A thermally stable color-tunable white phosphor CaGa0.5Nb0.5O3: Dy3+/Sm3+ for warm WLEDs

Abstract

Rare-earth-doped double perovskite phosphors often exhibit excellent lumines-cent properties, high color rendering, and stability. However, there is little research on Dy³⁺-doped double perovskite white phosphors. Additionally, the white luminescence of Dy³⁺ ions has drawbacks such as high color temperature and low color ren-dering index. These drawbacks can often be improved by selecting appropriate co-doping ions such as Sm³⁺, which can be excited by ultraviolet and near-ultraviolet light to achieve good orange-red emission. Therefore, we synthesized a novel double perovskite phosphor CaGa₀.₅Nb₀.₅O₃ (CGNO): Dy³⁺/Sm³⁺ using the high-temperature solid-state method. The properties of the phosphors, such as crystal structure, elemental composition, absorption spectra, photoluminescence spectra, thermal stability, and CIE chromaticity coordinates, fluorescence lifetimes and quantum yield, were investigated in detail. It was found that the CGNO: 0.04Dy³⁺ phosphor and CGNO: 0.04Dy³⁺, 0.05Sm³⁺ phosphor were pure phase compounds with a particle size of about 5 μm. Under excitation at 351 nm or 363 nm, two prominent peaks of Dy³⁺ emerge around 481 nm and 575 nm, in that order. In this co-doped phosphor CGNO: 0.04Dy³⁺, 0.05Sm³⁺, the correlated color temperature (CCT) value decreases and the color purity increases with the concentration of Sm³⁺ ions increasing, and the tones of the white light emitted are gradually becoming mild and warm from a single cold. Fluorescence lifetime fitting indicates that energy transfer occurs between Dy³⁺ and Sm³⁺ through dipole-dipole interactions. The low chromaticity shift and low luminescence attenuation indicate that both phosphors have very stable luminescence and color performance at high temperatures, and using 365 nm InGaN chip excitation, the CGNO: 0.04Dy³⁺ phosphor and the CGNO: 0.04Dy³⁺, 0.05Sm³⁺ phosphor emit white light with CCT values of 3480 and 2893 K respectively, which have the potential to be applied to indoor lighting.