Synthesis, structural characterization, and photoluminescence properties of Dy<SUP>3+</SUP>-Doped CaB₄O₇ Phosphors: Influence of Li<SUP>+</SUP> and K<SUP>+</SUP> Co-doping

This study examines the structural and photoluminescence properties of Dy3+-doped CaB4O7 phosphors co-doped with Li+ and K+, synthesized via the high-temperature solid-state reaction method. X-ray diffraction (XRD) and Rietveld refinement confirmed the successful incorporation of Dy3+ (substituting for Ca2+), Li+ (interstitial), and K+ (interstitial) ions within the CaB4O7 lattice at co-doping concentrations of x = 0.02 wt percent (wt%), y = 0.05 wt%, and z = 0.10 wt%, respectively. This co-doping induced localized lattice distortions while maintaining the overall crystal symmetry. Fourier-transform infrared (FTIR) and Raman spectroscopy reveal modifications in borate network vibrational modes, indicating the stabilizing effects of Li+ and K+ co-doping. Photoluminescence (PL) analysis demonstrates an unusually intense red emission (4F9/2 -> 6H11/2), deviating from typical Dy3+ emission trends, which is attributed to local symmetry distortions and enhanced electric dipole transitions. JuddOfelt analysis confirms a high Omega 6 parameter (5.42 x 10-20 cm2), further supporting this enhancement. Li+ co-doping significantly enhances PL, increasing yellow emission by a factor of 7.64 and red emission by 4.03. Similarly, K+ co-doping influences the crystal field environment, leading to a 6.36-fold boost in yellow luminescence and a 3.60-fold increase in red luminescence. Temperature-dependent PL studies reveal an anti-thermal quenching effect, with red emission intensity increasing up to 550 K, indicating potential applications in high-temperature environments. The findings demonstrate that Li+ and K+ co-doping modulates the emission characteristics of Dy3+-doped CaB4O7, reinforcing its applicability in solid-state lighting and optoelectronic devices.