Exploring structural, optical and temperature-dependent luminescence features of UVC-emitting Sr₂Al₂SiO₇: Pr³⁺ Phosphors for temperature sensing applications

The article examines the structural, luminescent, and temperature-dependent emission properties of UVC-emitting Sr₂Al₂SiO₇: Pr³⁺ phosphors, which were synthesised using the combustion method. X-ray diffraction (XRD) analysis confirmed the formation of a tetragonal crystal structure with the P-421 m space group. Characteristic vibrational modes of SiO₄, Sr-O, and AlO₄ were identified using Fourier-transform infrared (FTIR) spectroscopy, confirming the structural framework of the host lattice. Surface morphological studies indicated a non-uniform and irregular microstructure. Energy-dispersive X-ray (EDAX) analysis confirmed the successful incorporation of the elements: Sr, Al, Si, O, and Pr. Photoluminescence (PL) studies revealed a prominent UVC emission peak at 315 nm, with an additional shoulder peak at 280 nm. These emissions are attributed to the 4f⁵5d¹→ ³F₂, and ³H_J (J = 4, 5, 6) transitions of Pr³⁺ ions. The optimal dopant concentration was determined to be 2 mol%; concentrations exceeding this value resulted in concentration quenching attributed to dipole-dipole interaction between the dopants. Temperature-dependent photoluminescence studies revealed a gradual decrease in emission intensity as the temperature increased, maintaining approximately 70% of the initial intensity at 498 K, indicating significant thermal stability. The activation energy (ΔE) for thermal quenching was determined to be 0.1856 eV, along with a high quenching temperature (T_Q = 394 K). The optical thermometric performance of Sr₂Al₂SiO₇: Pr³⁺ was assessed through fluorescence intensity ratio (FIR) analysis, resulting in maximum absolute and relative sensitivities of (S_A)_max = 7.8 × 10⁻⁴ K⁻¹and (S_R)_max = 0.068 % K⁻¹ at 498 K, respectively. This study elucidates the temperature-sensitive luminescent features of Pr³⁺-activated Sr₂Al₂SiO₇ and identifies it as a viable candidate for high-temperature optical thermometry and photonic device applications.