Effect of charge compensation on the photoluminescence and thermal stability of trivalent samarium-doped calcium barium phosphate phosphors

A series of Ca₆BaP₄O₁₇:Sm³⁺ phosphors without or with different charge compensation approaches (co-doping Li⁺ or Na⁺ ions) were synthesized by using a conventional solid-state reaction method. The crystal structure and morphologies of the phosphors were investigated by using X-ray diffraction pattern and scanning electron microscope after synthesizing the phosphor, respectively. The luminescence and spectral properties were studied by photoluminescence and diffuse reflectance spectroscopy. By introducing the charge compensator alkali metal ions A⁺ (A = Li and Na) into the lattice of Ca₆BaP₄O₁₇:Sm³⁺ phosphor, its emission intensity can be enhanced. The phosphors under 405 nm excitation show characteristic emission of Sm³⁺ ion with the main orange–red peak centered at 602 nm. The results suggested that the Li⁺ ion is a good charge compensator in Ca₆BaP₄O₁₇:Sm³⁺ phosphors due to its enhancement in luminescence and as a flux for improving the morphology of phosphors. The calculated CIE coordinates and color purity of phosphors with charge compensation of optimal Li⁺ ions co-doping concentration are (0.6090, 0.3892) in the orange–red region of the spectrum and ~ 99.5% under 405 nm excitation. Besides, the thermal stability of proposed samples can be improved from 84% to 93% which is pretty high compared with published data. The mechanism is detailed in this paper.