Enhancement of luminescence properties of Ca₂Al₂SiO₇: Eu³⁺ red phosphors by Li⁺, Na⁺, K⁺, Mg²⁺ charge compensators

Rare-earth doped Ca2Al2SiO7 (CAS) phosphors have been widely investigated due to their luminescent properties and low price. However, the luminescence intensity and thermal stability of CAS based phosphors are still not favorable due to rare-earth doping induced vacancies. In this study, to compensate the Ca2+ vacancies by charge unbalanced substitution of Eu3+ in Ca2Al2SiO7: 0.07Eu(3+) phosphor, a series of Ca2Al2SiO7: 0.07R, 0.07Eu(3+) (RLi+, Na+, K+, Mg2+) phosphors with charge compensators are prepared by sol-gel method. The effects of different charge compensators Li+, Na+, K+, Mg2+ on the phase purity, surface morphology, luminescence properties and thermal stability of the CAS: 0.07Eu(3+) phosphors are investigated. It is found that the structures and microstructures of the phosphors are seldom influenced by the co-doped charge compensators R, while the photoluminescence properties are strongly reinforced. Compared with the uncompensated phosphor, all R co-doped samples exhibit remarkable enhancement on luminescence intensity. Among them, Mg2+ compensated phosphor demonstrates the largest enhancement effect with intensity up to 4 times of uncompensated sample. CAS: 0.07 Mg2+, 0.07Eu(3+) exhibits a good color purity (87%) with chromaticity coordinates (0.6454, 0.3542), which is very close to the standard red light. Furthermore, the luminous intensity can maintain 76.1% of the initial intensity at 438 K, indicating its excellent thermal stability. These results indicate that charge compensated CAS: Eu3+ phosphors can be used as a candidate material for red phosphor in white LED.