In this work, aminopropylmethylpolysiloxane (AMS) functionalized luminescent carbon dots (AMS-CDs) were prepared via a one-step solvothermal method. AMS-CDs could be self- or co-cross-linking with AMS to form 3D flexible transparent silicone rubbers (SRs) where CDs acted as cross-linking points, so the loading fraction of AMS-CDs could be adjusted from 10 to 100 wt %, thus modulating fluorescence properties and flexibility of silicone rubbers. Because of the self-curing property and high thermal stability, AMS-CDs were also studied in white LEDs (WLEDs), serving as a color conversion and encapsulation layer of GaN based blue LEDs simultaneously that would avoid the traditional problem of poor compatibility between emitting and packaging materials. And the color coordinate of AMS-CDs based WLEDs (0.33, 0.28) was very close to the pure white light. In addition, the obtained CDs cross-linked SRs had good transparency (T > 80%) at 510–1400 nm and high refractive indexes (1.33–1.54) that could meet the need of...

Polysiloxane Functionalized Carbon Dots and Their Cross-Linked Flexible Silicone Rubbers for Color Conversion and Encapsulation of White LEDs

Recently, carbon dots have emerged as novel luminous materials due to their excellent luminous performance. However, it is still challenging to obtain high quantum yields of red emission in carbon dots. Herein, we synthesized a new type of high efficiency red emission-carbon dots from 1,4-phenylene diisocyanate by a solvothermal method. Furthermore, the carbon dots were used to fabricate trichromatic white LEDs that possess a high luminous efficacy and color rendering index. In this study, we propose an approach for achieving high carbon dots with quantum yields by introducing more conjugated nitrogen groups in a graphitic layered structure. Moreover, the high efficiency red emission carbon dots can greatly promote carbon dots’ application in white LEDs, demonstrating that the as-prepared carbon dots are promising materials in LEDs, displays and even in other light applications.

High efficiency red emission carbon dots based on phenylene diisocyanate for trichromatic white and red LEDs

We report on the methodology and implementation of a robust and accurate double integrating sphere system for measuring the absolute photoluminescence quantum yield and its temperature dependence of commercially available phosphors (garnets, silicates and nitrides). The potential of our instrument for the examination of light interaction with samples of different absorption and diffusion coefficients is also presented, as optical properties of luminescent materials have a major impact on the efficiency of LED’s packaging. Our work gives special attention to the control and the optimization of light losses in the optical system in order to ensure reliable measurements. The YAG:Ce phosphor shows the highest luminescence quantum yield at 97% efficiency, the green silicate the lowest with 79% efficiency. Silicate phosphors show up to 15% loss of luminescence intensity when temperature is raised to 140°C.

/pdf/optical-efficiency-characterization-of-led-phosphors-using-a-nysx8bvtam.pdf

Optical efficiency characterization of LED phosphors using a double integrating sphere system

This work concerns a novel blue emitting LED phosphor activated by Eu2+. It was found that this luminescent material can be efficiently pumped by near UV or UV-A radiation sources while it exhibits a high quantum yield at a doping level between 0.3 and 3.0%. More impressively, this material has a very high quenching temperature T1/2 and will thus be applicable on-chip in high power phosphor converted LEDs or even in laser diodes. The emission and thermal stability are almost identical to that of BAM:Eu2+ while the absorption band is broader and reaches into the near UV range. Therefore, Na3RbMg7(PO4)6:Eu2+ is a promising candidate as a blue emitter in high CRI full conversion LEDs. To investigate the site preference of Eu2+, DFT and Ligand Field Theory based calculations were performed to successfully predict the emission spectrum. An unusual decay behavior was observed at low temperatures and the underlying mechanism involving spin-forbidden transitions of Eu2+ is discussed.

On a blue emitting phosphor Na3RbMg7(PO4)6:Eu2+ showing ultra high thermal stability

Understanding the effect of particle size on the optical properties of phosphor is important to increase packaging efficiency in white light-emitting diodes (LEDs). We have investigated the effect of particle size (10–20 μm, 20–25 μm, 25–32 μm) on the optical properties of a yellow silicate phosphor adopted in white LEDs. X-ray diffraction results show negligible modification in crystallinity as the particle size of the yellow silicate phosphor varies, whereas the photoluminescence excitation intensity and quantum yield are enhanced as the particle size increased. LED packages fabricated using phosphors with different mean particle sizes, and their optical properties were analyzed. The radiant flux improved with increasing particle size, whereas the luminous flux increased with decreasing particle size. The effect of immersion on the optical properties of the LED light source has been also measured, and the details are discussed.

Effect of Particle Size on the Optical Properties of Yellow Silicate Phosphor in Light-Emitting Diodes

Enhanced reliability of phosphor-converted white light-emitting diodes based on a laser-cured silicone encapsulant layer

This preliminary study aimed to realize the potential use of titanium dioxide–carbonized medium-density fiberboard (TiO2–cMDF) as a biomaterial for dye wastewater treatment. TiO2–cMDF, which was prepared by carbonizing MDF treated with titanium tetraisopropoxide in isopropyl alcohol, was investigated for adsorption and then photodegradation of methylene blue (MB) under UV-A (390 nm, 19 W) and UV-C (280 nm, 12 W) light emitting diodes (LEDs). After two full cycles of adsorption, four successive cycles of photodegradation were conducted under UV-A LED. For every adsorption or photodegradation cycle, TiO2–cMDF practically removed MB. Both adsorption and photodegradation followed pseudo-first-order kinetics. The rate constants for adsorption decreased by half. The rate constants for photodegradation were similar. This finding suggests that UV-A LED is a robust and steady source of UV light. Photodegradation under UV-C LED was also performed. However, due to its high-energy output, the UV-C LED module overheated even though a cooling fan was present. Although the results indicate a slow photodegradation under UV LEDs, because of the limited number of specimens, increasing the number of specimens and UV LED modules will improve its performance.

Preliminary investigation of the UV LED photodegradation of methylene blue using TiO2–carbonized medium-density fiberboard

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Effect of Particle Size on the Optical Properties of Yellow Silicate Phosphor in Light-Emitting Diodes

Enhanced reliability of phosphor-converted white light-emitting diodes based on a laser-cured silicone encapsulant layer

Preliminary investigation of the UV LED photodegradation of methylene blue using TiO2–carbonized medium-density fiberboard