Using SiO2 nano-particles for better color uniformity and lumen output in 8500 K conformal and in-cup white LEDs

<span>In the effort of improving the performance of white light LEDs devices (WLEDs), the SiO₂ nano-particles were applied and have shown a significant impact on the optical properties. Specifically, the light output of the lighting devices is enhanced when a mixture of SiO₂ particles and silicone gel is diffused on the encapsulation layer surface. This enhancement is the result of light scattering from SiO₂ that strengthens the emitted blue light at further angles and reduces the color discrepancy. The evidence is that CCT deviation in SiO₂-doped structure decline from 1000 K to 420 K in -70° to 70°. In addition, the SiO₂ with refractive index in between the phosphor material and outside environment allows light to be emitted outward more effectively. This lighting enhancement of SiO₂-doped structure increases the lumen output by 2.25% at 120 mA power source in comparison to structure without SiO₂. These experimental outcomes suggest that SiO₂ is an effective material to add in WLEDs structure for better lighting efficiency.</span>

(Ce, Gd):YAG-Al2O3 composite ceramics for high-brightness yellow light-emitting diode applications

Gd3+ ions were doped in Ce:YAG ceramics as the phosphor material for the high-brightness yellow LED (565-590 nm). Besides the role of spectral modulation, the introduction of Gd3+ ions also exacerbates the thermal quenching effect. To increase its thermal performance, Al2O3 were introduced as the second phase and (Ce0.6%Y69.4%Gd30%)3Al5O12-z% Al2O3 (z=0, 10, 20, 30, 40) composite ceramics were fabricated by vacuum sintering. Their composite microstructures and phase structures were characterized. As the amount of Al2O3 increases from 0 wt% to 40 wt%, there is a noticeable improvement on the thermal conductivity. The thermal stability also increases and the operating temperature of ceramics reduced from 141.1 °C to 132.2 °C. Collaborating composite ceramics with InGaN blue chips, the steady-state luminous efficiency of 40 wt%-Al2O3 yellow LED reaches the highest value of 109.49 lm/W, which is 8.54 % higher than that of Al2O3-free sample. Additionally, scattering behavior and conversion efficiency of composite ceramics with different thicknesses were investigated.

Application of BaY2F8:Er3+,Yb3+ and Mg8Ge2O11F2:Mn4+ in improving the lighting quality of phosphor-in-glass based white light-emitting diodes with the dual-convex design

<span>Although the luminous of the remote phosphor structure tends to be better than that of the in-cup or conformal phosphor structures, the poor light quality prevents this lighting method from being widely used. It is recognized through experiments that the two-layer remote phosphorus structure should be used to improve color rendering index (CRI) and color quality ratio (CQS) for WLEDs. In the experiments, WLED structures containing green BaY2F8:Er3+,Yb3+ or red Mg8Ge2O11F2:Mn4+ phosphor on the yellow YAG:Ce3+ phosphor were performed at 8500 K.. After that, Mg8Ge2O11F2:Mn4+ and BaY2F8:Er3+,Yb3+ concentrations in each WLED structure is adjusted until chromatic performance reached the finest quality. As a result, Mg8Ge2O11F2:Mn4+is proved to bring great benefits to the increase of CRI and CQS. Specifically, the greater the concentration of Mg8Ge2O11F2:Mn4+, the better CRI and CQS because of the additional red-light material from this phosphor. The other phosphor material, green BaY2F8:Er3+,Yb3+ phosphor, is beneficial for the expansion of luminous flux. However, if the concentration of Mg8Ge2O11F2:Mn4+ or BaY2F8:Er3+,Yb3+ is over the limit, the decrease in lumen output and chromatic quality will occur. While doing the experiment, Mie-scattering theory and the Beer’s law are great tools to verify the accuracy of results. The results of this article can serve the purpose of improving WLEDs fabrication to produce higher quality product.</span>

Evolution of Monoclinic CaAl2O4 Nanocrystallites via Chemical Route and Its Optical Investigations

Nanocrystalline calcium aluminate (CaAl2O4) powder is an adequate phosphor material. Calcium aluminate is a versatile member belongs to a category of alkaline earth aluminates phosphor. It has multifaceted applications in different areas such as photocatalysis, sensing, optoelectronic devices, displays, and imaging etc. In the present study, calcium aluminate has been prepared by well-known citrate sol-gel technique. X-ray diffraction (XRD) method has been used to analysis the amorphous and crystalline behavior of the prepared samples. The sample annealed at 800° indicates the monoclinic phase with enhanced intensity of the prominent diffraction peaks. By using Debye-Scherrer formula the grain size of crystalline powder is calculated ~10 nm. FTIR spectra confirmed the molecular orientation and bond structure in the prepared nanomaterial. Surface morphology and elemental composition present in prepared samples has been examined by Scanning electron microscope and energy dispersive spectroscopy. Uv-vis spectroscopy result showed red shift in the nanopowder with thermal treatment. In material science, due to their long-lasting photo-luminescence properties in visible region these aluminates are very attractive for evolution of new generation inorganic phosphor materials.

Eu3+/Eu2+/Tb3+ co-activated single-phase Gd2O2S: A high-performance white light emitting phosphor for light emitting diode

In this work, we report Eu3+/Tb3+/Eu2+ co-activated Gd2O2 S as novel phosphor materials that can be effectively applied in the white-light emitting diode based on a near-UV chip with sensational performances. The luminescent properties and energy transfer mechanism have been thoroughly investigated. The as-prepared europium/terbium co-doped Gd2O2 S phosphors exhibit strong fluorescence with tunable color output under UV-vis light excitation. Furthermore, a high response to ultraviolet illumination of 398 nm wavelength was observed in the excitation spectra, indicating an excellent match with a light-emitting-diode chip in the dominant emissions. It is found that a tricolor (blue, green and red) emission band which results in a white light emission can be acquired when Eu3+, Eu2+ and Tb3+ ions are all co-doped into the single phase Gd2O2S, and an optimum ion doping level (10 at.% Eu and 0.7 at.% Tb) can effectively emit nearly pure white color photoluminescence with lifetime effectively tuned from 0.55 ms to 1.10 ms. The CIE (Commission International de I'Eclairage 1931 chromaticity) is X = 0.3507, Y = 0.3029. It is therefore expected that the newly found phosphor material with high-performance properties possess great potentials for the future advanced white LED applications.

Photoluminescence Studies of CaAl2O4: EU2+ Blue Phosphors Co-Doped with ND3+ Ion Synthesized by Solid- State Reaction Method

In this work, the polycrystalline CaAl2O4: Eu2+, Nd3+ based blue phosphor was prepared by solid-state reaction method. The rare earth metal ions doped calcium aluminate phosphors have been studied in depth. The high quantum efficiency make them useful for anomalous long phosphorescence, good stability, luminous paints, radiation dosimetry, X-ray imaging, color display, and light emitting diodes. Phase, crystallinity and luminescent properties of the synthesized phosphors were examined by using powder X-ray diffraction (XRD). In the phosphor material, the photoluminescence (PL) spectrum has a broad emission peak of Eu2+ ion in blue region at (λmax = 440 nm) due to the energy transitions between the ground state 4f7 and the excited state 4f65d1 of the Eu2+ ion. This has importance in making the visible phosphor devices from this material. In this study the single dopant phosphors were synthesized; therefore, it is important to improve the long afterglow of the phosphors by codoping. The phosphors of CaAl2O4: Eu2+, Nd3+ had long persistence luminescence. In these phosphors, Eu2+ ions play the role of activators. Whereas Nd3+ ions generate deep traps that lead to the long persistent phosphorescence and act as the co-activators in the phosphors simultaneously. The concentration of Nd3+ ion co-doped has strong influence on the luminescence of phosphor.

pH Response of a Hydroxyl-Functionalized Luminescent Metal-Organic Framework based Phosphor

A terbium doped yttrium based metal-organic framework [Y1.8Tb0.2(CAM)3(H2O)4].2H2O, 1{where H2CAM = chelidamic acid}, has been successfully synthesized using hydrothermal technique to use it as phosphor material along with large Stokes...

Lead-free zero dimensional tellurium(iv) chloride-organic hybrid with strong room temperature emission as a luminescent material

Present 0D Te(IV)-chloride organic hybrid luminescent material shows broad, yellow-orange, strong room temperature emission (PLQY ∼15%), ambient/thermal stability, and excitation features in the visible (445 nm) allowing its use as phosphor material.

Exploring color tunable emission characteristics of Eu3+-doped La2(MoO4)3 phosphors in the glass–ceramic form

The glass–ceramic Eu-LMO-1050 is more suitable as a red-color-emitting phosphor material than the ceramic Eu-LMO-750. Further, Eu-LMO-1050 can overcome the problems related to the phosphor/silicone composite in commercial LEDs.