Charge compensation-driven downconverted luminescence enhancement in Er³⁺-doped SrTiO₃ phosphors by co-doping with alkali ions (M⁺ = Li, Na, K) for solid-state lighting applications

In this study, we synthesized near-ultraviolet (n-UV) excitable green-emitting SrTiO₃: x Er³⁺ (1% ≤ x ≤ 6%) phosphors using the solution combustion method. To address charge compensation issues, alkali metal ions (Li⁺, Na⁺, and K⁺) were co-doped into the SrTiO₃: 3%Er³⁺ phosphor. Characterization of the synthesized phosphor included phase identification and morphology analysis using powder X-ray Diffraction and field emission scanning electron microscopy, respectively. Additionally, fourier transform infrared spectroscopy was employed for vibrational studies. Photoluminescence (PL) emission spectra revealed green emission attributed to the transitions of Er³⁺ ions. Concentration quenching was observed beyond a 3 mol % doping level, and Dexter’s theory was applied to elucidate the interaction mechanisms responsible for this phenomenon. Lifetime studies were conducted on the synthesized phosphors to evaluate various decay parameters. An enhancement in PL emission due to charge compensation was observed when SrTiO₃:Er³⁺ was co-doped with alkali metal ions such as Li⁺, Na⁺, and K⁺. Maximum PL emission was observed in SrTiO₃: 3% Er³⁺, 3% Na⁺ phosphor. Color coordinates (CIE coordinates) were determined for SrTiO₃:Er³⁺ and SrTiO₃:Er³⁺, Na⁺ phosphors. The observed high color purity (~ 80%) suggests that the synthesized phosphor could be effectively used as a green component in solid-state lighting applications.