Structural and luminescence properties of alkali-co-doped LiCaBO3: Dy3+ phosphors

Abstract

Dysprosium (Dy3+)-doped lithium calcium borate (LiCaBO3, LiCOB) phosphors were synthesized via a sol–gel combustion route and systematically investigated with respect to their structural, vibrational, and luminescence characteristics, with emphasis on the role of alkali co-doping (Na+, K+). XRD with Rietveld refinement confirmed the orthorhombic phase formation, indicating that Dy3+ ions substitute Ca2+ sites, while alkali co-doping provided effective charge compensation and mitigated lattice strain. FTIR and Raman analyses verified the preservation of the borate framework, with Na+ yielding more efficient structural stabilization than K+. Photoluminescence spectra revealed the characteristic Dy3+ blue ( 4 F9/2 → 6 H15/2) and yellow ( 4 F9/2 → 6 H13/2) emissions, enabling quasi-white light generation. The emission intensity was maximized at 2 wt% Dy3+, with quenching beyond this level governed by dipole–quadrupole interactions, as confirmed by Dexter analysis. Alkali co-doping significantly enhanced PL output, with Na+ producing stronger and more stable emission than K+ due to superior charge compensation. Judd–Ofelt analysis based on emission spectra yielded Ω2, Ω4, and Ω6 parameters consistent with experimental lifetimes, demonstrating that Na+ co-doping promotes red-shifted transitions via enhanced Ω6, whereas K+ favors yellow emission through Ω2 enhancement. Remarkably, temperaturedependent PL studies showed anomalous thermal enhancement in Dy3+-only samples, while Na+/K+ co-doped systems exhibited trap-assisted recovery with low activation energies (0.21–0.22 eV), indicating excellent thermal stability. Chromaticity coordinates confirmed tunable near-white emission, underlining the potential of alkali-modified LiCOB:Dy3+ phosphors not only for solid-state lighting but also for future radiation detector applications.