Adjusting the luminescence properties by the substitution of alkali metal ions in MGd9(SiO4)6O2:Dy3+: Preparation, DFT calculation and optical properties

Abstract

A series of Dy3+-doped MGd9(SiO4)6O2:Dy3+ (M = Li, Na, K) phosphors that generated white emission were prepared using the high temperature solid-state technique. Simultaneously, the phase composition, crystal structure, electronic structure, as well as the luminescence properties of the as-prepared phosphors were investigated in detail. The structural refinement showed that the MGd9(SiO4)6O2 crystallized with the hexagonal apatite-type structure. The unit cell parameters increased gradually and the main peaks of the samples in XRD patterns shifted towards high angles with the substitution of alkali-metal ions (from Li+ to K+). Under the excitation of 350 nm, the as-obtained MGd9(SiO4)6O2:Dy3+ phosphors gave bright white emission with the major emission peaks centering at 454, 477 and 573 nm. And the Ry/b, CIE chromaticity coordinate and the corrected color temperature (CCT) of the phosphors were adjusted from 0.96, (0.3256, 0.3625) and 4602 K to 1.13, (0.3369, 0.3582) and 4201 K attributing to the substitution in the crystal structure. The thermoluminescence study of MGd8.90(SiO4)6O2:0.10Dy3+ (M = Li, Na, K) showed good stability and the decay lifetimes of the samples were estimated to be about 470 μs. All the results suggested that the luminescence properties could be modified by the substitution of alkali metal ions, and the MGd9(SiO4)6O2:Dy3+ (M = Li, Na, K) phosphors have potential application as white emission candidate for w-LEDs.