White Light-emitting Diode Packages Research Articles

Stereolithography 3D printing of transparent resin lens for high-power phosphor-coated WLEDs packaging

Advanced lens fabricating techniques are urgently required for the development of white light-emitting diodes (WLEDs) packaging, due to the traditional LED lenses molding possesses presents many disadvantages like high cost, long-fabrication period, less compactness and low accuracy. The current study demonstrated the fabrication of lenses with transparent resin utilizing stereolithography (SLA) 3D printing. The SLA 3D printing parameters were optimized to accurately regulate the spheric and ellipsoidal lenses with the smooth surface and the acceptable transmittance. The illuminances, lighting efficiency (LE) and lighting distribution curves of the SLA-fabricated lens packaged WLEDs highly depended on the lens structure. The WLEDs with lower lens height exhibited more intense lighting energy density, higher LE and wider light output angle. SLA 3D printing offers a flexible approach of fabricating WLED lens, which provides a novel technical route for WLEDs to meet different lighting requirements.

Ca8MgY(PO4)7:Eu2+,Mn2+ for better angular chromatic harmony and high lumen for white diode

<p>The multifunctional phosphor Ca<sub>8</sub>MgY(PO4)7doping with Eu2+ and Mn2+ ions (CaMn) is utilized to stimulate the rate of light extraction and color harmony of the white light-emitting diode (WLED) package using remote phosphor design with two sheets of phosphor. The CaMn sheet helps to reduce the color variation and light scattering backward mainly caused by high concentration of yellow phosphor YAG:Ce3+ film. The experimental results show a gradual increase of luminous flux and significant reduction of chromatic deviation in direct proportion to the increasing concentration of CaMn phosphor. Meanwhile, with more than 9% wt of CaMn concentration, the reduction of color rendering properties is presented because of the redundant green emission, leading to the lack of blue and yellow emission energies. Good color quality scale that peaks at 63 can be achieved with 2-4%wt. CaMn in the WLED packages. It is advisable to manage the concentration the green phosphor CaMn to attain desirable optical objectives.</p>

Enhanced Luminous Efficacy and Stability of InP/ZnSeS/ZnS Quantum Dot-Embedded SBA-15 Mesoporous Particles for White Light-Emitting Diodes.

Environmentally friendly quantum dots (QDs) of InP-based materials are widely investigated, but their reliability remains inadequate to realize their full potential and wide application. In this study, InP/ZnSeS/ZnS QDs (pristine QDs) were dispersed and embedded into Santa Barbara Amorphous-15 mesoporous particles (SBA-15 MPs) for the first time. A solvent-free method for preparing QD white light-emitting diodes (WLEDs) that is compatible with the WLED packaging process was developed. The photoluminescence (PL) spectrum of pristine QD powder exhibited cluster states and had huge redshift of approximately 23 nm. By comparison, the PL spectrum of the SBA-15 MP/QD hybrid powder had a slight redshift of approximately 8 nm, only because the pristine QDs were dispersed and embedded well in the SBA-15 MPs. The PL intensity of the SBA-15 MP/QD hybrid powder slightly decreased after heating and cooling compared with that of the pristine QDs. Moreover, the luminous efficacy of the SBA-15 MP/QD hybrid WLEDs was enhanced by approximately 14% compared with that of the pristine QD-WLEDs. Furthermore, reliability analysis revealed that the SBA-15 MPs could improve the stability of the pristine QDs on chips. Thus, these MPs promise good potential for applications in mini-LEDs in the future.

Using CaCO3-doped package to improve correlated color temperature uniformity of white light-emitting diodes

<span>The white light-emitting diode (WLED) has been the most advance lighting method currently, however, the fabrication process of this configuration still has drawbacks which negatively affect its color quality. This research was conducted to provide a method for WLED’s lighting output enhancement. Since CaCO<sub>3</sub> particles are excellent for thermal stability enhancement, especially when being combined with an adhesive substance, we decided to integrate CO<sub>3</sub> particles into resin matrix such as melamine formaldehyde (MF) and investigate their influences on the optical properties, including color uniformity and lumen output, of the WLED. The results showed that CaCO3 and MF resin are beneficial to the light scattering efficiency, which results in higher luminous flux and chromatic quality for WLED packages. In addition to that, the appropriate amounts of MF resin and CaCO<sub>3</sub> for reaching the best lumen efficiency and color quality are figured out at 1% and 10%, respectively. Moreover, another advantage of using MF resin and CaCO<sub>3</sub> for fabricating WLEDs is cost effectiveness. Hence, it has turned out that CaCO<sub>3</sub> and MF resins can be potential materials for next high-quality WLED generations.</span>

Investigation on the application of ZnO nanostructures to improve the optical performance of white light-emitting diodes

Though combining blue LED chips with yellow phosphor has been the most common method in white light-emitting diode (WLED) production, the attained angular correlated color temperature (CCT) uniformity is still poor. Thus, this article proposes to add ZnO nanostructures to WLED packages to promote the color uniformity of the WLEDs. The outcomes of the research demonstrate that utilizing ZnO at different amount can affect the scattering energy and the CCT deviations in WLEDs packages in different extents. Particularly, adding the node-like (N-ZnO), sheet-like (S-ZnO), and rod-like (R-ZnO) leads to the corresponding decreases of CCT deviations from 3455.49 K to 96.30 K, 40.03 K, and 60.09 K, respectively. Meanwhile, with 0.25% N-ZnO, 0.75% S-ZnO, and 0.25 % R-ZnO, WLED devices can achieve both better CCT homogeneity and lower reduction in luminous flux. The results of this article can be a valuable document for the manufacturer to use as reference in improving their WLED products.

White LEDs With High Optical Consistency Packaged Using 3D Ceramic Substrate

Packaging efficiency and optical performances are important indexes for white light-emitting diodes (WLEDs) packaging. In this letter, wafer-level WLEDs packaging were presented by printing phosphor on three-dimensional (3D) ceramic substrate to improve packaging efficiency and optical consistency. The 3D ceramic substrate was prepared by repeatedly electroplating copper cups on the planar direct plated copper (DPC) ceramic substrate. The phosphor concentration was adjusted to realize natural white light. The fabrication errors of the 3D ceramic substrate and the optical performances of WLED modules were analyzed to evaluate the optical consistency of the WLED modules packaged by using 3D ceramic substrate. Consequently, the fabrication errors of 3D ceramic substrate are less than 1%. When the phosphor concentration was set at 12.5 wt%, the packaged LEDs achieve a natural white light with luminous efficiency (LE) of 94.55 lm/W, correlated color temperature (CCT) of 5915 K, and chromaticity coordinate of (0.3166, 0.3345). The WLED modules exhibit small standard deviations in LE (1%), color rendering index (1%), correlated color temperature (98 K), and high reliability. The results indicate that the WLEDs packaged using 3D ceramic substrate have excellent optical consistency.

Effects of humidity and phosphor on silicone/phosphor composite in white light-emitting diode package

Silicone/phosphor composite, which serve as mechanical protection and light conversion material, is an integral part of white light-emitting diode (LED) package. In this paper, a comprehensive study is conducted to investigate the effect of humidity and phosphor on moisture absorption, hygroscopic swelling, mechanical behavior, as well as thermal properties of silicone/phosphor composite in comparison with the pure silicone. SEM/EDAX and FTIR were performed to identify the phosphor and silicone compositions. Through moisture sorption test, it has been observed that the addition of phosphor significantly lowers the capacity of moisture absorption, but accelerates the diffusivity of moisture absorption. The hygroscopic swelling test showed that the phosphor has little effect on the swelling compared to the pure silicone sample. Both moisture absorption/desorption and hygroscopic swelling/de-swelling are reversible. Strain ramp test revealed that the phosphor enhances the stiffness of the composite. The moisture absorption, however, has negligible impact on mechanical stiffness for both pure and composite samples. Finally, thermal expansion test showed that the coefficient of thermal expansion does not change with the addition of phosphor into pure silicone.

Phosphor–silicone interaction effects in high power white light emitting diode packages

As a widespread application of high power phosphor-converted white light emitting diodes (pc-WLEDs) with long lifetime and color-consistence, the highly reliable phosphor/silicone composite, one of core materials used for light-conversion, working under severe operation conditions has become increasingly necessary. This paper selects three widely used monochromatic phosphors (Aluminates, Silicates and Nitrides based) as well as a pristine silicone to determine the potential interaction effects in their phosphor/silicone composites operated under different environments. Firstly, the transient thermal quenching and long-term high temperature ageing tests are used to investigate the thermal stabilities of both monochromatic phosphor powders and phosphor/silicone composites. Furthermore, the degradation mechanisms of phosphor/silicone composites aged under the high temperature & blue light exposure and high temperature & high humidity conditions are studied by considering the interaction effect. The results show that: (1) the thermal stabilities of different phosphors are different and the phosphor/silicone composites have more severe thermal quenching effects than those of their corresponding phosphor powders, but with the similar degradation trends; (2) the blue light irradiation can deteriorate silicone which is related to the photolysis effect; (3) the moisture can accelerate the degradation of phosphor/silicone composites because the change of pH condition, owing to the dissolution of phosphor powders in moisture, can degrade both phosphors and silicone.

An Experimental and Computational Study on Efficiency of White LED Packages With a Thermocaloric Approach

Thermal management of light-emitting diode (LED) chips is crucial for light extraction and lifetime. It is well known that the light output of an LED decreases with the elevated temperatures. For higher light extraction, the power input to the chip should be substantially high leading nonuniform current spreading and local joule heating at the chip active layers. However, this leads to a high amount of heat generation at the chip and a considerable amount of increase in the junction temperature. Besides shortening the lifetime of the chip, it also strongly affects the light output of the system. Although nominal driving currents for LEDs are around 350–400 mA, the ideal operating condition for the cost effectiveness at higher driving currents and corresponding efficiency of an LED chip is to be explored. In this paper, LED chips’ thermal and optical behaviors were investigated for different driving conditions while the board temperature is controlled using a thermoelectric cooler and the input current to the chip. The system was numerically investigated using a computational fluid dynamics software and validated with experimental studies. Consequently, a correlation for efficiency covering a wide range of operating conditions is presented. The efficiency of the LED that is obtained for 30 °C is 42%, whereas it drops to 30% for 50 °C board temperature. If one assumes a logarithmic relationship between the efficiency and the board temperature, the efficiency is expected to be around 20% for a typical LED operating temperature of between 80 °C and 100 °C.

Preparation and luminescent properties of the coating of phosphor in lead-free glass by multilayer screen-printing

The coating of phosphor in glass (PiG) for white light emitting diodes (WLEDs) has been prepared by multilayer screen-printing and low sintering-temperature. The lead-free and low-melting glass was synthesized, and the main compositions were P2O5-ZnO-B2O3 (PZB). The microstructure, luminescence spectra and lifetime behaviours of coating were investigated. The results of microstructure revealed that decreasing content of phosphor and increasing sintering temperatures were benefit for the coating because of better sintering. Based on the luminescence spectra, the suitable content of phosphor was 25% and sintering temperature was 600 °C. Under blue light (460 nm) exciting, the broad yellow band around 550 nm was obtained. It’s indicated that the white light can be achieved. The coating showed longer lifetime with increasing content of phosphor and lower sintering temperature. The obtained coating of PiG is expected to be an excellent material instead of organic resin for high-power WLEDs packaging.

A Silicon-Based LED Packaging Substrate With an Island Structure for Phosphor Encapsulation Shaping

This paper proposes an encapsulation shaping method for white light-emitting diode packaging, using a silicon substrate with an island structure and using a simple yttrium aluminum garnet phosphor dispensing process. The technology utilizes the interaction of the interfacial tension between silicon island structure and silicone phosphor material for encapsulation shaping at an appropriate curing temperature. Various encapsulation structures, such as hemispherical and shell-type lenses, are fabricated using different encapsulation doses, which allow specific optical requirements to be fulfilled. The experimental results show that a hemispherical encapsulation lens with a radius of curvature of 0.9 mm is formed, when the diameter of the island structure is 1.8 mm and the dispensing dose is 1.5 mL. When the dispensing doses are 2.5 and 4.0 mL, shell-type lens structures with short and long cylinders, respectively, are fabricated. In terms of optical characteristics of the shell-type structure, there is a large measured variation in chromaticity at different view angles, but for the short encapsulation cylinder the uniformity of the lighting is significantly improved. The simulation result for the luminance profile is in agreement with the experimental results.

Improving Performance and Reducing Amount of Phosphor Required in Packaging of White LEDs With ${\rm TiO}_{2}$ -Doped Silicone

White light-emitting diodes (LEDs) assembled by doping TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles with phosphor silicone encapsulation are investigated. The proposed method can improve lumen output by 2.7% and correlated color temperature deviation by 39%, and it can reduce the required amount of phosphor by 5% and junction temperature by 6.5 °C in white LED packaging. These improvements are attributed to the enhanced light scattering ability and refractive index of the encapsulation material and reduced light loss due to color mixing inside the packages, and they enhance light performance and reduce thermal accumulation. Therefore, results show that improving light output performance of white LEDs makes these LEDs advantageous for use in solid-state lighting.

Effect of Nano-Silica Filler on the Uniform Packaging of White Light Emitting Diodes

The packaging process of white light-emitting diodes (WLEDs) take a relatively long time, even when utilizing an automated dispensing system. Therefore the silicone-based packaging formulation and control of rheology during the packaging of LEDs are very important. The effect of phosphor settling during the curing state of LED packaging has been reported. In this work we studied the effect of phosphor paste on the dispensing stage of the WLEDs packaging process utilizing nanosilica particles as viscosity modifiers. With nano-silica in the silicone resin the sedimentation of YAG phosphor particles were effectively blocked and a uniform distribution of YAG phosphor in the cured silicon resin could be achieved. We also examined the incorporation of red quantum dots (QDs) to improve the color rendering index of the WLEDs with the aid of nano-silica as a rheological additive. The application of nano-silica in the layer-by-layer type encapsulation of red QDs was found to be effective in WLEDs packaging, which improved the color rendering index with warm white emission.

High-Efficiency White LED Packaging With Reduced Phosphor Concentration

In this letter, important factors for white light emitting diodes (LED) packaging, including lens encapsulation, reflectivity of cavity reflectors, and phosphor concentration are studied. Simulation as well as the corresponding experiment shows that reflectivity of the reflectors in packaging cavity is more effective than lens encapsulation to reach high efficiency. Besides, a white LED packaging without lens encapsulation but with high reflectivity of cavity reflectors may increase interaction possibility between blue photons and the phosphor so that the phosphor concentration can be reduced to meet the requested correlated color temperature.

Study on phosphor sedimentation effect in white light-emitting diode packages by modeling multi-layer phosphors with the modified Kubelka-Munk theory

In this study, we studied the phosphor sedimentation effect in white phosphor-converted light-emitting diode packages by modeling the multi-layer phosphors with gradient concentrations. The essence of phosphor sedimentation can attribute to the variation of phosphor concentrations. By modifying the Kubelka-Munk theory, we built a multi-layer phosphor model with considering the light scattering, light absorption, and light conversion process simultaneously. With a brief review of Kubelka-Munk theory, multi-layer phosphors were modeled on the basis of single-layer phosphor model. The phosphor sedimentation effect was characterized by modeling multi-layer phosphors with gradient concentrations, whereas keeping the total amount of phosphors at the same level. It is found from the five calculation cases that phosphor sedimentation will cause the drop of light extraction efficiency (LEE) by 13.04%. Furthermore, the phosphor layer with inverse-gradient concentrations will enhance the LEE 16.56%. To figure out the reasons, the light losses were calculated, and it is proved that the light loss is enhanced when phosphor sedimentation happens.

Optical constants study of YAG:Ce phosphor layer blended with SiO2 particles by Mie theory for white light-emitting diode package

Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets (YAG:Ce) phosphor blended with SiO2 particle for white light-emitting diode (LED) packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction (or concentration) will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.

On the Adjustment of the Color Temperature of White Light-Emitting Diodes by Femtosecond Laser Patterning

We show that femtosecond (fs) laser microstructuring of light-emitting diode (LED) encapsulates has a high potential for the fine-tuning of the color temperatures of white LED packages. The number of scattering centers that are fabricated within the volume of the encapsulate allows the precise adjustment of the color temperature of the device to the desired value. This opens possibilities to achieve color reproducibility among individual LED packages with highest accuracy.

Measurement and numerical studies of optical properties of YAG:Ce phosphor for white light-emitting diode packaging

The optical properties of YAG:Ce phosphor were measured by a double-integrating-sphere system and calculated by Mie theory and Monte Carlo ray tracing to provide precise optical characterizations of YAG:Ce phosphor for white light-emitting diode (LED) packaging design. Measurement results showed that the phosphor presents strong absorption for blue light, high reflection for yellow light, and an isotropic emission pattern of converted light. The conversion efficiency and quantum efficiency for the saturated phosphor are around 70% and 87%, respectively. Based on the measurement results, the absorption coefficient, scattering coefficient, and anisotropy factor of the phosphor calculated by Mie theory were compared with those calculated by ray-tracing simulation to modify Mie theory to find a reasonable method that can easily obtain the optical constants of YAG:Ce phosphor. Comparisons revealed that Mie theory can predict the variation of the optical constants of phosphor, but the absorption and scattering cross sections should be multiplied with two fitting parameters. The fitting parameters have been given in this study and can be obtained by testing packaged LEDs with different phosphor concentrations.