Microstructural characteristics and luminescence behavior of Tm ³⁺ /Dy ³⁺ co-activated LiCaPO ₄ phosphors

Tm3+- and Dy3+-activated LiCaPO4 phosphors were synthesized to evaluate their structural characteristics and photoluminescence behavior under near-UV excitation for potential solid-state lighting applications. X-ray diffraction analysis confirmed the formation of a single-phase LiCaPO4 lattice, indicating that the host structure remains stable upon incorporation of rare-earth ions, while crystallite size and lattice strain estimated using multiple analytical models consistently revealed nanocrystalline dimensions with low internal strain, reflecting good crystallinity of the prepared samples. FTIR spectroscopy verified the preservation of the phosphate framework after doping, and SEM coupled with elemental analysis showed a relatively uniform particle morphology along with successful incorporation of Tm³+ and Dy³+ ions without detectable impurity phases. Photoluminescence measurements under near-UV excitation exhibited intense blue emission from Tm³+ ions and characteristic blue and yellow emissions from Dy³+ ions; in the co-doped compositions, a gradual reduction in Tm³+ emission accompanied by a systematic enhancement of Dy³+ emission was observed with increasing Dy³+ concentration, suggesting efficient non-radiative energy transfer between the dopant ions. This energy transfer process resulted in tunable emission characteristics, as evidenced by a continuous shift of the CIE chromaticity coordinates toward the yellow-red region with increasing Dy³+ content. These findings demonstrate that LiCaPO4 provides a structurally robust and chemically stable host lattice for Tm³+/Dy³+ co-doping and support the potential of these phosphors for near-UV-pumped LED applications.