Regulating anti-thermal quenching to zero thermal quenching for highly efficient blue-emitting Eu2+-doped K-beta-alumina phosphors

Abstract

High quantum efficiency and high thermal stability have always been two indicators to measure whether phosphors have excellent luminescence performance. In this paper, a series of blue-emitting K-beta-alumina phosphors K_0.90−xSr_xAl₁₁O_17+d:0.2Eu²⁺ were successfully synthesized by introducing Sr²⁺ to partially replace K⁺ ions. The internal and external quantum efficiencies can be improved to 92.4 and 73.4%, respectively, for x = 0.06 with the introduction of Sr²⁺. More importantly, the anti-thermal quenching properties of the original phosphor (without Sr²⁺) can be successfully regulated to zero thermal quenching within 150 °C by partially replacing K⁺ with Sr²⁺. Thermoluminescence spectra suggest that the introduction of Sr²⁺ reduces the content of shallow traps related to V_O and increases the deep traps related to V_K. The introduction of Sr²⁺ is accompanied by the decrease of the (K,Sr,Eu)/Al ratio, which leads to the weakening of structural rigidity. As a result, the dynamic equilibrium between the non-radiative process and the anti-thermal quenching process facilitates the zero thermal quenching. A phosphor-converted light-emitting diode (pc-LED) with a high color rendering index (CRI = 91.6) and low correlated color temperature (CCT = 5108 K) also shows the great potential of this phosphor in white pc-LEDs.