Novel highly efficient Bi3+-activated phosphors for warm WLEDs

Abstract

In this paper, novel Bi³⁺-activated Ca₂LuZrScAl₂GeO₁₂ (CLZSAG) phosphors with a garnet structure were prepared by a high temperature solid-state method. There are two kinds of luminescent centers in the CLZSAG:Bi³⁺ phosphors, which exhibit a blue emission under 365 nm excitation and a rare near-ultraviolet emission with a narrow band (FWHM = 34 nm) under 290 nm excitation. The combination of the structure and luminescence reveals that the Bi³⁺ ions occupy the sites of the LuO₈ and ScO₆ polyhedra with different local coordination environments, leading to two different luminescence behaviors. In addition, the prepared phosphors also have excellent thermostability (I_423K/298K = 80%), and high quantum efficiencies of 72% and 60% under 290 and 365 nm excitation, respectively. Since the absorption band of the phosphor in the UV-visible region can match well with the commercial 365 nm chips, a high-performance WLED device with a high color rendering index (R_a = 98.5) and a low correlated color temperature (CCT = 4455 K) was obtained by combining commercial phosphors Lu-YAG:Ce³⁺ and CaAlSiN₃:Eu²⁺ and samples of the CLZSAG:Bi³⁺ phosphor with 365 nm chips. Our results demonstrate that CLZSAG:Bi³⁺ has great potential application in WLED devices.