Thermally stable and highly efficient red-emitting Eu 3+-doped Cs 3 GdGe 3 O 9 phosphors for WLEDs: non-concentration quenching and negative thermal expansion

Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 − xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1–1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175–250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = −5.06 × 10−5/°C, 25–250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials. A luminescent material that undergoes an unusual heat-shrinking process shows promise for enhancing the efficiency of white light-emitting diodes (LEDs). Current technologies for generating white LEDs often combine near-ultraviolet light with background radiation from red, green, and blue phosphors. J.L. from China’s Changchun Institute of Applied Chemistry and colleagues have now developed a red phosphor that remains active at temperatures which shut down other red-light emitters. The team’s compound, a cesium-based metal oxide doped with rare earth ions, has a crystal structure that contracts upon heating and avoids symmetry-distorting effects associated with thermal quenching. This unique structure also supports higher dopant concentrations than typical phosphors for improved colour rendering in prototype white LEDs. A highly efficient red-emitting Cs3EuGe3O9 phosphor for high-performance pc-WLEDs is discovered with non-concentration quenching, favourable thermal stability, high colour purity and negative thermal expansion.