Synthesis, structural characterization, and photoluminescence properties of Dy3+-Doped CaB4O7 Phosphors: Influence of Li+ and K+ 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 (⁴F_9/2 → ⁶H_11/2), deviating from typical Dy³⁺ emission trends, which is attributed to local symmetry distortions and enhanced electric dipole transitions. Judd-Ofelt analysis confirms a high Ω₆ parameter (5.42 × 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.