CaSi₂O₅:Sm³⁺ Orange -Red Emitting Phosphors for Latent Fingerprint Detection Application

Orange-red emitting CaSi₂O₅:xSm³⁺ (x = 0.1, 0.2, 0.5, 1, 1.5, 2, and 2.5 mol% of Sm³⁺) phosphors were synthesized by a high-temperature solid-state reaction. In this study, the crystal structure, phase purity, functional group presence, and their bending and stretching vibrations, photoluminescence (PL) spectra, thermoluminescence (TL) spectra, and colour purity was systematically investigated. The phosphor exhibits a strong excitation with the charge transfer band (CTB) of O^2- and Sm³⁺ at 263 nm. Under 263 nm excitation, the CaSi₂O₅:Sm³⁺ phosphor shows characteristic peaks at 595 nm and 629 nm, which are attributed to the characteristic ⁴G_5/2→⁶H_7/2 and ⁴G_5/2→⁶H_9/2 transitions of the Sm³⁺ ions, respectively. The doping concentration x = 2 mol% is found to be the optimal doping concentration. The CIE coordinates of the optimal concentration phosphor CaSi₂O₅:2Sm³⁺ are found to be (0.589, 0.41) in the orange-red region with a colour purity percentage of 96.93%. Judd-Ofelt analysis was also carried out with the photoluminescence emission spectrum, in order to investigate the transition dynamics. Fingerprints were developed on non-porous glass and aluminium foil substrates. The experimental results display that the CaSi₂O₅:xSm³⁺ phosphors have a huge potential for practical applications.