Chromaticity-tunable phosphor-in-glass for long-lifetime high-power warm w-LEDs

Abstract

The commercially dominant phosphor-converted illumination white light-emitting-diodes (w-LEDs) generally suffer from red deficiency and the poor thermal stability of the organic encapsulants, resulting in cool white light, luminous degradation and chromatic aberration for the embedded YAG:Ce³⁺ phosphors after long-term working. Aiming to solve these problems, herein, a chromaticity-tunable robust phosphor-in-glass (PiG) inorganic color converter was successfully fabricated by co-sintering YAG:Ce³⁺,Mn²⁺,Si⁴⁺ phosphor particles and the innovatively-designed TeO₂–B₂O₃–ZnO–Na₂O–Al₂O₃ low-melting precursor glass. At first, the spectrally-modified YAG:Ce³⁺,Mn²⁺,Si⁴⁺ phosphor was prepared by doping Mn²⁺ as the red emitter and doping Si⁴⁺ as the charge compensator through a solid-state reaction route. Then, the YAG:Ce³⁺,Mn²⁺,Si⁴⁺ powder was incorporated into a specifically prepared precursor glass to form the PiG composite at 550 °C. Owing to the density and the refractive index matches for the phosphor particles and the glass matrix, the particle dispersion in PiG is quite homogeneous and the adverse light-scattering is depressed. The high-power warm w-LED was constructed by coupling a PiG plate with an InGaN blue chip. Remarkably, the chromaticity coordinate of such a w-LED can be well tuned to follow along the Planckian locus with the correlated color temperature evolving from cool white (5541 K) to warm white (3050 K) and a color rendering index around 70, under a driving current of 350 mA. Moreover, the PiG-based warm w-LED presents much superior thermal stability to the traditional phosphor-in-silicone (PiS)-based one. This work highlights the practical applications of the PiG luminescent material in the long-lifetime high-power warm w-LEDs.