Insight into Cr3+-activated NIR phosphor with extremely high thermal stability for NIR LEDs

Recently, Cr 3+ -activated near-infrared (NIR) phosphors have been widely explored and used in many fields because of the good photoluminescence (PL) properties. However, their luminous efficiency usually decreases obviously with increasing temperature, which is a major barrier to practical application. In this study, CaLu 2 Ga 4 GeO 12 :Cr 3+ with broadband NIR emission is synthesized, but it shows poor thermal stability ( I 425 K =42.4 %). To improve the thermal quenching performance, a series of Ca 1-x Lu 2+x Ga 4+x Ge 1-x O 12 :Cr 3+ solid solution is proposed. The energy difference between 4 T 2 and 2 E states is calculated to show an increasing trend with the increase of crystal field strength , which is conductive for the thermal population of 2 E state. Besides the crystal field strength, the Cr 3+ concentration also shows a great influence on the electron occupation between 4 T 2 and 2 E energy levels. Under the optimal conditions, the thermal stability of the sample is significantly improved and the PL intensity reaches as high as 128.9 % at 425 K compared with that at room temperature (RT). Phosphor-converted light-emitting diodes (pc-LEDs) are fabricated with the thermally stable NIR phosphors, which show great promise in the fields of key information identification and nondestructive detection. This work may provide some guidelines for the design of NIR phosphors with improved thermal stability. • Ca 1-x Lu 2+x Ga 4+x Ge 1-x O 12 :Cr 3+ solid solution with controllable thermal quenching performance is synthesized. • The energy difference between 4 T 2 and 2 E states is calculated. • The PL intensity reaches as high as 128.9 % at 425 K compared with that at room temperature.