.8 V and sustain a continuous operation for 54 h at ∼5000 cd m -2 without degradation of brightness. In addition, a whispering-gallery-mode cavity and exciton-exciton interaction in the perovskite microplatelets have both been observed that can be potentially useful for achieving electrically driven laser diodes based on single-crystalline organometal halide perovskite semiconductors.

High-Efficiency All-Solution-Processed Light-Emitting Diodes Based on Anisotropic Colloidal Heterostructures with Polar Polymer Injecting Layers.

PubMed

Castelli, Andrea; Meinardi, Francesco; Pasini, Mariacecilia; Galeotti, Francesco; Pinchetti, Valerio; Lorenzon, Monica; Manna, Liberato; Moreels, Iwan; Giovanella, Umberto; Brovelli, Sergio

2015-08-12

Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogers, John A.; Nuzzo, Ralph; Kim, Hoon-sik

Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

DOEpatents

Rogers, John A; Nuzzo, Ralph; Kim, Hoon-sik; Brueckner, Eric; Park, Sang Il; Kim, Rak Hwan

2014-10-21

Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Temperature changes in the pulpal chamber and the sealing performance of various methods of direct pulp capping of primary teeth.

PubMed

Yilmaz, Y; Keles, S; Mete, A

2013-06-01

To compare changes in pulpal chamber temperature during the visible-light curing of direct pulp capping compounds and various modes of diode laser irradiation without prior placement of a pulp capping compound and the resultant seals. Pulp exposure holes were made in 100 extracted human primary first molars, which were randomly assigned to ten equal groups. The holes were sealed by (a= Group 1, 2, 3, 4, 5, 6 and 7) different pulp capping compounds which were cured using various types of visible-light curing units or (b=Group 8, 9 and 10) diode laser irradiation without prior application of a pulp capping compound. Pulpal chamber temperatures were recorded during the procedure, and the resultant seals were examined under a scanning electron microscope. Visible-light curing of the pulp capping compounds and diode laser irradiation at a 0.7 W output power can cause non-injurious temperature rises in the pulpal chamber. At higher output powers of the diode laser, the temperature rises are sufficient to cause thermal injury. The seals were complete when pulp capping compounds were used for direct pulp capping, but were incomplete when laser irradiation without prior placement of a pulp capping compound was used for the identical purpose. The visible-light curing of pulp capping compounds is not harmful to vital pulp, and provides an effective seal of the pulp exposure hole. Laser irradiation is not an effective sealant, and can cause thermal injury to vital pulp at high output powers.

Usability of light-emitting diodes in precision approach path indicator systems by individuals with marginal color vision.

DOT National Transportation Integrated Search

2014-05-01

To save energy, the FAA is planning to convert from incandescent lights to light-emitting diodes (LEDs) in : precision approach path indicator (PAPI) systems. Preliminary work on the usability of LEDs by color vision-waivered pilots (Bullough, Skinne...

Optical Properties of Hybrid Inorganic/Organic Thin Film Encapsulation Layers for Flexible Top-Emission Organic Light-Emitting Diodes.

PubMed

An, Jae Seok; Jang, Ha Jun; Park, Cheol Young; Youn, Hongseok; Lee, Jong Ho; Heo, Gi-Seok; Choi, Bum Ho; Lee, Choong Hun

2015-10-01

Inorganic/organic hybrid thin film encapsulation layers consist of a thin Al2O3 layer together with polymer material. We have investigated optical properties of thin film encapsulation layers for top-emission flexible organic light-emitting diodes. The transmittance of hybrid thin film encapsulation layers and the electroluminescent spectrum of organic light-emitting diodes that were passivated by hybrid organic/inorganic thin film encapsulation layers were also examined as a function of the thickness of inorganic Al203 and monomer layers. The number of interference peaks, their intensity, and their positions in the visible range can be controlled by varying the thickness of inorganic Al2O3 layer. On the other hand, changing the thickness of monomer layer had a negligible effect on the optical properties. We also verified that there is a trade-off between transparency in the visible range and the permeation of water vapor in hybrid thin film encapsulation layers. As the number of dyads decreased, optical transparency improved while the water vapor permeation barrier was degraded. Our study suggests that, in top-emission organic light-emitting diodes, the thickness of each thin film encapsulation layer, in particular that of the inorganic layer, and the number of dyads should be controlled for highly efficient top-emission flexible organic light-emitting diodes.

Optical design of tunnel lighting with white light-emitting diodes.

PubMed

Tsai, Ming-Shiou; Lee, Xuan-Hao; Lo, Yi-Chien; Sun, Ching-Cherng

2014-10-10

This paper presents a tunnel lighting design consisting of a cluster light-emitting diode and a free-form lens. Most of the energy emitted from the proposed luminaire is transmitted onto the surface of the road in front of drivers, and the probability that that energy is emitted directly into drivers' eyes is low. Compared with traditional fluorescent lamps, the proposed luminaire, of which the optical utilization factor, optical efficiency, and uniformity are, respectively, 44%, 92.5%, and 0.72, exhibits favorable performance in energy saving, glare reduction, and traffic safety.

Organic light-emitting diode materials

DOEpatents

Aspuru-Guzik, Alan; Gomez-Bombarelli, Rafael; Aguilera-Iparraguirre, Jorge; Baldo, Marc; Van Voorhis, Troy; Hirzel, Timothy D.; Bahlke, Matthias; McMahon, David; Wu, Tony Chang-Chi

2018-05-15

Described herein are molecules for use in organic light emitting diodes. Example molecules comprise at least one moiety A and at least one moiety D. Values and preferred values of the moieties A and D are described herein. The molecules comprise at least one atom selected from Si, Se, Ge, Sn, P, or As.

Response of adult mosquitoes to light emitting diodes placed in resting boxes and in the field.

USDA-ARS?s Scientific Manuscript database

Resting boxes are passive devices used to attract and capture mosquitoes seeking shelter. Increasing the attractiveness of these devices could improve their effectiveness. Light emitting diodes (LEDs) can be attractive to mosquitoes when used together with other trapping devices. Therefore restin...

Polymer Light-Emitting Diode (PLED) Process Development

DTIC Science & Technology

2003-12-01

conclusions and recommendations for Phase II of the Flexible Display Program. 15. SUBJECT TERMS LIGHT EMITTING DIODES LIQUID CRYSTAL DISPLAY SYSTEMS...space for Phase I and II confined by backplane complexity and substrate form...12 Figure 6. Semi automated I-V curve measurement setup consisting of Keithley power supply, computer and

Unitary lens semiconductor device

DOEpatents

Lear, Kevin L.

1997-01-01

A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.

Thermally evaporated hybrid perovskite for hetero-structured green light-emitting diodes

NASA Astrophysics Data System (ADS)

Mariano, Fabrizio; Listorti, Andrea; Rizzo, Aurora; Colella, Silvia; Gigli, Giuseppe; Mazzeo, Marco

2017-10-01

Thermal evaporation of green-light emitting perovskite (MaPbBr3) films is reported. Morphological studies show that a soft thermal treatment is needed to induce an outstanding crystal growth and film organization. Hetero-structured light-emitting diodes, embedding as-deposited and annealed MAPbBr3 films as active layers, are fabricated and their performances are compared, highlighting that the perovskite evolution is strongly dependent on the growing substrate, too.

Unclassified Publications of Lincoln Laboratory. Volume 5

DTIC Science & Technology

1975-12-15

10 TN-1974-36 LIGHT - EMITTING DIODES (LED) JA-4295 LIGHT SCATTERING JA-4456 LINCOLN DIGITAL VOICE TERMINAL TN-1975-53, TN-1975-65 LINCOLN...Hinkley J. O. Sample G. Dresselhaus T. C. Harman J. P. McVittie J. Filson p-n Junction PbSi_xSex Photo- J. P. Donnelly diodes Fabricated by Se...Room-Temperature Operation of GalnAsP/lnP Double- Heterostructure Diode Lasers Emitting at 1.1 (im Transparent Heat Mirrors for Solar-Energy

Monomer Release from Resin Based Dental Materials Cured With LED and Halogen Lights

PubMed Central

Ak, Asli Topaloglu; Alpoz, A. Riza; Bayraktar, Oguz; Ertugrul, Fahinur

2010-01-01

Objectives: To measure the release of TEGDMA and BisGMA from two commercially available composite resins; Filtek Z 250 (3M ESPE, Germany), Leaddent (Leaddent, Germany) and two fissure sealants; Helioseal F (3M ESPE, Germany) Enamel Loc (Premiere Rev, USA) over 1, 3 and 7 days after polymerization with standard quartz-tungsten halogen Coltolux II (QHL) (Coltene Switzerland) and a standard blue light emitting diode Elipar Freelight 2 (3M ESPE, Germany). Methods: 9 samples of each material were placed in disc shaped specimens in 1 mm of thickness and 10 mm in diameter (n=36). Each material was polymerized using LED for 20 s (n=12), 40 s (n=12) and halogen for 40 s (n=12), respectively. High Performance Liquid Chromatography (HPLC) was used to measure the amount of monomers released over 1, 3 and 7 days. Data was analyzed using one way ANOVA and Bonferroni test for multiple comparisons with a significance level of .05. Results: LED 20 sec group showed the highest release of monomers at 1, 3 and 7 days in sealant groups. Halogen 40 sec group resulted highest release of monomers for Leaddent at all time intervals (P<.05) Conclusions: Efficiency of the curing unit and applying the recommended curing time of the light activated resin based dental materials is very important to protect the patient from potential hazards of residual monomers. PMID:20046478

Vacuum Nanohole Array Embedded Phosphorescent Organic Light Emitting Diodes

PubMed Central

Jeon, Sohee; Lee, Jeong-Hwan; Jeong, Jun-Ho; Song, Young Seok; Moon, Chang-Ki; Kim, Jang-Joo; Youn, Jae Ryoun

2015-01-01

Light extraction from organic light-emitting diodes that utilize phosphorescent materials has an internal efficiency of 100% but is limited by an external quantum efficiency (EQE) of 30%. In this study, extremely high-efficiency organic light emitting diodes (OLEDs) with an EQE of greater than 50% and low roll-off were produced by inserting a vacuum nanohole array (VNHA) into phosphorescent OLEDs (PhOLEDs). The resultant extraction enhancement was quantified in terms of EQE by comparing experimentally measured results with those produced from optical modeling analysis, which assumes the near-perfect electric characteristics of the device. A comparison of the experimental data and optical modeling results indicated that the VNHA extracts the entire waveguide loss into the air. The EQE obtained in this study is the highest value obtained to date for bottom-emitting OLEDs. PMID:25732061

Stacked Device of Polymer Light-Emitting Diode Driven by Metal-Base Organic Transistor

NASA Astrophysics Data System (ADS)

Yoneda, Kazuhiro; Nakayama, Ken-ichi; Yokoyama, Masaaki

2008-02-01

We fabricated a new light-emitting device that combined a polymer light-emitting diode (PLED) and a vertical-type metal-base organic transistor (MBOT) through a floating electrode. By employing a layered floating electrode of Mg:Ag/Au, the MBOT on the PLED was operated successfully and a current amplification factor of approximately 20 was observed. The PLED luminescence exceeding 100 cd/m2 can be modulated using the MBOT with a low base voltage (2.8 V) and VCC (8 V). The emission contrast (on/off ratio) was improved with insertion of an insulating layer under the base, and the cut-off frequency was estimated to be 8 kHz. This device is expected to be a promising driving system of organic light-emitting diode (OLED), realizing low voltage and high numerical aperture.

III-nitride nanowire LEDs and diode lasers: monolithic light sources on (001) Si emitting in the 600-1300nm range

NASA Astrophysics Data System (ADS)

Bhattacharya, P.; Hazari, A.; Jahangir, S.

2018-02-01

GaN-based nanowire heterostructure arrays epitaxially grown on (001)Si substrates have unique properties and present the potential to realize useful devices. The active light-emitting region in the nanowire heterostructures are usually InGaN disks, whose composition can be varied to tune the emission wavelength. We have demonstrated light emitting diodes and edgeemitting diode lasers with power outputs 10mW with emission in the 600-1300nm wavelength range. These light sources are therefore useful for a variety of applications, including silicon photonics. Molecular beam epitaxial growth of the nanowire heterostructure arrays on (001)Si substrates and the characteristics of 1.3μm nanowire array edge emitting lasers, guided wave photodiodes and a monolithic photonic integrated circuit designed for 1.3μm operation are described.

Broadband visible light source based on AllnGaN light emitting diodes

DOEpatents

Crawford, Mary H.; Nelson, Jeffrey S.

2003-12-16

A visible light source device is described based on a light emitting diode and a nanocluster-based film. The light emitting diode utilizes a semiconductor quantum well structure between n-type and p-type semiconductor materials on the top surface a substrate such as sapphire. The nanocluster-based film is deposited on the bottom surface of the substrate and can be derived from a solution of MoS.sub.2, MoSe.sub.2, WS.sub.2, and WSe.sub.2 particles of size greater than approximately 2 nm in diameter and less than approximately 15 nm in diameter, having an absorption wavelength greater than approximately 300 nm and less than approximately 650 nm.

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

NASA Astrophysics Data System (ADS)

Anthopoulos, Thomas D.; Markham, Jonathan P. J.; Namdas, Ebinazar B.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2003-06-01

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4'-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.

Efficiency of dual-cured resin cement polymerization induced by high-intensity LED curing units through ceramic material.

PubMed

Watanabe, H; Kazama, Re; Asai, T; Kanaya, F; Ishizaki, H; Fukushima, M; Okiji, T

2015-01-01

This study aimed to evaluate the ability of high-intensity light-emitting diode (LED) and other curing units to cure dual-cured resin cement through ceramic material. A halogen curing unit (Jetlite 3000, Morita), a second-generation LED curing unit (Demi, Kerr), and two high-intensity LED curing units (PenCure 2000, Morita; Valo, Ultradent) were tested. Feldspathic ceramic plates (VITABLOCS Mark II, A3; Vita Zahnfabrik) with thicknesses of 1.0, 2.0, and 3.0 mm were prepared. Dual-cured resin cement samples (Clearfil Esthetic Cement, Kuraray Noritake Dental) were irradiated directly or through one of the ceramic plates for different periods (5, 10, 15, or 20 seconds for the high-intensity LED units and 20, 40, 60, or 80 seconds for the others). The Knoop hardness test was used to determine the level of photopolymerization that had been induced in the resin cement. Data were analyzed by one-way analysis of variance and Dunnett's post-hoc test to identify test-control (maximum irradiation without a ceramic plate) differences for each curing unit (p<0.05). For all curing units, the curing conditions had a statistically significant effect on the Knoop hardness numbers (KHNs) of the irradiated cement samples (p<0.001). In general, the KHN decreased with increasing plate thickness and increased as the irradiation period was extended. Jetlite 3000 achieved control-level KHN values only when the plate thickness was 1.0 mm. At a plate thickness ≥2.0 mm, the LED units (except for PenCure 2000 at 3.0 mm) were able to achieve control-level KHN values when the irradiation time was extended. At a plate thickness of 3.0 mm, irradiation for 20 seconds with the Valo or for 80 seconds with the Demi were the only methods that produced KHN values equivalent to those produced by direct irradiation. Regardless of the type of curing unit used, indirect irradiation of dual-cured resin cement through a ceramic plate resulted in decreased KHN values compared with direct irradiation. When the irradiation period was extended, only the LED units were able to achieve similar KHN values to those observed under direct irradiation in the presence of plates ≥2.0-mm thick. High-intensity LED units require a shorter irradiation period than halogen and second-generation LED curing units to obtain KHN values similar to those observed during direct irradiation.

Unitary lens semiconductor device

DOEpatents

Lear, K.L.

1997-05-27

A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.

Light intensity and quality from sole-source light-emitting diodes impact growth, morphology, and nutrient content of Brassica microgreens

USDA-ARS?s Scientific Manuscript database

Multi-layer vertical production systems using sole-source (SS) lighting can be used for microgreen production; however, traditional SS lighting can consume large amounts of electrical energy. Light-emitting diodes (LEDs) offer many advantages over conventional light sources including: high photoelec...

Light-Emitting Diodes: Learning New Physics

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2015-01-01

This is the third paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide the readers with the description of experiments and pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper, published…

Light-Emitting Diodes: Solving Complex Problems

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2015-01-01

This is the fourth paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide readers with the description of experiments and the pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper provided…

Demonstration Assessment of Light-Emitting Diode (LED) Post-Top Lighting at Central Park in New York City

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myer, Michael; Goettel, Russell T.; Kinzey, Bruce R.

2012-09-30

A review of five post-top light-emitting diode (LED) pedestrian luminaires installed in New York City's Central Park for possible replacement to the existing metal halide post-top luminaire. This report reviews the energy savings potential and lighting delivered by the LED post-top luminaires.

A Simple, Small-Scale Lego Colorimeter with a Light-Emitting Diode (LED) Used as Detector

ERIC Educational Resources Information Center

Asheim, Jonas; Kvittingen, Eivind V.; Kvittingen, Lise; Verley, Richard

2014-01-01

This article describes how to construct a simple, inexpensive, and robust colorimeter from a few Lego bricks, in which one light-emitting diode (LED) is used as a light source and a second LED as a light detector. The colorimeter is suited to various grades and curricula.

Rosin-enabled ultraclean and damage-free transfer of graphene for large-area flexible organic light-emitting diodes

PubMed Central

Zhang, Zhikun; Du, Jinhong; Zhang, Dingdong; Sun, Hengda; Yin, Lichang; Ma, Laipeng; Chen, Jiangshan; Ma, Dongge; Cheng, Hui-Ming; Ren, Wencai

2017-01-01

The large polymer particle residue generated during the transfer process of graphene grown by chemical vapour deposition is a critical issue that limits its use in large-area thin-film devices such as organic light-emitting diodes. The available lighting areas of the graphene-based organic light-emitting diodes reported so far are usually <1 cm2. Here we report a transfer method using rosin as a support layer, whose weak interaction with graphene, good solubility and sufficient strength enable ultraclean and damage-free transfer. The transferred graphene has a low surface roughness with an occasional maximum residue height of about 15 nm and a uniform sheet resistance of 560 Ω per square with about 1% deviation over a large area. Such clean, damage-free graphene has produced the four-inch monolithic flexible graphene-based organic light-emitting diode with a high brightness of about 10,000 cd m−2 that can already satisfy the requirements for lighting sources and displays. PMID:28233778

II-VI Semiconductor Superlattices

DTIC Science & Technology

1992-12-01

N. Otsuka, H. icon, J. Ding, and A.V. Nurmikko, " Blue /Green Injection Lasers and Light Emitting Diodes" J. Vac. Sci. Technology B, 10(2) March/April...34Indium tin oxide as transparent electrode material for ZnSe-based blue quantum well light emitters" AppI. Phys. Lett. 60(23) 8 June 1992, p. 2825...characteristics of this contact scheme have been demon- strated tI)gether with their use Jn both blue ,/groen light lip emitting diodes and diode laser:- The

Low-threshold voltage ultraviolet light-emitting diodes based on (Al,Ga)N metal-insulator-semiconductor structures

NASA Astrophysics Data System (ADS)

Liang, Yu-Han; Towe, Elias

2017-12-01

Al-rich III-nitride-based deep-ultraviolet (UV) (275-320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal-insulator-semiconductor UV light-emitting Schottky diodes with low turn-on voltages of <3 V, which are about half those of typical (Al,Ga)N p-i-n diodes. Our devices use a thin AlN film as the insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al x Ga1- x N semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.

Mechanical properties and polymerization shrinkage of composite resins light-cured using two different lasers.

PubMed

Kim, Tae-Wan; Lee, Jang-Hoon; Jeong, Seung-Hwa; Ko, Ching-Chang; Kim, Hyung-Il; Kwon, Yong Hoon

2015-04-01

The purpose of the present study was to investigate the usefulness of 457 and 473 nm lasers for the curing of composite resins during the restoration of damaged tooth cavity. Monochromaticity and coherence are attractive features of laser compared with most other light sources. Better polymerization of composite resins can be expected. Eight composite resins were light cured using these two lasers and a light-emitting diode (LED) light-curing unit (LCU). To evaluate the degrees of polymerization achieved, polymerization shrinkage and flexural and compressive properties were measured and compared. Polymerization shrinkage values by 457 and 473 nm laser, and LED ranged from 10.9 to 26.8, from 13.2 to 26.1, and from 11.5 to 26.3 μm, respectively. The values by 457 nm laser was significantly different from those by 473 and LED LCU (p<0.05). However, there was no statistical difference between values by 473 and LED LCU. Before immersion in distilled water, flexural strength (FS) and compressive modulus (CM) of the specimens were inconsistently influenced by LCUs. On the other hand, flexural modulus (FM) and compressive strength (CS) were not significantly different for the three LCUs (p>0.05). For the tested LCUs, no specific LCU could consistently achieve highest strength and modulus from the specimens tested. Two lasers (457 and 473 nm) can polymerize composite resins to the level that LED LCU can achieve despite inconsistent trends of polymerization shrinkage and flexural and compressive properties of the tested specimens.

Comparative study of the bactericidal effects of indocyanine green- and methyl aminolevulinate-based photodynamic therapy on Propionibacterium acnes as a new treatment for acne.

PubMed

Choi, Seung-Hwan; Seo, Jeong-Wan; Kim, Ki-Ho

2018-05-03

Acne vulgaris is one of the most common dermatological problems, and its therapeutic options include topical and systemic retinoids and antibiotics. However, increase in problems associated with acne treatment, such as side-effects from conventional agents and bacterial resistance to antibiotics, has led to greater use of photodynamic therapy. The purpose of this study was to compare the bactericidal effects of indocyanine green- and methyl aminolevulinate-based photodynamic therapy on Propionibacterium acnes. P. acnes were cultured under anaerobic conditions; then they were divided into three groups (control, treated with indocyanine green and treated with methyl aminolevulinate) and illuminated with different lights (630-nm light-emitting diode, 805-nm diode laser and 830-nm light-emitting diode). The bactericidal effects were evaluated by comparing each group's colony-forming units. The cultured P. acnes were killed with an 805-nm diode laser and 830-nm light-emitting diode in the indocyanine green group. No bactericidal effects of methyl aminolevulinate-based photodynamic therapy were identified. The clinical efficacy of indocyanine green-based photodynamic therapy in 21 patients was retrospectively analyzed. The Korean Acne Grading System was used to evaluate treatment efficacy, which was significantly decreased after treatment. The difference in the efficacy of the 805-nm diode laser and 830-nm light-emitting diode was not statistically significant. Although the methyl aminolevulinate-based photodynamic therapy showed no bactericidal effect, the indocyanine green-based photodynamic therapy has bactericidal effect and clinical efficacy. © 2018 Japanese Dermatological Association.

Blackbody material

DOEpatents

Lauf, Robert J.; Hamby, Jr., Clyde; Akerman, M. Alfred; Trivelpiece, Alvin W.

1994-01-01

A light emitting article comprises a composite of carbon-bonded carbon fibers, prepared by: blending carbon fibers with a carbonizable organic powder to form a mixture; dispersing the mixture into an aqueous slurry; vacuum molding the aqueous slurry to form a green article; drying and curing the green article to form a cured article; and, carbonizing the cured article at a temperature of at least about 1000.degree. C. to form a carbon-bonded carbon fiber light emitting composite article having a bulk density less than 1 g/cm.sup.3.

Cd-free Cu-Zn-In-S/ZnS quantum dots@SiO2 multiple cores nanostructure: preparation and application for white LEDs

NASA Astrophysics Data System (ADS)

Jiang, Tongtong; Shen, Mohan; Dai, Peng; Wu, Mingzai; Yu, Xinxin; Li, Guang; Xu, Xiaoliang; Zeng, Haibo

2017-10-01

The work reports the fabrication of Cu doped Zn-In-S (CZIS) alloy quantum dots (QDs) using dodecanethiol and oleic acid as stabilizing ligands. With the increase of doped Cu element, the photoluminescence (PL) peak is monotonically red shifted. After coating ZnS shell, the PL quantum yield of CZIS QDs can reach 78%. Using reverse micelle microemulsion method, CZIS/ZnS QDs@SiO2 multi-core nanospheres were synthesized to improve the colloidal stability and avoid the aggregation of QDs. The obtained multi-core nanospheres were dispersed in curing adhesive, and applied as a color conversion layer in down converted light-emitting diodes. After encapsulation in curing adhesive, the newly designed LEDs show artifically regulated color coordinates with varying the weight ratio of green QDs and red QDs, and the concentrations of these two types of QDs. Moreover, natural white and warm white LEDs with correlated color temperature of 5287, 6732, 2731, and 3309 K can be achieved, which indicates that CZIS/ZnS QDs@SiO2 nanostructures are promising color conversion layer material for solid-state lighting application.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Degradation phenomena in laser diodes

NASA Astrophysics Data System (ADS)

Beister, G.; Krispin, P.; Maege, J.; Richter, G.; Weber, H.; Rechenberg, I.

1988-11-01

Accelerated tests on GaAlAs/GaAs double heterostructure laser diodes showed, in agreement with earlier results on light-emitting diodes, that ageing appeared in three distinct forms: initial and slow degradation stages, both obeying a logarithmic time dependence, and a superimposed "gradation" (enhancement of the output power). Measurements made by the method of deep level transient spectroscopy during the accelerated tests on these lasers, operated as light-emitting diodes, revealed the appearance right from the beginning of B levels attributed to the antisite GaAs defects. The B levels appeared again in diodes tested in the lasing mode. In the case of a group of 21 laser diodes the mean time-to-failure was 9000 h at 70°C for 5 mW (in accordance with the Weibull statistics of degradation rates).

A flexible top-emitting organic light-emitting diode on steel foil

NASA Astrophysics Data System (ADS)

Xie, Zhiyuan; Hung, Liang-Sun; Zhu, Furong

2003-11-01

An efficient flexible top-emitting organic light-emitting diode (FTOLED) was developed on a thin steel foil. The FTOLED was constructed on the spin-on-glass (SOG)-coated steel substrate with an organic stack of NPB/Alq 3 sandwiched by a highly reflective Ag anode and a semitransparent Sm cathode. An ultrathin plasma-polymerized hydrocarbon film (CF X) was interposed between the Ag anode and the NPB layer to enhance hole-injection, and an additional Alq 3 layer was overlaid on the Sm cathode to increase light output. The FTOLED showed a peak efficiency of 4.4 cd/A higher than 3.7 cd/A of a convention NPB/Alq 3-based bottom-emitting OLED.

Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials.

PubMed

Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

2016-06-03

Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9'-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9',9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials

NASA Astrophysics Data System (ADS)

Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

2016-06-01

Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9‧-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9‧,9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices

PubMed Central

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-01-01

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers. PMID:27181337

Flip-chip light emitting diode with resonant optical microcavity

DOEpatents

Gee, James M.; Bogart, Katherine H.A.; Fischer, Arthur J.

2005-11-29

A flip-chip light emitting diode with enhanced efficiency. The device structure employs a microcavity structure in a flip-chip configuration. The microcavity enhances the light emission in vertical modes, which are readily extracted from the device. Most of the rest of the light is emitted into waveguided lateral modes. Flip-chip configuration is advantageous for light emitting diodes (LEDs) grown on dielectric substrates (e.g., gallium nitride LEDs grown on sapphire substrates) in general due to better thermal dissipation and lower series resistance. Flip-chip configuration is advantageous for microcavity LEDs in particular because (a) one of the reflectors is a high-reflectivity metal ohmic contact that is already part of the flip-chip configuration, and (b) current conduction is only required through a single distributed Bragg reflector. Some of the waveguided lateral modes can also be extracted with angled sidewalls used for the interdigitated contacts in the flip-chip configuration.

Manufacturing polymer light emitting diode with high luminance efficiency by solution process

NASA Astrophysics Data System (ADS)

Kim, Miyoung; Jo, SongJin; Yang, Ho Chang; Yoon, Dang Mo; Kwon, Jae-Taek; Lee, Seung-Hyun; Choi, Ju Hwan; Lee, Bum-Joo; Shin, Jin-Koog

2012-06-01

While investigating polymer light emitting diodes (polymer-LEDs) fabricated by solution process, surface roughness influences electro-optical (E-O) characteristics. We expect that E-O characteristics such as luminance and power efficiency related to surface roughness and layer thickness of emitting layer with poly-9-Vinylcarbazole. In this study, we fabricated polymer organic light emitting diodes by solution process which guarantees easy, eco-friendly and low cost manufacturing for flexible display applications. In order to obtain high luminescence efficiency, E-O characteristics of these devices by varying parameters for printing process have been investigated. Therefore, we optimized process condition for polymer-LEDs by adjusting annealing temperatures of emission, thickness of emission layer showing efficiency (10.8 cd/A) at 10 mA/cm2. We also checked wavelength dependent electroluminescence spectrum in order to find the correlation between the variation of efficiency and the thickness of the layer.

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices.

PubMed

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-05-16

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers.

Synthesis and characterization of organic/inorganic heterostructure films for hybrid light emitting diode

NASA Astrophysics Data System (ADS)

Toyama, Toshihiko; Ichihara, Tokuyuki; Yamaguchi, Daisuke; Okamoto, Hiroaki

2007-10-01

Thin-film light emitting devices based on organic materials have been gathering attentions for applying a flat-panel display and a solid-state lighting. Alternatively, inorganic technologies such as Si-based thin-film technology have been growing almost independently. It is then expected that combining the Si-based thin-film technology with the organic light emitting diode (OLED) technology will develop innovative devices. Here, we report syntheses of the hybrid light emitting diode (LED) with a heterostructure consisting of p-type SiC x and tris-(8-hydroxyquinoline) aluminum films and characterization for the hybrid LEDs. We present the energy diagram of the heterostructure, and describe that the use of high dark conductivities of the p-type SiC x as well as inserting wide-gap intrinsic a-SiC x at the p-type SiC x/Alq interface are effective for improving device performance.

Effect of arylamine hole-transport units on the performance of blue polyspirobifulorene light-emitting diodes

NASA Astrophysics Data System (ADS)

Abbaszadeh, Davood; Nicolai, Herman T.; Crǎciun, N. Irina; Blom, Paul W. M.

2014-11-01

The operation of blue light-emitting diodes based on polyspirobifluorene with a varying number of N ,N ,N',N' tetraaryldiamino biphenyl (TAD) hole-transport units (HTUs) is investigated. Assuming that the electron transport is not affected by the incorporation of TAD units, model calculations predict that a concentration of 5% HTU leads to an optimal efficiency for this blue-emitting polymer. However, experimentally an optimum performance is achieved for 10% TAD HTUs. Analysis of the transport and recombination shows that polymer light-emitting diodes with 5%, 7.5%, and 12.5% TAD units follow the predicted behavior. The enhanced performance of the polymer with 10% TAD originates from a decrease in the number of electron traps, which is typically a factor of three lower than the universal value found in many polymers. This reduced number of traps leads to a reduction of nonradiative recombination and exciton quenching at the cathode.

Electronic Two-Transition-Induced Enhancement of Emission Efficiency in Polymer Light-Emitting Diodes

PubMed Central

Chen, Ren-Ai; Wang, Cong; Li, Sheng; George, Thomas F.

2013-01-01

With the development of experimental techniques, effective injection and transportation of electrons is proven as a way to obtain polymer light-emitting diodes (PLEDs) with high quantum efficiency. This paper reveals a valid mechanism for the enhancement of quantum efficiency in PLEDs. When an external electric field is applied, the interaction between a negative polaron and triplet exciton leads to an electronic two-transition process, which induces the exciton to emit light and thus improve the emission efficiency of PLEDs. PMID:28809346

High-efficiency orange and tandem white organic light-emitting diodes using phosphorescent dyes with horizontally oriented emitting dipoles.

PubMed

Lee, Sunghun; Shin, Hyun; Kim, Jang-Joo

2014-09-03

Tandem white organic light-emitting diodes (WOLEDs) using horizontally oriented phosphorescent dyes in an exciplex-forming co-host are presented, along with an orange OLED. A high external quantum efficiency of 32% is achieved for the orange OLED at 1000 cd m(-2) and the tandem WOLEDs exhibit a high maximum EQE of 54.3% (PE of 63 lm W(-1)). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of voltage decrease in organic light emitting diodes during the initial stage of lifetime

NASA Astrophysics Data System (ADS)

Cusumano, P.

2016-02-01

We report the results of lifetime DC testing at constant current of not-encapsulated organic light emitting diodes (OLEDs) based on Tris (8 idroxyquinoline) aluminum (Alq3) as emitting material. In particular, a voltage decrease during the initial stage of the lifetime test is observed. The cause of this behavior is also discussed, mainly linked to initial Joule self-heating of the device, rising its temperature above room temperature until thermal equilibrium is reached at steady state.

Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Blanchard, Richard A. (Inventor); Lewandowski, Mark Allan (Inventor); Lowenthal, Mark D. (Inventor); Fuller, Kirk A. (Inventor); Frazier, Donald Odell (Inventor); Shotton, Neil O. (Inventor); Ray, William Johnstone (Inventor)

2016-01-01

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of lenses suspended in a polymer deposited or attached over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes are substantially spherical, and have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Shotton, Neil O. (Inventor); Lewandowski, Mark Allan (Inventor); Lowenthal, Mark D. (Inventor); Ray, William Johnstone (Inventor); Blanchard, Richard A. (Inventor); Fuller, Kirk A. (Inventor); Frazier, Donald Odell (Inventor)

2018-01-01

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of lenses suspended in a polymer deposited or attached over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes are substantially spherical, and have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Ray, William Johnstone (Inventor); Shotton, Neil O. (Inventor); Lewandowski, Mark Allan (Inventor); Lowenthal, Mark D. (Inventor); Blanchard, Richard A. (Inventor); Fuller, Kirk A. (Inventor); Frazier, Donald Odell (Inventor)

2016-01-01

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of substantially spherical or optically resonant diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of substantially spherical lenses suspended in a polymer attached or deposited over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Light emitting, photovoltaic or other electronic apparatus and system

NASA Technical Reports Server (NTRS)

Ray, William Johnstone (Inventor); Lowenthal, Mark D. (Inventor); Shotton, Neil O. (Inventor); Blanchard, Richard A. (Inventor); Lewandowski, Mark Allan (Inventor); Fuller, Kirk A. (Inventor); Frazier, Donald Odell (Inventor)

2013-01-01

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of lenses suspended in a polymer deposited or attached over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes are substantially spherical, and have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Light emitting, photovoltaic or other electronic apparatus and system

NASA Technical Reports Server (NTRS)

Lowenthal, Mark D. (Inventor); Blanchard, Richard A. (Inventor); Lewandowski, Mark Allan (Inventor); Frazier, Donald Odell (Inventor); Shotton, Neil O. (Inventor); Ray, William Johnstone (Inventor); Fuller, Kirk A. (Inventor)

2013-01-01

The present invention provides an electronic apparatus, such as a lighting device comprised of light emitting diodes (LEDs) or a power generating apparatus comprising photovoltaic diodes, which may be created through a printing process, using a semiconductor or other substrate particle ink or suspension and using a lens particle ink or suspension. An exemplary apparatus comprises a base; at least one first conductor; a plurality of substantially spherical or optically resonant diodes coupled to the at least one first conductor; at least one second conductor coupled to the plurality of diodes; and a plurality of substantially spherical lenses suspended in a polymer attached or deposited over the diodes. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes have a ratio of mean diameters or lengths between about 10:1 and 2:1. The diodes may be LEDs or photovoltaic diodes, and in some embodiments, have a junction formed at least partially as a hemispherical shell or cap.

Light-Emitting Diodes: A Hidden Treasure

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2014-01-01

LEDs, or light-emitting diodes, are cheap, easy to purchase, and thus commonly used in physics instruction as indicators of electric current or as sources of light (Fig. 1). In our opinion LEDs represent a unique piece of equipment that can be used to collect experimental evidence, and construct and test new ideas in almost every unit of a general…

Methods and apparatus of spatially resolved electroluminescence of operating organic light-emitting diodes using conductive atomic force microscopy

NASA Technical Reports Server (NTRS)

Hersam, Mark C. (Inventor); Pingree, Liam S. C. (Inventor)

2008-01-01

A conductive atomic force microscopy (cAFM) technique which can concurrently monitor topography, charge transport, and electroluminescence with nanometer spatial resolution. This cAFM approach is particularly well suited for probing the electroluminescent response characteristics of operating organic light-emitting diodes (OLEDs) over short length scales.

Diode-pumped quasi-three-level Nd:GdV O4-Nd:YAG sum-frequency laser at 464 nm

NASA Astrophysics Data System (ADS)

Lu, Jie

2014-04-01

We report a laser architecture to obtain continuous-wave (cw) blue radiation at 464 nm. A 808 nm diode pumped a Nd:GdV O4 crystal emitting at 912 nm. A part of the pump power was then absorbed by the Nd:GdV O4 crystal. The remainder was used to pump a Nd:YAG crystal emitting at 946 nm. Intracavity sum-frequency mixing at 912 and 946 nm was then realized in a LiB3O5 (LBO) crystal to produce blue radiation. We obtained a cw output power of 1.52 W at 464 nm with a pump laser diode emitting 18.4 W at 808 nm.

Organic light-emitting diodes from homoleptic square planar complexes

DOEpatents

Omary, Mohammad A

2013-11-12

Homoleptic square planar complexes [M(N.LAMBDA.N).sub.2], wherein two identical N.LAMBDA.N bidentate anionic ligands are coordinated to the M(II) metal center, including bidentate square planar complexes of triazolates, possess optical and electrical properties that make them useful for a wide variety of optical and electrical devices and applications. In particular, the complexes are useful for obtaining white or monochromatic organic light-emitting diodes ("OLEDs"). Improved white organic light emitting diode ("WOLED") designs have improved efficacy and/or color stability at high brightness in single- or two-emitter white or monochrome OLEDs that utilize homoleptic square planar complexes, including bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) ("Pt(ptp).sub.2").

Effect of reduced exposure times on the cytotoxicity of resin luting cements cured by high-power led

PubMed Central

ERGUN, Gulfem; EGILMEZ, Ferhan; YILMAZ, Sukran

2011-01-01

Objective Applications of resin luting agents and high-power light-emitting diodes (LED) light-curing units (LCUs) have increased considerably over the last few years. However, it is not clear whether the effect of reduced exposure time on cytotoxicity of such products have adequate biocompatibility to meet clinical success. This study aimed at assessing the effect of reduced curing time of five resin luting cements (RLCs) polymerized by high-power LED curing unit on the viability of a cell of L-929 fibroblast cells. Material and Methods Disc-shaped samples were prepared in polytetrafluoroethylene moulds with cylindrical cavities. The samples were irradiated from the top through the ceramic discs and acetate strips using LED LCU for 20 s (50% of the manufacturer's recommended exposure time) and 40 s (100% exposure time). After curing, the samples were transferred into a culture medium for 24 h. The eluates were obtained and pipetted onto L-929 fibroblast cultures (3x104 per well) and incubated for evaluating after 24 h. Measurements were performed by dimethylthiazol diphenyltetrazolium assay. Statistical significance was determined by two-way ANOVA and two independent samples were compared by t-test. Results Results showed that eluates of most of the materials polymerized for 20 s (except Rely X Unicem and Illusion) reduced to a higher extent cell viability compared to samples of the same materials polymerized for 40 s. Illusion exhibited the least cytotoxicity for 20 s exposure time compared to the control (culture without samples) followed by Rely X Unicem and Rely X ARC (90.81%, 88.90%, and 83.11%, respectively). For Rely X ARC, Duolink and Lute-It 40 s exposure time was better (t=-1.262 p=0,276; t=-9.399 p=0.001; and t=-20.418 p<0.001, respectively). Conclusion The results of this study suggest that reduction of curing time significantly enhances the cytotoxicity of the studied resin cement materials, therefore compromising their clinical performance. PMID:21625748

Recent advances in conjugated polymers for light emitting devices.

PubMed

Alsalhi, Mohamad Saleh; Alam, Javed; Dass, Lawrence Arockiasamy; Raja, Mohan

2011-01-01

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review.

Recent Advances in Conjugated Polymers for Light Emitting Devices

PubMed Central

AlSalhi, Mohamad Saleh; Alam, Javed; Dass, Lawrence Arockiasamy; Raja, Mohan

2011-01-01

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review. PMID:21673938

Wireless Power Transmission to Organic Light Emitting Diode Lighting Panel with Magnetically Coupled Resonator

NASA Astrophysics Data System (ADS)

Kim, Yong-Hae; Han, Jun-Han; Kang, Seung-Youl; Cheon, Sanghoon; Lee, Myung-Lae; Ahn, Seong-Deok; Zyung, Taehyoung; Lee, Jeong-Ik; Moon, Jaehyun; Chu, Hye Yong

2012-09-01

We are successful to lit the organic light emitting diode (OLED) lighting panel through the magnetically coupled wireless power transmission technology. For the wireless power transmission, we used the operation frequency 932 kHz, specially designed double spiral type transmitter, small and thin receiver on the four layered printed circuit board, and schottky diodes for the full bridge rectifier. Our white OLED is a hybrid type, in which phosphorescent and fluorescent organics are used together to generate stable white color. The total efficiency of power transmission is around 72%.

Poly (p-phenyleneneacetylene) light-emitting diodes

DOEpatents

Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei; Barton, Thomas J.; Vardeny, Zeev V.

1994-10-04

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

Poly (p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.; Barton, T.J.; Vardeny, Z.V.

1994-10-04

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.

1994-08-02

Acetylene-containing poly(p-phenyleneacetylene) (PPA)-based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei

1994-08-02

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as A1 or A1/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

Thermal characterization of GaN-based laser diodes by forward-voltage method

NASA Astrophysics Data System (ADS)

Feng, M. X.; Zhang, S. M.; Jiang, D. S.; Liu, J. P.; Wang, H.; Zeng, C.; Li, Z. C.; Wang, H. B.; Wang, F.; Yang, H.

2012-05-01

An expression of the relation between junction temperature and forward voltage common for both GaN-based laser diodes (LDs) and light emitting diodes is derived. By the expression, the junction temperature of GaN-based LDs emitting at 405 nm was measured at different injection current and compared with the result of micro-Raman spectroscopy, showing that the expression is reasonable. In addition, the activation energy of Mg in AlGaN/GaN superlattice layers is obtained based on the temperature dependence of forward voltage.

Hybrid electroluminescent devices

DOEpatents

Shiang, Joseph John; Duggal, Anil Raj; Michael, Joseph Darryl

2010-08-03

A hybrid electroluminescent (EL) device comprises at least one inorganic diode element and at least one organic EL element that are electrically connected in series. The absolute value of the breakdown voltage of the inorganic diode element is greater than the absolute value of the maximum reverse bias voltage across the series. The inorganic diode element can be a power diode, a Schottky barrier diode, or a light-emitting diode.

Wheat Under LED's (Light Emitting Diodes)

NASA Technical Reports Server (NTRS)

2004-01-01

Astroculture is a suite of technologies used to produce and maintain a closed controlled environment for plant growth. The two most recent missions supported growth of potato, dwarf wheat, and mustard plants, and provided scientists with the first opportunity to conduct true plant research in space. Light emitting diodes have particular usefulness for plant growth lighting because they emit a much smaller amount of radiant heat than do conventional lighting sources and because they have potential of directing a higher percentage of the emitted light onto plants surfaces. Furthermore, the high output LED's have emissions in the 600-700 nm waveband, which is of highest efficiency for photosynthesis by plants.

Colonic Marking With Near-Infrared, Light-Emitting, Diode-Activated Indocyanine Green for Laparoscopic Colorectal Surgery.

PubMed

Nagata, Jun; Fukunaga, Yosuke; Akiyoshi, Takashi; Konishi, Tsuyoshi; Fujimoto, Yoshiya; Nagayama, Satoshi; Yamamoto, Noriko; Ueno, Masashi

2016-02-01

Accurate identification of the location of colorectal lesions is crucial during laparoscopic surgery. Endoscopic marking has been used as an effective preoperative marker for tumor identification. We investigated the feasibility and safety of an imaging method using near-infrared, light-emitting, diode-activated indocyanine green fluorescence in colorectal laparoscopic surgery. This was a single-institution, prospective study. This study was conducted in a tertiary referral hospital. We enrolled 24 patients who underwent laparoscopic surgery. Indocyanine green and India ink were injected into the same patients undergoing preoperative colonoscopy for colon cancer. During subsequent laparoscopic resection of colorectal tumors, the colon was first observed with white light. Then, indocyanine green was activated with a light-emitting diode at 760 nm as the light source. Near-infrared-induced fluorescence showed tumor location clearly and accurately in all 24 of the patients. All of the patients who underwent laparoscopic surgery after marking had positive indocyanine green staining at the time of surgery. Perioperative complications attributed to dye use were not observed. This study is limited by the cost of indocyanine green detection, the timing of the colonoscopy and tattooing in relation to the operation and identification with indocyanine green, and the small size of the series. These data suggest that our novel method for colonic marking with fluorescence imaging of near-infrared, light-emitting, diode-activated indocyanine green is feasible and safe. This method is useful, has no adverse effects, and can be used for perioperative identification of tumor location. Near-infrared, light-emitting, diode-activated indocyanine green has potential use as a colonic marking agent.

High-Fluence Light-Emitting Diode-Generated Red Light Modulates the Transforming Growth Factor-Beta Pathway in Human Skin Fibroblasts.

PubMed

Mamalis, Andrew; Jagdeo, Jared

2018-05-24

Skin fibrosis is a significant medical problem with limited available treatment modalities. The key cellular characteristics include increased fibroblast proliferation, collagen production, and transforming growth factor-beta (TGF-B)/SMAD pathway signaling. The authors have previously shown that high-fluence light-emitting diode red light (HF-LED-RL) decreases cellular proliferation and collagen production. Herein, the authors investigate the ability of HF-LED-RL to modulate the TGF-B/SMAD pathway. Normal human dermal fibroblasts were cultured and irradiated with a commercially available hand-held LED array. After irradiation, cell lysates were collected and levels of pSMAD2, TGF-Beta 1, and TGF-Beta I receptor were measured using Western blot. High-fluence light-emitting diode red light decreased TGF-Beta 1 ligand (TGF-B1) levels after irradiation. 320 J/cm HF-LED-RL resulted in 59% TGF-B1 and 640 J/cm HF-LED-RL resulted in 54% TGF-B1, relative to controls. 640 J/cm HF-LED-RL resulted in 62% pSMAD2 0 hours after irradiation, 65% pSMAD2 2 hours after irradiation, and 95% 4 hours after irradiation, compared with matched controls. High-fluence light-emitting diode red light resulted in no significant difference in transforming growth factor-beta receptor I levels compared with matched controls. Skin fibrosis is a significant medical problem with limited available treatment modalities. Light-emitting diode-generated red light is a safe, economic, and noninvasive modality that has a body of in vitro evidence supporting the reduction of key cellular characteristics associated with skin fibrosis.

Dynamics of electronic transitions and frequency dependence of negative capacitance in semiconductor diodes under high forward bias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bansal, Kanika; Datta, Shouvik; Henini, Mohamed

2014-09-22

We observed qualitatively dissimilar frequency dependence of negative capacitance under high charge injection in two sets of functionally different junction diodes: III-V based light emitting and Si-based non-light emitting diodes. Using an advanced approach based on bias activated differential capacitance, we developed a generalized understanding of negative capacitance phenomenon which can be extended to any diode based device structure. We explained the observations as the mutual competition of fast and slow electronic transition rates which are different in different devices. This study can be useful in understanding the interfacial effects in semiconductor heterostructures and may lead to superior device functionality.

The Light-Emitting Diode as a Light Detector

ERIC Educational Resources Information Center

Baird, William H.; Hack, W. Nathan; Tran, Kiet; Vira, Zeeshan; Pickett, Matthew

2011-01-01

A light-emitting diode (LED) and operational amplifier can be used as an affordable method to provide a digital output indicating detection of an intense light source such as a laser beam or high-output LED. When coupled with a microcontroller, the combination can be used as a multiple photogate and timer for under $50. A similar circuit is used…

The Use of Light-Emitting Diodes (LEDs) as Green and Red/Far-Red Light Sources in Plant Physiology.

ERIC Educational Resources Information Center

Jackson, David L.; And Others

1985-01-01

The use of green, red, and far-red light-emitting diodes (LEDs) as light sources for plant physiological studies is outlined and evaluated. Indicates that LED lamps have the advantage over conventional light sources in that they are lightweight, low-cost, portable, easily constructed, and do not require color filters. (Author/DH)

Light Emitting Diode Flashlights as Effective and Inexpensive Light Sources for Fluorescence Microscopy

PubMed Central

Robertson, J. Brian; Zhang, Yunfei; Johnson, Carl Hirschie

2009-01-01

Summary Light-emitting diodes (LEDs) are becoming more commonly used as light sources for fluorescence microscopy. We describe the adaptation of a commercially available LED flashlight for use as a source for fluorescence excitation. This light source is long-lived, inexpensive, and is effective for excitation in the range of 440–600 nm. PMID:19772530

Frequency-Downconversion Stability of PMMA Coatings in Hybrid White Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Caruso, Fulvio; Mosca, Mauro; Rinella, Salvatore; Macaluso, Roberto; Calì, Claudio; Saiano, Filippo; Feltin, Eric

2016-01-01

We report on the properties of a poly(methyl methacrylate)-based coating used as a host for an organic dye in hybrid white light-emitting diodes. The device is composed by a pump source, which is a standard inorganic GaN/InGaN blue light-emitting diode (LED) emitting at around 450 nm, and a spin-coated conversion layer making use of Lumogen® F Yellow 083. Under prolonged irradiation, the coating exhibits significant bleaching, thus degrading the color rendering performance of the LED. We present experimental results that confirm that the local temperature rise of the operating diode does not affect the conversion layer. It is also proven that, during the test, the photostability of the organic dye is compromised, resulting in a chromatic shift from Commission Internationale de l'Eclairage (CIE) ( x; y) coordinates (0.30;0.39) towards the color of the pump (0.15;0.04). Besides photodegradation of the dye, we address a phenomenon attributed to modification of the polymer matrix activated by the LED's blue light energy as confirmed by ultraviolet-visible and Fourier-transform infrared spectroscopic analyses. Three methods for improving the overall stability of the organic coating are presented.

Embeded photonic crystal at the interface of p-GaN and Ag reflector to improve light extraction of GaN-based flip-chip light-emitting diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhen, Aigong; Ma, Ping, E-mail: maping@semi.ac.cn; Zhang, Yonghui

2014-12-22

In this experiment, a flip-chip light-emitting diode with photonic crystal was fabricated at the interface of p-GaN and Ag reflector via nanospheres lithography technique. In this structure, photonic crystal could couple with the guide-light efficiently by reason of the little distance between photonic crystal and active region. The light output power of light emitting diode with embedded photonic crystal was 1.42 times larger than that of planar flip-chip light-emitting diode. Moreover, the embedded photonic crystal structure makes the far-field divergence angle decreased by 18° without spectra shift. The three-dimensional finite difference time domain simulation results show that photonic crystal couldmore » improve the light extraction, and enhance the light absorption caused by Ag reflector simultaneously, because of the roughed surface. The depth of photonic crystal is the key parameter affecting the light extraction and absorption. Light extraction efficiency increases with the depth photonic crystal structure rapidly, and reaches the maximum at the depth 80 nm, beyond which light extraction decrease drastically.« less

Auger-generated hot carrier current in photo-excited forward biased single quantum well blue light emitting diodes

NASA Astrophysics Data System (ADS)

Espenlaub, Andrew C.; Alhassan, Abdullah I.; Nakamura, Shuji; Weisbuch, Claude; Speck, James S.

2018-04-01

We report on measurements of the photo-modulated current-voltage and electroluminescence characteristics of forward biased single quantum well, blue InGaN/GaN light emitting diodes with and without electron blocking layers. Low intensity resonant optical excitation of the quantum well was observed to induce an additional forward current at constant forward diode bias, in contrast to the usual sense of the photocurrent in photodiodes and solar cells, as well as an increased electroluminescence intensity. The presence of an electron blocking layer only slightly decreased the magnitude of the photo-induced current at constant forward bias. Photo-modulation at constant forward diode current resulted in a reduced diode bias under optical excitation. We argue that this decrease in diode bias at constant current and the increase in forward diode current at constant applied bias can only be due to additional hot carriers being ejected from the quantum well as a result of an increased Auger recombination rate within the quantum well.

Highly luminescent and photostable quantum dot-silica monolith and its application to light-emitting diodes.

PubMed

Jun, Shinae; Lee, Junho; Jang, Eunjoo

2013-02-26

A highly luminescent and photostable quantum dot-silica monolith (QD-SM) substance was prepared by preliminary surface exchange of the QDs and base-catalyzed sol-gel condensation of silica. The SM was heavily doped with 6-mercaptohexanol exchanged QDs up to 12 vol % (26 wt %) without particle aggregation. Propylamine catalyst was important in maintaining the original luminescence of the QDs in the SM during sol-gel condensation. The silica layer was a good barrier against oxygen and moisture, so that the QD-SM maintained its initial luminescence after high-power UV radiation (∼1 W) for 200 h and through the 150 °C LED encapsulant curing process. Green and red light-emitting QD-SMs were applied as color-converting layers on blue LEDs, and the external quantum efficiency reached up to 89% for the green QD-SM and 63% for the red one. A white LED made with a mixture of green and red QDs in the SM, in which the color coordinate was adjusted at (0.23, 0.21) in CIE1931 color space for a backlight application, showed an efficacy of 47 lm/W, the highest value yet reported.

An efficient continuous-wave 591 nm light source based on sum-frequency mixing of a diode pumped Nd:GdVO4-Nd:CNGG laser

NASA Astrophysics Data System (ADS)

Zhao, Y. D.; Liu, J. H.

2013-08-01

We report a laser architecture to obtain continuous-wave (CW) yellow-orange light sources at the 591 nm wavelength. An 808 nm diode pumped a Nd:GdVO4 crystal emitting at 1063 nm. A part of the pump power was then absorbed by the Nd:CNGG crystal. The remaining pump power was used to pump a Nd:CNGG crystal emitting at 1329 nm. Intracavity sum-frequency mixing at 1063 and 1329 nm was then realized in a LiB3O5 (LBO) crystal to reach the yellow-orange radiation. We obtained a CW output power of 494 mW at 591 nm with a pump laser diode emitting 17.8 W at 808 nm.

Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Cho, Himchan; Jeong, Su-Hun; Park, Min-Ho; Kim, Young-Hoon; Wolf, Christoph; Lee, Chang-Lyoul; Heo, Jin Hyuck; Sadhanala, Aditya; Myoung, NoSoung; Yoo, Seunghyup; Im, Sang Hyuk; Friend, Richard H.; Lee, Tae-Woo

2015-12-01

Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.

In Vitro Effect of Bleaching With 810 nm and 980 nm Diode Laser on Microhardness of Self-cure and Light-Cure Glass Ionomer Cements.

PubMed

Ranjbar Omrani, Ladan; Khoshamad, Sara; Tabatabaei Ghomshe, Elham; Chiniforush, Nasim; Hashemi Kamangar, Sedighe Sadat

2017-01-01

Introduction: This study sought to assess the effect of bleaching combined with irradiation of 810 nm and 980 nm diode laser on microhardness of 2 commonly used self-cure and light-cure glass ionomer cements (GICs) in comparison with conventional bleaching (without laser). Methods: In this in vitro, experimental study, 60 samples were fabricated of A2 shade of Fuji IX and Fuji II LC GICs (n=30) and each group was divided into 3 subgroups (n=10). The first subgroups were subjected to bleaching with Opalescence Xtra Boost plus 980 nm diode laser irradiation. The second subgroups were subjected to bleaching with Opalescence Boost plus 810 nm diode laser irradiation and the third subgroups were subjected to bleaching with Opalescence Xtra Boost without laser. Microhardness was measured at baseline and after the intervention using Vickers hardness tester. The data were analyzed using two-way analysis of variance (ANOVA) ( P <0.05). Results: Microhardness decreased in all subgroups after the intervention (P<0.001) irrespective of the type of GIC ( P =0.201) or surface treatment ( P =0.570). The baseline microhardness of the three subgroups within each group of GIC was not significantly different ( P =0.456), but the baseline microhardness of conventional GIC was significantly higher than that of resin modified GIC ( P =0.004). Conclusion: Bleaching with/without laser irradiation decreases the microhardness of GICs. The baseline microhardness of conventional GIC is higher than that of resin modified GIC.

Extraction of surface plasmons in organic light-emitting diodes via high-index coupling.

PubMed

Scholz, Bert J; Frischeisen, Jörg; Jaeger, Arndt; Setz, Daniel S; Reusch, Thilo C G; Brütting, Wolfgang

2012-03-12

The efficiency of organic light-emitting diodes (OLEDs) is still limited by poor light outcoupling. In particular, the excitation of surface plasmon polaritons (SPPs) at metal-organic interfaces represents a major loss channel. By combining optical simulations and experiments on simplified luminescent thin-film structures we elaborate the conditions for the extraction of SPPs via coupling to high-index media. As a proof-of-concept, we demonstrate the possibility to extract light from wave-guided modes and surface plasmons in a top-emitting white OLED by a high-index prism.

Naturally formed graded junction for organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Shao, Yan; Yang, Yang

2003-09-01

In this letter, we report naturally-formed graded junctions (NFGJ) for organic light-emitting diodes (OLEDs). These junctions are fabricated using single thermal evaporation boat loaded with uniformly mixed charge transport and light-emitting materials. Upon heating, materials sublimate sequentially according to their vaporizing temperatures forming the graded junction. Two kinds of graded structures, sharp and shallow graded junctions, can be formed based on the thermal properties of the selected materials. The NFGJ OLEDs have shown excellent performance in both brightness and lifetime compared with heterojunction devices.

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Le, H. Q.; Lim, S. K.; Goh, G. K. L.; Chua, S. J.; Ang, N. S. S.; Liu, W.

2010-09-01

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl2O4 spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×1020 cm-3 (and carrier mobility of 28 cm2/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.

Organic Light-Emitting Diode-on-Silicon Pixel Circuit Using the Source Follower Structure with Active Load for Microdisplays

NASA Astrophysics Data System (ADS)

Kwak, Bong-Choon; Lim, Han-Sin; Kwon, Oh-Kyong

2011-03-01

In this paper, we propose a pixel circuit immune to the electrical characteristic variation of organic light-emitting diodes (OLEDs) for organic light-emitting diode-on-silicon (OLEDoS) microdisplays with a 0.4 inch video graphics array (VGA) resolution and a 6-bit gray scale. The proposed pixel circuit is implemented using five p-channel metal oxide semiconductor field-effect transistors (MOSFETs) and one storage capacitor. The proposed pixel circuit has a source follower with a diode-connected transistor as an active load for improving the immunity against the electrical characteristic variation of OLEDs. The deviation in the measured emission current ranges from -0.165 to 0.212 least significant bit (LSB) among 11 samples while the anode voltage of OLED is 0 V. Also, the deviation in the measured emission current ranges from -0.262 to 0.272 LSB in pixel samples, while the anode voltage of OLED varies from 0 to 2.5 V owing to the electrical characteristic variation of OLEDs.

Light Converting Inorganic Phosphors for White Light-Emitting Diodes

PubMed Central

Chen, Lei; Lin, Chun-Che; Yeh, Chiao-Wen; Liu, Ru-Shi

2010-01-01

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or near-ultraviolet (nUV) LEDs) and photoluminescence phosphors. These solid-state LED lamps, rather than organic light emitting diode (OLED) or polymer light-emitting diode (PLED), have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability and long operating lifetime. To meet with the further requirement of high color rendering index, warm light with low color temperature, high thermal stability and higher energy efficiency for WLEDs, new phosphors that can absorb excitation energy from blue or nUV LEDs and generate visible emissions efficiently are desired. The criteria of choosing the best phosphors, for blue (450−480 nm) and nUV (380−400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance of light between the emission from blue-nUV LEDs and the emissions from phosphors (such as yellow from Y3Al5O12:Ce3+) is important to obtain white light with proper color rendering index and color temperature. Here, we will review the status of phosphors for LEDs and prospect the future development.

Influence of energy density of different light sources on Knoop hardness of a dual-cured resin cement.

PubMed

Piva, Evandro; Correr-Sobrinho, Lourenço; Sinhoreti, Mario Alexandre Coelho; Consani, Simonides; Demarco, Flávio Fernando; Powers, John Michael

2008-01-01

The purpose of this study was to evaluate the Knoop hardness of a dual-cured resin-based luting cement irradiated with different light sources as well energy density through a ceramic sample. Three light-curing unit (LCUs) were tested: tungsten halogen light (HAL), light-emitting diode (LED) and xenon plasma-arc (PAC) lamp. Disc-shaped specimens were fabricated from a resin-based cement (Enforce). Three energy doses were used by modifying the irradiance (I) of each LCU and the irradiation time (T): 24 Jcm(-2) (I/2x2T), 24 Jcm(-2) (IxT) and 48 Jcm(-2) (Ix2T). Energy doses were applied through a 2.0-mm-thick ceramic sample (Duceram Plus). Three groups underwent direct irradiation over the resin cement with the different LCUs and a chemically-activated group served as a control. Thirteen groups were tested (n=10). Knoop hardness number (KHN) means were obtained from cross-sectional areas. Two-way ANOVA and the Holm-Sidak method were used for statistical comparisons of activation mode and energy doses (alpha=5%). Application of 48 J.cm(-2) energy dose through the ceramic using LED (50.5+/-2.8) and HAL (50.9+/-3.7) produced significantly higher KHN means (p<0.05) than the control (44.7+/-3.8). LED showed statistically similar performance to HAL. Only HAL showed a relationship between the increase of LCU energy dose and hardness increase.

Comparative clinical study using laser and LED-therapy for orofacial pain relief: dentin hypersensitivity and cervicogenic headache

NASA Astrophysics Data System (ADS)

Lizarelli, Rosane F. Z.; Pizzo, Renata C. A.; Florez, Fernando L. E.; Grecco, Clovis; Speciali, Jose G.; Bagnato, Vanderlei S.

2015-06-01

Considering several clinical situations, low intensity laser therapy has been widely applied in pain relief or analgesia mechanism. With the advent of new LED-based (light emitting diode) light sources, the need of further clinical experiments aiming to compare the effectiveness among them is paramount. The LED system therapeutic use can be denominated as LEDT - Light Emitting Diode Therapy. This study proposed two clinical evaluations of pain relief effect: to dentin hypersensitivity and to cervicogenic headache using different sources of lasers (low and high intensity) and light emitting diodes (LEDs), one emitting at the spectral band of red (630+/- 5nm) and the other one at infrared band (880+/- 5nm). Two different clinical studies were performed and presented interesting results. Considering dentin hypersensitivity, red and infrared led were so effective than the control group (high intensity laser system); by the other side, considering cervicogenic headache, control group (infrared laser) was the best treatment in comparison to red and infrared led system.

Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern.

PubMed

Han, Nam; Cuong, Tran Viet; Han, Min; Ryu, Beo Deul; Chandramohan, S; Park, Jong Bae; Kang, Ji Hye; Park, Young-Jae; Ko, Kang Bok; Kim, Hee Yun; Kim, Hyun Kyu; Ryu, Jae Hyoung; Katharria, Y S; Choi, Chel-Jong; Hong, Chang-Hee

2013-01-01

The future of solid-state lighting relies on how the performance parameters will be improved further for developing high-brightness light-emitting diodes. Eventually, heat removal is becoming a crucial issue because the requirement of high brightness necessitates high-operating current densities that would trigger more joule heating. Here we demonstrate that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance. The fabrication process involves the generation of scalable graphene oxide microscale patterns on a sapphire substrate, followed by its thermal reduction and epitaxial lateral overgrowth of gallium nitride in a metal-organic chemical vapour deposition system under one-step process. The device with embedded graphene oxide outperforms its conventional counterpart by emitting bright light with relatively low-junction temperature and thermal resistance. This facile strategy may enable integration of large-scale graphene into practical devices for effective heat removal.

Effect of Stepwise Doping on Lifetime and Efficiency of Blue and White Phosphorescent Organic Light Emitting Diodes.

PubMed

Lee, Song Eun; Lee, Ho Won; Lee, Seok Jae; Koo, Ja-ryong; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Hye Jeong; Yoon, Seung Soo; Kim, Young Kwan

2015-02-01

We investigated a light emission mechanism of blue phosphorescent organic light emitting diodes (PHOLEDs), using a stepwise doping profile of 2, 8, and 14 wt.% within the emitting layer (EML). We fabricated several blue PHOLEDs with phosphorescent blue emitter iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate doped in N,N'-dicarbazolyl-3,5-benzene as a p-type host material. A blue PHOLED with the highest doping concentration as part of the EML close to an electron transporting layer showed a maximum luminous efficiency of 20.74 cd/A, and a maximum external quantum efficiency of 10.52%. This can be explained by effective electron injection through a highly doped EML side. Additionally, a white OLED based on the doping profile was fabricated with two thin red EMLs within a blue EML maintaining a thickness of 30 nm for the entire EML. Keywords: Blue Phosphorescent Organic Light Emitting Diodes, Stepwise Doping Structure, Charge Trapping Effect.

Response of conifer species from three latitudinal populations to light spectra generated by light-emitting diodes and high-pressure sodium lamps

Treesearch

Kent G. Apostol; Kas Dumroese; Jeremy Pinto; Anthony S. Davis

2015-01-01

Light-emitting diode (LED) technology shows promise for supplementing photosynthetically active radiation (PAR) in forest nurseries because of the potential reduction in energy consumption and an ability to supply discrete wavelengths to optimize seedling growth. Our objective was to examine the effects of light spectra supplied by LED and traditional high-pressure...

Hand-Drawn Resistors and a Simple Tester Using a Light-Emitting Diode

ERIC Educational Resources Information Center

Kamata, Masahiro; Abe, Mayumi

2012-01-01

A thick line drawn on a sheet of paper with a 6B pencil is electrically conductive and its resistance can be roughly estimated using a simple tester made of a light-emitting diode (LED) and a lithium coin-type cell. Using this hand-drawn resistor and the LED tester, we developed teaching materials that help students to understand how electrical…

Comment on "Enhancement of flip-chip white light-emitting diodes with a one-dimensional photonic crystal".

PubMed

Liu, Zong-Yuan; Liu, Sheng; Wang, Kai; Luo, Xiao-Bing

2010-06-01

We show that research presented in Opt. Lett.34, 301 (2009)OPLEDP0146-959210.1364/OL.34.000301 applied questionable phosphor definitions and a questionable simulation procedure for light-emitting diodes. Our simulation indicates that a one-dimensional photonic crystal is beneficial for color control but cannot improve the light extraction as asserted in that Letter.

Rapid laser fabrication of microlens array using colorless liquid photopolymer for AMOLED devices

NASA Astrophysics Data System (ADS)

Kim, Kwang-Ryul; Jeong, Han-Wook; Lee, Kong-Soo; Yi, Junsin; Yoo, Jae-Chern; Cho, Myung-Woo; Cho, Sung-Hak; Choi, Byoungdeog

2011-01-01

Microlens array (MLA) is microfabricated using Ultra Violet (UV) laser for display device applications. A colorless liquid photopolymer, Norland Optical Adhesive (NOA) 60, is spin-coated and pre-cured via UV light for completing the laser process. The laser energy controlled by a galvano scanner is radiated on the surface of the NOA 60. A rapid thermal volume expansion inside the material creates microlens array when the Gaussian laser energy is absorbed. The fabrication process conditions for various shapes and densities of MLA using a non-contact surface profiler are investigated. Furthermore, we analyze the optical and display characteristics for the Organic Light Emitting Diode (OLED) devices. Optimized condition furnishes the OLED with the enhancement of light emission by 15%. We show that UV laser technique, which is installed with NOA 60 MLA layer, is eligible for improving the performance of the next generation display devices.

Light Emitting Diodes for Fiber Optic Communications.

DTIC Science & Technology

1981-03-31

asC.3~~ in.(c)- above and do- (1) pcait by volu.3 of dicst.iLle =zto.- Pazo 10 .61Edd, tcxcopt colvonts used cha-l bo: * ( a ) Methyl. alcohbl I7or 04...AD £101 480 LASER DIODE LABS INC NEW BRUNSWICK NJ / 1 / L I GT EMITTING DIODES FOR FIBER OPTIC COWMICATIONS.Cul AR, at A GENNARO DAARO-76-C-813 NA 1...PRArrcmA. P . 1"UNISPE-D TO DDC CONTAINE A II&~-’llryBE v., R OF :AO , MflG DO 9W CORADCOM U S ARMY COMMUNICATIONS RESEARCH 9 DEVELOPMENT COMMAND

Quantum-dot light-emitting diodes utilizing CdSe /ZnS nanocrystals embedded in TiO2 thin film

NASA Astrophysics Data System (ADS)

Kang, Seung-Hee; Kumar, Ch. Kiran; Lee, Zonghoon; Kim, Kyung-Hyun; Huh, Chul; Kim, Eui-Tae

2008-11-01

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe /ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2/QDs /p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2/QDs /Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

Characteristics of blue organic light emitting diodes with different thick emitting layers

NASA Astrophysics Data System (ADS)

Li, Chong; Tsuboi, Taiju; Huang, Wei

2014-08-01

We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shamirzaev, V. T., E-mail: tim@isp.nsc.ru; Gaisler, V. A.; Shamirzaev, T. S.

The spectrum of ultraviolet (UV) InGaN/GaN light-emitting diodes and its dependence on the current flowing through the structure are studied. The intensity of the UV contribution to the integrated diode luminescence increases steadily with increasing density of current flowing through the structure, despite a drop in the emission quantum efficiency. The electroluminescence excitation conditions that allow the fraction of UV emission to be increased to 97% are established. It is shown that the nonuniform generation of extended defects, which penetrate the active region of the light-emitting diodes as the structures degrade upon local current overheating, reduces the integrated emission intensitymore » but does not affect the relative intensity of diode emission in the UV (370 nm) and visible (550 nm) spectral ranges.« less

Pulp chamber temperature rise during curing of resin-based composites with different light-curing units.

PubMed

Durey, Kathryn; Santini, Ario; Miletic, Vesna

2008-01-01

The purpose of the present study was to measure the intrapulpal temperature rise occurring during polymerisation of different shades of resin-based composites (RBCs), and two light-emitting diode (LED) units. Seventy non-carious permanent molars, that had been extracted for orthodontic purposes and stored in 2% thymol for not more than four months, were selected. Patient age range was 11-18 years. Standard cavity preparation with standardised remaining dentine thickness and placement of thermocouples (TCs) was prepared using a novel split-tooth technique. Cavities were filled with one of two shades of RBC (A2 and C4, Filtek Z250, 3M ESPE, Seefeld, Germany), and cured with two LED high-intensity units (Elipar Freelight2, 3M ESPE, Seefeld, Germany; Bluephase, Ivoclar Vivadent, Schaan, Liechtenstein) and a conventional halogen light-curing unit (LCU) (Prismetics Lite 2, Dentsply, Weybridge, Surrey, UK) as a control. Pulp temperature rises during bonding [A2 results: H;2.67/0.48:E;5.24/1.32;B;5.99/1.61] were always greater than during RBC curing [A2 results: 2.44/0.63;E3.34/0.70;B3.38/0.60], and these were significant for both LED lights but not for the halogen control, irrespective of shade (Mann-Whitney test: 95% confidence limits). Temperature rises were at times in excess of the values normally quoted as causing irreversible pulp damage. Pulp temperature rises during bonding were higher with the LED lights than with the halogen control. There was no significant difference in temperature rise between the two LED lights when bonding but there was a significant difference between the two LED lights and the halogen control LCUs (Kruskal-Wallis Test: 95% confidence limits). The results support the view that there is a potential risk for heat-induced pulpal injury when light-curing RBCs. The risk is greater during bonding and with high energy, as compared to low-energy output systems. As the extent of tolerable thermal trauma by the pulp tissues is unknown, care and consideration should be given to the choice of LCU and the exposure time when curing RBCs, and especially during bonding.

Effects of Light-Emitting Diode Therapy on Muscle Hypertrophy, Gene Expression, Performance, Damage, and Delayed-Onset Muscle Soreness: Case-control Study with a Pair of Identical Twins.

PubMed

Ferraresi, Cleber; Bertucci, Danilo; Schiavinato, Josiane; Reiff, Rodrigo; Araújo, Amélia; Panepucci, Rodrigo; Matheucci, Euclides; Cunha, Anderson Ferreira; Arakelian, Vivian Maria; Hamblin, Michael R; Parizotto, Nivaldo; Bagnato, Vanderlei

2016-10-01

The aim of this study was to verify how a pair of monozygotic twins would respond to light-emitting diode therapy (LEDT) or placebo combined with a strength-training program during 12 weeks. This case-control study enrolled a pair of male monozygotic twins, allocated randomly to LEDT or placebo therapies. Light-emitting diode therapy or placebo was applied from a flexible light-emitting diode array (λ = 850 nm, total energy = 75 J, t = 15 seconds) to both quadriceps femoris muscles of each twin immediately after each strength training session (3 times/wk for 12 weeks) consisting of leg press and leg extension exercises with load of 80% and 50% of the 1-repetition maximum test, respectively. Muscle biopsies, magnetic resonance imaging, maximal load, and fatigue resistance tests were conducted before and after the training program to assess gene expression, muscle hypertrophy and performance, respectively. Creatine kinase levels in blood and visual analog scale assessed muscle damage and delayed-onset muscle soreness, respectively, during the training program. Compared with placebo, LEDT increased the maximal load in exercise and reduced fatigue, creatine kinase, and visual analog scale. Gene expression analyses showed decreases in markers of inflammation (interleukin 1β) and muscle atrophy (myostatin) with LEDT. Protein synthesis (mammalian target of rapamycin) and oxidative stress defense (SOD2 [mitochondrial superoxide dismutase]) were up-regulated with LEDT, together with increases in thigh muscle hypertrophy. Light-emitting diode therapy can be useful to reduce muscle damage, pain, and atrophy, as well as to increase muscle mass, recovery, and athletic performance in rehabilitation programs and sports medicine.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

NASA Astrophysics Data System (ADS)

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-01

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method of enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

DOE PAGES

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-12

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

Fabrication of white light-emitting diodes based on UV light-emitting diodes with conjugated polymers-(CdSe/ZnS) quantum dots as hybrid phosphors.

PubMed

Jung, Hyunchul; Chung, Wonkeun; Lee, Chang Hun; Kim, Sung Hyun

2012-07-01

White light-emitting diodes (LEDs) were fabricated using GaN-based 380-nm UV LEDs precoated with the composite of blue-emitting polymer (poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(2-methoxy-5-{2-ethylhexyloxy)-1 ,4-phenylene)]), yellow green-emitting polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)]), and 605-nm red-emitting quantum dots (QDs). CdSe cores were obtained by solvothermal route using CdO, Se precursors and ZnS shells were synthesized by using diethylzinc, and hexamethyldisilathiane precursors. The optical properties of CdSe/ZnS QDs were characterized by UV-visible and photoluminescence (PL) spectra. The structural data and composition of the QDs were transmission electron microscopy (TEM), and EDX technique. The quantum yield and size of the QDs were 58.7% and about 6.7 nm, respectively. Three-band white light was generated by hybridizing blue (430 nm), green (535 nm), and red (605 nm) emission. The color-rendering index (CRI) of the device was extremely improved by introducing the QDs. The CIE-1931 chromaticity coordinate, color temperature, and CRI of a white LED at 20 mA were (0.379, 0.368), 3969 K, and 90, respectively.

The use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Chondroudis, Konstantinos; Mitzi, David B.

2000-01-01

The conversion of two neutral dye molecules (D) to ionic salts (H2N-D-NH2ṡ2HX) and their utilization as emitting layers in organic light-emitting diodes (OLEDs) is described. The dye salts, AEQTṡ2HCl and APTṡ2HCl, can be deposited as amorphous films using conventional evaporation techniques. X-ray diffraction and scanning electron microscopy analysis, coupled with thermal annealing studies, demonstrate the resistance of the films to crystallization. This stability is attributed to strong ionic forces between the relatively rigid molecules. OLEDs incorporating such salts for emitting layers exhibit better thermal stability compared with devices made from the corresponding neutral dyes (H2N-D-NH2). These results suggest that ionic salts may more generally enable the formation of thermally stable, amorphous emitting, and charge transporting layers.

Superluminescent light emitting diodes: the best out of two worlds

NASA Astrophysics Data System (ADS)

Rossetti, M.; Napierala, J.; Matuschek, N.; Achatz, U.; Duelk, M.; Vélez, C.; Castiglia, A.; Grandjean, N.; Dorsaz, J.; Feltin, E.

2012-03-01

Since pico-projectors were starting to become the next electronic "must-have" gadget, the experts were discussing which light-source technology seems to be the best for the existing three major projection approaches for the optical scanning module such as digital light processing, liquid crystal on silica and laser beam steering. Both so-far used light source technologies have distinct advantages and disadvantages. Though laser-based pico-projectors are focus-free and deliver a wider color gamut, their major disadvantages are speckle noise, cost and safety issues. In contrast, projectors based on cheaper Light Emitting Diodes (LEDs) as light source are criticized for a lack of brightness and for having limited focus. Superluminescent Light Emitting Diodes (SLEDs) are temporally incoherent and spatially coherent light sources merging in one technology the advantages of both Laser Diodes (LDs) and LEDs. With almost no visible speckle noise, focus-free operation and potentially the same color gamut than LDs, SLEDs could potentially answer the question which light source to use in future projector applications. In this quest for the best light source, we realized visible SLEDs emitting both in the red and blue spectral region. While the technology required for the realization of red emitters is already well established, III-nitride compounds required for blue emission have experienced a major development only in relatively recent times and the technology is still under development. The present paper is a review of the status of development reached for the blue superluminescent diodes based on the GaN material system.

Development and future of ultraviolet light-emitting diodes: UV-LED will replace the UV lamp

NASA Astrophysics Data System (ADS)

Muramoto, Yoshihiko; Kimura, Masahiro; Nouda, Suguru

2014-06-01

Ultraviolet light-emitting diodes (UV-LEDs) have started replacing UV lamps. The power per LED of high-power LED products has reached 12 W (14 A), which is 100 times the values observed ten years ago. In addition, the cost of these high-power LEDs has been decreasing. In this study, we attempt to understand the technologies and potential of UV-LEDs.

Safety of light emitting diodes in toys.

PubMed

Higlett, M P; O'Hagan, J B; Khazova, M

2012-03-01

Light emitting diodes (LEDs) are increasingly being used in toys. An assessment methodology is described for determining the accessible emission limits for the optical radiation from the toys, which takes account of expected use and reasonably foreseeable misuse of toys. Where data are available, it may be possible to assess the toy from the data sheet alone. If this information is not available, a simple measurement protocol is proposed.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, Richard P.; Lott, James A.

1994-01-01

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, R.P.; Lott, J.A.

1994-09-27

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors. 5 figs.

Solid State Research, 1975:4

DTIC Science & Technology

1975-11-15

2.8kA/cm for broad- area devices, has been achieved for Ga. In As, _ P /inP double-heterostructure 1 -x x 1 -y y diode lasers emitting ... LIGHT (b) reverse-biasing the p -n~ junction). This should facilitate the fabrication of modulators and switches using electroabsorption and...temperature operation of Ga In As, P /inP double-heterostructure (DH) diode lasers has been achieved. Broad-area devices emitting at 1.1

An electron transporting unit linked multifunctional Ir(III) complex: a promising strategy to improve the performance of solution-processed phosphorescent organic light-emitting diodes.

PubMed

Giridhar, Thota; Saravanan, Chinnusamy; Cho, Woosum; Park, Young Geun; Lee, Jin Yong; Jin, Sung-Ho

2014-04-18

An oxadiazole based electron transporting (ET) unit was glued to the heteroleptic Ir(III) complex (TPQIr-ET) and used as a dopant for phosphorescent organic light-emitting diodes (PhOLEDs). It shows superior device performance than the dopant without the ET unit (TPQIr) due to the balanced charge carrier injection by the ET unit.

Note: A portable, light-emitting diode-based ruby fluorescence spectrometer for high-pressure calibration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng Yejun

2011-04-15

Ruby (Al{sub 2}O{sub 3}, with {approx}0.5 wt. % Cr doping) is one of the most widely used manometers at the giga-Pascal scale. Traditionally, its fluorescence is excited with intense laser sources. Here, I present a simple, robust, and portable design that employs light-emitting diodes (LEDs) instead. This LED-based system is safer in comparison with laser-based ones.

Light emitting diodes (LED): applications in forest and native plant nurseries

Treesearch

Thomas D. Landis; Jeremiah R. Pinto; R. Kasten Dumroese

2013-01-01

It was quotes like this that made us want to learn more about light emitting diodes (LED). Other than knowing that LEDs were the latest innovation in artificial lighting, we knew that we had a lot to learn. So we started by reviewing some of the basics. The following review is a brief synopsis of how light affects plants and some discussion about LED lighting. If you...

Topical methyl-aminolevulinate photodynamic therapy using red light-emitting diode light for treatment of multiple actinic keratoses: A randomized, double-blind, placebo-controlled study.

PubMed

Pariser, David; Loss, Robert; Jarratt, Michael; Abramovits, William; Spencer, James; Geronemus, Roy; Bailin, Philip; Bruce, Suzanne

2008-10-01

The use of light-emitting diode light offers practical advantages in photodynamic therapy (PDT) with topical methyl-aminolevulinate (MAL) for management of actinic keratoses (AK). We sought to evaluate the efficacy of MAL PDT using red light-emitting diode light. We conducted a multicenter, double-blind, randomized study. A total of 49 patients with 363 AK lesions had 16.8% MAL cream applied under occlusion for 3 hours, and 47 patients with 360 AK lesions had vehicle cream similarly applied. The lesions were then illuminated (630 nm, light dose 37 J/cm2) with repeated treatment 1 week later. Complete lesion and patient (all lesions showing complete response) response rates were evaluated 3 months after last treatment. MAL PDT was superior (P<.0001) to vehicle PDT with respect to lesion complete response (86.2% vs 52.2%, odds ratio 6.9 [95% confidence interval 4.7-10.3]) and patient complete response (59.2% vs 14.9%, odds ratio 13.2 [95% confidence interval 4.1-43.1]). The study population may not be representative of all patients with AK. MAL PDT using red light-emitting diode light is an appropriate treatment alternative for multiple AK lesions.

Clinical comparison between the bleaching efficacy of light-emitting diode and diode laser with sodium perborate.

PubMed

Koçak, Sibel; Koçak, Mustafa Murat; Sağlam, Baran Can

2014-04-01

The aim of this clinical study was to test the efficacy of a light-emitting diode (LED) light and a diode laser, when bleaching with sodium perborate. Thirty volunteers were selected to participate in the study. The patients were randomly divided into two groups. The initial colour of each tooth to be bleached was quantified with a spectrophotometer. In group A, sodium perborate and distilled water were mixed and placed into the pulp chamber, and the LED light was source applied. In group B, the same mixture was used, and the 810 nm diode laser was applied. The final colour of each tooth was quantified with the same spectrophotometer. Initial and final spectrophotometer values were recorded. Mann-Whitney U-test and Wicoxon tests were used to test differences between both groups. Both devices successfully whitened the teeth. No statistical difference was found between the efficacy of the LED light and the diode laser. © 2013 The Authors. Australian Endodontic Journal © 2013 Australian Society of Endodontology.

Direct observation of back energy transfer in blue phosphorescent materials for organic light emitting diodes by time-resolved optical waveguide spectroscopy.

PubMed

Hirayama, H; Sugawara, Y; Miyashita, Y; Mitsuishi, M; Miyashita, T

2013-02-25

We demonstrate a high-sensitive transient absorption technique for detection of excited states in an organic thin film by time-resolved optical waveguide spectroscopy. By using a laser beam as a probe light, we detect small change in the transient absorbance which is equivalent to 10 -7 absorbance unit in a conventional method. This technique was applied to organic thin films of blue phosphorescent materials for organic light emitting diodes. We directly observed the back energy transfer from emitting guest molecules to conductive host molecules.

Method of Manufacturing a Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Blanchard, Richard A. (Inventor); Lewandowski, Mark Allan (Inventor); Frazier, Donald Odell (Inventor); Ray, William Johnstone (Inventor); Fuller, Kirk A. (Inventor); Lowenthal, Mark David (Inventor); Shotton, Neil O. (Inventor)

2014-01-01

The present invention provides a method of manufacturing an electronic apparatus, such as a lighting device having light emitting diodes (LEDs) or a power generating device having photovoltaic diodes. The exemplary method includes depositing a first conductive medium within a plurality of channels of a base to form a plurality of first conductors; depositing within the plurality of channels a plurality of semiconductor substrate particles suspended in a carrier medium; forming an ohmic contact between each semiconductor substrate particle and a first conductor; converting the semiconductor substrate particles into a plurality of semiconductor diodes; depositing a second conductive medium to form a plurality of second conductors coupled to the plurality of semiconductor diodes; and depositing or attaching a plurality of lenses suspended in a first polymer over the plurality of diodes. In various embodiments, the depositing, forming, coupling and converting steps are performed by or through a printing process.

Method of Manufacturing a Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Lowenthal, Mark D. (Inventor); Shotton, Neil O. (Inventor); Lewandowski, Mark Allan (Inventor); Frazier, Donald Odell (Inventor); Ray, William Johnstone (Inventor); Blanchard, Richard A. (Inventor); Fuller, Kirk A. (Inventor)

2013-01-01

The present invention provides a method of manufacturing an electronic apparatus, such as a lighting device having light emitting diodes (LEDs) or a power generating device having photovoltaic diodes. The exemplary method includes forming at least one first conductor coupled to a base; coupling a plurality of substrate particles to the at least one first conductor; converting the plurality of substrate particles into a plurality of diodes; forming at least one second conductor coupled to the plurality of spherical diodes; and depositing or attaching a plurality of substantially spherical lenses suspended in a first polymer, with the lenses and the suspending polymer having different indices of refraction. In some embodiments, the lenses and diodes have a ratio of mean diameters or lengths between about 10:1 and 2:1. In various embodiments, the forming, coupling and converting steps are performed by or through a printing process.

Method of manufacturing a light emitting, photovoltaic or other electronic apparatus and system

NASA Technical Reports Server (NTRS)

Fuller, Kirk A. (Inventor); Frazier, Donald Odell (Inventor); Blanchard, Richard A. (Inventor); Lowenthal, Mark D. (Inventor); Lewandowski, Mark Allan (Inventor); Ray, William Johnstone (Inventor); Shotton, Neil O. (Inventor)

2012-01-01

The present invention provides a method of manufacturing an electronic apparatus, such as a lighting device having light emitting diodes (LEDs) or a power generating device having photovoltaic diodes. The exemplary method includes depositing a first conductive medium within a plurality of channels of a base to form a plurality of first conductors; depositing within the plurality of channels a plurality of semiconductor substrate particles suspended in a carrier medium; forming an ohmic contact between each semiconductor substrate particle and a first conductor; converting the semiconductor substrate particles into a plurality of semiconductor diodes; depositing a second conductive medium to form a plurality of second conductors coupled to the plurality of semiconductor diodes; and depositing or attaching a plurality of lenses suspended in a first polymer over the plurality of diodes. In various embodiments, the depositing, forming, coupling and converting steps are performed by or through a printing process.

Method of Manufacturing a Light Emitting, Photovoltaic or Other Electronic Apparatus and System

NASA Technical Reports Server (NTRS)

Blanchard, Richard A. (Inventor); Fuller, Kirk A. (Inventor); Ray, William Johnstone (Inventor); Shotton, Neil O. (Inventor); Frazier, Donald Odell (Inventor); Lowenthal, Mark D. (Inventor); Lewandowski, Mark Allan (Inventor)

2013-01-01

The present invention provides a method of manufacturing an electronic apparatus, such as a lighting device having light emitting diodes (LEDs) or a power generating device having photovoltaic diodes. The exemplary method includes forming at least one first conductor coupled to a base; coupling a plurality of substantially spherical substrate particles to the at least one first conductor; converting the substrate particles into a plurality of substantially spherical diodes; forming at least one second conductor coupled to the substantially spherical diodes; and depositing or attaching a plurality of substantially spherical lenses suspended in a first polymer. The lenses and the suspending polymer have different indices of refraction. In some embodiments, the lenses and diodes have a ratio of mean diameters or lengths between about 10:1 and 2:1. In various embodiments, the forming, coupling and converting steps are performed by or through a printing process.

Hybrid Structure White Organic Light Emitting Diode for Enhanced Efficiency by Varied Doping Rate.

PubMed

Kim, Dong-Eun; Kang, Min-Jae; Park, Gwang-Ryeol; Kim, Nam-Kyu; Lee, Burm-Jong; Kwon, Young-Soo; Shin, Hoon-Kyu

2016-03-01

Novel materials based on Zn(HPB)2 and Ir-complexes were synthesized as blue or red emitters, respectively. White organic light emitting diodes were fabricated using the Zn(HPB)2 as a blue emitting layer, Ir-complexes as a red emitting layer and Alq3 as a green emitting layer. The obtained experimental results, were based on white OLEDs fabricated using double emission layers of Zn(HPB)2 and Alq3:Ir-complexes. The doping rate of the Ir-complexes was varied at 0.4%, 0.6%, 0.8% and 1.0%. When the doping rate of the Alq3:Ir-complexes was 0.6%, a white emission was achieved. The Commission Internationale de l'Eclairage coordinates of the device's white emission were (0.316, 0.331) at an applied voltage of 10.75 V.

A promising red-emitting phosphor for white-light-emitting diodes prepared by a modified solid-state reaction

NASA Astrophysics Data System (ADS)

Ren, Fuqiang; Chen, Donghua

2010-02-01

Using urea, boric acid and polyethylene glycol (PEG) as auxiliary reagents, the novel red-emitting phosphors Ca 19Zn 2 (PO 4) 14:Eu 3+ have been successfully synthesized by a modified solid-state reaction. Thermogravimetric (TG) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectra were used to characterize the resulting phosphors. The dependence of the photoluminescence properties of Ca 19Zn 2 (PO 4) 14:Eu 3+ phosphors upon urea, boric acid and PEG concentration and the quadric-sintered temperature were investigated. Luminescent measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a red light with a peak wavelength of 616 nm. The material has potential application as a fluorescent material for ultraviolet light-emitting diodes (UV-LEDs).

In vitro pulp chamber temperature rise from irradiation and exotherm of flowable composites.

PubMed

Baroudi, Kusai; Silikas, Nick; Watts, David C

2009-01-01

The aim of this study was to investigate the pulpal temperature rise induced during the polymerization of flowable and non-flowable composites using light-emitting diode (LED) and halogen (quartz-tungsten-halogen) light-curing units (LCUs). Five flowable and three non-flowable composites were examined. Pulpal temperature changes were recorded over 10 min in a sample primary tooth by a thermocouple. A conventional quartz-tungsten-halogen source and two LEDs, one of which was programmable, were used for light curing the resin composites. Three repetitions per material were made for each LCU. There was a wide range of temperature rises among the materials (P < 0.05). Temperature rises ranged between 1.3 degrees C for Filtek Supreme irradiated by low-power LED and 4.5 degrees C for Grandio Flow irradiated by high-power LED. The highest temperature rises were observed with both the LED high-power and soft-start LCUs. The time to reach the exothermic peak varied significantly between the materials (P < 0.05). Pulpal temperature rise is related to both the radiant energy output from LCUs and the polymerization exotherm of resin composites. A greater potential risk for heat-induced pulp damage might be associated with high-power LED sources. Flowable composites exhibited higher temperature rises than non-flowable materials, because of higher resin contents.

High-performance planar green light-emitting diodes based on a PEDOT:PSS/CH3NH3PbBr3/ZnO sandwich structure

NASA Astrophysics Data System (ADS)

Shi, Zhi-Feng; Sun, Xu-Guang; Wu, Di; Xu, Ting-Ting; Zhuang, Shi-Wei; Tian, Yong-Tao; Li, Xin-Jian; Du, Guo-Tong

2016-05-01

Recently, perovskite-based light-emitting diodes based on organometal halide emitters have attracted much attention because of their excellent properties of high color purity, tunable emission wavelength and a low-temperature processing technique. As is well-known, organic light-emitting diodes have shown powerful capabilities in this field; however, the fabrication of these devices typically relies on high-temperature and high-vacuum processes, which increases the final cost of the product and renders them uneconomical for use in large-area displays. Organic/inorganic hybrid halide perovskites match with these material requirements, as it is possible to prepare such materials with high crystallinity through solution processing at low temperature. Herein, we demonstrated a high-brightness green light-emitting diode based on PEDOT:PSS/CH3NH3PbBr3/ZnO sandwich structures by a spin-coating method combined with a sputtering system. Under forward bias, a dominant emission peak at ~530 nm with a low full width of half-maximum (FWHM) of 30 nm can be achieved at room temperature. Owing to the high surface coverage of the CH3NH3PbBr3 layer and a device design based on carrier injection and a confinement configuration, the proposed diode exhibits good electroluminescence performance, with an external quantum efficiency of 0.0645%. More importantly, we investigated the working stability of the studied diode under continuous operation to verify the sensitivity of the electroluminescence performance to ambient atmosphere and to assess the suitability of the diode for practical applications. Moreover, the underlying reasons for the undesirable emission decay are tentatively discussed. This demonstration of an effective green electroluminescence based on CH3NH3PbBr3 provides valuable information for the design and development of perovskites as efficient emitters, thus facilitating their use in existing applications and suggesting new potential applications.

Color-tunable and high-efficiency organic light-emitting diode by adjusting exciton bilateral migration zone

NASA Astrophysics Data System (ADS)

Liu, Shengqiang; Wu, Ruofan; Huang, Jiang; Yu, Junsheng

2013-09-01

A voltage-controlled color-tunable and high-efficiency organic light-emitting diode (OLED) by inserting 16-nm N,N'-dicarbazolyl-3,5-benzene (mCP) interlayer between two complementary emitting layers (EMLs) was fabricated. The OLED emitted multicolor ranging from blue (77.4 cd/A @ 6 V), white (70.4 cd/A @ 7 V), to yellow (33.7 cd/A @ 9 V) with voltage variation. An equivalent model was proposed to reveal the color-tunable and high-efficiency emission of OLEDs, resulting from the swing of exciton bilateral migration zone near mCP/blue-EML interface. Also, the model was verified with a theoretical arithmetic using single-EML OLEDs to disclose the crucial role of mCP exciton adjusting layer.

P-doping-free III-nitride high electron mobility light-emitting diodes and transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Baikui; Tang, Xi; Chen, Kevin J., E-mail: eekjchen@ust.hk

2014-07-21

We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ∼2 V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level de-pinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a “universal” property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward andmore » seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated.« less

Origin of Negative Capacitance in Bipolar Organic Diodes

NASA Astrophysics Data System (ADS)

Niu, Quan; Crǎciun, N. Irina; Wetzelaer, Gert-Jan A. H.; Blom, Paul W. M.

2018-03-01

Negative differential capacitance (NC) occurring at low frequencies in organic light-emitting diodes (OLEDs) is a poorly understood phenomenon. We study the origin of the NC effect by systematically varying the number of electron traps in OLEDs based on the polymeric semiconductor poly(p -phenylene vinylene). Increasing the electron trap density enhances the NC effect. The magnitude and observed decrease of the relaxation time is consistent with the (inverse) rate of trap-assisted recombination. The absence of NC in a nearly trap-free light-emitting diode unambiguously shows that trap-assisted recombination is the responsible mechanism for the negative contribution to the capacitance in bipolar organic diodes. Our results reveal that the NC effect can be exploited to quantitatively determine the number of traps in organic semiconductors in a nondestructive fashion.

Fabrication and characterization of n-ZnO nanonails array/p(+)-GaN heterojunction diode.

PubMed

Zhu, G Y; Chen, G F; Li, J T; Shi, Z L; Lin, Y; Ding, T; Xu, X Y; Dai, J; Xu, C X

2012-10-01

A novel heterojunctional structure of n-ZnO nanonails array/p(+)-GaN light-emitting diode was fabricated by Chemical Vapor Deposition method. A broad electroluminescence spectrum shows two peaks centered at 435 nm and 478 nm at room temperature, respectively. By comparing the photoluminescence and electroluminescence spectra, together with analyzing the energy band structure of heterojunction light emitting diode, it suggested that the electroluminescence peak located at 435 nm originates from Mg acceptor level of p(+)-GaN layer, whereas the electroluminescence peak located at 478 nm originates from the defects of n-ZnO nanonails array.

Investigation of Light-Emitting Diode (LED) Point Light Source Color Visibility against Complex Multicolored Backgrounds

DTIC Science & Technology

2017-11-01

sent from light-emitting diodes (LEDs) of 5 colors ( green , red, white, amber, and blue). Experiment 1 involved controlled laboratory measurements of...A-4 Red LED calibration curves and quadratic curve fits with R2 values . 37 Fig. A-5 Green LED calibration curves and quadratic curve fits with R2...36 Table A-4 Red LED calibration measurements ................................................... 36 Table A-5 Green LED

Dual-Color Emission in Hybrid III-Nitride/ZnO Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Namkoong, Gon; Trybus, Elaissa; Cheung, Maurice C.; Doolittle, W. Alan; Cartwright, Alexander N.; Ferguson, Ian; Seong, Tae-Yeon; Nause, Jeff

2010-02-01

We report dual-color production of the blue and green regions using hybrid nitride/ZnO light emitting diode (LED) structures grown on ZnO substrates. The blue emission is ascribed to the near-band edge transition in InGaN while green emission is related to Zn-related defect levels formed by the unintentional interdiffusion of Zn into the InGaN active layer from the ZnO substrates.

Inkjet Printing of Organic Light-Emitting Diodes Based on Alcohol-Soluble Polyfluorenes

NASA Astrophysics Data System (ADS)

Odod, A. V.; Gadirov, R. M.; Solodova, T. A.; Kurtsevich, A. E.; Il'gach, D. M.; Yakimanskii, A. V.; Burtman, V.; Kopylova, T. N.

2018-04-01

Ink compositions for inkjet printing based on poly(9.9-dioctylfluorene) and its alcohol-soluble analog are created. Current-voltage, brightness-voltage, and spectral characteristics are compared for one- and twolayer polymer structures of organic light-emitting diodes. It is shown that the efficiency of the alcohol-soluble polyfluorene analog is higher compared to poly(9.9-dioctylfluorene), and the possibility of viscosity optimization is higher compared to aromatic chlorinated solvents.

Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering.

PubMed

Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Murali, Banavoth; Sarmah, Smritakshi P; Yuan, Mingjian; Sinatra, Lutfan; Alyami, Noktan M; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N; Mohammed, Omar F; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H; Bakr, Osman M

2016-10-01

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX 3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High extraction efficiency ultraviolet light-emitting diode

DOEpatents

Wierer, Jonathan; Montano, Ines; Allerman, Andrew A.

2015-11-24

Ultraviolet light-emitting diodes with tailored AlGaN quantum wells can achieve high extraction efficiency. For efficient bottom light extraction, parallel polarized light is preferred, because it propagates predominately perpendicular to the QW plane and into the typical and more efficient light escape cones. This is favored over perpendicular polarized light that propagates along the QW plane which requires multiple, lossy bounces before extraction. The thickness and carrier density of AlGaN QW layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. At Al>0.3, thinner QW layers (<2.5 nm are preferred) result in light preferentially polarized parallel to the QW plane. Also, active regions consisting of six or more QWs, to reduce carrier density, and with thin barriers, to efficiently inject carriers in all the QWs, are preferred.

Axial diffusion barriers in near-infrared nanopillar LEDs.

PubMed

Scofield, Adam C; Lin, Andrew; Haddad, Michael; Huffaker, Diana L

2014-11-12

The growth of GaAs/GaAsP axial heterostructures is demonstrated and implemented as diffusion current barriers in nanopillar light-emitting diodes at near-infrared wavelengths. The nanopillar light-emitting diodes utilize an n-GaAs/i-InGaAs/p-GaAs axial heterostructure for current injection. Axial GaAsP segments are inserted into the n- and p-GaAs portions of the nanopillars surrounding the InGaAs emitter region, acting as diffusion barriers to provide enhanced carrier confinement. Detailed characterization of growth of the GaAsP inserts and electronic band-offset measurements are used to effectively implement the GaAsP inserts as diffusion barriers. The implementation of these barriers in nanopillar light-emitting diodes provides a 5-fold increase in output intensity, making this a promising approach to high-efficiency pillar-based emitters in the near-infrared wavelength range.

On the effect of ballistic overflow on the temperature dependence of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prudaev, I. A., E-mail: funcelab@gmail.com; Kopyev, V. V.; Romanov, I. S.

The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulationmore » results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.« less

Improvement in Brightness Uniformity by Compensating for the Threshold Voltages of Both the Driving Thin-Film Transistor and the Organic Light-Emitting Diode for Active-Matrix Organic Light-Emitting Diode Displays

NASA Astrophysics Data System (ADS)

Ching-Lin Fan,; Hui-Lung Lai,; Jyu-Yu Chang,

2010-05-01

In this paper, we propose a novel pixel design and driving method for active-matrix organic light-emitting diode (AM-OLED) displays using low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs). The proposed threshold voltage compensation circuit, which comprised five transistors and two capacitors, has been verified to supply uniform output current by simulation work using the automatic integrated circuit modeling simulation program with integrated circuit emphasis (AIM-SPICE) simulator. The driving scheme of this voltage programming method includes four periods: precharging, compensation, data input, and emission. The simulated results demonstrate excellent properties such as low error rate of OLED anode voltage variation (<1%) and high output current. The proposed pixel circuit shows high immunity to the threshold voltage deviation characteristics of both the driving poly-Si TFT and the OLED.

New Driving Scheme to Improve Hysteresis Characteristics of Organic Thin Film Transistor-Driven Active-Matrix Organic Light Emitting Diode Display

NASA Astrophysics Data System (ADS)

Yamamoto, Toshihiro; Nakajima, Yoshiki; Takei, Tatsuya; Fujisaki, Yoshihide; Fukagawa, Hirohiko; Suzuki, Mitsunori; Motomura, Genichi; Sato, Hiroto; Tokito, Shizuo; Fujikake, Hideo

2011-02-01

A new driving scheme for an active-matrix organic light emitting diode (AMOLED) display was developed to prevent the picture quality degradation caused by the hysteresis characteristics of organic thin film transistors (OTFTs). In this driving scheme, the gate electrode voltage of a driving-OTFT is directly controlled through the storage capacitor so that the operating point for the driving-OTFT is on the same hysteresis curve for every pixel after signal data are stored in the storage capacitor. Although the number of OTFTs in each pixel for the AMOLED display is restricted because OTFT size should be large enough to drive organic light emitting diodes (OLEDs) due to their small carrier mobility, it can improve the picture quality for an OTFT-driven flexible OLED display with the basic two transistor-one capacitor circuitry.

Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

NASA Astrophysics Data System (ADS)

Wang, Min-Shuai; Huang, Xiao-Jing

2013-08-01

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN-based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaN-based light-emitting diodes (LEDs) with surface V-pits in different densities and regions were grown by metal—organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Enhanced light extraction from a GaN-based green light-emitting diode with hemicylindrical linear grating structure.

PubMed

Jin, Yuanhao; Yang, Fenglei; Li, Qunqing; Zhu, Zhendong; Zhu, Jun; Fan, Shoushan

2012-07-02

Significant enhancement in the light output from GaN-based green light-emitting diodes (LEDs) was achieved with a hemicylindrical grating structure on the top layer of the diodes. The grating structure was first optimized by the finite-difference time-domain (FDTD) method, which showed that the profile of the grating structure was critical for light extraction efficiency. It was found that the transmission efficiency of the 530 nm light emitted from the inside of the GaN LED increased for incidence angles between 23.58° and 60°. Such a structure was fabricated by electron-beam lithography and an etching method. The light output power from the LED was increased approximately 4.7 times compared with that from a conventional LED. The structure optimization is the key to the great increase in transmission efficiency. Furthermore, the light emitted from the edge of the LED units could be collected and extracted by the grating structures in adjacent LED units, thus enhancing the performance of the whole LED chip.

White organic light-emitting diodes with ultra-thin mixed emitting layer

NASA Astrophysics Data System (ADS)

Jeon, T.; Forget, S.; Chenais, S.; Geffroy, B.; Tondelier, D.; Bonnassieux, Y.; Ishow, E.

2012-02-01

White light can be obtained from Organic Light Emitting Diodes by mixing three primary colors, (i.e. red, green and blue) or two complementary colors in the emissive layer. In order to improve the efficiency and stability of the devices, a host-guest system is generally used as an emitting layer. However, the color balance to obtain white light is difficult to control and optimize because the spectrum is very sensitive to doping concentration (especially when a small amount of material is used). We use here an ultra-thin mixed emitting layer (UML) deposited by thermal evaporation to fabricate white organic light emitting diodes (WOLEDs) without co-evaporation. The UML was inserted in the hole-transporting layer consisting of 4, 4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPB) instead of using a conventional doping process. The UML was formed from a single evaporation boat containing a mixture of two dipolar starbust triarylamine molecules (fvin and fcho) presenting very similar structures and thermal properties and emitting in complementary spectral regions (orange and blue respectively) and mixed according to their weight ratio. The composition of the UML specifically allows for fine tuning of the emission color despite its very thin thickness down to 1 nm. Competitive energy transfer processes from fcho and the host interface toward fvin are key parameters to control the relative intensity between red and blue emission. White light with very good CIE 1931 color coordinate (0.34, 0.34) was obtained by simply adjusting the UML film composition.

VLED for Si wafer-level packaging

NASA Astrophysics Data System (ADS)

Chu, Chen-Fu; Chen, Chiming; Yen, Jui-Kang; Chen, Yung-Wei; Tsou, Chingfu; Chang, Chunming; Doan, Trung; Tran, Chuong Anh

2012-03-01

In this paper, we introduced the advantages of Vertical Light emitting diode (VLED) on copper alloy with Si-wafer level packaging technologies. The silicon-based packaging substrate starts with a <100> dou-ble-side polished p-type silicon wafer, then anisotropic wet etching technology is done to construct the re-flector depression and micro through-holes on the silicon substrate. The operating voltage, at a typical cur-rent of 350 milli-ampere (mA), is 3.2V. The operation voltage is less than 3.7V under higher current driving conditions of 1A. The VLED chip on Si package has excellent heat dissipation and can be operated at high currents up to 1A without efficiency degradation. The typical spatial radiation pattern emits a uniform light lambertian distribution from -65° to 65° which can be easily fit for secondary optics. The correlated color temperature (CCT) has only 5% variation for daylight and less than 2% variation for warm white, when the junction temperature is increased from 25°C to 110°C, suggesting a stable CCT during operation for general lighting application. Coupled with aspheric lens and micro lens array in a wafer level process, it has almost the same light distribution intensity for special secondary optics lighting applications. In addition, the ul-tra-violet (UV) VLED, featuring a silicon substrate and hard glass cover, manufactured by wafer level pack-aging emits high power UV wavelengths appropriate for curing, currency, document verification, tanning, medical, and sterilization applications.

Weak-microcavity organic light-emitting diodes with improved light out-coupling.

PubMed

Cho, Sang-Hwan; Song, Young-Woo; Lee, Joon-gu; Kim, Yoon-Chang; Lee, Jong Hyuk; Ha, Jaeheung; Oh, Jong-Suk; Lee, So Young; Lee, Sun Young; Hwang, Kyu Hwan; Zang, Dong-Sik; Lee, Yong-Hee

2008-08-18

We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays with improved light-extraction and viewing-angle characteristics. A single pair of low- and high-index layers is inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red, green, and blue weak-microcavity OLEDs are enhanced by 56%, 107%, and 26%, respectively, with improved color purity. Moreover, full-color passive-matrix bottom-emitting OLED displays are fabricated by employing low-index layers of two thicknesses. As a display, the EL efficiency of white color was 27% higher than that of a conventional OLED display.

A tunable lighting system integrated by inorganic and transparent organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Jing-jing; Zhang, Tao; Jin, Ya-fang; Liu, Shi-shen; Yuan, Shi-dong; Cui, Zhao; Zhang, Li; Wang, Wei-hui

2014-05-01

A tunable surface-emitting integrated lighting system is constructed using a combination of inorganic light-emitting diodes (LEDs) and transparent organic LEDs (OLEDs). An RB two-color LED is used to supply red and blue light emission, and a green organic LED is used to supply green light emission. Currents of the LED and OLED are tuned to produce a white color, showing different Commission Internationale d'Eclairage (CIE) chromaticity coordinates and correlated color temperatures with a wide adjustable range. Such an integration can compensate for the lack of the LED's luminance uniformity and the transparent OLED's luminance intensity.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

NASA Astrophysics Data System (ADS)

Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

2007-06-01

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

Mn2- x Y x (MoO4)3 Phosphor Excited by UV GaN-Based Light-Emitting Diode for White Emission

NASA Astrophysics Data System (ADS)

Chen, Lung-Chien; Tseng, Zong-Liang; Hsu, Ting-Chun; Yang, Shengyi; Chen, Yuan-Bin

2017-04-01

One option for low-cost white light-emitting diodes (LEDs) is the combination of a near-ultraviolet (UV) LED chip (382 nm) and a single phosphor. Such Mn2- x Y x (MoO4)3 single phosphors have been fabricated by a simple solid-state reaction route and their emission color tuned by controlling the Mn doping amount. The chromaticity coordinates of the white light emitted by the UV GaN LED with the MnY(MoO4)3 phosphor were x = 0.5204 and y = 0.4050 [correlated color temperature (CCT) = 7958 K].

Efficient blue emission of ytterbium-doped Sr5(PO4)3F under quasi-three-level intracavity pumping

NASA Astrophysics Data System (ADS)

Yang, Y.; Cao, G. H.

2012-02-01

We report an Yb:Sr5(PO4)3F (Yb:S-FAP) laser emitting at 985 nm intracavity pumped by a 912 nm diode-pumped Nd:GdVO4 laser. A 808 nm diode laser is used to pump the Nd:GdVO4 crystal emitting at 912 nm, and the Yb:S-FAP laser emitting at 985 nm intracavity pumped at 912 nm. With incident pump power of 17.5 W, intracavity second harmonic generation has been demonstrated with a power of 131 mW at 492.5 nm by using a LBO nonlinear crystal.

Flexible bottom-emitting white organic light-emitting diodes with semitransparent Ni/Ag/Ni anode.

PubMed

Koo, Ja-Ryong; Lee, Seok Jae; Lee, Ho Won; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Woo Young; Kim, Young Kwan

2013-05-06

We fabricated a flexible bottom-emitting white organic light-emitting diode (BEWOLED) with a structure of PET/Ni/Ag/Ni (3/6/3 nm)/ NPB (50 nm)/mCP (10 nm)/7% FIrpic:mCP (10 nm)/3% Ir(pq)(2) acac:TPBi (5 nm)/7% FIrpic:TPBi (5 nm)/TPBi (10 nm)/Liq (2 nm)/ Al (100 nm). To improve the performance of the BEWOLED, a multilayered metal stack anode of Ni/Ag/Ni treated with oxygen plasma for 60 sec was introduced into the OLED devices. The Ni/Ag/Ni anode effectively enhanced the probability of hole-electron recombination due to an efficient hole injection into and charge balance in an emitting layer. By comparing with a reference WOLED using ITO on glass, it is verified that the flexible BEWOLED showed a similar or better electroluminescence (EL) performance.

Methodological comparison on OLED and OLET fabrication

NASA Astrophysics Data System (ADS)

Suppiah, Sarveshvaran; Hambali, Nor Azura Malini Ahmad; Wahid, Mohamad Halim Abd; Retnasamy, Vithyacharan; Shahimin, Mukhzeer Mohamad

2018-02-01

The potential of organic semiconductor devices for light generation is demonstrated by the commercialization of display technologies based on organic light emitting diode (OLED). In OLED, organic materials play the role of light emission once the current is passed through. However, OLED do have major drawbacks whereby it suffers from photon loss and exciton quenching. Organic light emitting transistor (OLET) emerged as the new technology to compensate the efficiency and brightness loss encountered in OLED. The structure has combinational capability to switch the electronic signal such as the field effect transistor (FET) as well as light generation. The aim of this study is to methodologically compare and contrast fabrication process and evaluate feasibility of both organic light emitting diode (OLED) and organic light emitting transistor (OLET). The proposed light emitting layer in this study is poly [2-methoxy-5- (2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV).

Solution-Grown ZnO Films toward Transparent and Smart Dual-Color Light-Emitting Diode.

PubMed

Huang, Xiaohu; Zhang, Li; Wang, Shijie; Chi, Dongzhi; Chua, Soo Jin

2016-06-22

An individual light-emitting diode (LED) capable of emitting different colors of light under different bias conditions not only allows for compact device integration but also extends the functionality of the LED beyond traditional illumination and display. Herein, we report a color-switchable LED based on solution-grown n-type ZnO on p-GaN/n-GaN heterojunction. The LED emits red light with a peak centered at ∼692 nm and a full width at half-maximum of ∼90 nm under forward bias, while it emits green light under reverse bias. These two lighting colors can be switched repeatedly by reversing the bias polarity. The bias-polarity-switched dual-color LED enables independent control over the lighting color and brightness of each emission with two-terminal operation. The results offer a promising strategy toward transparent, miniaturized, and smart LEDs, which hold great potential in optoelectronics and optical communication.

Enhanced electron injection into inverted polymer light-emitting diodes by combined solution-processed zinc oxide/polyethylenimine interlayers.

PubMed

Höfle, Stefan; Schienle, Alexander; Bruns, Michael; Lemmer, Uli; Colsmann, Alexander

2014-05-01

Inverted device architectures for organic light-emitting diodes (OLEDs) require suitable interfaces or buffer layers to enhance electron injection from highwork-function transparent electrodes. A solution-processable combination of ZnO and PEI is reported, that facilitates electron injection and enables efficient and air-stable inverted devices. Replacing the metal anode by highly conductive polymers enables transparent OLEDs. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solution-processed multilayer polymer light-emitting diode without intermixing

NASA Astrophysics Data System (ADS)

Kasparek, C.; Blom, P. W. M.

2017-01-01

The intermixing of two emissive layers in a four-layer solution-processed polymeric light-emitting diode with a hole injection, two emissive layers, and one hole-blocking layer is investigated. The relative emission of both emissive layers is measured and compared to a calculated recombination profile across the device using drift-diffusion simulations. A good agreement between the measured and calculated relative emission was found, supporting that there is no intermixing in the two emissive materials.

Ultraviolet Light Emitting Diode Use in Advanced Oxidation Processes

DTIC Science & Technology

2014-03-27

or medium pressure mercury lamps , but UV light emitting diodes ( LEDs ) have the capacity to be used for water disinfection also. Traditional mercury...based upon the phosphors that are selected and used to coat the inside of the glass tube from which these lamps are produced. A UV LED is...Research has demonstrated the ability to use UV LEDs in place of mercury lamps to achieve the same 7 disinfection capacity, and limited research has

High efficiency III-nitride light-emitting diodes

DOEpatents

Crawford, Mary; Koleske, Daniel; Cho, Jaehee; Zhu, Di; Noemaun, Ahmed; Schubert, Martin F; Schubert, E. Fred

2013-05-28

Tailored doping of barrier layers enables balancing of the radiative recombination among the multiple-quantum-wells in III-Nitride light-emitting diodes. This tailored doping enables more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop in high-power III-Nitride LEDs. Mitigation of the efficiency droop in III-Nitride LEDs may enable the pervasive market penetration of solid-state-lighting technologies in high-power lighting and illumination.

Silicon Based Colloidal Quantum Dot and Nanotube Lasers

DTIC Science & Technology

2013-03-01

carrier density is theoretically and experimentally derived to be inversely proportional to the diameter; (b) demonstration of InGaN/ GaN light emitting...diodes and GaN single nanowire photonic crystal laser on silicon characterized by a lasing transition at λ=371.3 nm with a linewidth of 0.55 nm. The...derived to be inversely proportional to the diameter; (b) demonstration of InGaN/ GaN light emitting diodes and GaN single nanowire photonic crystal

Evaluation of Ho:KPb2Cl5 as a Diode-Pumpable Mid-IR Laser Material

DTIC Science & Technology

2016-09-01

is the decay of the upper laser level without emitting light , due to the simultaneous emission of enough lattice vibrational quanta (phonons) to...have an energy level spacing that can result in emission at the desired laser wavelength, and that state must emit light efficiently. It is also...extremely desirable that it absorb light in the wavelength region where laser diodes operate most efficiently, approximately 800–1000 nm. This enables

Amber light-emitting diode comprising a group III-nitride nanowire active region

DOEpatents

Wang, George T.; Li, Qiming; Wierer, Jr., Jonathan J.; Koleske, Daniel

2014-07-22

A temperature stable (color and efficiency) III-nitride based amber (585 nm) light-emitting diode is based on a novel hybrid nanowire-planar structure. The arrays of GaN nanowires enable radial InGaN/GaN quantum well LED structures with high indium content and high material quality. The high efficiency and temperature stable direct yellow and red phosphor-free emitters enable high efficiency white LEDs based on the RGYB color-mixing approach.

Finger blood content, light transmission, and pulse oximetry errors.

PubMed

Craft, T M; Lawson, R A; Young, J D

1992-01-01

The changes in light emitting diode current necessary to maintain a constant level of light incident upon a photodetector were measured in 20 volunteers at the two wavelengths employed by pulse oximeters. Three states of finger blood content were assessed; exsanguinated, hyperaemic, and normal. The changes in light emitting diode current with changes in finger blood content were small and are not thought to represent a significant source of error in saturation as measured by pulse oximetry.

Trap-assisted tunneling in InGaN/GaN single-quantum-well light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Auf der Maur, M., E-mail: auf.der.maur@ing.uniroma2.it; Di Carlo, A.; Galler, B.

Based on numerical simulation and comparison with measured current characteristics, we show that the current in InGaN/GaN single-quantum-well light-emitting diodes at low forward bias can be accurately described by a standard trap-assisted tunneling model. The qualitative and quantitative differences in the current characteristics of devices with different emission wavelengths are demonstrated to be correlated in a physically consistent way with the tunneling model parameters.

Blue phosphorescent organic light-emitting diodes using an exciplex forming co-host with the external quantum efficiency of theoretical limit.

PubMed

Shin, Hyun; Lee, Sunghun; Kim, Kwon-Hyeon; Moon, Chang-Ki; Yoo, Seung-Jun; Lee, Jeong-Hwan; Kim, Jang-Joo

2014-07-16

A high-efficiency blue-emitting organic light-emitting diode (OLED) approaching theoretical efficiency using an exciplex-forming co-host composed of N,N'-dicarbazolyl-3,5-benzene (mCP) and bis-4,6-(3,5-di-3-pyridylphenyl)- 2-methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis[(4,6-difluorophenyl)- pyridinato-N,C2']picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A(-1) ), which is in perfect agreement with the theoretical prediction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin

2015-06-28

We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){submore » 3} as phosphorescent red dopant in electron transport layer.« less

Edge-emitting ultraviolet n-ZnO:Al/i-ZnO/p-GaN heterojunction light-emitting diode with a rib waveguide.

PubMed

Liang, H K; Yu, S F; Yang, H Y

2010-02-15

An edge-emitting ultraviolet n-ZnO:Al/i-ZnO/p-GaN heterojunction light-emitting diode with a rib waveguide is fabricated by filtered cathodic vacuum arc technique at low deposition temperature (approximately 150 degrees C). Electroluminescence with emission peak at 387 nm is observed. Good correlation between electro- and photo- luminescence spectra suggests that the i-ZnO layer of the heterojunction supports radiative excitonic recombination. Furthermore, it is found that the emission intensity can be enhanced by approximately 5 times due to the presence of the rib waveguide. Only fundamental TE and TM polarizations are supported inside the rib waveguide and the intensity of TE polarization is approximately 2.2 time larger than that of TM polarization.

Broadband light-emitting diode

DOEpatents

Fritz, Ian J.; Klem, John F.; Hafich, Michael J.

1998-01-01

A broadband light-emitting diode. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3-2 .mu.m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-division-multiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft.

Broadband light-emitting diode

DOEpatents

Fritz, I.J.; Klem, J.F.; Hafich, M.J.

1998-07-14

A broadband light-emitting diode is disclosed. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3--2 {micro}m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-divisionmultiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft. 10 figs.

A simple and portable colorimeter using a red-green-blue light-emitting diode and its application to the on-site determination of nitrite and iron in river-water.

PubMed

Suzuki, Yasutada; Aruga, Terutomi; Kuwahara, Hiroyuki; Kitamura, Miki; Kuwabara, Tetsuo; Kawakubo, Susumu; Iwatsuki, Masaaki

2004-06-01

A portable colorimeter using a red-green-blue light-emitting diode as a light source has been developed. An embedded controller sequentially turns emitters on and off, and acquires the signals detected by two photo diodes synchronized with their blinking. The controller calculates the absorbance and displays it on a liquid-crystal display. The whole system, including a 006P dry cell, is contained in a 100 x 70 x 50 mm aluminum case and its mass is 280 g. This colorimeter was successfully applied to the on-site determination of nitrite and iron in river-water.

High-brightness and high-color purity red-emitting Ca3Lu(AlO)3(BO3)4:Eu3+ phosphors with internal quantum efficiency close to unity for near-ultraviolet-based white-light-emitting diodes.

PubMed

Huang, Xiaoyong; Wang, Shaoying; Li, Bin; Sun, Qi; Guo, Heng

2018-03-15

In this work, we reported on high-brightness Eu 3+ -activated Ca 3 Lu(AlO) 3 (BO 3 ) 4 (CLAB) red-emitting phosphors. Under 397 nm excitation, the CLAB:Eu 3+ phosphors showed intense red emissions at around 621 nm with CIE coordinates of (0.657, 0.343). The optimal doping concentration of Eu 3+ ions was found to be 30 mol. %, and the CLAB:0.3Eu 3+ sample possessed high-color purity of 93% and ultra-high internal quantum efficiency as great as 98.5%. Importantly, the CLAB:0.3Eu 3+ also had good thermal stability. Finally, a white-light-emitting diode (WLED) lamp with good color-rendering index was fabricated by using a 365 nm ultraviolet chip and the phosphor blends of CLAB:0.3Eu 3+ red-emitting phosphors, (Ba,Sr) 2 SiO 4 :Eu 2+ green-emitting phosphors, and BaMgAl 10 O 7 :Eu 2+ blue-emitting phosphors.

Effect of inhomogeneity of light from light curing units on the surface hardness of composite resin.

PubMed

Arikawa, Hiroyuki; Kanie, Takahito; Fujii, Koichi; Takahashi, Hideo; Ban, Seiji

2008-01-01

This study investigated the characteristics of output light from different types of light curing units, and their effects on polymerization of light-activated composite resin. Three quartz-tungsten-halogen lamps, one plasma arc lamp, and one LED light curing unit were used. Intensity distribution of light emitted from the light guide tip was measured at 1.0-mm intervals across the guide tip. Distribution of Knoop hardness number on the surface of resin irradiated with the light curing units was also measured. For all units, inhomogeneous distribution of light intensity across the guide tip was observed. Minimum light intensity values were 19-80% of the maximum values. In terms of surface hardness, inhomogeneous distribution was also observed for the materials irradiated with the tested units. Minimum values were 53-92% of the maximum values. Our results indicated that markedly inhomogeneous light emitted from light curing unit could result in inhomogeneous polymerization in some areas of the restoration below the light guide tip.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Y. L., E-mail: yilu.chang@mail.utoronto.ca; Gong, S., E-mail: sgong@chem.utoronto.ca; White, R.

We have demonstrated high-efficiency greenish-blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a dimesitylboryl-functionalized C^N chelate Pt(II) phosphor, Pt(m-Bptrz)(t-Bu-pytrz-Me). Using a high triplet energy platform and optimized double emissive zone device architecture results in greenish-blue PHOLEDs that exhibit an external quantum efficiency of 24.0% and a power efficiency of 55.8 lm/W. This record high performance is comparable with that of the state-of-the-art Ir-based sky-blue organic light-emitting diodes.

Low threshold distributed Bragg reflector surface emitting laser diode with semiconductor air-bridge-supported top mirror

NASA Astrophysics Data System (ADS)

Hsin, W.; Du, G.; Gamelin, J. K.; Malloy, K. J.; Wang, S.

1990-03-01

A surface emitting laser diode (SELD) with two distributed Bragg reflectors (DBR) and semiconductor multilayer air-bridge-supported top mirror is fabricated. A low threshold current of 1.5 mA is achieved under room temperature CW operation. The spectrum shows a strong peak at 891 nm with a FWHM of 10 A. With light emission from the top Bragg reflector instead of from the back side of the substrate, laser arrays are easily formed with this novel structure.

Quantitative description of charge-carrier transport in a white organic light-emitting diode

NASA Astrophysics Data System (ADS)

Schober, M.; Anderson, M.; Thomschke, M.; Widmer, J.; Furno, M.; Scholz, R.; Lüssem, B.; Leo, K.

2011-10-01

We present a simulation model for the analysis of charge-carrier transport in organic thin-film devices, and apply it to a three-color white hybrid organic light-emitting diode (OLED) with fluorescent blue and phosphorescent red and green emission. We simulate a series of single-carrier devices, which reconstruct the OLED layer sequence step by step. Thereby, we determine the energy profiles for hole and electron transport, show how to discern bulk from interface limitation, and identify trap states.

Time-of-flight Measurement Of Hole-tunneling Properties And Emission Color Control In Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Kurata, K.; Kashiwabara, K.; Nakajima, K.; Mizoguchi, Y.; Ohtani, N.

2011-12-01

Hole transport properties of organic light-emitting diodes (OLEDs) with a thin hole-blocking layer (HBL) were evaluated by time-of-flight measurement. Electroluminescence (EL) spectra of OLEDs with various HBL thicknesses were also evaluated. The results clearly show that the time-resolved photocurrent response and the emission color strongly depend on HBL thickness. This can be attributed to hole-tunneling through the thin HBL. We successfully fabricated a white OLED by controlling the thickness of HBL.

Fabrication and characterization of the Si-photonics-integrated vertical resonant-cavity light-emitting diode

NASA Astrophysics Data System (ADS)

Kong, Duanhua; Kim, Taek; Kim, Sihan; Hong, Hyungi; Shcherbatko, Igor; Park, Youngsoo; Shin, Dongjae; Ha, Kyoung-Ho; Jeong, Gitae

2014-03-01

We designed and fabricated a 1.3-um hybrid vertical Resonant-Cavity Light-Emitting Diode for optical interconnect by using direct III-V wafer bonding on silicon on insulator (SOI). The device included InP based front distributed Bragg reflector (DBR), InGaAlAs based active layer, and SOI-based high-contrast-grating (HCG) as a back reflector. 42-uW continuous wave optical power was achieved at 20mA at room temperature.

Program For A Pushbutton Display

NASA Technical Reports Server (NTRS)

Busquets, Anthony M.; Luck, William S., Jr.

1989-01-01

Programmable Display Pushbutton (PDP) is pushbutton device available from Micro Switch having programmable 16X35 matrix of light-emitting diodes on pushbutton surface. Any desired legends display on PDP's, producing user-friendly applications reducing need for dedicated manual controls. Interacts with operator, calls for correct response before transmitting next message. Both simple manual control and sophisticated programmable link between operator and host system. Programmable Display Pushbutton Legend Editor (PDPE) computer program used to create light-emitting-diode (LED) displays for pushbuttons. Written in FORTRAN.

Nanobeam Photonic Crystal Cavity Light-Emitting Diodes

DTIC Science & Technology

2011-01-01

Nanobeam photonic crystal cavity light-emitting diodes Gary Shambat,1,a) Bryan Ellis,1 Jan Petykiewicz,1 Marie A. Mayer,2 Tomas Sarmiento ,1 James...J. H. Ryou, P. B. Deotare, R. Dupuis, and M. Loncar, Appl. Phys. Lett. 97, 051104 (2010). 5Y. Gong, B. Ellis, G. Shambat, T. Sarmiento , J. S. Harris...F. Karouta, S. He, and R. W. van der Heijden, Appl. Phys. Lett. 97, 151105 (2010). 9B. Ellis, M. A. Mayer, G. Shambat, T. Sarmiento , J. Harris, E. E

Efficient Flexible Organic/Inorganic Hybrid Perovskite Light-Emitting Diodes Based on Graphene Anode.

PubMed

Seo, Hong-Kyu; Kim, Hobeom; Lee, Jaeho; Park, Min-Ho; Jeong, Su-Hun; Kim, Young-Hoon; Kwon, Sung-Joo; Han, Tae-Hee; Yoo, Seunghyup; Lee, Tae-Woo

2017-03-01

Highly efficient organic/inorganic hybrid perovskite light-emitting diodes (PeLEDs) based on graphene anode are developed for the first time. Chemically inert graphene avoids quenching of excitons by diffused metal atom species from indium tin oxide. The flexible PeLEDs with graphene anode on plastic substrate show good bending stability; they provide an alternative and reliable flexible electrode for highly efficient flexible PeLEDs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultraviolet electroluminescence from zinc oxide nanorods/deoxyribonucleic acid hybrid bio light-emitting diode

NASA Astrophysics Data System (ADS)

Gupta, Rohini Bhardwaj; Nagpal, Swati; Arora, Swati; Bhatnagar, Pramod Kumar; Mathur, Parmatma Chandra

2011-01-01

Ultraviolet (UV) light-emitting diode using salmon deoxyribonucleic acid (sDNA)-cetyltrimethylammonium complex as an electron blocking layer and zinc oxide (ZnO) nanorods as emissive material was fabricated. UV emission, which was blue shifted up to 335 nm with respect to the band edge emission of 390 nm, was observed. This blue shift was caused due to accumulation of electrons in the conduction band of ZnO because of a high potential barrier existing at the sDNA/ZnO interface.

Products Claiming to "Cure" Cancer Are a Cruel Deception

MedlinePlus

... Products For Consumers Home For Consumers Consumer Updates Products Claiming to "Cure" Cancer Are a Cruel Deception ... About FDA Contact FDA Browse by Product Area Product Areas back Food Drugs Medical Devices Radiation-Emitting ...

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

NASA Astrophysics Data System (ADS)

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob

2015-07-01

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq)2(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq)2(acac). The lifetime of device (t95: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

Arbitrary helicity control of circularly polarized light from lateral-type spin-polarized light-emitting diodes at room temperature

NASA Astrophysics Data System (ADS)

Nishizawa, Nozomi; Aoyama, Masaki; Roca, Ronel C.; Nishibayashi, Kazuhiro; Munekata, Hiro

2018-05-01

We demonstrate arbitrary helicity control of circularly polarized light (CPL) emitted at room temperature from the cleaved side facet of a lateral-type spin-polarized light-emitting diode (spin-LED) with two ferromagnetic electrodes in an antiparallel magnetization configuration. Driving alternate currents through the two electrodes results in polarization switching of CPL with frequencies up to 100 kHz. Furthermore, tuning the current density ratio in the two electrodes enables manipulation of the degree of circular polarization. These results demonstrate arbitrary electrical control of polarization with high speed, which is required for the practical use of lateral-type spin-LEDs as monolithic CPL light sources.

White Light-Emitting Diodes Based on AgInS2/ZnS Quantum Dots with Improved Bandwidth in Visible Light Communication

PubMed Central

Ruan, Cheng; Zhang, Yu; Lu, Min; Ji, Changyin; Sun, Chun; Chen, Xiongbin; Chen, Hongda; Colvin, Vicki L.; Yu, William W.

2016-01-01

Quantum dot white light-emitting diodes (QD-WLEDs) were fabricated from green- and red-emitting AgInS2/ZnS core/shell QDs coated on GaN LEDs. Their electroluminescence (EL) spectra were measured at different currents, ranging from 50 mA to 400 mA, and showed good color stability. The modulation bandwidth of previously prepared QD-WLEDs was confirmed to be much wider than that of YAG:Ce phosphor-based WLEDs. These results indicate that the AgInS2/ZnS core/shell QDs are good color-converting materials for WLEDs and they are capable in visible light communication (VLC). PMID:28344270

Emission Testing Results of Thermally Stable, Metamaterial, Selective-Emitters for Thermophotovoltaics

NASA Astrophysics Data System (ADS)

Levinson, Katherine; Naka, Norihito; Pfiester, Nicole; Licht, Abigail; Vandervelde, Tom

2015-03-01

In thermophotovoltaics, the energy from a heated emitter is converted to electricity by a photovoltaic diode. A selective emitter can be used to emit a narrow band of wavelengths tailored to the bandgap of the photovoltaic diode. This spectral shaping improves the conversion efficiency of the diode and reduces undesirable diode heating. In our research, we study selective emitters based on metamaterials composed of repeating nanoscale structures. The emission characteristics of these materials vary based on the compositional structure, allowing the emitted spectrum to be tunable. Simulations were performed with CST Microwave Studio to design emitters with peak wavelengths ranging from 1-10 microns. The structures were then fabricated using physical vapor deposition and electron beam lithography on a sapphire substrate. Emitter materials studied include gold, platinum, and iridium. Here we report on the emission spectra of the selective emitters and the post-heating structural integrity.

Low driving voltage blue, green, yellow, red and white organic light-emitting diodes with a simply double light-emitting structure.

PubMed

Zhang, Zhensong; Yue, Shouzhen; Wu, Yukun; Yan, Pingrui; Wu, Qingyang; Qu, Dalong; Liu, Shiyong; Zhao, Yi

2014-01-27

Low driving voltage blue, green, yellow, red and white phosphorescent organic light-emitting diodes (OLEDs) with a common simply double emitting layer (D-EML) structure are investigated. Our OLEDs without any out-coupling schemes as well as n-doping strategies show low driving voltage, e.g. < 2.4 V for onset and < 3 V for 1000 cd/m2, and high efficiency of 32.5 lm/W (13.3%), 58.8 lm/W (14.3%), 55.1 lm/W (14.6%), 24.9 lm/W (13.7%) and 45.1 lm/W (13.5%) for blue, green, yellow, red and white OLED, respectively. This work demonstrates that the low driving voltages and high efficiencies can be simultaneously realized with a common simply D-EML structure.

Phosphorescence white organic light-emitting diodes with single emitting layer based on isoquinolinefluorene-carbazole containing host.

PubMed

Koo, Ja Ryong; Lee, Seok Jae; Hyung, Gun Woo; Kim, Bo Young; Shin, Hyun Su; Lee, Kum Hee; Yoon, Seung Soo; Kim, Woo Young; Kim, Young Kwan

2013-03-01

We have demonstrated a stable phosphorescent white organic light-emitting diodes (WOLEDs) using an orange emitter, Bis(5-benzoyl-2-(4-fluorophenyl)pyridinato-C,N) iridium(III)acetylacetonate [(Bz4Fppy)2Ir(III)acac] doped into a newly synthesized blue host material, 2-(carbazol-9-yl)-7-(isoquinolin-1-yl)-9,9-diethylfluorene (CzFliq). When 1 wt.% (Bz4Fppy)2Ir(III)acac was doped into emitting layer, it was realized an improved EL performance and a pure white color in the OLED. The optimum WOLED showed maximum values as a luminous efficiency of 10.14 cd/A, a power efficiency of 10.24 Im/W, a peak external quantum efficiency 4.07%, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39) at 8 V.

Inkjet-Printed Small-Molecule Organic Light-Emitting Diodes: Halogen-Free Inks, Printing Optimization, and Large-Area Patterning.

PubMed

Zhou, Lu; Yang, Lei; Yu, Mengjie; Jiang, Yi; Liu, Cheng-Fang; Lai, Wen-Yong; Huang, Wei

2017-11-22

Manufacturing small-molecule organic light-emitting diodes (OLEDs) via inkjet printing is rather attractive for realizing high-efficiency and long-life-span devices, yet it is challenging. In this paper, we present our efforts on systematical investigation and optimization of the ink properties and the printing process to enable facile inkjet printing of conjugated light-emitting small molecules. Various factors on influencing the inkjet-printed film quality during the droplet generation, the ink spreading on the substrates, and its solidification processes have been systematically investigated and optimized. Consequently, halogen-free inks have been developed and large-area patterning inkjet printing on flexible substrates with efficient blue emission has been successfully demonstrated. Moreover, OLEDs manufactured by inkjet printing the light-emitting small molecules manifested superior performance as compared with their corresponding spin-cast counterparts.

Monolithic Flexible Vertical GaN Light-Emitting Diodes for a Transparent Wireless Brain Optical Stimulator.

PubMed

Lee, Han Eol; Choi, JeHyuk; Lee, Seung Hyun; Jeong, Minju; Shin, Jung Ho; Joe, Daniel J; Kim, DoHyun; Kim, Chang Wan; Park, Jung Hwan; Lee, Jae Hee; Kim, Daesoo; Shin, Chan-Soo; Lee, Keon Jae

2018-05-18

Flexible inorganic-based micro light-emitting diodes (µLEDs) are emerging as a significant technology for flexible displays, which is an important area for bilateral visual communication in the upcoming Internet of Things era. Conventional flexible lateral µLEDs have been investigated by several researchers, but still have significant issues of power consumption, thermal stability, lifetime, and light-extraction efficiency on plastics. Here, high-performance flexible vertical GaN light-emitting diodes (LEDs) are demonstrated by silver nanowire networks and monolithic fabrication. Transparent, ultrathin GaN LED arrays adhere to a human fingernail and stably glow without any mechanical deformation. Experimental studies provide outstanding characteristics of the flexible vertical μLEDs (f-VLEDs) with high optical power (30 mW mm -2 ), long lifetime (≈12 years), and good thermal/mechanical stability (100 000 bending/unbending cycles). The wireless light-emitting system on the human skin is successfully realized by transferring the electrical power f-VLED. Finally, the high-density GaN f-VLED arrays are inserted onto a living mouse cortex and operated without significant histological damage of brain. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

White light emitting diode based on InGaN chip with core/shell quantum dots

NASA Astrophysics Data System (ADS)

Shen, Changyu; Hong, Yan; Ma, Jiandong; Ming, Jiangzhou

2009-08-01

Quantum dots have many applications in optoelectronic device such as LEDs for its many superior properties resulting from the three-dimensional confinement effect of its carrier. In this paper, single chip white light-emitting diodes (WLEDs) were fabricated by combining blue InGaN chip with luminescent colloidal quantum dots (QDs). Two kinds of QDs of core/shell CdSe /ZnS and core/shell/shell CdSe /ZnS /CdS nanocrystals were synthesized by thermal deposition using cadmium oxide and selenium as precursors in a hot lauric acid and hexadecylamine trioctylphosphine oxide hybrid. This two kinds of QDs exhibited high photoluminescence efficiency with a quantum yield more than 41%, and size-tunable emission wavelengths from 500 to 620 nm. The QDs LED mainly consists of flip luminescent InGaN chip, glass ceramic protective coating, glisten cup, QDs using as the photoluminescence material, pyroceram, gold line, electric layer, dielectric layer, silicon gel and bottom layer for welding. The WLEDs had the CIE coordinates of (0.319, 0.32). The InGaN chip white-light-emitting diodes with quantum dots as the emitting layer are potentially useful in illumination and display applications.

Purely organic electroluminescent material realizing 100% conversion from electricity to light

PubMed Central

Kaji, Hironori; Suzuki, Hajime; Fukushima, Tatsuya; Shizu, Katsuyuki; Suzuki, Katsuaki; Kubo, Shosei; Komino, Takeshi; Oiwa, Hajime; Suzuki, Furitsu; Wakamiya, Atsushi; Murata, Yasujiro; Adachi, Chihaya

2015-01-01

Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylaminocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet–triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3,000 cd m−2. PMID:26477390

Laser diode bars based on strain-compensated AlGaPAs/GaAs heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marmalyuk, Aleksandr A; Ladugin, M A; Yarotskaya, I V

2012-01-31

Traditional (in the AlGaAs/GaAs system) and phosphorus-compensated (in the AlGaAs/AlGaPAs/GaAs system) laser heterostructures emitting at a wavelength of 850 nm are grown by MOVPE and studied. Laser diode bars are fabricated and their output characteristics are studied. The method used to grow heterolayers allowed us to control (minimise) mechanical stresses in the AlGaPAs/GaAs laser heterostructure, which made it possible to keep its curvature at the level of the initial curvature of the substrate. It is shown that the use of a compensated AlGaPAs/GaAs heterostructure improves the linear distribution of emitting elements in the near field of laser diode arrays andmore » allows the power - current characteristic to retain its slope at high pump currents owing to a uniform contact of all emitting elements with the heat sink. The radius of curvature of the grown compensated heterostructures turns out to be smaller than that of traditional heterostructures.« less

Oxygen measurements at high pressures with vertical cavity surface-emitting lasers

NASA Astrophysics Data System (ADS)

Wang, J.; Sanders, S. T.; Jeffries, J. B.; Hanson, R. K.

Measurements of oxygen concentration at high pressures (to 10.9 bar) were made using diode-laser absorption of oxygen A-band transitions near 760 nm. The wide current-tuning frequency range (>30 cm-1) of vertical cavity surface-emitting lasers (VCSELs) was exploited to enable the first scanned-wavelength demonstration of diode-laser absorption at high pressures; this strategy is more robust than fixed-wavelength strategies, particularly in hostile environments. The wide tuning range and rapid frequency response of the current tuning were further exploited to demonstrate wavelength-modulation absorption spectroscopy in a high-pressure environment. The minimum detectable absorbance demonstrated, 1×10-4, corresponds to 800 ppm-m oxygen detectivity at room temperature and is limited by etalon noise. The rapid- and wide-frequency tunability of VCSELs should significantly expand the application domain of absorption-based sensors limited in the past by the small current-tuning frequency range (typically <2 cm-1) of conventional edge-emitting diode lasers.

Reduced Graphene Oxide/Single-Walled Carbon Nanotube Hybrid Films Using Various p-Type Dopants and Their Application to GaN-Based Light-Emitting Diodes.

PubMed

Lee, Byeong Ryong; Kim, Tae Geun

2017-01-01

This article reports the electrical and optical properties of the reduced graphene oxide (RGO)/single-walled carbon nanotube (SWCNT) films using various p-type dopants and their application to GaN-based light-emitting diodes. To enhance the current injection and spreading of the RGO/SWCNT films on the light-emitting diodes (LEDs), we increased the work function (Φ) of the films using chemical doping with AuCl₃, poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and MoO₃; thereby reduced the Schottky barrier height between the RGO/SWCNT films and p-GaN. By comparison, LEDs fabricated with work-function-tuned RGO/SWCNT film doped with MoO₃ exhibited the decrease of the forward voltage from 5.3 V to 5.02 V at 20 mA and the increase of the output power up to 1.26 times. We also analyzed the current injection mechanism using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy.

Electrical degradation of triarylamine-based light-emitting polymer diodes monitored by micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Kim, Ji-Seon; Ho, Peter K. H.; Murphy, Craig E.; Seeley, Alex J. A. B.; Grizzi, Ilaria; Burroughes, Jeremy H.; Friend, Richard H.

2004-03-01

Although much progress has been made in improving polymer light-emitting diode performance, there has been little work to address device intrinsic degradation mechanisms due to the challenge of tracking minute chemical reactions in the 100-nm-thick buried active layers during operation. Here we have elucidated a hole-mediated electrical degradation of triarylamine-based blue polymer diodes using in situ Raman microspectroscopy. A slow irreversible hole-doping of polymer adjacent to the hole-injecting conducting-polymer leads to formation of oxidised triarylamine species counterbalanced by anions from the conducting-polymer. These charged species act as luminescence quenchers and hinder further hole injection across the interface leading to significant decreases in current density at low voltages.

A route to improved extraction efficiency of light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhu, H.; Shan, C. X.; Wang, L. K.; Yang, Y.; Zhang, J. Y.; Yao, B.; Shen, D. Z.; Fan, X. W.

2010-01-01

The electroluminescence from an n-MgZnO/i-ZnO/MgO/p-GaN asymmetric double heterojunction has been demonstrated. With the injection of electrons from n-MgZnO and holes from p-GaN, an intense ultraviolet emission coming from the ZnO active layer was observed. It is revealed that the emission intensity of the diode recorded from the MgZnO side is significantly larger than that from the MgO side because of the asymmetric waveguide structure formed by the lower refractive index of MgO than that of MgZnO. The asymmetric waveguide structure reported in this letter may promise a simple and effective route to light-emitting diodes with improved light-extraction efficiency.

Fabrication of 3D nano-structures using reverse imprint lithography

NASA Astrophysics Data System (ADS)

Han, Kang-Soo; Hong, Sung-Hoon; Kim, Kang-In; Cho, Joong-Yeon; Choi, Kyung-woo; Lee, Heon

2013-02-01

In spite of the fact that the fabrication process of three-dimensional nano-structures is complicated and expensive, it can be applied to a range of devices to increase their efficiency and sensitivity. Simple and inexpensive fabrication of three-dimensional nano-structures is necessary. In this study, reverse imprint lithography (RIL) with UV-curable benzylmethacrylate, methacryloxypropyl terminated poly-dimethylsiloxane (M-PDMS) resin and ZnO-nano-particle-dispersed resin was used to fabricate three-dimensional nano-structures. UV-curable resins were placed between a silicon stamp and a PVA transfer template, followed by a UV curing process. Then, the silicon stamp was detached and a 2D pattern layer was transferred to the substrate using diluted UV-curable glue. Consequently, three-dimensional nano-structures were formed by stacking the two-dimensional nano-patterned layers. RIL was applied to a light-emitting diode (LED) to evaluate the optical effects of a nano-patterned layer. As a result, the light extraction of the patterned LED was increased by about 12% compared to an unpatterned LED.

Fabrication of 3D nano-structures using reverse imprint lithography.

PubMed

Han, Kang-Soo; Hong, Sung-Hoon; Kim, Kang-In; Cho, Joong-Yeon; Choi, Kyung-Woo; Lee, Heon

2013-02-01

In spite of the fact that the fabrication process of three-dimensional nano-structures is complicated and expensive, it can be applied to a range of devices to increase their efficiency and sensitivity. Simple and inexpensive fabrication of three-dimensional nano-structures is necessary. In this study, reverse imprint lithography (RIL) with UV-curable benzylmethacrylate, methacryloxypropyl terminated poly-dimethylsiloxane (M-PDMS) resin and ZnO-nano-particle-dispersed resin was used to fabricate three-dimensional nano-structures.UV-curable resins were placed between a silicon stamp and a PVA transfer template, followed by a UV curing process. Then, the silicon stamp was detached and a 2D pattern layer was transferred to the substrate using diluted UV-curable glue. Consequently, three-dimensional nano-structures were formed by stacking the two-dimensional nano-patterned layers. RIL was applied to a light-emitting diode (LED) to evaluate the optical effects of a nano-patterned layer. As a result, the light extraction of the patterned LED was increased by about 12% compared to an unpatterned LED.

White polymer light-emitting diodes based on star-shaped polymers with an orange dendritic phosphorescent core.

PubMed

Zhu, Minrong; Li, Yanhu; Cao, Xiaosong; Jiang, Bei; Wu, Hongbin; Qin, Jingui; Cao, Yong; Yang, Chuluo

2014-12-01

A series of new star-shaped polymers with a triphenylamine-based iridium(III) dendritic complex as the orange-emitting core and poly(9,9-dihexylfluorene) (PFH) chains as the blue-emitting arms is developed towards white polymer light-emitting diodes (WPLEDs). By fine-tuning the content of the orange phosphor, partial energy transfer and charge trapping from the blue backbone to the orange core is realized to achieve white light emission. Single-layer WPLEDs with the configuration of ITO (indium-tin oxide)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer/CsF/Al exhibit a maximum current efficiency of 1.69 cd A(-1) and CIE coordinates of (0.35, 0.33), which is very close to the pure white-light point of (0.33, 0.33). To the best of our knowledge, this is the first report on star-shaped white-emitting single polymers that simultaneously consist of fluorescent and phosphorescent species. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Conversion degrees of resin composites using different light sources.

PubMed

Ozturk, Bora; Cobanoglu, Nevin; Cetin, Ali Rıza; Gunduz, Beniz

2013-01-01

The objective of this study was to compare the conversion degree of six different composite materials (Filtek Z 250, Filtek P60, Spectrum TPH, Pertac II, Clearfil AP-X, and Clearfil Photo Posterior) using three different light sources (blue light-emitting diode [LED], plasma arc curing [PAC], and conventional halogen lamp [QTH]). Composites were placed in a 2 mm thick and 5 mm diameter Teflon molds and light cured from the top using three methods: LED for 40 s, PAC for 10 s, and QTH for 40 s. A Fourier Transform Infrared Spectroscopy (FTIR) was used to evaluate the degree of conversion (DC) (n=5). The results were analyzed with two-way analysis of variance and Tukey HSD test. DC was significantly influenced by two variables, light source and composite (P<.05). QTH revealed significantly higher DC values than LED (P<.05). However, there were no significant differences between DC values of QTH and PAC or between DC values of LED and PAC (P>.05). The highest DC was observed in the Z 250 composite specimens following photopolymerization with QTH (70%). The lowest DC was observed in Clearfil Photo Posterior composite specimens following photo-polymerization with LED (43%). The DC was found to be changing according to both light sources and composite materials used. Conventional light halogen (QTH) from light sources and Filtek Z 250 and Filtek P 60 among composite materials showed the most DC performance.

Synthesis and photoluminescence properties of a cyan-emitting phosphor Ca3(PO4)2:Eu2+ for white light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhou, Wenli; Han, Jin; Zhang, Xuejie; Qiu, Zhongxian; Xie, Qingji; Liang, Hongbin; Lian, Shixun; Wang, Jing

2015-01-01

In this paper, a cyan-emitting phosphor Ca3(PO4)2:Eu2+ (TCP:Eu2+) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 250-450 nm region, but the emission spectrum is prominent at around 480 nm. The emission intensity of the TCP:Eu2+ was found to be 60% and 82% of that of the commercial BaMgAl10O17:Eu2+ (BAM) under excitation at 340 nm and 370 nm, respectively. Upon excitation at 370 nm, the absolute internal and external quantum efficiencies of the Ca3(PO4)2:1.5%Eu2+ are 60% and 42%, respectively. Moreover, a white LED lamp was fabricated by coating TCP:Eu2+ with a blue-emitting BAM and a red-emitting CaAlSiN3:Eu2+ on a near-ultraviolet (375 nm) LED chip, driven by a 350 mA forward bias current, and it produces an intense white light with a color rendering index of 75.

Holographic injection locking of a broad area laser diode via a photorefractive thin-film device.

PubMed

van Voorst, P D; de Wit, M R; Offerhaus, H L; Tay, S; Thomas, J; Peyghambarian, N; Boller, K-J

2007-12-24

We demonstrate locking of a high power broad area laser diode to a single frequency using holographic feedback from a photorefractive polymer thin-film device for the first time. A four-wave mixing setup is used to generate feedback for the broad area diode at the wavelength of the single frequency source (Ti:Sapphire laser) while the spatial distribution adapts to the preferred profile of the broad area diode. The result is an injection-locked broad area diode emitting with a linewidth comparable to the Ti:Sapphire laser.

Optical sectioning microscopes with no moving parts using a micro-stripe array light emitting diode.

PubMed

Poher, V; Zhang, H X; Kennedy, G T; Griffin, C; Oddos, S; Gu, E; Elson, D S; Girkin, M; French, P M W; Dawson, M D; Neil, M A

2007-09-03

We describe an optical sectioning microscopy system with no moving parts based on a micro-structured stripe-array light emitting diode (LED). By projecting arbitrary line or grid patterns onto the object, we are able to implement a variety of optical sectioning microscopy techniques such as grid-projection structured illumination and line scanning confocal microscopy, switching from one imaging technique to another without modifying the microscope setup. The micro-structured LED and driver are detailed and depth discrimination capabilities are measured and calculated.

High-efficiency non-blocking phosphorescent organic light emitting diode with ultrathin emission layer

NASA Astrophysics Data System (ADS)

Qiu, Jacky; Helander, Michael G.; Wang, Zhibin; Chang, Yi-Lu; Lu, ZhengHong

2012-09-01

Non-blocking Phosphorescent Organic Light Emitting Diode (NB-PHOLED) is a highly simplified device structure that has achieved record high device performance on chlorinated ITO[1], flexible substrates[2], also with Pt based phosphorescent dopants[3] and NB-PHOLED has significantly reduced efficiency roll-off[4]. The principle novel features of NB-PHOLED is the absence of blocking layer in the OLED stack, as well as the absence of organic hole injection layer, this allows for reduction of carrier accumulation in between organic layers and result in higher efficiencies.

Room temperature polariton light emitting diode with integrated tunnel junction.

PubMed

Brodbeck, S; Jahn, J-P; Rahimi-Iman, A; Fischer, J; Amthor, M; Reitzenstein, S; Kamp, M; Schneider, C; Höfling, S

2013-12-16

We present a diode incorporating a large number (12) of GaAs quantum wells that emits light from exciton-polariton states at room temperature. A reversely biased tunnel junction is placed in the cavity region to improve current injection into the device. Electroluminescence studies reveal two polariton branches which are spectrally separated by a Rabi splitting of 6.5 meV. We observe an anticrossing of the two branches when the temperature is lowered below room temperature as well as a Stark shift of both branches in a bias dependent photoluminescence measurement.

Accuracy Improvement for Light-Emitting-Diode-Based Colorimeter by Iterative Algorithm

NASA Astrophysics Data System (ADS)

Yang, Pao-Keng

2011-09-01

We present a simple algorithm, combining an interpolating method with an iterative calculation, to enhance the resolution of spectral reflectance by removing the spectral broadening effect due to the finite bandwidth of the light-emitting diode (LED) from it. The proposed algorithm can be used to improve the accuracy of a reflective colorimeter using multicolor LEDs as probing light sources and is also applicable to the case when the probing LEDs have different bandwidths in different spectral ranges, to which the powerful deconvolution method cannot be applied.

Plastic cup traps equipped with light-emitting diodes for monitoring adult Bemisia tabaci (Homoptera: Aleyrodidae).

PubMed

Chu, Chang-Chi; Jackson, Charles G; Alexander, Patrick J; Karut, Kamil; Henneberry, Thomas J

2003-06-01

Equipping the standard plastic cup trap, also known as the CC trap, with lime-green light-emitting diodes (LED-plastic cup trap) increased its efficacy for catching Bemisia tabaci by 100%. Few Eretmocerus eremicus Rose and Zolnerowich and Encarsia formosa Gahan were caught in LED-plastic cup traps. The LED-plastic cup traps are less expensive than yellow sticky card traps for monitoring adult whiteflies in greenhouse crop production systems and are more compatible with whitefly parasitoids releases for Bemisia nymph control.

Highly efficient organic light-emitting diodes with a quantum dot interfacial layer.

PubMed

Ryu, Seung Yoon; Hwang, Byoung Har; Park, Ki Wan; Hwang, Hyeon Seok; Sung, Jin Woo; Baik, Hong Koo; Lee, Chang Ho; Song, Seung Yong; Lee, Jun Yeob

2009-02-11

Advanced organic light-emitting diodes (OLEDs), based on a multiple structure, were achieved in combination with a quantum dot (QD) interfacial layer. The authors used core/shell CdSe/ZnS QDs passivated with trioctylphosphine oxide (TOPO) and TOPO-free QDs as interlayers. Multiple-structure OLEDs (MOLEDs) with TOPO-free QDs showed higher device efficiency because of a well-defined interfacial monolayer formation. Additionally, the three-unit MOLED showed high performance for device efficiency with double-structured QD interfacial layers due to the enhanced charge balance and recombination probability.

Colloidal quantum dot active layers for light emitting diodes

NASA Astrophysics Data System (ADS)

Pagan, Jennifer G.; Stokes, Edward B.; Patel, Kinnari; Burkhart, Casey C.; Ahrens, Michael T.; Barletta, Philip T.; O'Steen, Mark

2006-07-01

In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. Properties of p-type Mg doped overgrowth GaN are examined via circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). Electroluminescence of LED test structures is reported, and an ideality factor of n = 1.6 is demonstrated.

Quantification of lycopene in the processed tomato-based products by means of the light-emitting diode (LED) and compact photoacoustic (PA) detector

NASA Astrophysics Data System (ADS)

Bicanic, D.; Skenderović, H.; Marković, K.; Dóka, O.; Pichler, L.; Pichler, G.; Luterotti, S.

2010-03-01

The combined use of a high power light emitting diode (LED) and the compact photoacoustic (PA) detector offers the possibility for a rapid (no extraction needed), accurate (precision 1.5%) and inexpensive quantification of lycopene in different products derived from the thermally processed tomatoes. The concentration of lycopene in selected products ranges from a few mg to several tens mg per 100 g fresh weight. The HPLC was used as the well established reference method.

Nonlinear symmetry breaking in photometamaterials

NASA Astrophysics Data System (ADS)

Gorlach, Maxim A.; Dobrykh, Dmitry A.; Slobozhanyuk, Alexey P.; Belov, Pavel A.; Lapine, Mikhail

2018-03-01

We design and analyze theoretically photometamaterials with each meta-atom containing both photodiode and light-emitting diode. Illumination of the photodiode by the light-emitting diode gives rise to an additional optical feedback within each unit cell, which strongly affects resonant properties and nonlinear response of the meta-atom. In particular, we demonstrate that inversion symmetry breaking occurs upon a certain threshold magnitude of the incident wave intensity resulting in an abrupt emergence of second-harmonic generation, which was not originally available, as well as in the reduced third-harmonic signal.

Light emission mechanism of mixed host organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Song, Wook; Lee, Jun Yeob

2015-03-01

Light emission mechanism of organic light-emitting diodes with a mixed host emitting layer was studied using an exciplex type mixed host and an exciplex free mixed host. Monitoring of the current density and luminance of the two type mixed host devices revealed that the light emission process of the exciplex type mixed host was dominated by energy transfer, while the light emission of the exciplex free mixed host was controlled by charge trapping. Mixed host composition was also critical to the light emission mechanism, and the contribution of the energy transfer process was maximized at 50:50 mixed host composition. Therefore, it was possible to manage the light emission process of the mixed host devices by managing the mixed host composition.

All-solution processed transparent organic light emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Min; Höfle, Stefan; Czolk, Jens; Mertens, Adrian; Colsmann, Alexander

2015-11-01

In this work, we report on indium tin oxide-free, all-solution processed transparent organic light emitting diodes (OLEDs) with inverted device architecture. Conductive polymer layers are employed as both transparent cathodes and transparent anodes, with the top anodes having enhanced conductivities from a supporting stochastic silver nanowire mesh. Both electrodes exhibit transmittances of 80-90% in the visible spectral regime. Upon the incorporation of either yellow- or blue-light emitting fluorescent polymers, the OLEDs show low onset voltages, demonstrating excellent charge carrier injection from the polymer electrodes into the emission layers. Overall luminances and current efficiencies equal the performance of opaque reference OLEDs with indium tin oxide and aluminium electrodes, proving excellent charge carrier-to-light conversion within the device.

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob, E-mail: sy96.lee@samsung.com

2015-07-27

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq){sub 2}(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq){sub 2}(acac). The lifetime of device (t{sub 95}: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

Single-photon emitting diode in silicon carbide.

PubMed

Lohrmann, A; Iwamoto, N; Bodrog, Z; Castelletto, S; Ohshima, T; Karle, T J; Gali, A; Prawer, S; McCallum, J C; Johnson, B C

2015-07-23

Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide an ideal material to build such devices. Here, we demonstrate the fabrication of bright single-photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of >300 kHz) and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single-photon source is proposed. These results provide a foundation for the large scale integration of single-photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.

Effect of broad recombination zone in multiple quantum well structures on lifetime and efficiency of blue organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Seok Jae; Lee, Song Eun; Lee, Dong Hyung; Koo, Ja Ryong; Lee, Ho Won; Yoon, Seung Soo; Park, Jaehoon; Kim, Young Kwan

2014-10-01

Blue phosphorescent organic light-emitting diodes with multiple quantum well (MQW) structures (from one to four quantum wells) within an emitting layer (EML) are fabricated with charge control layers (CCLs) to control carrier movement. The distributed recombination zone and balanced charge carrier injection within EML are achieved through the MQW structure with CCLs. Remarkably, the half-decay lifetime of a blue device with three quantum wells, measured at an initial luminance of 500 cd/m2, is 3.5 times longer than that using a conventional structure. Additionally, the device’s efficiency improved. These results are explained with the effects of triplet exciton confinement and triplet-triplet annihilation within each EML.

Selective epitaxial growth of monolithically integrated GaN-based light emitting diodes with AlGaN/GaN driving transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zhaojun; Ma, Jun; Huang, Tongde

2014-03-03

In this Letter, we report selective epitaxial growth of monolithically integrated GaN-based light emitting diodes (LEDs) with AlGaN/GaN high-electron-mobility transistor (HEMT) drivers. A comparison of two integration schemes, selective epitaxial removal (SER), and selective epitaxial growth (SEG) was made. We found the SER resulted in serious degradation of the underlying LEDs in a HEMT-on-LED structure due to damage of the p-GaN surface. The problem was circumvented using the SEG that avoided plasma etching and minimized device degradation. The integrated HEMT-LEDs by SEG exhibited comparable characteristics as unintegrated devices and emitted modulated blue light by gate biasing.

GaN-Based Light-Emitting Diodes Grown on Nanoscale Patterned Sapphire Substrates with Void-Embedded Cortex-Like Nanostructures

NASA Astrophysics Data System (ADS)

Lin, Yu-Sheng; Yeh, J. Andrew

2011-09-01

High-efficiency GaN-based light-emitting diodes (LEDs) with an emitting wavelength of 438 nm were demonstrated utilizing nanoscale patterned sapphire substrates with void-embedded cortex-like nanostructures (NPSS-VECN). Unlike the previous nanopatterned sapphire substrates, the presented substrate has a new morphology that can not only improve the crystalline quality of GaN epilayers but also generate a void-embedded nanostructural layer to enhance light extraction. Under a driving current of 20 mA, the external quantum efficiency of an LED with NPSS-VECN is enhanced by 2.4-fold compared with that of the conventional LED. Moreover, the output powers of two devices respectively are 33.1 and 13.9 mW.

Visible light surface emitting semiconductor laser

DOEpatents

Olbright, Gregory R.; Jewell, Jack L.

1993-01-01

A vertical-cavity surface-emitting laser is disclosed comprising a laser cavity sandwiched between two distributed Bragg reflectors. The laser cavity comprises a pair of spacer layers surrounding one or more active, optically emitting quantum-well layers having a bandgap in the visible which serve as the active optically emitting material of the device. The thickness of the laser cavity is m .lambda./2n.sub.eff where m is an integer, .lambda. is the free-space wavelength of the laser radiation and n.sub.eff is the effective index of refraction of the cavity. Electrical pumping of the laser is achieved by heavily doping the bottom mirror and substrate to one conductivity-type and heavily doping regions of the upper mirror with the opposite conductivity type to form a diode structure and applying a suitable voltage to the diode structure. Specific embodiments of the invention for generating red, green, and blue radiation are described.

GaN-based photon-recycling green light-emitting diodes with vertical-conduction structure.

PubMed

Sheu, Jinn-Kong; Chen, Fu-Bang; Yen, Wei-Yu; Wang, Yen-Chin; Liu, Chun-Nan; Yeh, Yu-Hsiang; Lee, Ming-Lun

2015-04-06

A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

Bluish-green color emitting Ba2Si3O8:Eu2+ ceramic phosphors for white light-emitting diodes.

PubMed

Xiao, F; Xue, Y N; Zhang, Q Y

2009-10-15

This paper reports on the structural and optical properties of Eu(2+) activated Ba(2)Si(3)O(8) ceramic phosphors synthesized by a sol-gel method. The ceramic phosphors have been characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and fluorescence measurements. The structural characterization results suggest that the as-prepared phosphors are of single phase monoclinic Ba(2)Si(3)O(8) with rod-like morphology. A broad excitation band ranging from 300 to 410 nm matches well with the ultraviolet (UV) radiation of light-emitting diodes (LEDs). Upon 380 nm UV light excitation, these phosphors emit bluish-green emission centered at 500 nm with color coordination (x=0.25, y=0.40). All the obtained results indicate that the Ba(2)Si(3)O(8):Eu(2+) ceramic phosphors are promising bluish-green candidates for the phosphor-converted white LEDs.

Organic light-emitting diodes with direct contact-printed red, green, blue, and white light-emitting layers

NASA Astrophysics Data System (ADS)

Chen, Sun-Zen; Peng, Shiang-Hau; Ting, Tzu-Yu; Wu, Po-Shien; Lin, Chun-Hao; Chang, Chin-Yeh; Shyue, Jing-Jong; Jou, Jwo-Huei

2012-10-01

We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.

Dimmable sunlight-like organic light emitting diodes with ultra-high color rendering index

NASA Astrophysics Data System (ADS)

Wu, Jin-Han; Chi, Chien-An; Chiang, Chang-Lin; Chen, Guan-Yu; Lin, Yi-Ping; Chen, Cheng-Chang; Ho, Shu-Yi; Chen, Shih-Pu; Li, Jung-Yu

2016-05-01

We propose novel dimmable sunlight-like white organic light-emitting diodes that were fabricated using three luminophores to form an emitting spectrum similar to black body radiation at 2250 K with ultra-high color rendering index (CRI) value of 91, which nearly remained the constant at various luminance values ranging from 100 to more than 2500 cd/m2 at Commission Internationale de l'Eclairage chromaticity coordinates of (0.51, 0.41). Introducing charge modification layers suppressed the energy transfer between the emitting material layers and increased the probability of carrier recombination. Moreover, we reveal that covering long-wavelength ranges played a vital role in achieving high CRI values; the CRI values of a spectrum artificially shifted toward a long-wavelength direction (from 610 to 620 nm) remained constant, whereas those of a spectrum shifted toward a short-wavelength direction (from 610 to 600 nm) dropped to 79.

Vertical cavity surface-emitting semiconductor lasers with injection laser pumping

NASA Astrophysics Data System (ADS)

McDaniel, D. L., Jr.; McInerney, J. G.; Raja, M. Y. A.; Schaus, C. F.; Brueck, S. R. J.

1990-05-01

Continuous-wave GaAs/GaAlAs edge-emitting diode lasers were used to pump GaAs/AlGaAs and InGaAs/AlGaAs vertical cavity surface-emitting lasers (VCSELs) with resonant periodic gain (RPG) at room temperature. Pump threshold as low as 11 mW, output powers as high as 27 mW at 850 nm, and external differential quantum efficiencies of about 70 percent were observed in GaAs/AlGaAs surface -emitters; spectral brightness 22 times that of the pump laser was also observed. Output powers as high as 85 mW at 950 nm and differential quantum efficiencies of up to 58 percent were recorded for the InGaAs surface-emitting laser. This is the highest quasi-CW output power ever reported for any RPG VCSEL, and the first time such a device has been pumped using an injection laser diode.

Si light-emitting device in integrated photonic CMOS ICs

NASA Astrophysics Data System (ADS)

Xu, Kaikai; Snyman, Lukas W.; Aharoni, Herzl

2017-07-01

The motivation for integrated Si optoelectronics is the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive biochemical sensors in the environmental control or medicine leads to the development of integrated high resolution sensors. Here CMOS-compatible Si light-emitting device structures are presented for investigating the effect of various depletion layer profiles and defect engineering on the photonic transition in the 1.4-2.8 eV. A novel Si device is proposed to realize both a two-terminal Si-diode light-emitting device and a three-terminal Si gate-controlled diode light-emitting device in the same device structure. In addition to the spectral analysis, differences between two-terminal and three-terminal devices are discussed, showing the light emission efficiency change. The proposed Si optical source may find potential applications in micro-photonic systems and micro-optoelectro-mechanical systems (MOEMS) in CMOS integrated circuitry.

Full down-conversion of amber-emitting phosphor-converted light-emitting diodes with powder phosphors and a long-wave pass filter.

PubMed

Oh, Jeong Rok; Cho, Sang-Hwan; Park, Hoo Keun; Oh, Ji Hye; Lee, Yong-Hee; Do, Young Rag

2010-05-24

This paper reports the possibility of a facile optical structure to realize a highly efficient monochromatic amber-emitting light-emitting diode (LED) using a powder-based phosphor-converted LED combined with a long-wave pass filter (LWPF). The capping of a blue-reflecting and amber-passing LWPF enhances both the amber emission from the silicate amber phosphor layer and the color purity due to the blocking and recycling of the pumping blue light from the InGaN LED. The enhancement of the luminous efficacy of the amber pc-LED with a LWPF (phosphor concentration 20 wt%, 39.4 lm/W) is 34% over that of an amber pc-LED without a LWPF (phosphor concentration 55 wt%, 29.4 lm/W) at 100 mA and a high color purity (>96%) with Commission International d'Eclairage (CIE) color coordinates of x=0.57 and y=0.42.

Non-Toxic Gold Nanoclusters for Solution-Processed White Light-Emitting Diodes.

PubMed

Chao, Yu-Chiang; Cheng, Kai-Ping; Lin, Ching-Yi; Chang, Yu-Li; Ko, Yi-Yun; Hou, Tzu-Yin; Huang, Cheng-Yi; Chang, Walter H; Lin, Cheng-An J

2018-06-11

Solution-processed optoelectronic devices are attractive because of the potential low-cost fabrication and the compatibility with flexible substrate. However, the utilization of toxic elements such as lead and cadmium in current optoelectronic devices on the basis of colloidal quantum dots raises environmental concerns. Here we demonstrate that white-light-emitting diodes can be achieved by utilizing non-toxic and environment-friendly gold nanoclusters. Yellow-light-emitting gold nanoclusters were synthesized and capped with trioctylphosphine. These gold nanoclusters were then blended with the blue-light-emitting organic host materials to form the emissive layer. A current efficiency of 0.13 cd/A was achieved. The Commission Internationale de l'Eclairage chromaticity coordinates of (0.27, 0.33) were obtained from our experimental analysis, which is quite close to the ideal pure white emission coordinates (0.33, 0.33). Potential applications include innovative lighting devices and monitor backlight.

Effect of different light sources in combination with a light-transmitting post on the degree of conversion of resin composite at different depths of simulated root canals.

PubMed

Zorba, Yahya Orcun; Erdemir, Ali; Ahmetoglu, Fuat; Yoldas, Oguz

2011-06-01

The aim of this study was to evaluate the degree of conversion (DC) of composite resin at different depths of simulated immature root canals using light-transmitting plastic post (LTPP) and three different light sources. Composite resin was packed into 60 black plastic cylinders 12mm in length with 4mm internal diameters to simulate immature root canals. LTPPs were inserted into half of the simulated canals and the other half acted as controls. Both the simulated canals with LTPPs and the controls were divided into three groups of 10, and each group was cured using either a quartz-tungsten-halogen (QTH), light-emitting diode (LED), or plasma arc (PAC) curing unit. Specimens were sectioned in three horizontally 24h after curing to represent cervical, middle, and apical levels. DC for each section of composite resin was measured using a Fourier transform infrared spectrophotometer, and data were analyzed using three-way anova and Tukey tests. At the cervical level, no significant differences were found between specimens cured using different light sources or between specimens with and without LTPPs (P>0.05). However, DC was significantly higher in specimens with LTPPs than in those without LTPPs at both the middle and apical levels (P<0.05). The mean DC of all specimens with LTPPs was significantly higher than that of specimens without LTPPs (P<0.05). PAC unit showed lower DC than QTH and LED units at both the middle and apical levels; however, the differences were not statistically significant (P > 0.05). The results of this study suggest that the use of a LTPP increased the DC of composite resin at the middle and apical levels of simulated immature root canals, but that DC was independent of type of light source. © 2011 John Wiley & Sons A/S.

Photopolymerization of N,N-dimethylaminobenzyl alcohol as amine co-initiator for light-cured dental resins.

PubMed

Schroeder, Walter F; Cook, Wayne D; Vallo, Claudia I

2008-05-01

The present study was carried out in order to assess the suitability of N,N-dimethylaminobenzyl alcohol (DMOH) as co-initiator of camphorquinone (CQ) and 1-phenyl-1,2-propanedione (PPD) in light-cured dental resins. DMOH was synthesized and used as co-initiator for the photopolymerization of a model resin based on {2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane} (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA). Experimental formulations containing CQ or PPD in combination with DMOH at different concentrations were studied. The photopolymerization was carried out by means of a commercial light-emitting diode (LED) curing unit. The evolution of double bonds consumption versus irradiation time was followed by near-infrared spectroscopy (NIR). The photon absorption efficiency (PAE) of the photopolymerization process was calculated from the spectral distribution of the LED unit and the molar absorption coefficient distributions of PPD and CQ. DMOH is an efficient photoreducer of CQ and PPD resulting in higher polymerization rate and higher double bond conversion compared with dimethylaminoethylmethacrylate. The PAE for PPD was higher than that for CQ. However, the polymerization initiated by PPD progressed at a lower rate and exhibited lower values of final conversion compared with the resins containing CQ. This observation indicates that the lower polymerization rate of the PPD/amine system should be explained in terms of the mechanism of generating primary radicals by PPD, which is less efficient compared with CQ. The DMOH/benzoyl peroxide redox system, has recently been proposed as a more biocompatible accelerator for the polymerization of bone cements based on poly(methyl methacrylate), because cytotoxity tests have demonstrated that DMOH possesses better biocompatibility properties compared with traditional tertiary amines. The results obtained in the present study reveal the suitability of the CQ/DMOH initiator system for the polymerization of light-cured dental composites.

A new light emitting diode-light emitting diode portable carbon dioxide gas sensor based on an interchangeable membrane system for industrial applications.

PubMed

de Vargas-Sansalvador, I M Pérez; Fay, C; Phelan, T; Fernández-Ramos, M D; Capitán-Vallvey, L F; Diamond, D; Benito-Lopez, F

2011-08-12

A new system for CO(2) measurement (0-100%) based on a paired emitter-detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO(2) sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO(2)-insensitive luminophore by an acid-base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid-base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter-detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO(2) response in terms of sensitivity. Copyright © 2011 Elsevier B.V. All rights reserved.

Simple Experimental Verification of the Relation between the Band-Gap Energy and the Energy of Photons Emitted by LEDs

ERIC Educational Resources Information Center

Precker, Jurgen W.

2007-01-01

The wavelength of the light emitted by a light-emitting diode (LED) is intimately related to the band-gap energy of the semiconductor from which the LED is made. We experimentally estimate the band-gap energies of several types of LEDs, and compare them with the energies of the emitted light, which ranges from infrared to white. In spite of…

Effect of two lasers on the polymerization of composite resins: single vs combination.

PubMed

Ro, Jung-Hoon; Son, Sung-Ae; Park, Jeong-kil; Jeon, Gye-Rok; Ko, Ching-Chang; Kwon, Yong Hoon

2015-07-01

The selection of a light-curing unit for the curing composite resins is important to achieve best outcomes. The purpose of the present study was to test lasers of 457 and 473 nm alone or in combination under different light conditions with respect to the cure of composite resins. Four different composite resins were light cured using five different laser combinations (530 mW/cm(2) 457 nm only, 530 mW/cm(2) 473 nm only, 177 mW/cm(2) 457 + 177 mW/cm(2) 473 nm, 265 mW/cm(2) 457 + 265 mW/cm(2) 473 nm, and 354 mW/cm(2) 457 + 354 mW/cm(2) 473 nm). Microhardness and polymerization shrinkage were evaluated. A light-emitting diode (LED) unit was used for comparison purposes. On top surfaces, after aging for 24 h, microhardness achieved using the LED unit and the lasers with different conditions ranged 42.4-65.5 and 38.9-67.7 Hv, respectively, and on bottom surfaces, corresponding ranges were 25.2-56.1 and 18.5-55.7 Hv, respectively. Of the conditions used, 354 mW/cm(2) 457 nm + 354 mW/cm(2) 473 nm produced the highest bottom microhardness (33.8-55.6 Hv). On top and bottom surfaces, microhardness by the lowest total light intensity, 354 (177 × 2) mW/cm(2), ranged 39.0-60.5 and 18.5-52.8 Hv, respectively. Generally, 530 mW/cm(2) at 457 nm produced the lowest polymerization shrinkage. However, shrinkage values obtained using all five laser conditions were similar. The study shows the lasers of 457 and 473 nm are useful for curing composite resins alone or in combination at much lower light intensities than the LED unit.

Diode-pumped cw Nd:YAG three-level laser at 869 nm.

PubMed

Lü, Yanfei; Xia, Jing; Cheng, Weibo; Chen, Jifeng; Ning, Guobin; Liang, Zuoliang

2010-11-01

We report for the first time (to our knowledge) a diode-pumped Nd:YAG laser emitting at 869 nm based on the (4)F(3/2)-(4)I(9/2) transition, generally used for a 946 nm emission. Power of 453 mW at 869 nm has been achieved in cw operation with a fiber-coupled laser diode emitting 35.4 W at 809 nm. Intracavity second-harmonic generation in the cw mode has also been demonstrated with power of 118 mW at 435 nm by using a BiB(3)O(6) nonlinear crystal. In our experiment, we used a LiNbO(3) crystal lens to complement the thermal lens of the laser rod, and we obtained good beam quality and high output power stability.

Formation of 2D bright spatial solitons in lithium niobate with photovoltaic response and incoherent background

NASA Astrophysics Data System (ADS)

Pustozerov, A.; Shandarov, V.

2017-12-01

The influence of incoherent background illumination produced by light-emitting diodes (LED's) of different average wavelengths and laser diode emitting in blue region of visible on diffraction characteristics of narrow coherent light beams of He-Ne laser due to refractive index changes of Fe-doped lithium niobate sample are studied. It has been experimentally demonstrated that nonlinear diffraction of red beams with wavelength 633 nm and diameters on full width of half maximum (FWHM) near to 15 μm may be totally compensated using background light with average wavelengths 450 - 465 nm. To provide the necessary intensity of incoherent background, the combinations of spherical and cylindrical concave lenses with blue LED and laser diode module without focusing its beam have been used.

Suppression of shunting current in a magnetically insulated coaxial vacuum diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yalandin, M. I.; Sharypov, K. A.; Shpak, V. G.

2015-06-08

Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of themore » cathode. These efforts provide conditions for stable emission of the working beam from a graphite cathode with a sharp emitting edge.« less

Direct Growth of III-Nitride Nanowire-Based Yellow Light-Emitting Diode on Amorphous Quartz Using Thin Ti Interlayer

NASA Astrophysics Data System (ADS)

Prabaswara, Aditya; Min, Jung-Wook; Zhao, Chao; Janjua, Bilal; Zhang, Daliang; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S.

2018-02-01

Consumer electronics have increasingly relied on ultra-thin glass screen due to its transparency, scalability, and cost. In particular, display technology relies on integrating light-emitting diodes with display panel as a source for backlighting. In this study, we undertook the challenge of integrating light emitters onto amorphous quartz by demonstrating the direct growth and fabrication of a III-nitride nanowire-based light-emitting diode. The proof-of-concept device exhibits a low turn-on voltage of 2.6 V, on an amorphous quartz substrate. We achieved 40% transparency across the visible wavelength while maintaining electrical conductivity by employing a TiN/Ti interlayer on quartz as a translucent conducting layer. The nanowire-on-quartz LED emits a broad linewidth spectrum of light centered at true yellow color ( 590 nm), an important wavelength bridging the green-gap in solid-state lighting technology, with significantly less strain and dislocations compared to conventional planar quantum well nitride structures. Our endeavor highlighted the feasibility of fabricating III-nitride optoelectronic device on a scalable amorphous substrate through facile growth and fabrication steps. For practical demonstration, we demonstrated tunable correlated color temperature white light, leveraging on the broadly tunable nanowire spectral characteristics across red-amber-yellow color regime.

Direct Growth of III-Nitride Nanowire-Based Yellow Light-Emitting Diode on Amorphous Quartz Using Thin Ti Interlayer.

PubMed

Prabaswara, Aditya; Min, Jung-Wook; Zhao, Chao; Janjua, Bilal; Zhang, Daliang; Albadri, Abdulrahman M; Alyamani, Ahmed Y; Ng, Tien Khee; Ooi, Boon S

2018-02-06

Consumer electronics have increasingly relied on ultra-thin glass screen due to its transparency, scalability, and cost. In particular, display technology relies on integrating light-emitting diodes with display panel as a source for backlighting. In this study, we undertook the challenge of integrating light emitters onto amorphous quartz by demonstrating the direct growth and fabrication of a III-nitride nanowire-based light-emitting diode. The proof-of-concept device exhibits a low turn-on voltage of 2.6 V, on an amorphous quartz substrate. We achieved ~ 40% transparency across the visible wavelength while maintaining electrical conductivity by employing a TiN/Ti interlayer on quartz as a translucent conducting layer. The nanowire-on-quartz LED emits a broad linewidth spectrum of light centered at true yellow color (~ 590 nm), an important wavelength bridging the green-gap in solid-state lighting technology, with significantly less strain and dislocations compared to conventional planar quantum well nitride structures. Our endeavor highlighted the feasibility of fabricating III-nitride optoelectronic device on a scalable amorphous substrate through facile growth and fabrication steps. For practical demonstration, we demonstrated tunable correlated color temperature white light, leveraging on the broadly tunable nanowire spectral characteristics across red-amber-yellow color regime.

Patterned mist deposition of tri-colour CdSe/ZnS quantum dot films toward RGB LED devices

NASA Astrophysics Data System (ADS)

Pickering, S.; Kshirsagar, A.; Ruzyllo, J.; Xu, J.

2012-06-01

In this experiment a technique of mist deposition was explored as a way to form patterned ultra-thin-films of CdSe/ZnS core/shell nanocrystalline quantum dots using colloidal solutions. The objective of this study was to investigate the feasibility of mist deposition as a patterning method for creating multicolour quantum dot light emitting diodes. Mist deposition was used to create three rows of quantum dot light emitting diodes on a single device with each row having a separate colour. The colours chosen were red, green and yellow with corresponding peak wavelengths of 620 nm, 558 nm, and 587 nm. The results obtained from this experiment show that it is possible to create multicolour devices on a single substrate. The peak brightnesses obtained in this experiment for the red, green, and yellow were 508 cd/m, 507 cd/m, and 665 cd/m, respectively. The similar LED brightness is important in display technologies using colloidal quantum dots in a precursor solution to ensure one colour does not dominate the emitted spectrum. Results obtained in-terms of brightness were superior to those achieved with inkjet deposition. This study has shown that mist deposition is a viable method for patterned deposition applied to quantum dot light emitting diode display technologies.

Light-extraction enhancement for light-emitting diodes: a firefly-inspired structure refined by the genetic algorithm

NASA Astrophysics Data System (ADS)

Bay, Annick; Mayer, Alexandre

2014-09-01

The efficiency of light-emitting diodes (LED) has increased significantly over the past few years, but the overall efficiency is still limited by total internal reflections due to the high dielectric-constant contrast between the incident and emergent media. The bioluminescent organ of fireflies gave incentive for light-extraction enhance-ment studies. A specific factory-roof shaped structure was shown, by means of light-propagation simulations and measurements, to enhance light extraction significantly. In order to achieve a similar effect for light-emitting diodes, the structure needs to be adapted to the specific set-up of LEDs. In this context simulations were carried out to determine the best geometrical parameters. In the present work, the search for a geometry that maximizes the extraction of light has been conducted by using a genetic algorithm. The idealized structure considered previously was generalized to a broader variety of shapes. The genetic algorithm makes it possible to search simultaneously over a wider range of parameters. It is also significantly less time-consuming than the previous approach that was based on a systematic scan on parameters. The results of the genetic algorithm show that (1) the calculations can be performed in a smaller amount of time and (2) the light extraction can be enhanced even more significantly by using optimal parameters determined by the genetic algorithm for the generalized structure. The combination of the genetic algorithm with the Rigorous Coupled Waves Analysis method constitutes a strong simulation tool, which provides us with adapted designs for enhancing light extraction from light-emitting diodes.

An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: preferential outcoupling of strong in-plane emission (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kim, Jong Kyu; Lee, Jong Won; Kim, Dong-Yeong; Park, Jun Hyuk; Schubert, E. Fred; Kim, Jungsub; Kim, Yong-Il

2016-09-01

AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) are being developed for their numerous applications such as purification of air and water, sterilization in food processing, UV curing, medical-, and defense-related light sources. However, external quantum efficiency (EQE) of AlGaN-based DUV LEDs is very poor (<5% for 250nm) particularly due to low hole concentration and light extraction efficiency (LEE). Conventional LEE-enhancing techniques used for GaInN-based visible LEDs turned out to be ineffective for DUV LEDs due to difference in intrinsic material property between GaInN and AlGaN (Al< 30%). Unlike GaInN visible LEDs, DUV light from a high Al-content AlGaN active region is strongly transverse-magnetic (TM) polarized, that is, the electric field vector is parallel to the (0001) c-axis and shows strong sidewall emission through m- or a-plane due to crystal-field split-off hole band being top most valence band. Therefore, a new LEE-enhancing approach addressing the unique intrinsic property of AlGaN DUV LEDs is strongly desired. In this study, an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells is presented. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage simultaneously. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes to maximize the power conversion efficiency.

Effect of interfacial composition on Ag-based Ohmic contact of GaN-based vertical light emitting diodes

NASA Astrophysics Data System (ADS)

Wu, Ning; Xiong, Zhihua; Qin, Zhenzhen

2018-02-01

By investigating the effect of a defective interface structure on Ag-based Ohmic contact of GaN-based vertical light-emitting diodes, we found a direct relationship between the interfacial composition and the Schottky barrier height of the Ag(111)/GaN(0001) interface. It was demonstrated that the Schottky barrier height of a defect-free Ag(111)/GaN(0001) interface was 2.221 eV, and it would be dramatically decreased to 0.375 eV with the introduction of one Ni atom and one Ga vacancy at the interface structure. It was found that the tunability of the Schottky barrier height can be attributed to charge accumulations around the interfacial defective regions and an unpinning of the Fermi level, which explains the experimental phenomenon of Ni-assisted annealing improving the p-type Ohmic contact characteristic. Lastly, we propose a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact. These results provide a guideline for the fabrication of high-quality Ag-based Ohmic contact of GaN-based vertical light-emitting diodes.

Stacking multiple connecting functional materials in tandem organic light-emitting diodes

PubMed Central

Zhang, Tao; Wang, Deng-Ke; Jiang, Nan; Lu, Zheng-Hong

2017-01-01

Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency. PMID:28225028

InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnamoorthy, Sriram, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu; Akyol, Fatih; Rajan, Siddharth, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu

InGaN/GaN tunnel junction contacts were grown using plasma assisted molecular beam epitaxy (MBE) on top of a metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN blue (450 nm) light emitting diode. A voltage drop of 5.3 V at 100 mA, forward resistance of 2 × 10{sup −2} Ω cm{sup 2}, and a higher light output power compared to the reference light emitting diodes (LED) with semi-transparent p-contacts were measured in the tunnel junction LED (TJLED). A forward resistance of 5 × 10{sup −4} Ω cm{sup 2} was measured in a GaN PN junction with the identical tunnel junction contact as the TJLED, grown completely by MBE. Themore » depletion region due to the impurities at the regrowth interface between the MBE tunnel junction and the MOCVD-grown LED was hence found to limit the forward resistance measured in the TJLED.« less

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

Gigabit-per-second white light-based visible light communication using near-ultraviolet laser diode and red-, green-, and blue-emitting phosphors.

PubMed

Lee, Changmin; Shen, Chao; Cozzan, Clayton; Farrell, Robert M; Speck, James S; Nakamura, Shuji; Ooi, Boon S; DenBaars, Steven P

2017-07-24

Data communication based on white light generated using a near-ultraviolet (NUV) laser diode (LD) pumping red-, green-, and blue-emitting (RGB) phosphors was demonstrated for the first time. A III-nitride laser diode (LD) on a semipolar (2021¯)  substrate emitting at 410 nm was used for the transmitter. The measured modulation bandwidth of the LD was 1 GHz, which was limited by the avalanche photodetector. The emission from the NUV LD and the RGB phosphor combination measured a color rendering index (CRI) of 79 and correlated color temperature (CCT) of 4050 K, indicating promise of this approach for creating high quality white lighting. Using this configuration, data was successfully transmitted at a rate of more than 1 Gbps. This NUV laser-based system is expected to have lower background noise from sunlight at the LD emission wavelength than a system that uses a blue LD due to the rapid fall off in intensity of the solar spectrum in the NUV spectral region.

Color tunable hybrid light-emitting diodes based on perovskite quantum dot/conjugated polymer

NASA Astrophysics Data System (ADS)

Germino, José C.; Yassitepe, Emre; Freitas, Jilian N.; Santiago, Glauco M.; Bonato, Luiz Gustavo; de Morais, Andréia; Atvars, Teresa D. Z.; Nogueira, Ana F.

2017-08-01

Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of the optical properties of the PQDs and their interaction with wide bandgap conjugated polymers, associated with the solution processing ability of these materials.

Hydrothermal growth of n-ZnO films on a patterned p-GaN epilayer and its application in heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Ko, Rong-Ming; Wang, Shui-Jinn; Chen, Ching-Yi; Wu, Cheng-Han; Lin, Yan-Ru; Lo, Hsin-Ming

2017-04-01

The hydrothermal growth (HTG) of crystalline n-ZnO films on both the nonpatterned and patterned p-GaN epilayers with a honeycomb array of etched holes is demonstrated, and its application in n-ZnO/p-GaN heterojunction light-emitting diodes (HJ-LEDs) is reported. The results reveal that an HTG n-ZnO film on a patterned p-GaN layer exhibits a high-quality single crystal with FWHMs of 0.463 and 0.983° obtained from a ω-rocking curve and a ϕ-scan pattern, respectively, which are much better than those obtained on a nonpatterned p-GaN layer. In addition, the n-ZnO/patterned p-GaN HJ-LED exhibited a much better rectifying diode behavior owing to having a higher n-ZnO film crystallinity quality and an improved interface with the p-GaN layer. Strong violet and violet-blue lights emitted from the n-ZnO/patterned p-GaN HJ-LED at around 405, 412, and 430 nm were analyzed.

Stacking multiple connecting functional materials in tandem organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Tao; Wang, Deng-Ke; Jiang, Nan; Lu, Zheng-Hong

2017-02-01

Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency.

Reduced Graphene Oxide/Single-Walled Carbon Nanotube Hybrid Film Using Various p-Type Dopants and Its Application to GaN-Based Light-Emitting Diodes.

PubMed

Lee, Byeong Ryong; Kim, Tae Geun

2016-06-01

This paper reports the electrical and optical properties of the reduced graphene oxide (RGO)/single-walled carbon nanotube (SWNT) films using various p-type dopants and its application to GaN-based light-emitting diodes. To enhance the current injection and spreading of the RGO/SWNT films on the light-emitting diodes (LEDs), we increased the work function (φ) of the films using chemical doping with AuCl3, poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) ( PSS) and MoO3; thereby reduced the Schottky barrier height between the RGO/SWNT films and p-GaN. By comparison, LEDs fabricated with work-function-tuned RGO/SWNT film doped with MoO3 exhibited the decrease of the forward voltage from 5.3 V to 5.02 V at 20 mA and the increase of the output power up to 1.26 times. We also analyzed the current injection mechanism using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy.

The fabrication of small molecule organic light-emitting diode pixels by laser-induced forward transfer

NASA Astrophysics Data System (ADS)

Shaw-Stewart, J. R. H.; Mattle, T.; Lippert, T. K.; Nagel, M.; Nüesch, F. A.; Wokaun, A.

2013-01-01

Laser-induced forward transfer (LIFT) is a versatile organic light-emitting diode (OLED) pixel deposition process, but has hitherto been applied exclusively to polymeric materials. Here, a modified LIFT process has been used to fabricate small molecule Alq3 organic light-emitting diodes (SMOLEDs). Small molecule thin films are considerably more mechanically brittle than polymeric thin films, which posed significant challenges for LIFT of these materials. The LIFT process presented here uses a polymeric dynamic release layer, a reduced environmental pressure, and a well-defined receiver-donor gap. The Alq3 pixels demonstrate good morphology and functionality, even when compared to conventionally fabricated OLEDs. The Alq3 SMOLED pixel performances show a significant amount of fluence dependence, not observed with polymerical OLED pixels made in previous studies. A layer of tetrabutyl ammonium hydroxide has been deposited on top of the aluminium cathode, as part of the donor substrate, to improve electron injection to the Alq3, by over 600%. These results demonstrate that this variant of LIFT is applicable for the deposition of functional small molecule OLEDs as well as polymeric OLEDs.

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

DOE PAGES

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei; ...

2017-09-05

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

An entangled-light-emitting diode.

PubMed

Salter, C L; Stevenson, R M; Farrer, I; Nicoll, C A; Ritchie, D A; Shields, A J

2010-06-03

An optical quantum computer, powerful enough to solve problems so far intractable using conventional digital logic, requires a large number of entangled photons. At present, entangled-light sources are optically driven with lasers, which are impractical for quantum computing owing to the bulk and complexity of the optics required for large-scale applications. Parametric down-conversion is the most widely used source of entangled light, and has been used to implement non-destructive quantum logic gates. However, these sources are Poissonian and probabilistically emit zero or multiple entangled photon pairs in most cycles, fundamentally limiting the success probability of quantum computational operations. These complications can be overcome by using an electrically driven on-demand source of entangled photon pairs, but so far such a source has not been produced. Here we report the realization of an electrically driven source of entangled photon pairs, consisting of a quantum dot embedded in a semiconductor light-emitting diode (LED) structure. We show that the device emits entangled photon pairs under d.c. and a.c. injection, the latter achieving an entanglement fidelity of up to 0.82. Entangled light with such high fidelity is sufficient for application in quantum relays, in core components of quantum computing such as teleportation, and in entanglement swapping. The a.c. operation of the entangled-light-emitting diode (ELED) indicates its potential function as an on-demand source without the need for a complicated laser driving system; consequently, the ELED is at present the best source on which to base future scalable quantum information applications.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN.

PubMed

Soh, C B; Liu, W; Yong, A M; Chua, S J; Chow, S Y; Tripathy, S; Tan, R J N

2010-08-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO(2) film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, η(extraction,) was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

NASA Astrophysics Data System (ADS)

Soh, C. B.; Liu, W.; Yong, A. M.; Chua, S. J.; Chow, S. Y.; Tripathy, S.; Tan, R. J. N.

2010-11-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

High Power Laser Diode Array Qualification and Guidelines for Space Flight Environments

NASA Technical Reports Server (NTRS)

Eegholm, Niels; Ott, Melanie; Stephen, Mark; Leidecker, Henning

2005-01-01

Semiconductor laser diodes emit coherent light by simulated emission generated inside the cavity formed by the cleaved end facets of a slab of semiconductor that is typically less than a millimeter in any dimension for single emitters. The diode is pumped by current injection in the p-n junction through the metallic contacts. Laser diodes emitting in the range of 0.8 micron to 1.06 micron have a wide variety of applications from pumping erbium doped fiber amplifiers, dual-clad fiber lasers, solid-state lasers used in telecom, aerospace, military, medical purposes and all the way to CD players, laser printers and other consumer and industrial products. Laser diode bars have many single emitters side by side and spaced approximately .5 mm on a single slab of semiconductor material approximately .5 mm x 10 mm. The individual emitters are connected in parallel maintaining the voltage at -2V but increasing the current to 50-100A/bar. Stacking these laser diode bars in multiple layers, 2 to 20+ high, yields high power laser diode arrays capable of emitting several hundreds of Watts. Electrically the bars are wired in series increasing the voltage by 2V/bar but maintaining the total current at 50-100A. These arrays are one of the enabling technologies for efficient, high power solid-state lasers. Traditionally these arrays are operated in QCW (Quasi CW) mode with pulse widths 10-200 (mu)s and with repetition rates of 10-200Hz. In QCW mode the wavelength and the output power of the laser reaches steady-state but the temperature does not. The advantage is a substantially higher output power than in CW mode, where the output power would be limited by the internal heating and hence the thermal and heat sinking properties of the device. The down side is a much higher thermal induced mechanical stress caused by the constant heating and cooling cycle inherent to the QCW mode.

Electrical properties of epitaxial 3C- and 6H-SiC p-n junction diodes produced side-by-side on 6H-SiC substrates

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Larkin, David J.; Starr, Jonathan E.; Powell, J. Anthony; Salupo, Carl S.; Matus, Lawrence G.

1994-01-01

3C-SiC (beta-SiC) and 6H-SiC p-n junction diodes have been fabricated in regions of both 3C-SiC and 6H-SiC epitaxial layers which were grown side-by-side on low-tilt-angle 6H-SiC substrates via a chemical vapor deposition (CVD) process. Several runs of diodes exhibiting state-of-the-art electrical characteristics were produced, and performance characteristics were measured and compared as a function of doping, temperature, and polytype. The first 3C-SiC diodes which rectify to reverse voltages in excess of 300 V were characterized, representing a six-fold blocking voltage improvement over experimental 3C-SiC diodes produced by previous techniques. When placed under sufficient forward bias, the 3C-SiC diodes emit significantly bright green-yellow light while the 6H-SiC diodes emit in the blue-violet. The 6H-SiC p-n junction diodes represent the first reported high-quality 6H-SiC devices to be grown by CVD on very low-tilt-angle (less than 0.5 deg off the (0001) silicon face) 6H substrates. The reverse leakage current of a 200 micron diameter circular device at 1100 V reverse bias was less than 20 nA at room temperature, and excellent rectification characteristics were demonstrated at the peak characterization temperature of 400 C.

High brightness diode lasers controlled by volume Bragg gratings

NASA Astrophysics Data System (ADS)

Glebov, Leonid

2017-02-01

Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass are holographic optical elements that are effective spectral and angular filters withstanding high power laser radiation. Reflecting VBGs are narrow-band spectral filters while transmitting VBGs are narrow-band angular filters. The use of these optical elements in external resonators of semiconductor lasers enables extremely resonant feedback that provides dramatic spectral and angular narrowing of laser diodes radiation without significant power and efficiency penalty. Spectral narrowing of laser diodes by reflecting VBGs demonstrated in wide spectral region from near UV to 3 μm. Commercially available VBGs have spectral width ranged from few nanometers to few tens of picometers. Efficient spectral locking was demonstrated for edge emitters (single diodes, bars, modules, and stacks), vertical cavity surface emitting lasers (VCSELs), grating coupled surface emitting lasers (GCSELs), and interband cascade lasers (ICLs). The use of multiplexed VBGs provides multiwavelength emission from a single emitter. Spectrally locked semiconductor lasers demonstrated CW power from milliwatts to a kilowatt. Angular narrowing by transmitting VBGs enables single transverse mode emission from wide aperture diode lasers having resonators with great Fresnel numbers. This feature provides close to diffraction limit divergence along a slow axis of wide stripe edge emitters. Radiation exchange between lasers by means of spatially profiled or multiplexed VBGs enables coherent combining of diode lasers. Sequence of VBGs or multiplexed VBGs enable spectral combining of spectrally narrowed diode lasers or laser modules. Thus the use of VBGs for diode lasers beam control provides dramatic increase of brightness.

An Exciplex Host for Deep-Blue Phosphorescent Organic Light-Emitting Diodes.

PubMed

Lim, Hyoungcheol; Shin, Hyun; Kim, Kwon-Hyeon; Yoo, Seung-Jun; Huh, Jin-Suk; Kim, Jang-Joo

2017-11-01

The use of exciplex hosts is attractive for high-performance phosphorescent organic light-emitting diodes (PhOLEDs) and thermally activated delayed fluorescence OLEDs, which have high external quantum efficiency, low driving voltage, and low efficiency roll-off. However, exciplex hosts for deep-blue OLEDs have not yet been reported because of the difficulties in identifying suitable molecules. Here, we report a deep-blue-emitting exciplex system with an exciplex energy of 3.0 eV. It is composed of a carbazole-based hole-transporting material (mCP) and a phosphine-oxide-based electron-transporting material (BM-A10). The blue PhOLEDs exhibited maximum external quantum efficiency of 24% with CIE coordinates of (0.15, 0.21) and longer lifetime than the single host devices.

Enhanced out-coupling efficiency of organic light-emitting diodes using an nanostructure imprinted by an alumina nanohole array

NASA Astrophysics Data System (ADS)

Endo, Kuniaki; Adachi, Chihaya

2014-03-01

We demonstrate organic light-emitting diodes (OLEDs) with enhanced out-coupling efficiency containing nanostructures imprinted by an alumina nanohole array template that can be applied to large-emitting-area and flexible devices using a roll-to-roll process. The nanostructures are imprinted on a glass substrate by an ultraviolet nanoimprint process using an alumina nanohole array mold and then an OLED is fabricated on the nanostructures. The enhancement of out-coupling efficiency is proportional to the root-mean-square roughness of the nanostructures, and a maximum improvement of external electroluminescence quantum efficiency of 17% is achieved. The electroluminescence spectra of the OLEDs indicate that this improvement is caused by enhancement of the out-coupling of surface plasmon polaritons.

Optimization of hybrid blue organic light-emitting diodes based on singlet and triplet exciton diffusion length

NASA Astrophysics Data System (ADS)

Lee, Song Eun; Lee, Ho Won; Lee, Jae Woo; Hwang, Kyo Min; Park, Soo Na; Yoon, Seung Soo; Kim, Young Kwan

2015-06-01

The hybrid blue organic light-emitting diodes (HB OLEDs) with triplet harvesting (TH) structures within an emitting layer (EML) are fabricated with fluorescent and phosphorescent EMLs. The TH is to transfer triplet excitons from fluorescence to phosphorescence, where they can decay radiatively. Remarkably, the half-decay lifetime of a hybrid blue device with fluorescent and phosphorescent EML thickness of 5 and 25 nm, measured at an initial luminance of 500 cd/m2, has improved twice than that of using a conventional structure. Additionally, the blue device’s efficiency improved. We attribute this improvement to the efficient triplet excitons energy transfer and the optimized distribution of the EML which depends on singlet and triplet excitons diffusion length that occurs within each the EML.

Triplet exciton confinement for enhanced fluorescent organic light-emitting diodes using a co-host system

NASA Astrophysics Data System (ADS)

Yoo, Han Kyu; Lee, Ho Won; Lee, Song Eun; Kim, Young Kwan; Kim, Se Hyun; Yoon, Seung Soo; Park, Jaehoon

2016-05-01

In this work, the co-host system within an emitting layer (EML) consists of the host and triplet managing (TM) host materials. A set of EML structures was fabricated with various concentrations of the TM host (0, 10, 30, 50, and 70%). The TM host triplet energy level is lower than the energy levels of the host and the guest, which leads to a reduction in the triplet exciton density and the singlet-triplet annihilation of the guest. Blue fluorescent organic light-emitting diodes exhibit a maximum luminous efficiency (LE) and an external quantum efficiency (EQE) of 9.74 cd/A and 4.92%, respectively. In addition, the efficiency roll-off ratios of the LE and the EQE are 14.25 and 13.16%, respectively.

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes

PubMed Central

2012-01-01

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer. PMID:23181826

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes.

PubMed

Bae, Yu Jeong; Lee, Nyun Jong; Kim, Tae Hee; Cho, Hyunduck; Lee, Changhee; Fleet, Luke; Hirohata, Atsufumi

2012-11-26

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.

Lithium salt doped conjugated polymers as electron transporting materials for highly efficient blue polymer light-emitting diodes

NASA Astrophysics Data System (ADS)

Huang, Fei; Shih, Ping-I.; Liu, Michelle S.; Shu, Ching-Fong; Jen, Alex K.-Y.

2008-12-01

Highly efficient blue polymer light-emitting diodes (PLEDs) are fabricated using a conjugated polymer, poly[9,9-bis(2-(2-(2-diethanol-amino-ethoxy) ethoxy) ethyl) fluorene-alt-4, 4'-phenylether] as an electron transporting layer (ETL). It was found that the performance of these blue-emitting devices could be greatly improved if the ETL was doped with LiF or Li2CO3 salts. A bis[(4,6-di-fluorophenyl)-pyridinato-N, C2] (picolinate) Ir(III) (FIrpic) complex based blue phosphorescent PLED exhibited a maximum luminance efficiency of 20.3 cd/A with a luminance of 1600 cd/m2 at the current density of 7.9 mA/cm2 and drive voltage of 8.0 V.

Integrated RGB laser light module for autostereoscopic outdoor displays

NASA Astrophysics Data System (ADS)

Reitterer, Jörg; Fidler, Franz; Hambeck, Christian; Saint Julien-Wallsee, Ferdinand; Najda, Stephen; Perlin, Piotr; Stanczyk, Szymon; Czernecki, Robert; McDougall, Stewart D.; Meredith, Wyn; Vickers, Garrie; Landles, Kennedy; Schmid, Ulrich

2015-02-01

We have developed highly compact RGB laser light modules to be used as light sources in multi-view autostereoscopic outdoor displays and projection devices. Each light module consists of an AlGaInP red laser diode, a GaInN blue laser diode, a GaInN green laser diode, as well as a common cylindrical microlens. The plano-convex microlens is a so-called "fast axis collimator", which is widely used for collimating light beams emitted from high-power laser diode bars, and has been optimized for polychromatic RGB laser diodes. The three light beams emitted from the red, green, and blue laser diodes are collimated in only one transverse direction, the so-called "fast axis", and in the orthogonal direction, the so-called "slow axis", the beams pass the microlens uncollimated. In the far field of the integrated RGB light module this produces Gaussian beams with a large ellipticity which are required, e.g., for the application in autostereoscopic outdoor displays. For this application only very low optical output powers of a few milliwatts per laser diode are required and therefore we have developed tailored low-power laser diode chips with short cavity lengths of 250 μm for red and 300 μm for blue. Our RGB laser light module including the three laser diode chips, associated monitor photodiodes, the common microlens, as well as the hermetically sealed package has a total volume of only 0.45 cm³, which to our knowledge is the smallest RGB laser light source to date.

LED's in Physics Demos: A Handful of Examples.

ERIC Educational Resources Information Center

Lottis, Dan; Jaeger, Herbert

1996-01-01

Describes the use of light-emitting diodes (LED) instead of incandescent bulbs in experiments that generally use battery and bulbs to enable students to explore and understand fundamental electrical phenomena. Presents the following examples: Faraday's Law demonstration, conductors and insulators, and rectifying action of a diode. (JRH)

High-speed GaN/GaInN nanowire array light-emitting diode on silicon(111).

PubMed

Koester, Robert; Sager, Daniel; Quitsch, Wolf-Alexander; Pfingsten, Oliver; Poloczek, Artur; Blumenthal, Sarah; Keller, Gregor; Prost, Werner; Bacher, Gerd; Tegude, Franz-Josef

2015-04-08

The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space.

Combination of carbon dot and polymer dot phosphors for white light-emitting diodes.

PubMed

Sun, Chun; Zhang, Yu; Sun, Kai; Reckmeier, Claas; Zhang, Tieqiang; Zhang, XiaoYu; Zhao, Jun; Wu, Changfeng; Yu, William W; Rogach, Andrey L

2015-07-28

We realized white light-emitting diodes with high color rendering index (85-96) and widely variable color temperatures (2805-7786 K) by combining three phosphors based on carbon dots and polymer dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.

Analysis of the external and internal quantum efficiency of multi-emitter, white organic light emitting diodes

NASA Astrophysics Data System (ADS)

Furno, Mauro; Rosenow, Thomas C.; Gather, Malte C.; Lüssem, Björn; Leo, Karl

2012-10-01

We report on a theoretical framework for the efficiency analysis of complex, multi-emitter organic light emitting diodes (OLEDs). The calculation approach makes use of electromagnetic modeling to quantify the overall OLED photon outcoupling efficiency and a phenomenological description for electrical and excitonic processes. From the comparison of optical modeling results and measurements of the total external quantum efficiency, we obtain reliable estimates of internal quantum yield. As application of the model, we analyze high-efficiency stacked white OLEDs and comment on the various efficiency loss channels present in the devices.

Enhanced efficiency of light emitting diodes with a nano-patterned gallium nitride surface realized by soft UV nanoimprint lithography

NASA Astrophysics Data System (ADS)

Zhou, Weimin; Min, Guoquan; Song, Zhitang; Zhang, Jing; Liu, Yanbo; Zhang, Jianping

2010-05-01

This paper reports a significant enhancement in the extraction efficiency of nano-patterned GaN light emitting diodes (LED) realized by soft UV nanoimprint lithography. The 2 inch soft stamp was fabricated using a replication stamp of anodic alumina oxide (AAO) membrane. The light output power was enhanced by 10.9% compared to that of the LED sample without a nano-patterned surface. Up to 41% enhancement in photoluminescence intensity was obtained from the nano-patterned GaN LED sample. The method is simple, cheap and suitable for mass production.

Fabrication and Measurement of Electroluminescence and Electrical Properties of Organic Light-Emitting Diodes Containing Mott Insulator Nanocrystals.

PubMed

Nozoe, Soichiro; Kinoshita, Nobuaki; Matsuda, Masaki

2016-04-01

By using the short-time electrocrystallization technique, phthalocyanine (Pc)-based Mott insulator Co(Pc)(CN)2 . 2CHCl3 nanocrystals were fabricated and applied to organic light-emiting diodes (OLEDs). The fabricated device having the configuration ITO/Co(Pc)(CN)2 . 2CHCl3/Alq3/Al, in which ITO is indium-tin oxide and Alq3 is tris(8-hydroxyquinolinato)aluminum, showed clear emission from Alq3, suggesting the Mott insulator Co(Pc)(CN)2 . 2CHCl3 can work as useful hole-injection and transport material in OLEDs.

Efficiency improvement of green light-emitting diodes by employing all-quaternary active region and electron-blocking layer

NASA Astrophysics Data System (ADS)

Usman, Muhammad; Saba, Kiran; Han, Dong-Pyo; Muhammad, Nazeer

2018-01-01

High efficiency of green GaAlInN-based light-emitting diode (LED) has been proposed with peak emission wavelength of ∼510 nm. By introducing quaternary quantum well (QW) along with the quaternary barrier (QB) and quaternary electron blocking layer (EBL) in a single structure, an efficiency droop reduction of up to 29% has been achieved in comparison to the conventional GaN-based LED. The proposed structure has significantly reduced electrostatic field in the active region. As a result, carrier leakage has been minimized and spontaneous emission rate has been doubled.

AlGaInP light-emitting diodes with SACNTs as current-spreading layer

PubMed Central

2014-01-01

Transparent conductive current-spreading layer is important for quantum efficiency and thermal performance of light-emitting diodes (LEDs). The increasing demand for tin-doped indium oxide (ITO) caused the price to greatly increase. Super-aligned carbon nanotubes (SACNTs) and Au-coated SACNTs as current-spreading layer were applied on AlGaInP LEDs. The LEDs with Au-coated SACNTs showed good current spreading effect. The voltage bias at 20 mA dropped about 0.15 V, and the optical power increased about 10% compared with the LEDs without SACNTs. PMID:24712527

Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls

PubMed Central

Wakefield, Andrew; Stone, Emma L.; Jones, Gareth; Harris, Stephen

2015-01-01

The light-emitting diode (LED) street light market is expanding globally, and it is important to understand how LED lights affect wildlife populations. We compared evasive flight responses of moths to bat echolocation calls experimentally under LED-lit and -unlit conditions. Significantly, fewer moths performed ‘powerdive’ flight manoeuvres in response to bat calls (feeding buzz sequences from Nyctalus spp.) under an LED street light than in the dark. LED street lights reduce the anti-predator behaviour of moths, shifting the balance in favour of their predators, aerial hawking bats. PMID:26361558

Flexible inorganic light emitting diodes based on semiconductor nanowires

PubMed Central

Guan, Nan; Dai, Xing; Babichev, Andrey V.; Julien, François H.

2017-01-01

The fabrication technologies and the performance of flexible nanowire light emitting diodes (LEDs) are reviewed. We first introduce the existing approaches for flexible LED fabrication, which are dominated by organic technologies, and we briefly discuss the increasing research effort on flexible inorganic LEDs achieved by micro-structuring and transfer of conventional thin films. Then, flexible nanowire-based LEDs are presented and two main fabrication technologies are discussed: direct growth on a flexible substrate and nanowire membrane formation and transfer. The performance of blue, green, white and bi-color flexible LEDs fabricated following the transfer approach is discussed in more detail. PMID:29568439

Organization of the Topical Meeting on Tunable Solid State Lasers Held in North Falmouth, Massachusetts on 1-3 May 1989

DTIC Science & Technology

1989-08-30

nm to produce blue light at 455 nm (Figure 1). A 20 Hz doubled Nd:YAG pump laser emitting up to 150 mJ at 532 nm 147 WA4-2 was used to resonantly...pumped by a diode laser, then in addition to the processes of Fig. 1, excited state absorption of the pump light from both 4I13,/z and 4I3112 may be...are visible and UV systems pumped at wavelengths that are available from semiconductor diode lasers and infrared emitting systems having high slope

Direct correlations of structural and optical properties of three-dimensional GaN/InGaN core/shell micro-light emitting diodes

NASA Astrophysics Data System (ADS)

Sadat Mohajerani, Matin; Müller, Marcus; Hartmann, Jana; Zhou, Hao; Wehmann, Hergo-H.; Veit, Peter; Bertram, Frank; Christen, Jürgen; Waag, Andreas

2016-05-01

Three-dimensional (3D) InGaN/GaN quantum-well (QW) core-shell light emitting diodes (LEDs) are a promising candidate for the future solid state lighting. In this contribution, we study direct correlations of structural and optical properties of the core-shell LEDs using highly spatially-resolved cathodoluminescence spectroscopy (CL) in combination with scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Temperature-dependent resonant photoluminescence (PL) spectroscopy has been performed to understand recombination mechanisms and to estimate the internal quantum efficiency (IQE).

Electroluminescent Properties in Organic Light-Emitting Diode Doped with Two Guest Dyes

NASA Astrophysics Data System (ADS)

Mori, Tatsuo; Kim, Hyeong-Gweon; Mizutani, Teruyoshi; Lee, Duck-Chool

2001-09-01

An organic light-emitting diode (OLED) with a squarylium dye-doped aluminium quinoline (Alq3) emission layer prepared by vapor deposition method has a pure red emission. However, since its luminance and electroluminescence (EL) efficiency is poor, the authors attended to improve the EL efficiency by doping a photosensitizer dye (a styryl dye, DCM) in an emission layer. The EL efficiency and luminance of DCM- and Sq-doped OLEDs are 2-3 times higher than those of only Sq-doped OLEDs. It was found that the excited energy is transferred from Alq3 to Sq through DCM.

The circular polarization inversion in δ〈Mn〉/InGaAs/GaAs light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorokhin, M. V., E-mail: dorokhin@nifti.unn.ru; Danilov, Yu. A.; Zvonkov, B. N.

We investigated light-emitting diodes consisting of an InGaAs/GaAs quantum well adjacent to a ferromagnetic δ〈Mn〉-layer. The magnetic field-dependent circular polarization obtained from both photo- and electroluminescence shows an unusual sign inversion depending on the growth parameters that can be explained by an interplay of the Zeeman splitting and Mn-hole interaction effects. Our results can help to understand the origin and control of the spin polarization on Mn doped GaAs structures, a fundamental step for the development of Mn-based spintronic devices.

Light-emitting diode technology status and directions: Opportunities for horticultural lighting

DOE PAGES

Tsao, Jeffrey Y.; Pattison, P. Morgan; Krames, Michael R.

2016-01-01

Here, light-emitting diode (LED) technology has advanced rapidly over the last decade, primarily driven by display and general illumination applications ("solid-state lighting (SSL) for humans"). These advancements have made LED lighting technically and economically advantageous not only for these applications, but also, as an indirect benefit, for adjacent applications such as horticultural lighting ("SSL for plants"). Moreover, LED technology has much room for continued improvement. In the near-term, these improvements will continue to be driven by SSL for humans (with indirect benefit to SSL for plants), the most important of which can be anticipated.

Fabrication and characterization of a germanium nanowire light emitting diode

NASA Astrophysics Data System (ADS)

Greil, Johannes; Bertagnolli, Emmerich; Salem, Bassem; Baron, Thierry; Gentile, Pascal; Lugstein, Alois

2017-12-01

In this letter, we demonstrate the feasibility of a germanium nanowire light emitting diode as a reasonable approach for downscaling of CMOS compatible light sources. We show room-temperature direct bandgap electroluminescence from axial p-n junction nanowire devices. The electron population in the Γ valley, necessary for direct bandgap emission, is achieved by high injection current densities. Carrier temperature is consistently found to be higher than the lattice temperature, indicating inhibited carrier cooling in small diameter wires. Strong polarization of the emission parallel to the nanowire axis is observed and attributed to dielectric contrast phenomena.

Infrared emitting device and method

DOEpatents

Kurtz, Steven R.; Biefeld, Robert M.; Dawson, L. Ralph; Howard, Arnold J.; Baucom, Kevin C.

1997-01-01

An infrared emitting device and method. The infrared emitting device comprises a III-V compound semiconductor substrate upon which are grown a quantum-well active region having a plurality of quantum-well layers formed of a ternary alloy comprising InAsSb sandwiched between barrier layers formed of a ternary alloy having a smaller lattice constant and a larger energy bandgap than the quantum-well layers. The quantum-well layers are preferably compressively strained to increase the threshold energy for Auger recombination; and a method is provided for determining the preferred thickness for the quantum-well layers. Embodiments of the present invention are described having at least one cladding layer to increase the optical and carrier confinement in the active region, and to provide for waveguiding of the light generated within the active region. Examples have been set forth showing embodiments of the present invention as surface- and edge-emitting light emitting diodes (LEDs), an optically-pumped semiconductor laser, and an electrically-injected semiconductor diode laser. The light emission from each of the infrared emitting devices of the present invention is in the midwave infrared region of the spectrum from about 2 to 6 microns.

Infrared emitting device and method

DOEpatents

Kurtz, S.R.; Biefeld, R.M.; Dawson, L.R.; Howard, A.J.; Baucom, K.C.

1997-04-29

The infrared emitting device comprises a III-V compound semiconductor substrate upon which are grown a quantum-well active region having a plurality of quantum-well layers formed of a ternary alloy comprising InAsSb sandwiched between barrier layers formed of a ternary alloy having a smaller lattice constant and a larger energy bandgap than the quantum-well layers. The quantum-well layers are preferably compressively strained to increase the threshold energy for Auger recombination; and a method is provided for determining the preferred thickness for the quantum-well layers. Embodiments of the present invention are described having at least one cladding layer to increase the optical and carrier confinement in the active region, and to provide for waveguiding of the light generated within the active region. Examples have been set forth showing embodiments of the present invention as surface- and edge-emitting light emitting diodes (LEDs), an optically-pumped semiconductor laser, and an electrically-injected semiconductor diode laser. The light emission from each of the infrared emitting devices of the present invention is in the midwave infrared region of the spectrum from about 2 to 6 microns. 8 figs.

A New Kind of Curing

NASA Technical Reports Server (NTRS)

2001-01-01

A new curing method using automated tape placement (ATP) with electron beam (EB), or e-beam, produces a combination known as in situ e-beam curing. Through a Small Business Innovation Research (SBIR) contract from NASA's Marshall Space Flight Center, Science Research Laboratory, Inc., created the in situ e-beam curing technique, which uses a low-energy electron beam gun to cure various composite materials. One important benefit is the technique's utilization of room temperature curing, which lessens the chance of mismatching the thermal expansion coefficients of different materials. For instance, metals and composites will expand at different rates when heated, but the low-energy e-beam gun reduces the expansion differential. Using a low-energy gun also results in less x-ray shielding, significantly reduced capital costs, reduced facility space, and increased processing capabilities for larger parts. However, using a low-energy gun also means that each tape layer is treated individually because the gun can penetrate only one layer at a time. The e-beam gun emits lower energy x-rays, which are more easily shielded than those emitted by previous guns. The low-energy system is relatively portable due to its light weight and small size. The gun weighs about 70 pounds and can be easily mounted on a robotic arm or an ATP head.

Greatly improved 3C-SiC p-n junction diodes grown by chemical vapor deposition

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Larkin, David J.; Starr, Jonathan E.; Powell, J. A.; Salupo, Carl S.; Matus, Lawrence G.

1993-01-01

This paper reports the fabrication and initial electrical characterization of greatly improved 3C-SiC (beta-SiC) p-n junction diodes. These diodes, which were grown on commercially available 6H-SiC substrates by chemical vapor deposition, demonstrate rectification to -200 V at room temperature, representing a fourfold improvement in reported 3C-SiC diode blocking voltage. The reverse leakage currents and saturation current densities measured on these diodes also show significant improvement compared to previously reported 3C-SiC p-n junction diodes. When placed under sufficient forward bias, the diodes emit significantly bright green-yellow light. These results should lead to substantial advancements in 3C-SiC transistor performance.

Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes.

PubMed

Neplokh, Vladimir; Messanvi, Agnes; Zhang, Hezhi; Julien, Francois H; Babichev, Andrey; Eymery, Joel; Durand, Christophe; Tchernycheva, Maria

2015-12-01

We report on the demonstration of substrate-free nanowire/polydimethylsiloxane (PDMS) membrane light-emitting diodes (LEDs). Metal-organic vapour-phase epitaxy (MOVPE)-grown InGaN/GaN core-shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent indium tin oxide (ITO) contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements, the samples were manually bonded using silver paint. The EL spectra measured at different applied voltages demonstrate a blue shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average indium content.

Note: An online testing method for lifetime projection of high power light-emitting diode under accelerated reliability test.

PubMed

Chen, Qi; Chen, Quan; Luo, Xiaobing

2014-09-01

In recent years, due to the fast development of high power light-emitting diode (LED), its lifetime prediction and assessment have become a crucial issue. Although the in situ measurement has been widely used for reliability testing in laser diode community, it has not been applied commonly in LED community. In this paper, an online testing method for LED life projection under accelerated reliability test was proposed and the prototype was built. The optical parametric data were collected. The systematic error and the measuring uncertainty were calculated to be within 0.2% and within 2%, respectively. With this online testing method, experimental data can be acquired continuously and sufficient amount of data can be gathered. Thus, the projection fitting accuracy can be improved (r(2) = 0.954) and testing duration can be shortened.

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

NASA Astrophysics Data System (ADS)

Shervin, Shahab; Oh, Seung Kyu; Park, Hyun Jung; Lee, Keon-Hwa; Asadirad, Mojtaba; Kim, Seung-Hwan; Kim, Jeomoh; Pouladi, Sara; Lee, Sung-Nam; Li, Xiaohang; Kwak, Joon Seop; Ryou, Jae-Hyun

2018-03-01

We report a new route to improve quantum efficiencies of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency is enhanced higher than three times, when the DUV LEDs are moderately bent with concave curvatures. Furthermore, an efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

Two stacked tandem white organic light-emitting diodes employing WO3 as a charge generation layer

NASA Astrophysics Data System (ADS)

Bin, Jong-Kwan; Lee, Na Yeon; Lee, SeungJae; Seo, Bomin; Yang, JoongHwan; Kim, Jinook; Yoon, Soo Young; Kang, InByeong

2016-09-01

Recently, many studies have been conducted to improve the electroluminescence (EL) performance of organic lightemitting diodes (OLEDs) by using appropriate organic or inorganic materials as charge generation layer (CGL) for their application such as full color displays, backlight units, and general lighting source. In a stacked tandem white organic light-emitting diodes (WOLEDs), a few emitting units are electrically interconnected by a CGL, which plays the role of generating charge carriers, and then facilitate the injection of it into adjacent emitting units. In the present study, twostacked WOLEDs were fabricated by using tungsten oxide (WO3) as inorganic charge generation layer and 1,4,5,8,9,11- hexaazatriphenylene hexacarbonitrile (HAT-CN) as organic charge generation layer (P-CGL). Organic P-CGL materials were used due to their ease of use in OLED fabrication as compared to their inorganic counterparts. To obtain high efficiency, we demonstrate two-stacked tandem WOLEDs as follows: ITO/HIL/HTL/HTL'/B-EML/ETL/N-CGL/P-CGL (WO3 or HAT-CN)/HTL″/YG-EML/ETL/LiF/Al. The tandem devices with blue- and yellow-green emitting layers were sensitive to the thickness of an adjacent layer, hole transporting layer for the YG emitting layer. The WOLEDs containing the WO3 as charge generation layer reach a higher power efficiency of 19.1 lm/W and the current efficiency of 51.2 cd/A with the white color coordinate of (0.316, 0.318) than the power efficiency of 13.9 lm/W, and the current efficiency of 43.7 cd/A for organic CGL, HAT-CN at 10 mA/cm2, respectively. This performance with inserting WO3 as CGL exhibited the highest performance with excellent CIE color coordinates in the two-stacked tandem OLEDs.

High power ultraviolet light emitting diodes based on GaN /AlGaN quantum wells produced by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Cabalu, J. S.; Bhattacharyya, A.; Thomidis, C.; Friel, I.; Moustakas, T. D.; Collins, C. J.; Komninou, Ph.

2006-11-01

In this paper, we report on the growth by molecular beam epitaxy and fabrication of high power nitride-based ultraviolet light emitting diodes emitting in the spectral range between 340 and 350nm. The devices were grown on (0001) sapphire substrates via plasma-assisted molecular beam epitaxy. The growth of the light emitting diode (LED) structures was preceded by detailed materials studies of the bottom n-AlGaN contact layer, as well as the GaN /AlGaN multiple quantum well (MQW) active region. Specifically, kinetic conditions were identified for the growth of the thick n-AlGaN films to be both smooth and to have fewer defects at the surface. Transmission-electron microscopy studies on identical GaN /AlGaN MQWs showed good quality and well-defined interfaces between wells and barriers. Large area mesa devices (800×800μm2) were fabricated and were designed for backside light extraction. The LEDs were flip-chip bonded onto a Si submount for better heat sinking. For devices emitting at 340nm, the measured differential on-series resistance is 3Ω with electroluminescence spectrum full width at half maximum of 18nm. The output power under dc bias saturates at 0.5mW, while under pulsed operation it saturates at approximately 700mA to a value of 3mW, suggesting that thermal heating limits the efficiency of these devices. The output power of the investigated devices was found to be equivalent with those produced by the metal-organic chemical vapor deposition and hydride vapor-phase epitaxy methods. The devices emitting at 350nm were investigated under dc operation and the output power saturates at 4.5mW under 200mA drive current.

An aluminium nitride light-emitting diode with a wavelength of 210 nanometres.

PubMed

Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki

2006-05-18

Compact high-efficiency ultraviolet solid-state light sources--such as light-emitting diodes (LEDs) and laser diodes--are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond and III-V nitride semiconductors (GaN, AlGaN and AlN; refs 3-10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.

Bandpass x-ray diode and x-ray multiplier detector

DOEpatents

Wang, C.L.

1982-09-27

An absorption-edge of an x-ray absorption filter and a quantum jump of a photocathode determine the bandpass characteristics of an x-ray diode detector. An anode, which collects the photoelectrons emitted by the photocathode, has enhanced amplification provided by photoelectron-multiplying means which include dynodes or a microchannel-plate electron-multiplier. Suppression of undesired high frequency response for a bandpass x-ray diode is provided by subtracting a signal representative of energies above the passband from a signal representative of the overall response of the bandpass diode.

Low Voltage, Low Power Organic Light Emitting Transistors for AMOLED Displays

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCarthy, M. A.; Liu, B.; Donoghue, E. P.

2011-01-01

Low voltage, low power dissipation, high aperture ratio organic light emitting transistors are demonstrated. The high level of performance is enabled by a carbon nanotube source electrode that permits integration of the drive transistor and the organic light emitting diode into an efficient single stacked device. Given the demonstrated performance, this technology could break the technical logjam holding back widespread deployment of active matrix organic light emitting displays at flat panel screen sizes.

Highly efficient inverted top emitting organic light emitting diodes using a transparent top electrode with color stability on viewing angle

NASA Astrophysics Data System (ADS)

Kim, Jung-Bum; Lee, Jeong-Hwan; Moon, Chang-Ki; Kim, Jang-Joo

2014-02-01

We report a highly efficient phosphorescent green inverted top emitting organic light emitting diode with excellent color stability by using the 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile/indium zinc oxide top electrode and bis(2-phenylpyridine)iridium(III) acetylacetonate as the emitter in an exciplex forming co-host system. The device shows a high external quantum efficiency of 23.4% at 1000 cd/m2 corresponding to a current efficiency of 110 cd/A, low efficiency roll-off with 21% at 10 000 cd/m2 and low turn on voltage of 2.4 V. Especially, the device showed very small color change with the variation of Δx = 0.02, Δy = 0.02 in the CIE 1931 coordinates as the viewing angle changes from 0° to 60°. The performance of the device is superior to that of the metal/metal cavity structured device.

Efficient and mechanically robust stretchable organic light-emitting devices by a laser-programmable buckling process

PubMed Central

Yin, Da; Feng, Jing; Ma, Rui; Liu, Yue-Feng; Zhang, Yong-Lai; Zhang, Xu-Lin; Bi, Yan-Gang; Chen, Qi-Dai; Sun, Hong-Bo

2016-01-01

Stretchable organic light-emitting devices are becoming increasingly important in the fast-growing fields of wearable displays, biomedical devices and health-monitoring technology. Although highly stretchable devices have been demonstrated, their luminous efficiency and mechanical stability remain impractical for the purposes of real-life applications. This is due to significant challenges arising from the high strain-induced limitations on the structure design of the device, the materials used and the difficulty of controlling the stretch-release process. Here we have developed a laser-programmable buckling process to overcome these obstacles and realize a highly stretchable organic light-emitting diode with unprecedented efficiency and mechanical robustness. The strained device luminous efficiency −70 cd A−1 under 70% strain - is the largest to date and the device can accommodate 100% strain while exhibiting only small fluctuations in performance over 15,000 stretch-release cycles. This work paves the way towards fully stretchable organic light-emitting diodes that can be used in wearable electronic devices. PMID:27187936

Application of highly ordered carbon nanotubes templates to field-emission organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Li, Chi-Shing; Su, Shui-Hsiang; Chi, Hsiang-Yu; Yokoyama, Meiso

2009-01-01

An anodic aluminum oxide (AAO) template was formed by a two-step anodization process. Carbon nanotubes (CNTs) were successfully synthesized along with AAO pores and the diameters of CNTs equaled those of AAO pores. The lengths of CNTs during a chemical vapor deposition synthesized process on the AAO template were effectively controlled. These AAO-CNTs exhibit excellent field emission with a low turn-on field (0.7 V/μm) and a low threshold field (1.4 V/μm). The field enhancement factor, calculated from the non-saturated region of the Fowler-Nordheim (F-N) plot, is about 8237. A novel field-emission organic light-emitting diode (FEOLED) combining AAO-CNTs cathodes as electron source with organic electroluminescent (EL) light-emitting layers coated on indium-tin-oxide (ITO) is produced. The uniform and dense luminescence image is obtained in the FEOLEDs. Organic EL light-emitting materials have lower working voltage than inorganic phosphor-coated fluorescent screens.

Effect of a broad recombination zone with a triple-emitting layer on the efficiency of blue phosphorescent organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Seok Jae; Koo, Ja Ryong; Lee, Ho Won; Lee, Song Eun; Yang, Hyung Jin; Yoon, Seung Soo; Park, Jaehoon; Kim, Young Kwan

2014-11-01

The device characteristics of blue phosphorescent organic lightemitting diodes (PHOLEDs) with a broad recombination region within emitting layers (EMLs) were investigated by changing the combination and the composition of the host materials. Six types of devices were fabricated with the novel host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole, hole transport-type host material N,N'-dicarbazolyl-3,5-benzene, and electron transporttype host material 2,2',2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] as diverse EML structures. Balanced chargecarrier injection and a distributed recombination zone within EMLs were achieved through a triple-emitting layer (T-EML). The properties of a device with a T-EML using a stepwise structure without any mixed host system were found to be superior to the other PHOLEDs. This can be explained in terms of improved charge balance and triplet-exciton confinement within the broad recombination region. [Figure not available: see fulltext.

Photobiology eye safety for horticultural LED lighting: Transmittance performance of eyewear protection using high-irradiant monochromatic LEDs.

PubMed

Wu, Bo-Sen; Lefsrud, Mark G

2018-02-01

Light emitting diodes have slowly gained market share as horticultural lighting systems in greenhouses due to their rapid improvement in color performances and light outputs. These advancements have increased the availability of the full spectrum of visible wavelengths and the corresponding irradiance outputs available to plants. However, light emitting diodes owners have limited information on the proper options for personal eyewear protection as the irradiance levels have increased. The objective of this study was to measure the light transmittance performance of 12 eyewear protection including welding goggles, safety goggles, polarized glasses, and sunglasses across the human visible spectrum (380-740 nm) up to an irradiance level of 1500 W·m -2 from high-irradiant light emitting diodes assemblies. Based on the spectral measurements, certain transmitted spectra exhibited spectrum shifts or an alteration in the bimodal distribution which were different than the light emitting diodes spectra, due to the uneven transmittance efficiencies of the glasses. As for the measured transmittance percentages in two experiments, each type of eyewear protection showed distinct transmittance performances, and the performance of the tested eyewear protection was not impacted by irradiance but was dependent on the wavelength. The mean light transmittance was 1.77% for the welding glasses, 13.12% for the polarized glasses, 15.27% for the safety goggles, and 27.65% for the sunglasses. According to these measured results and the spectral weighting exposure limits from the International Electrotechnical Commission 62471 and EU directive 2006/25, consumers and workers using horticultural lighting can select welding goggles or polarized glasses, to limit the possible ocular impact of the high irradiance of monochromatic light in electrical lighting environment. Sunglasses and safety goggles would not be advised as protection, especially if infrared radiation was used.

Dental composite polymerization: a three different sources comparison

NASA Astrophysics Data System (ADS)

Sozzi, Michele; Fornaini, Carlo; Lagori, Giuseppe; Merigo, Elisabetta; Cucinotta, Annamaria; Vescovi, Paolo; Selleri, Stefano

2015-02-01

The introduction of photo-activators, with absorption spectra in the violet region, in composite resins raised interest in the use of 405 nm diode lasers for polymerization. The purpose of this research is the evaluation of the resins polymerization by means of violet diode laser compared to traditional lamps. Two different resins have been used for the experiments: Filtek Supreme XT flow (3M ESPE, USA) and Tetric Evo flow (Ivoclar, Vivadent). The photo-activator used is Camphoroquinone, alone, or in combination with Lucirin TPO. The resins have been cured with an halogen lamp (Heliolux DXL, Vivadent Ivoclar, Austria), a broadband LED curing light (Valo Ultradent, USA) and a 405 nm laser (Euphoton, Italy). The measure of cure depth, of the volumetric shrinkage, and the conversion degree (DC%) of the double bond during the curing process have been evaluated. A composite layer of 3 mm was cured in Filtek Supreme resin (Camphoroquinone activator), lower if compared to the use of the other two light sources. Tests on Tetric Evo (Camphoroquinone + Lucirin) didn't show any improvement of the use of laser compared to the halogen lamp and the broadband LED. By measuring the volumetric shrinkage the laser induced the lower change with both the composites. In terms of DC% the lower performance was obtained with the laser. Considering that the polymerization process strongly depends on the kind of composite used the effectiveness of 405 nm laser proved to be lower than halogen lamps and broadband LEDs.

High-performance light-emitting diodes based on carbene-metal-amides

NASA Astrophysics Data System (ADS)

Di, Dawei; Romanov, Alexander S.; Yang, Le; Richter, Johannes M.; Rivett, Jasmine P. H.; Jones, Saul; Thomas, Tudor H.; Abdi Jalebi, Mojtaba; Friend, Richard H.; Linnolahti, Mikko; Bochmann, Manfred; Credgington, Dan

2017-04-01

Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kashiwagi, Y., E-mail: kasiwagi@omtri.or.jp; Yamamoto, M.; Saitoh, M.

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

Sodium bromide additive improved film morphology and performance in perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Li, Jinghai; Cai, Feilong; Yang, Liyan; Ye, Fanghao; Zhang, Jinghui; Gurney, Robert S.; Liu, Dan; Wang, Tao

2017-07-01

Organometal halide perovskite is a promising material to fabricate light-emitting diodes (LEDs) via solution processing due to its exceptional optoelectronic properties. However, incomplete precursor conversion and various defect states in the perovskite light-emitting layer lead to low luminance and external quantum efficiency of perovskite LEDs. We show here the addition of an optimum amount of sodium bromide in the methylammonium lead bromide (MAPbBr3) precursor during a one-step perovskite solution casting process can effectively improve the film coverage, enhance the crystallinity, and passivate ionic defects on the surface of MAPbBr3 crystal grains, resulting in LEDs with a reduced turn-on voltage from 2.8 to 2.3 V and an enhanced maximum luminance from 1059 to 6942 Cd/m2 when comparing with the pristine perovskite-based device.

Polarization of edge emission from III-nitride light emitting diodes of emission wavelength from 395 to 455 nm

NASA Astrophysics Data System (ADS)

Jia, Chuanyu; Yu, Tongjun; Mu, Sen; Pan, Yaobo; Yang, Zhijian; Chen, Zhizhong; Qin, Zhixin; Zhang, Guoyi

2007-05-01

Polarization-resolved edge-emitting electroluminescence of InGaN /GaN multiple quantum well (MQW) light emitting diodes (LEDs) from 395to455nm was measured. Polarization ratio decreased from 3.2 of near-ultraviolet LEDs (395nm) to 1.9 of blue LEDs (455nm). Based on TE mode dominant emissions in InGaN /GaN MQWs, compressive strain in well region favors TE mode, indium induced quantum-dot-like behavior leads to an increased TM component. As wavelength increased, indium enhanced quantum-dot-like behavior became obvious and E ‖C electroluminescence signal increased thus lower polarization ratio. Electroluminescence spectrum shifts confirmed that quantum dotlike behaviors rather than strain might be dominant in modifying luminescence mode of InGaN /GaN MQWs from near ultraviolet to blue.

Al x Ga1‑ x N-based semipolar deep ultraviolet light-emitting diodes

NASA Astrophysics Data System (ADS)

Akaike, Ryota; Ichikawa, Shuhei; Funato, Mitsuru; Kawakami, Yoichi

2018-06-01

Deep ultraviolet (UV) emission from Al x Ga1‑ x N-based light-emitting diodes (LEDs) fabricated on semipolar (1\\bar{1}02) (r-plane) AlN substrates is presented. The growth conditions are optimized. A high NH3 flow rate during metalorganic vapor phase epitaxy yields atomically flat Al y Ga1‑ y N (y > x) on which Al x Ga1‑ x N/Al y Ga1‑ y N multiple quantum wells with abrupt interfaces and good periodicity are fabricated. The fabricated r-Al x Ga1‑ x N-based LED emits at 270 nm, which is in the germicidal wavelength range. Additionally, the emission line width is narrow, and the peak wavelength is stable against the injection current, so the semipolar LED shows promise as a UV emitter.

White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode

PubMed Central

2010-01-01

We report the fabrication of heterostructure white light–emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet–blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour. PMID:20672120

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

NASA Astrophysics Data System (ADS)

Kashiwagi, Y.; Koizumi, A.; Takemura, Y.; Furuta, S.; Yamamoto, M.; Saitoh, M.; Takahashi, M.; Ohno, T.; Fujiwara, Y.; Murahashi, K.; Ohtsuka, K.; Nakamoto, M.

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

Highly efficient green phosphorescent organic light emitting diodes with improved efficiency roll-off

NASA Astrophysics Data System (ADS)

Thangaraju, K.; Lee, Jonghee; Lee, Jeong-Ik; Chu, Hye Yong; Kim, Yun-Hi; Kwon, Soon-Ki

2015-06-01

A 10-nm thick 4,4',4″-tris(carbazole-9-yl)tri-phenylamine (TcTa) interlayer effectively confines triplet excitons within the emissive layer (EML) of phosphorescent organic light emitting diodes (PHOLEDs) based on green-emitting Ir(ppy)3 dopant and improves the charge balance in the EML of the device, resulting the higher device efficiencies of 61.7 cd/A, 19.7 %, and 43.2 lm/W with the maximum luminance of 75,310 cd/m2 and highly improved efficiency roll-off (22.2% at 20 mA/cm2) when compared to those (61.1 cd/A, 19.6 %, and 47.2 lm/W with a maximum luminance of 38,350 cd/m2) of the standard device with efficiency roll-off of 62.3 % at 20 mA/cm2.

Effect of trapped electrons on the transient current density and luminance of organic light-emitting diode

NASA Astrophysics Data System (ADS)

Lee, Jiun-Haw; Chen, Chia-Hsun; Lin, Bo-Yen; Shih, Yen-Chen; Lin, King-Fu; Wang, Leeyih; Chiu, Tien-Lung; Lin, Chi-Feng

2018-04-01

Transient current density and luminance from an organic light-emitting diode (OLED) driven by voltage pulses were investigated. Waveforms with different repetition rate, duty cycle, off-period, and on-period were used to study the injection and transport characteristics of electron and holes in an OLED under pulse operation. It was found that trapped electrons inside the emitting layer (EML) and the electron transporting layer (ETL) material, tris(8-hydroxyquinolate)aluminum (Alq3) helped for attracting the holes into the EML/ETL and reducing the driving voltage, which was further confirmed from the analysis of capacitance-voltage and displacement current measurement. The relaxation time and trapped filling time of the trapped electrons in Alq3 layer were ~200 µs and ~600 µs with 6 V pulse operation, respectively.

Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts.

PubMed

Cui, Lin-Song; Ruan, Shi-Bin; Bencheikh, Fatima; Nagata, Ryo; Zhang, Lei; Inada, Ko; Nakanotani, Hajime; Liao, Liang-Sheng; Adachi, Chihaya

2017-12-21

Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

Degree of conversion and cross-link density within a resin-matrix composite.

PubMed

Al-Zain, Afnan O; Eckert, George J; Lukic, Henry; Megremis, Spiro J; Platt, Jeffrey A

2018-05-01

The aims of this study were to profile light radiated from two light-curing units (LCUs) and evaluate profile relationship to polymerization patterns within a resin-matrix composite (RMC). Beam profiles of one multiple emission peak light-emitting-diode and one quartz-tungsten-halogen curing-unit were measured using a beam profiler/spectrometer system. A camera-based profiler and an integrating sphere/spectrometer assembly were used to evaluate each LCU beam. Polymerization patterns within a nano-hybrid RMC were investigated using a mapping approach by assessing the degree of conversion utilizing micro-Raman spectroscopy and indirectly estimating cross-link-density by repeated microhardness testing before and after exposure to ethanol (%KH reduction, n = 3). The irradiance received on the top and bottom specimen surfaces from both LCUs was measured using a MARC-RC system. The investigated beam profile area from both LCUs was non-uniform and yielded localized discrepancies in DC (55.7-74.9%) and %KH reduction (26.7-54.1%). The LCU irradiance received at the bottom of the specimens was ∼10% of the top value. This study demonstrated that LCU beam profiles were non-uniform in the area explored. Localized differences in DC and %KH reduction existed throughout the RMC specimens but did not follow a specific pattern. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1496-1504, 2018. © 2017 Wiley Periodicals, Inc.

High power cascade diode lasers emitting near 2 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosoda, Takashi; Feng, Tao; Shterengas, Leon, E-mail: leon.shterengas@stonybrook.edu

2016-03-28

High-power two-stage cascade GaSb-based type-I quantum well diode lasers emitting near 2 μm were designed and fabricated. Coated devices with cavity length of 3 mm generated about 2 W of continuous wave power from 100-μm-wide aperture at the current of 6 A. The power conversion efficiency peaked at 20%. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in GaSb/AlSb/InAs heterostructure complemented with optimized electron and hole injector regions. Design optimization eliminated parasitic optical absorption and thermionic emission, and included modification of the InAs quantum wells of electron and composition and doping profile of hole injectors. Utilization of the cascade pumpingmore » scheme yielded 2 μm lasers with improved output power and efficiency compared to existing state-of-the-art diodes.« less

Monolithic photonic integrated circuit with a GaN-based bent waveguide

NASA Astrophysics Data System (ADS)

Cai, Wei; Qin, Chuan; Zhang, Shuai; Yuan, Jialei; Zhang, Fenghua; Wang, Yongjin

2018-06-01

Integration of a transmitter, waveguide and receiver into a single chip can generate a multicomponent system with multiple functionalities. Here, we fabricate and characterize a GaN-based photonic integrated circuit (PIC) on a GaN-on-silicon platform. With removal of the silicon and back wafer thinning of the epitaxial film, ultrathin membrane-type devices and highly confined suspended GaN waveguides were formed. Two suspended-membrane InGaN/GaN multiple-quantum-well diodes (MQW-diodes) served as an MQW light-emitting diode (MQW-LED) to emit light and an MQW photodiode (MQW-PD) to sense light. The optical interconnects between the MQW-LED and MQW-PD were achieved using the GaN bent waveguide. The GaN-based PIC consisting of an MQW-LED, waveguides and an MQW-PD forms an in-plane light communication system with a data transmission rate of 70 Mbps.

Detection and modeling of leakage current in AlGaN-based deep ultraviolet light-emitting diodes

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2015-03-01

Current-voltage (IV) characteristics of two AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) with differing densities of open-core threading dislocations (nanopipes) are analyzed. A three-diode circuit is simulated to emulate the IV characteristics of the DUV-LEDs, but is only able to accurately model the lower leakage current, lower nanopipe density DUV-LED. It was found that current leakage through the nanopipes in these structures is rectifying, despite nanopipes being previously established as inherently n-type. Using defect-sensitive etching, the nanopipes are revealed to terminate within the p-type GaN capping layer of the DUV-LEDs. The circuit model is modified to account for another p-nmore » junction between the n-type nanopipes and the p-type GaN, and an excellent fit to the IV characteristics of the leaky DUV-LED is achieved.« less

Organic light-emitting diodes with a spacer enhanced exciplex emission

NASA Astrophysics Data System (ADS)

Yan, Fei; Chen, Rui; Sun, Handong; Wei Sun, Xiao

2014-04-01

By introducing a spacer molecule into the blended exciplex emissive layer, the performance of the bulk heterojunction exciplex organic light-emitting diodes (OLEDs) was improved dramatically; the maximum luminous efficiency was enhanced by about 22% from 7.9 cd/A to 9.7 cd/A, and the luminous efficiency drop was reduced by 28% at 400 mA/cm2. Besides the suppressed annihilation of exciton, the time-resolved photoluminescence measurements indicated that the spacer enhanced the delayed fluorescence through increasing the backward intersystem crossing rate from the triplet to singlet exciplex state. This method is useful for developing high performance exciplex OLEDs.

Natural substrate lift-off technique for vertical light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Chia-Yu; Lan, Yu-Pin; Tu, Po-Min; Hsu, Shih-Chieh; Lin, Chien-Chung; Kuo, Hao-Chung; Chi, Gou-Chung; Chang, Chun-Yen

2014-04-01

Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to 1 × 108 cm-2. Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved.

Staining-free malaria diagnostics by multispectral and multimodality light-emitting-diode microscopy

NASA Astrophysics Data System (ADS)

Merdasa, Aboma; Brydegaard, Mikkel; Svanberg, Sune; Zoueu, Jeremie T.

2013-03-01

We report an accurate optical differentiation technique between healthy and malaria-infected erythrocytes by quasi-simultaneous measurements of transmittance, reflectance, and scattering properties of unstained blood smears using a multispectral and multimode light-emitting diode microscope. We propose a technique for automated imaging, identification, and counting of malaria-infected erythrocytes for real-time and cost-effective parasitaemia diagnosis as an effective alternative to the manual screening of stained blood smears, now considered to be the gold standard in malaria diagnosis. We evaluate the performance of our algorithm against manual estimations of an expert and show a spectrally resolved increased scattering from malaria-infected blood cells.

Monolithic translucent BaMgAl 10O 17:Eu 2+ phosphors for laser-driven solid state lighting

DOE PAGES

Cozzan, Clayton; Brady, Michael J.; O’Dea, Nicholas; ...

2016-10-11

With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl 10O 17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). Lastly, the resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

Importance of 'blue' photon levels for lettuce seedlings grown under red-light-emitting diodes

NASA Technical Reports Server (NTRS)

Hoenecke, M. E.; Bula, R. J.; Tibbitts, T. W.

1992-01-01

Light-emitting diodes (LEDs) with high-intensity output are being studied as a photosynthetic light source for plants. High-output LEDs have peak emission at approximately 660 nm concentrated in a waveband of +/- 30 nm. Lettuce (Lactuca sativa Grand Rapids') seedlings developed extended hypocotyls and elongated cotyledons when grown under these LEDs as a sole source of irradiance. This extension and elongation was prevented when the red LED radiation was supplemented with more than 15 micromoles m-2 s-1 of 400- to 500-nm photons from blue fluorescent lamps. Blue radiation effects were independent of the photon level of the red radiation.

Using copper substrate to enhance the thermal conductivity of top-emission organic light-emitting diodes for improving the luminance efficiency and lifetime

NASA Astrophysics Data System (ADS)

Tsai, Yu-Sheng; Wang, Shun-Hsi; Chen, Chuan-Hung; Cheng, Chien-Lung; Liao, Teh-Chao

2009-12-01

The influence of heat dissipation on the performances of organic light-emitting diode (OLED) is investigated by measuring junction temperature and by calculating the rate of heat flow. The calculated rate of heat flow reveals that the key factors include the thermal conductivity, the substrate thickness, and the UV glue. Moreover, the use of copper substrate can effectively dissipate the joule heat, which then reduces the temperature gradient. Finally, it is shown that the use of a high thermal conductivity thinner substrate can enhance the thermal conductivity of OLED and the luminance efficiency as well.

Optimization of freeform lightpipes for light-emitting-diode projectors.

PubMed

Fournier, Florian; Rolland, Jannick

2008-03-01

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

Influence of dehydrated nanotubed titanic acid on charge transport and luminescent properties of polymer light-emitting diodes with fluorescent dye

NASA Astrophysics Data System (ADS)

Qian, Lei; Bera, Debasis; Jin, Zhen-Sheng; Du, Zu-Liang; Xu, Zheng; Teng, Feng; Liu, Wei

2007-09-01

In this paper, we discuss the influence of dehydrated nanotubed titanic acid (DNTA) on charge transport and luminescent properties of polymer light-emitting diodes (PLEDs) doped with fluorescent dye. Photoluminescence results confirm the efficient energy transfer from PVK to 4-(dicyanom-ethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris-(8-hydroxtquinoline) aluminum (Alq 3) in a DNTA-doped device. The device showed lower turn-on voltages and higher charge current by doping with DNTA, which also caused a shift in the exciton's recombination region.

Two-step narrow ridge cascade diode lasers emitting near $$2~\\mu$$ m

DOE PAGES

Feng, Tao; Hosoda, Takashi; Shterengas, Leon; ...

2017-01-02

Nearly diffraction limited GaSb-based type-I quantum well cascade diode lasers emitting in the spectral region 1.95-2 μm were designed and fabricated. Two-step 5.5-μm-wide shallow and 14-μm-wide deep etched ridge waveguide design yielded devices generating stable single lobe beams with 250 mW of continuous wave output power at 20 °C. Quantum well radiative recombination current contributes about 13% to laser threshold as estimated from true spontaneous emission and modal gain analysis. Here, recombination at etched sidewalls of the 14-μmwide deep ridges controls about 30% of the threshold.

Versatile light-emitting-diode-based spectral response measurement system for photovoltaic device characterization.

PubMed

Hamadani, Behrang H; Roller, John; Dougherty, Brian; Yoon, Howard W

2012-07-01

An absolute differential spectral response measurement system for solar cells is presented. The system couples an array of light emitting diodes with an optical waveguide to provide large area illumination. Two unique yet complementary measurement methods were developed and tested with the same measurement apparatus. Good agreement was observed between the two methods based on testing of a variety of solar cells. The first method is a lock-in technique that can be performed over a broad pulse frequency range. The second method is based on synchronous multifrequency optical excitation and electrical detection. An innovative scheme for providing light bias during each measurement method is discussed.

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices

PubMed Central

O'Toole, Martina; Diamond, Dermot

2008-01-01

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements. PMID:27879829

LIGHT-EMITTING DIODE TECHNOLOGY IMPROVES INSECT TRAPPING

PubMed Central

GILLEN, JONATHON I.; MUNSTERMANN, LEONARD E.

2008-01-01

In a climate of increased funding for vaccines, chemotherapy, and prevention of vector-borne diseases, fewer resources have been directed toward improving disease and vector surveillance. Recently developed light-emitting diode (LED) technology was applied to standard insect-vector traps to produce a more effective lighting system. This approach improved phlebotomine sand fly capture rates by 50%, and simultaneously reduced the energy consumption by 50–60%. The LEDs were incorporated into 2 lighting designs, 1) a LED combination bulb for current light traps and 2) a chip-based LED design for a modified Centers for Disease Control and Prevention light trap. Detailed descriptions of the 2 designs are presented. PMID:18666546

Small feature sizes and high aperture ratio organic light-emitting diodes by using laser-patterned polyimide shadow masks

NASA Astrophysics Data System (ADS)

Kajiyama, Yoshitaka; Joseph, Kevin; Kajiyama, Koichi; Kudo, Shuji; Aziz, Hany

2014-02-01

A shadow mask technique capable of realizing high resolution (>330 pixel-per-inch) and ˜100% aperture ratio Organic Light-Emitting Diode (OLED) full color displays is demonstrated. The technique utilizes polyimide contact shadow masks, patterned by laser ablation. Red, green, and blue OLEDs with very small feature sizes (<25 μm) are fabricated side by side on one substrate. OLEDs fabricated via this technique have the same performance as those made by established technology. This technique has a strong potential to achieve high resolution OLED displays via standard vacuum deposition processes even on flexible substrates.

Charge injection and transport properties of an organic light-emitting diode

PubMed Central

Juhasz, Peter; Nevrela, Juraj; Micjan, Michal; Novota, Miroslav; Uhrik, Jan; Stuchlikova, Lubica; Jakabovic, Jan; Harmatha, Ladislav

2016-01-01

Summary The charge behavior of organic light emitting diode (OLED) is investigated by steady-state current–voltage technique and impedance spectroscopy at various temperatures to obtain activation energies of charge injection and transport processes. Good agreement of activation energies obtained by steady-state and frequency-domain was used to analyze their contributions to the charge injection and transport. We concluded that charge is injected into the OLED device mostly through the interfacial states at low voltage region, whereas the thermionic injection dominates in the high voltage region. This comparison of experimental techniques demonstrates their capabilities of identification of major bottleneck of charge injection and transport. PMID:26925351

GaAs/AlGaAs core multishell nanowire-based light-emitting diodes on Si.

PubMed

Tomioka, Katsuhiro; Motohisa, Junichi; Hara, Shinjiroh; Hiruma, Kenji; Fukui, Takashi

2010-05-12

We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.

Passively mode-locked diode-pumped Tm3+:YLF laser emitting at 1.91 µm using a GaAs-based SESAM

NASA Astrophysics Data System (ADS)

Tyazhev, A.; Soulard, R.; Godin, T.; Paris, M.; Brasse, G.; Doualan, J.-L.; Braud, A.; Moncorgé, R.; Laroche, M.; Camy, P.; Hideur, A.

2018-04-01

We report on a diode-pumped Tm:YLF laser passively mode-locked with an InGaAs saturable absorber. The laser emits a train of 31 ps pulses at a wavelength of 1.91 µm with a repetition rate of 94 MHz and a maximum average power of 95 mW. A sustained and robust mode-locking with a signal-to-noise ratio of ~70 dB is obtained even at high relative air humidity, making this system attractive for applications requiring ultra-short pulses in the spectral window just below 2 µm.

Noniterative algorithm for improving the accuracy of a multicolor-light-emitting-diode-based colorimeter.

PubMed

Yang, Pao-Keng

2012-05-01

We present a noniterative algorithm to reliably reconstruct the spectral reflectance from discrete reflectance values measured by using multicolor light emitting diodes (LEDs) as probing light sources. The proposed algorithm estimates the spectral reflectance by a linear combination of product functions of the detector's responsivity function and the LEDs' line-shape functions. After introducing suitable correction, the resulting spectral reflectance was found to be free from the spectral-broadening effect due to the finite bandwidth of LED. We analyzed the data for a real sample and found that spectral reflectance with enhanced resolution gives a more accurate prediction in the color measurement.

Noniterative algorithm for improving the accuracy of a multicolor-light-emitting-diode-based colorimeter

NASA Astrophysics Data System (ADS)

Yang, Pao-Keng

2012-05-01

We present a noniterative algorithm to reliably reconstruct the spectral reflectance from discrete reflectance values measured by using multicolor light emitting diodes (LEDs) as probing light sources. The proposed algorithm estimates the spectral reflectance by a linear combination of product functions of the detector's responsivity function and the LEDs' line-shape functions. After introducing suitable correction, the resulting spectral reflectance was found to be free from the spectral-broadening effect due to the finite bandwidth of LED. We analyzed the data for a real sample and found that spectral reflectance with enhanced resolution gives a more accurate prediction in the color measurement.

Compact light-emitting diode lighting ring for video-assisted thoracic surgery.

PubMed

Lu, Ming-Kuan; Chang, Feng-Chen; Wang, Wen-Zhe; Hsieh, Chih-Cheng; Kao, Fu-Jen

2014-01-01

In this work, a foldable ring-shaped light-emitting diode (LED) lighting assembly, designed to attach to a rubber wound retractor, is realized and tested through porcine animal experiments. Enabled by the small size and the high efficiency of LED chips, the lighting assembly is compact, flexible, and disposable while providing direct and high brightness lighting for more uniform background illumination in video-assisted thoracic surgery (VATS). When compared with a conventional fiber bundle coupled light source that is usually used in laparoscopy and endoscopy, the much broader solid angle of illumination enabled by the LED assembly allows greatly improved background lighting and imaging quality in VATS.

High efficient white organic light-emitting diodes with single emissive layer using phosphorescent red, green, and blue dopants

NASA Astrophysics Data System (ADS)

Kim, You-Hyun; Wai Cheah, Kok; Young Kim, Woo

2013-07-01

Phosphorescent white organic light-emitting diodes (PHWOLEDs) with single emissive layer were fabricated by co-doping phosphorescent blue, green, and red emitters with different concentrations. WOLEDs using Ir(piq)3 and Ir(ppy)3 as red and green dopants along with 8% of Firpic as blue dopant with host materials of 4CzPBP in the emissive layer were compared under various doping ratio between Ir(piq)3 and Ir(ppy)3. Triplet-triplet Dexter energy transfer in single emissive PHWOLEDs including three primary colors was saturated from higher triplet energy levels to lower triplet energy levels directly.

Optimization of freeform lightpipes for light-emitting-diode projectors

NASA Astrophysics Data System (ADS)

Fournier, Florian; Rolland, Jannick

2008-03-01

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

Organometal halide perovskite light-emitting diodes with laminated carbon nanotube electrodes

NASA Astrophysics Data System (ADS)

Shan, Xin; Bade, Sri Ganesh R.; Geske, Thomas; Davis, Melissa; Smith, Rachel; Yu, Zhibin

2017-08-01

Organometal halide perovskite light-emitting diodes (LEDs) with laminated carbon nanotube (CNT) electrodes are reported. The LEDs have an indium tin oxide (ITO) bottom electrode, a screen printed methylammonium lead tribromide (MAPbBr3)/polymer composite thin film as the emissive layer, and laminated CNT as the top electrode. The devices can be turned on at 2.2 V, reaching a brightness of 4,960 cd m-2 and a current efficiency of 1.54 cd A-1 at 6.9 V. The greatly simplified fabrication process in this work can potentially lead to the scalable manufacturing of large size and low cost LED panels in the future.

Ag/SiO2 nanoparticle-based plasmonic enhancement of light output in nanohole-patterned InGaN/GaN blue light-emitting diodes

NASA Astrophysics Data System (ADS)

Yun, Jin-Hyeon; Kim, Kyu Cheol; Yu, Yeon Tae; Yang, Jin Kyu; Polyakov, Alexander Y.; Lee, In-Hwan

2017-10-01

Improved performance of blue InGaN/GaN light-emitting diodes (LEDs) is realized as a result of fabricating nanohole patterns in the p-GaN contact layer and embedding the nanoholes with Ag/SiO2 nanoparticles to generate localized surface plasmons (LSPs). Good matching between LSP resonance energy and LED emission energy together with the close proximity between nanoparticles and the active region results in strong coupling between them. Consequently, the photoluminescence and electroluminescence intensities increased to 1.75 and 1.10, respectively, compared with nanohole patterned reference LEDs.

Surface plasmon-enhanced light-emitting diodes using silver nanoparticles embedded in p-GaN.

PubMed

Cho, Chu-Young; Kwon, Min-Ki; Lee, Sang-Jun; Han, Sang-Heon; Kang, Jang-Won; Kang, Se-Eun; Lee, Dong-Yul; Park, Seong-Ju

2010-05-21

We demonstrate the surface plasmon-enhanced blue light-emitting diodes (LEDs) using Ag nanoparticles embedded in p-GaN. A large increase in optical output power of 38% is achieved at an injection current of 20 mA due to an improved internal quantum efficiency of the LEDs. The enhancement of optical output power is dependent on the density of the Ag nanoparticles. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Ag nanoparticles embedded in p-GaN.

Near-ultraviolet light-emitting diodes with transparent conducting layer of gold-doped multi-layer graphene

NASA Astrophysics Data System (ADS)

Cho, Chu-Young; Choe, Minhyeok; Lee, Sang-Jun; Hong, Sang-Hyun; Lee, Takhee; Lim, Wantae; Kim, Sung-Tae; Park, Seong-Ju

2013-03-01

We report on gold (Au)-doped multi-layer graphene (MLG), which can be used as a transparent conducting layer in near-ultraviolet light-emitting diodes (NUV-LEDs). The optical output power of NUV-LEDs with thermally annealed Au-doped MLG was increased by 34% compared with that of NUV-LEDs with a bare MLG. This result is attributed to the reduced sheet resistance and the enhanced current injection efficiency of NUV-LEDs by the thermally annealed Au-doped MLG film, which shows high transmittance in NUV and UV regions and good adhesion of Au-doped MLG on p-GaN layer of NUV-LEDs.

White polymeric light-emitting diodes with high color rendering index

NASA Astrophysics Data System (ADS)

Niu, Xiaodi; Ma, Liang; Yao, Bing; Ding, Junqiao; Tu, Guoli; Xie, Zhiyuan; Wang, Lixiang

2006-11-01

The efficient white polymeric light-emitting diodes based on a white emissive polymer doped with a red phosphorescent dopant were fabricated by spin-coating method. The emission spectrum of the device is broadened to cover the full visible region by doping the red phosphorescent dye and thereby realizes white emission with high color-rendering index (CRI). By controlling the contents of the doped electron-transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and the red phosphorescent dopant, a luminous efficiency as high as 5.3cd/A and a power efficiency of 3lm/W were obtained with a CRI of 92.

Novel Encapsulation Method for Flexible Organic Light-Emitting Diodes using Poly(dimethylsiloxane)

NASA Astrophysics Data System (ADS)

Han, Jeong-Min; Han, Jin-Woo; Chun, Ji-Yun; Ok, Chul-Ho; Seo, Dae-Shik

2008-12-01

We have developed a novel encapsulation method for flexible organic light-emitting diodes (OLEDs) using poly(dimethylsiloxane) (PDMS). The new method, which uses polycarbonate film, silicon dioxide, and PDMS, was found to enhance the lifetime of OLEDs in air. Optical measurements of the preservation of calcium films encapsulated with PDMS showed that the water and oxygen permeation rates of the PDMS encapsulation were reduced from a level of 0.57 g m-2 d-1 (bare substrate) to 1×10-7 g m-2 d-1. These results indicate that the PDMS barrier coatings have a good potential for flexible OLED applications.

Solution-Processed Organic Thin-Film Transistor Array for Active-Matrix Organic Light-Emitting Diode

NASA Astrophysics Data System (ADS)

Harada, Chihiro; Hata, Takuya; Chuman, Takashi; Ishizuka, Shinichi; Yoshizawa, Atsushi

2013-05-01

We developed a 3-in. organic thin-film transistor (OTFT) array with an ink-jetted organic semiconductor. All layers except electrodes were fabricated by solution processes. The OTFT performed well without hysteresis, and the field-effect mobility in the saturation region was 0.45 cm2 V-1 s-1, the threshold voltage was 3.3 V, and the on/off current ratio was more than 106. We demonstrated a 3-in. active-matrix organic light-emitting diode (AMOLED) display driven by the OTFT array. The display could provide clear moving images. The peak luminance of the display was 170 cd/m2.

Threshold-Voltage-Shift Compensation and Suppression Method Using Hydrogenated Amorphous Silicon Thin-Film Transistors for Large Active Matrix Organic Light-Emitting Diode Displays

NASA Astrophysics Data System (ADS)

Oh, Kyonghwan; Kwon, Oh-Kyong

2012-03-01

A threshold-voltage-shift compensation and suppression method for active matrix organic light-emitting diode (AMOLED) displays fabricated using a hydrogenated amorphous silicon thin-film transistor (TFT) backplane is proposed. The proposed method compensates for the threshold voltage variation of TFTs due to different threshold voltage shifts during emission time and extends the lifetime of the AMOLED panel. Measurement results show that the error range of emission current is from -1.1 to +1.7% when the threshold voltage of TFTs varies from 1.2 to 3.0 V.

One-Step Borylation of 1,3-Diaryloxybenzenes Towards Efficient Materials for Organic Light-Emitting Diodes.

PubMed

Hirai, Hiroki; Nakajima, Kiichi; Nakatsuka, Soichiro; Shiren, Kazushi; Ni, Jingping; Nomura, Shintaro; Ikuta, Toshiaki; Hatakeyama, Takuji

2015-11-09

The development of a one-step borylation of 1,3-diaryloxybenzenes, yielding novel boron-containing polycyclic aromatic compounds, is reported. The resulting boron-containing compounds possess high singlet-triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light-emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one-step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron-fused benzo[6]helicene. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laser-induced periodic structures for light extraction efficiency enhancement of GaN-based light emitting diodes.

PubMed

Chen, Jiun-Ting; Lai, Wei-Chih; Kao, Yu-Jui; Yang, Ya-Yu; Sheu, Jinn-Kong

2012-02-27

The laser-induced periodic surface structure technique was used to form simultaneously dual-scale rough structures (DSRS) with spiral-shaped nanoscale structure inside semi-spherical microscale holes on p-GaN surface to improve the light-extraction efficiency of light-emitting diodes (LEDs). The light output power of DSRS-LEDs was 30% higher than that of conventional LEDs at an injection current of 20 mA. The enhancement in the light output power could be attributed to the increase in the probability of photons to escape from the increased surface area of textured p-GaN surface.

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices.

PubMed

O'Toole, Martina; Diamond, Dermot

2008-04-07

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

High-efficiency tris(8-hydroxyquinoline)aluminum (Alq3) complexes for organic white-light-emitting diodes and solid-state lighting.

PubMed

Pérez-Bolívar, César; Takizawa, Shin-ya; Nishimura, Go; Montes, Victor A; Anzenbacher, Pavel

2011-08-08

Combinations of electron-withdrawing and -donating substituents on the 8-hydroxyquinoline ligand of the tris(8-hydroxyquinoline)aluminum (Alq(3)) complexes allow for control of the HOMO and LUMO energies and the HOMO-LUMO gap responsible for emission from the complexes. Here, we present a systematic study on tuning the emission and electroluminescence (EL) from Alq(3) complexes from the green to blue region. In this study, we explored the combination of electron-donating substituents on C4 and C6. Compounds 1-6 displayed the emission tuning between 478 and 526 nm, and fluorescence quantum yield between 0.15 and 0.57. The compounds 2-6 were used as emitters and hosts in organic light-emitting diodes (OLEDs). The highest OLED external quantum efficiency (EQE) observed was 4.6%, which is among the highest observed for Alq(3) complexes. Also, the compounds 3-5 were used as hosts for red phosphorescent dopants to obtain white light-emitting diodes (WOLED). The WOLEDs displayed high efficiency (EQE up to 19%) and high white color purity (color rendering index (CRI≈85). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of SiO 2/Si 3N 4 dielectric distributed Bragg reflectors (DDBRs) for Alq 3/NPB thin-film resonant cavity organic light emitting diodes

NASA Astrophysics Data System (ADS)

Lei, Po-Hsun; Wang, Shun-Hsi; Juang, Fuh Shyang; Tseng, Yung-Hsin; Chung, Meng-Jung

2010-05-01

In this article, we report on the effect of SiO 2/Si 3N 4 dielectric distributed Bragg reflectors (DDBRs) for Alq 3/NPB thin-film resonant cavity organic light emitting diode (RCOLED) in increasing the light output intensity and reducing the linewidth of spontaneous emission spectrum. The optimum DDBR number is found as 3 pairs. The device performance will be bad by further increasing or decreasing the number of DDBR. As compared to the conventional Alq 3/NPB thin-film organic light emitting diode (OLED), the Alq 3/NPB thin-film RCOLED with 3-pair DDBRs has the superior electrical and optical characteristics including a forward voltage of 6 V, a current efficiency of 3.4 cd/A, a luminance of 2715 cd/m 2 under the injection current density of 1000 A/m 2, and a full width at half maximum (FWHM) of 12 nm for emission spectrum over the 5-9 V bias range. These results represent that the Alq 3/NPB thin-film OLED with DDBRs shows a potential as the light source for plastic optical fiber (POF) communication system.

Development of gallium aluminum phosphide electroluminescent diodes

NASA Technical Reports Server (NTRS)

Chicotka, R. J.; Lorenz, M. R.; Nethercot, A. H.; Pettit, G. D.

1972-01-01

Work done on the development of gallium aluminum phosphide alloys for electroluminescent light sources is described. The preparation of this wide band gap semiconductor alloy, its physical properties (particularly the band structure, the electrical characteristics, and the light emitting properties) and work done on the fabrication of diode structures from these alloys are broadly covered.

Developing a new supplemental lighting device with ultra-bright white LED for vegetables

NASA Astrophysics Data System (ADS)

Hu, Yongguang; Li, Pingping; Jiang, Jianghai

2007-02-01

It has been proved that monochromatic or compound light-emitting diode (LED) or laser diode (LD) can promote the photosynthesis of horticultural crops, but the promotion of polychromatic light like white LED is unclear. A new type of ultra-bright white LED (LUW56843, InGaN, \

A Novel, Free-Space Optical Interconnect Employing Vertical-Cavity Surface Emitting Laser Diodes and InGaAs Metal-Semiconductor-Metal Photodetectors for Gbit/s RF/Microwave Systems

NASA Technical Reports Server (NTRS)

Savich, Gregory R.; Simons, Rainee N.

2006-01-01

Emerging technologies and continuing progress in vertical-cavity surface emitting laser (VCSEL) diode and metal-semiconductor-metal (MSM) photodetector research are making way for novel, high-speed forms of optical data transfer in communication systems. VCSEL diodes operating at 1550 nm have only recently become commercially available, while MSM photodetectors are pushing the limits of contact lithography with interdigitated electrode widths reaching sub micron levels. We propose a novel, free-space optical interconnect operating at about 1Gbit/s utilizing VCSEL diodes and MSM photodetectors. We report on development, progress, and current work, which are as follows: first, analysis of the divergent behavior of VCSEL diodes for coupling to MSM photodetectors with a 50 by 50 m active area and second, the normalized frequency response of the VCSEL diode as a function of the modulating frequency. Third, the calculated response of MSM photodetectors with varying electrode width and spacing on the order of 1 to 3 m as well as the fabrication and characterization of these devices. The work presented here will lead to the formation and characterization of a fully integrated 1Gbit/s free-space optical interconnect at 1550 nm and demonstrates both chip level and board level functionality for RF/microwave digital systems.

Evaluating UV-C LED disinfection performance and investigating potential dual-wavelength synergy

EPA Science Inventory

This study evaluated ultraviolet (UV) light emitting diodes (LEDs) emitting at 260 nm, 280 nm, and the combination of 260|280 nm together for their efficacy at inactivating Escherichia. coli, MS2 coliphage, human adenovirus type 2 (HAdV2), and Bacillus pumilus spores; research in...

Analysis of complex samples using a portable multi-wavelength light emitting diode (LED) fluorescence spectrometer

USDA-ARS?s Scientific Manuscript database

Spectroscopic analysis of chemically complex samples often requires an increase n the dimensionality of the measured response surface. This often involves the measurement of emitted light intensities as functions of both wavelengths of excitation and emission resulting in the generation of an excita...

Impulse radar studfinder

DOEpatents

McEwan, Thomas E.

1995-01-01

An impulse radar studfinder propagates electromagnetic pulses and detects reflected pulses from a fixed range. Unmodulated pulses, about 200 ps wide, are emitted. A large number of reflected pulses are sampled and averaged. Background reflections are subtracted. Reflections from wall studs or other hidden objects are detected and displayed using light emitting diodes.

Impulse radar studfinder

DOEpatents

McEwan, T.E.

1995-10-10

An impulse radar studfinder propagates electromagnetic pulses and detects reflected pulses from a fixed range. Unmodulated pulses, about 200 ps wide, are emitted. A large number of reflected pulses are sampled and averaged. Background reflections are subtracted. Reflections from wall studs or other hidden objects are detected and displayed using light emitting diodes. 9 figs.

Conversion of Biowaste Asian Hard Clam (Meretrix lusoria) Shells into White-Emitting Phosphors for Use in Neutral White LEDs.

PubMed

Chang, Tsung-Yuan; Wang, Chih-Min; Lin, Tai-Yuan; Lin, Hsiu-Mei

2016-12-02

The increasing volume and complexity of waste associated with the modern economy poses a serious risk to ecosystems and human health. However, the remanufacturing and recycling of waste into usable products can lead to substantial resource savings. In the present study, clam shell waste was first transformed into pure and well-crystallized single-phase white light-emitting phosphor Ca₉Gd(PO₄)₇:Eu 2+ ,Mn 2+ materials. The phosphor Ca₉Gd(PO₄)₇:Eu 2+ ,Mn 2+ materials were synthesized by the solid-state reaction method and the carbothermic reduction process, and then characterized and analyzed by means of X-ray diffraction (XRD) and photoluminescence (PL) measurements. The structural and luminescent properties of the phosphors were investigated as well. The PL and quantum efficiency measurements showed that the luminescence properties of clam shell-based phosphors were comparable to that of the chemically derived phosphors. Moreover, white light-emitting diodes were fabricated through the integration of 380 nm chips and single-phase white light-emitting phosphors (Ca 0.979 Eu 0.006 Mn 0.015 )₉Gd(PO₄)₇ into a single package of a white light emitting diode (WLED) emitting a neutral white light of 5298 K with color coordinates of (0.337, 0.344).

Conversion of Biowaste Asian Hard Clam (Meretrix lusoria) Shells into White-Emitting Phosphors for Use in Neutral White LEDs

PubMed Central

Chang, Tsung-Yuan; Wang, Chih-Min; Lin, Tai-Yuan; Lin, Hsiu-Mei

2016-01-01

The increasing volume and complexity of waste associated with the modern economy poses a serious risk to ecosystems and human health. However, the remanufacturing and recycling of waste into usable products can lead to substantial resource savings. In the present study, clam shell waste was first transformed into pure and well-crystallized single-phase white light-emitting phosphor Ca9Gd(PO4)7:Eu2+,Mn2+ materials. The phosphor Ca9Gd(PO4)7:Eu2+,Mn2+ materials were synthesized by the solid-state reaction method and the carbothermic reduction process, and then characterized and analyzed by means of X-ray diffraction (XRD) and photoluminescence (PL) measurements. The structural and luminescent properties of the phosphors were investigated as well. The PL and quantum efficiency measurements showed that the luminescence properties of clam shell-based phosphors were comparable to that of the chemically derived phosphors. Moreover, white light-emitting diodes were fabricated through the integration of 380 nm chips and single-phase white light-emitting phosphors (Ca0.979Eu0.006Mn0.015)9Gd(PO4)7 into a single package of a white light emitting diode (WLED) emitting a neutral white light of 5298 K with color coordinates of (0.337, 0.344). PMID:28774101

Highly Efficient White Organic Light-Emitting Diodes with Ultrathin Emissive Layers and a Spacer-Free Structure

PubMed Central

Wu, Shengfan; Li, Sihua; Sun, Qi; Huang, Chenchao; Fung, Man-Keung

2016-01-01

Ultrathin emissive layers (UEMLs) of phosphorescent materials with a layer thickness of less than 0.3 nm were introduced for high-efficiency organic light-emitting diodes (OLEDs). All the UEMLs for white OLEDs can be prepared without the use of interlayers or spacers. Compared with devices fabricated with interlayers inserted in-between the UEMLs, our spacer-free structure not only significantly improves device efficiency, but also simplifies the fabrication process, thus it has a great potential in lowering the cost of OLED panels. In addition, its spacer-free structure decreases the number of interfaces which often introduce unnecessary energy barriers in these devices. In the present work, UEMLs of red, green and blue-emitting phosphorescent materials and yellow and blue phosphorescent emitters are utilized for the demonstration of spacer-free white OLEDs. Upon optimization of the device structure, we demonstrated spacer-free and simple-structured white-emitting OLEDs with a good device performance. The current and power efficiencies of our white-emitting devices are as high as 56.0 cd/A and 55.5 lm/W, respectively. These efficiencies are the highest ever reported for OLEDs fabricated with the UEML approach. PMID:27170543

Highly efficient and stable white organic light emitting diode base on double recombination zones of phosphorescent blue/orange emitters.

PubMed

Lee, Seok Jae; Koo, Ja Ryong; Lim, Dong Hwan; Park, Hye Rim; Kim, Young Kwan; Ha, Yunkyoung

2011-08-01

We demonstrated efficient and stable white phosphorescent organic light-emitting diodes (OLEDs) with double-emitting layers (D-EMLs), which were comprised of two emissive layers with a hole transport-type host of N,N'-dicarbazolyl-3,5-benzene (mCP) and a electron transport-type host of 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) with blue/orange emitters, respectively. We fabricated two type white devices with single emitting layer (S-EML) and D-EML of orange emitter, maintaining double recombination zone of blue emitter. In addition, the device architecture was developed to confine excitons inside the D-EMLs and to manage triplet excitons by controlling the charge injection. As a result, light-emitting performances of white OLED with D-EMLs were improved and showed the steady CIE coordinates compared to that with S-EML of orange emitter, which demonstrated the maximum luminous efficiency and external quantum efficiency were 21.38 cd/A and 11.09%. It also showed the stable white emission with CIE(x,y) coordinates from (x = 0.36, y = 0.37) at 6 V to (x = 0.33, y = 0.38) at 12 V.

Highly Efficient White Organic Light-Emitting Diodes with Ultrathin Emissive Layers and a Spacer-Free Structure.

PubMed

Wu, Shengfan; Li, Sihua; Sun, Qi; Huang, Chenchao; Fung, Man-Keung

2016-05-12

Ultrathin emissive layers (UEMLs) of phosphorescent materials with a layer thickness of less than 0.3 nm were introduced for high-efficiency organic light-emitting diodes (OLEDs). All the UEMLs for white OLEDs can be prepared without the use of interlayers or spacers. Compared with devices fabricated with interlayers inserted in-between the UEMLs, our spacer-free structure not only significantly improves device efficiency, but also simplifies the fabrication process, thus it has a great potential in lowering the cost of OLED panels. In addition, its spacer-free structure decreases the number of interfaces which often introduce unnecessary energy barriers in these devices. In the present work, UEMLs of red, green and blue-emitting phosphorescent materials and yellow and blue phosphorescent emitters are utilized for the demonstration of spacer-free white OLEDs. Upon optimization of the device structure, we demonstrated spacer-free and simple-structured white-emitting OLEDs with a good device performance. The current and power efficiencies of our white-emitting devices are as high as 56.0 cd/A and 55.5 lm/W, respectively. These efficiencies are the highest ever reported for OLEDs fabricated with the UEML approach.

Highly Efficient White Organic Light-Emitting Diodes with Ultrathin Emissive Layers and a Spacer-Free Structure

NASA Astrophysics Data System (ADS)

Wu, Shengfan; Li, Sihua; Sun, Qi; Huang, Chenchao; Fung, Man-Keung

2016-05-01

Ultrathin emissive layers (UEMLs) of phosphorescent materials with a layer thickness of less than 0.3 nm were introduced for high-efficiency organic light-emitting diodes (OLEDs). All the UEMLs for white OLEDs can be prepared without the use of interlayers or spacers. Compared with devices fabricated with interlayers inserted in-between the UEMLs, our spacer-free structure not only significantly improves device efficiency, but also simplifies the fabrication process, thus it has a great potential in lowering the cost of OLED panels. In addition, its spacer-free structure decreases the number of interfaces which often introduce unnecessary energy barriers in these devices. In the present work, UEMLs of red, green and blue-emitting phosphorescent materials and yellow and blue phosphorescent emitters are utilized for the demonstration of spacer-free white OLEDs. Upon optimization of the device structure, we demonstrated spacer-free and simple-structured white-emitting OLEDs with a good device performance. The current and power efficiencies of our white-emitting devices are as high as 56.0 cd/A and 55.5 lm/W, respectively. These efficiencies are the highest ever reported for OLEDs fabricated with the UEML approach.

Recipient luminophoric mediums having narrow spectrum luminescent materials and related semiconductor light emitting devices and methods

DOEpatents

LeToquin, Ronan P; Tong, Tao; Glass, Robert C

2014-12-30

Light emitting devices include a light emitting diode ("LED") and a recipient luminophoric medium that is configured to down-convert at least some of the light emitted by the LED. In some embodiments, the recipient luminophoric medium includes a first broad-spectrum luminescent material and a narrow-spectrum luminescent material. The broad-spectrum luminescent material may down-convert radiation emitted by the LED to radiation having a peak wavelength in the red color range. The narrow-spectrum luminescent material may also down-convert radiation emitted by the LED into the cyan, green or red color range.

Iodine-stabilized single-frequency green InGaN diode laser.

PubMed

Chen, Yi-Hsi; Lin, Wei-Chen; Shy, Jow-Tsong; Chui, Hsiang-Chen

2018-01-01

A 520-nm InGaN diode laser can emit a milliwatt-level, single-frequency laser beam when the applied current slightly exceeds the lasing threshold. The laser frequency was less sensitive to diode temperature and could be finely tuned by adjusting the applied current. Laser frequency was stabilized onto a hyperfine component in an iodine transition through the saturated absorption spectroscopy. The uncertainty of frequency stabilization was approximately 8×10 -9 at a 10-s integration time. This compact laser system can replace the conventional green diode-pumped solid-state laser and applied as a frequency reference. A single longitudinal mode operational region with diode temperature, current, and output power was investigated.

High brightness laser-diode device emitting 160 watts from a 100 μm/NA 0.22 fiber.

PubMed

Yu, Junhong; Guo, Linui; Wu, Hualing; Wang, Zhao; Tan, Hao; Gao, Songxin; Wu, Deyong; Zhang, Kai

2015-11-10

A practical method of achieving a high-brightness and high-power fiber-coupled laser-diode device is demonstrated both by experiment and ZEMAX software simulation, which is obtained by a beam transformation system, free-space beam combining, and polarization beam combining based on a mini-bar laser-diode chip. Using this method, fiber-coupled laser-diode module output power from the multimode fiber with 100 μm core diameter and 0.22 numerical aperture (NA) could reach 174 W, with equalizing brightness of 14.2  MW/(cm2·sr). By this method, much wider applications of fiber-coupled laser-diodes are anticipated.

Effect of the fabrication conditions of SiGe LEDs on their luminescence and electrical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalyadin, A. E.; Sobolev, N. A., E-mail: nick@sobolev.ioffe.rssi.ru; Strel’chuk, A. M.

2016-02-15

SiGe-based n{sup +}–p–p{sup +} light-emitting diodes (LEDs) with heavily doped layers fabricated by the diffusion (of boron and phosphorus) and CVD (chemical-vapor deposition of polycrystalline silicon layers doped with boron and phosphorus) techniques are studied. The electroluminescence spectra of both kinds of LEDs are identical, but the emission intensity of CVD diodes is ∼20 times lower. The reverse and forward currents in the CVD diodes are substantially higher than those in diffusion-grown diodes. The poorer luminescence and electrical properties of the CVD diodes are due to the formation of defects at the interface between the emitter and base layers.

Deep blue exciplex organic light-emitting diodes with enhanced efficiency; P-type or E-type triplet conversion to singlet excitons?

PubMed

Jankus, Vygintas; Chiang, Chien-Jung; Dias, Fernando; Monkman, Andrew P

2013-03-13

Simple trilayer, deep blue, fluorescent exciplex organic light-emitting diodes (OLEDs) are reported. These OLEDs emit from an exciplex state formed between the highest occupied molecular orbital (HOMO) of N,N'-bis(1-naphthyl)N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) and lowest unoccupied molecular orbital (LUMO) of 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi) and the NPB singlet manifold, yielding 2.7% external quantum efficiency at 450 nm. It is shown that the majority of the delayed emission in electroluminescence arises from P-type triplet fusion at NPB sites not E-type reverse intersystem crossing because of the presence of the NPB triplet state acting as a deep trap. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Novel Strategy for Photopatterning Emissive Polymer Brushes for Organic Light Emitting Diode Applications

PubMed Central

2017-01-01

A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red–green–blue arrays to yield white emission. PMID:28691078

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal-Organic Framework for Fast White-Light Communication.

PubMed

Wang, Zhiye; Wang, Zi; Lin, Bangjiang; Hu, XueFu; Wei, YunFeng; Zhang, Cankun; An, Bing; Wang, Cheng; Lin, Wenbin

2017-10-11

A dye@metal-organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y 3 Al 5 O 12 :Ce 3+ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency.

PubMed

Zhang, Zi-Hui; Huang Chen, Sung-Wen; Chu, Chunshuang; Tian, Kangkai; Fang, Mengqian; Zhang, Yonghui; Bi, Wengang; Kuo, Hao-Chung

2018-04-24

This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result, the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally.

Organic Light-Emitting Diodes Using Multifunctional Phosphorescent Dendrimers with Iridium-Complex Core and Charge-Transporting Dendrons

NASA Astrophysics Data System (ADS)

Tsuzuki, Toshimitsu; Shirasawa, Nobuhiko; Suzuki, Toshiyasu; Tokito, Shizuo

2005-06-01

We report a novel class of light-emitting materials for use in organic light-emitting diodes (OLEDs): multifunctional phosphorescent dendrimers that have a phosphorescent core and dendrons based on charge-transporting building blocks. We synthesized first-generation and second-generation dendrimers consisting of a fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] core and hole-transporting phenylcarbazole-based dendrons. Smooth amorphous films of these dendrimers were formed by spin-coating them from solutions. The OLEDs using the dendrimer exhibited bright green or yellowish-green emission from the Ir(ppy)3 core. The OLEDs using the film containing a mixture of the dendrimer and an electron-transporting material exhibited higher efficiency than those using the neat dendrimer film. The external quantum efficiency of OLEDs using the film containing a mixture of the first-generation dendrimer and an electron-transporting material was as high as 7.6%.

Investigation of organic light emitting diodes for interferometric purposes

NASA Astrophysics Data System (ADS)

Pakula, Anna; Zimak, Marzena; Sałbut, Leszek

2011-05-01

Recently the new type of light source has been introduced to the market. Organic light emitting diode (OLED) is not only interesting because of the low applying voltage, wide light emitting areas and emission efficiency. It gives the possibility to create a light source of a various shape, various color and in the near future very likely even the one that will change shape and spectrum in time in controlled way. Those opportunities have not been in our reach until now. In the paper authors try to give an answer to the question if the new light source -OLED - is suitable for interferometric purposes. Tests cover the short and long term spectrum stability, spectrum changes due to the emission area selection. In the paper the results of two OLEDs (red and white) are shown together with the result of an attempt to use them in an interferometric setup.

Novel Strategy for Photopatterning Emissive Polymer Brushes for Organic Light Emitting Diode Applications.

PubMed

Page, Zachariah A; Narupai, Benjaporn; Pester, Christian W; Bou Zerdan, Raghida; Sokolov, Anatoliy; Laitar, David S; Mukhopadhyay, Sukrit; Sprague, Scott; McGrath, Alaina J; Kramer, John W; Trefonas, Peter; Hawker, Craig J

2017-06-28

A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red-green-blue arrays to yield white emission.

Trap-assisted and Langevin-type recombination in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Wetzelaer, G. A. H.; Kuik, M.; Nicolai, H. T.; Blom, P. W. M.

2011-04-01

Trapping of charges is known to play an important role in the charge transport of organic semiconductors, but the role of traps in the recombination process has not been addressed. Here we show that the ideality factor of the current of organic light-emitting diodes (OLEDs) in the diffusion-dominated regime has a temperature-independent value of 2, which reveals that nonradiative trap-assisted recombination dominates the current. In contrast, the ideality factor of the light output approaches unity, demonstrating that luminance is governed by recombination of the bimolecular Langevin type. This apparent contradiction can be resolved by measuring the current and luminance ideality factor for a white-emitting polymer, where both free and trapped charge carriers recombine radiatively. With increasing bias voltage, Langevin recombination becomes dominant over trap-assisted recombination due to its stronger dependence on carrier density, leading to an enhancement in OLED efficiency.

High-brightness blue organic light emitting diodes with different types of guest-host systems

NASA Astrophysics Data System (ADS)

Wang, Xiao; Zhang, Jing-shuang; Peng, Cui-yun; Guo, Kun-ping; Wei, Bin; Zhang, Hao

2016-03-01

We demonstrate high-brightness blue organic light emitting diodes (OLEDs) using two types of guest-host systems. A series of blue OLEDs were fabricated using three organic emitters of dibenz anthracene (perylene), di(4-fluorophenyl) amino-di (styryl) biphenyl (DSB) and 4,4'-bis[2-(9-ethyl-3-carbazolyl)vinyl]biphenyl (BCzVBi) doped into two hosting materials of 4,4'-bis(9-carbazolyl) biphenyl (CBP) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) as blue emitting layers, respectively. We achieve three kinds of devices with colors of deep-blue, pure-blue and sky-blue with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.10), (0.15, 0.15) and (0.17, 0.24), respectively, by employing PBD as host material. In addition, we present a microcavity device using the PBD guest-host system and achieve high-purity blue devices with narrowed spectrum.

Electrical and optical analyses of tandem organic light-emitting diodes with organic charge-generation layer

NASA Astrophysics Data System (ADS)

Kim, Bong Sung; Chae, Heeyeop; Chung, Ho Kyoon; Cho, Sung Min

2018-06-01

The electrical and optical properties of tandem organic light-emitting diodes (OLEDs), in which a fluorescent and phosphorescent emitting units are connected by an organic charge-generation layer (CGL), were experimentally analyzed. To investigate the internal properties of the tandem OLEDs, we fabricated and compared two single, two homo-tandem, and two hetero-tandem OLEDs using the fluorescent and phosphorescent units. From the experimental results of the OLEDs obtained at the same current density, the voltage across the CGL as well as the individual emission spectra and luminance of each unit of tandem OLEDs were obtained and compared with the theoretical simulation results. The analysis method proposed in this study can be utilized as a method to verify the accuracy of optical or electrical computer simulation of tandem OLED and it will be useful to understand the overall electrical and optical characteristics of tandem OLEDs.

Suspended light-emitting diode featuring a bottom dielectric distributed Bragg reflector

NASA Astrophysics Data System (ADS)

Cai, Wei; Wang, Wei; Zhu, Bingcheng; Gao, Xumin; Zhu, Guixia; Yuan, Jialei; Wang, Yongjin

2018-01-01

Here, we propose, fabricate and characterize the light manipulation of a suspended-membrane InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED) with a dielectric distributed Bragg reflector (DBR) positioned at the bottom, implemented on a GaN-on-silicon platform. Silicon removal is conducted to obtain the suspended MQW-LED architecture, and back wafer thinning of the epitaxial film is performed to improve the device performance. A 6-pair SiO2/Ta2O5 DBR is deposited on the backside to manipulate the emitted light. The experimental results demonstrate that the bottom dielectric DBR exhibits high reflectivity and distinctly changes the light emission, which are consistent with the performed simulation results. This work represents a significant step towards the realization of inexpensive, electrically driven and simply fabricated GaN VCSELs for potential use in number of applications.

Stolephorus sp Behavior in Different LED (Light Emitting Diode) Color and Light Intensities

NASA Astrophysics Data System (ADS)

Fitri Aristi, D. P.; Ramadanita, I. A.; Hapsari, T. D.; Susanto, A.

2018-02-01

This research aims to observe anchovy (Stolephorus sp) behavior under different LED light intensities that affect eye physiology (cell cone structure). The materials used were Stolephorus sp taken from the waters off Jepara and 13 and 10 watt light emitting diode (LED). The research method was an experiment conducted from March through August 2015 in the waters off Jepara. Data analysis of visual histology and fish respond was carried out at the fishing gear material laboratory, anatomy and cultivate. Cone cell structure (mosaic cone) of Stolephorus sp forms a connected regular square pattern with every single cone surrounded by four double cones, which indicate that anchovies are sensitive to light. The 13 watt LED (628 lux) has faster response than the 10 watt LED (531 lux) as it has wider and higher emitting intensity, which also attracts fish to gather quicker.

Molecular Engineering of UV/Vis Light-Emitting Diode (LED)-Sensitive Donor-π-Acceptor-Type Sulfonium Salt Photoacid Generators: Design, Synthesis, and Study of Photochemical and Photophysical Properties.

PubMed

Wu, Xingyu; Jin, Ming; Xie, Jianchao; Malval, Jean-Pierre; Wan, Decheng

2017-11-07

A series of donor-π-acceptor-type sulfonium salt photoacid generators (PAGs) were designed and synthesized by systematically changing electron-donating groups, π-conjugated systems, electron-withdrawing groups, and the number of branches through molecular engineering. These PAGs can effectively decompose under UV/Vis irradiation from a light-emitting diode (LED) light source because of the matching absorption and emitting spectra of the LEDs. The absorption and acid-generation properties of these sulfonium salts were elucidated by UV/Vis spectroscopy and so forth. Results indicated that the PAG performance benefited from the introduction of strong electron-donating groups, specific π-conjugated structures, certain electron-withdrawing groups, or two-branched structures. Most sulfonium salts showed potential as photoinitiators under irradiation by a wide variety of UV and visible LEDs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Luminescent carbon quantum dots with high quantum yield as a single white converter for white light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, X. T.; Zhang, Y.; Liu, X. G., E-mail: liuxuguang@tyut.edu.cn

Carbon quantum dots (CQDs) with high quantum yield (51.4%) were synthesized by a one-step hydrothermal method using thiosalicylic acid and ethylenediamine as precursor. The CQDs have the average diameter of 2.3 nm and possess excitation-independent emission wavelength in the range from 320 to 440 nm excitation. Under an ultraviolet (UV) excitation, the CQDs aqueous solutions emit bright blue fluorescence directly and exhibit broad emission with a high spectral component ratio of 67.4% (blue to red intensity to total intensity). We applied the CQDs as a single white-light converter for white light emitting diodes (WLEDs) using a UV-LED chip as the excitation lightmore » source. The resulted WLED shows superior performance with corresponding color temperature of 5227 K and the color coordinates of (0.34, 0.38) belonging to the white gamut.« less

Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency

NASA Astrophysics Data System (ADS)

Zhang, Zi-Hui; Huang Chen, Sung-Wen; Chu, Chunshuang; Tian, Kangkai; Fang, Mengqian; Zhang, Yonghui; Bi, Wengang; Kuo, Hao-Chung

2018-04-01

This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result, the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally.

Enhanced light output from a nitride-based power chip of green light-emitting diodes with nano-rough surface using nanoimprint lithography.

PubMed

Huang, H W; Lin, C H; Yu, C C; Lee, B D; Chiu, C H; Lai, C F; Kuo, H C; Leung, K M; Lu, T C; Wang, S C

2008-05-07

Enhanced light extraction from a GaN-based power chip (PC) of green light-emitting diodes (LEDs) with a rough p-GaN surface using nanoimprint lithography is presented. At a driving current of 350 mA and with a chip size of 1 mm × 1 mm packaged on transistor outline (TO)-cans, the light output power of the green PC LEDs with nano-rough p-GaN surface is enhanced by 48% when compared with the same device without a rough p-GaN surface. In addition, by examining the radiation patterns, the green PC LED with nano-rough p-GaN surface shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices by using the technique of nanoimprint lithography under suitable nanopattern design.