Optical properties and thermal stability of LiYGeO4: Pr3+ red phosphor for solid-state lighting

The red-emitting phosphor LiYGeO₄: Pr³⁺ was synthesized by a conventional high-temperature solid-state reaction. Various analytical techniques were employed to investigate its properties, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), photoluminescence spectroscopy, and afterglow decay measurements. Density functional theory (DFT) calculations were conducted to examine the energy band structure, density of states, and pressure-dependent optical properties. Under 480 nm excitation, LiYGeO₄: Pr³⁺ shows a broad emission band covering 500–660 nm, with the most intense red emission at 599 nm originating from the ¹D₂→³H₄ transition of Pr³⁺. The luminescence intensity remained 65.56 % of its initial value at a temperature of 423 K. Fluorescence intensity ratio (FIR) analysis demonstrated excellent optical thermometric performance with a maximum relative sensitivity of 2.6 % K⁻¹ at 298 K. DFT calculations indicate that Pr³⁺ doping narrows the bandgap of the host lattice and enhances electron transition probabilities. Moreover, the optical absorption coefficient shows pressure dependence, suggesting potential applications in pressure-tunable optoelectronic devices. These findings establish LiYGeO₄: Pr³⁺ as a promising candidate for blue-light-excited solid-state lighting and pressure-sensitive photonic applications.