Influence of temperature on near-infrared luminescence, energy transfer mechanism and the temperature sensing ability of La2MgTiO6: Nd3+ double perovskites

Abstract La2MgTiO6: Nd3+ samples synthesized by the coprecipitation method crystallized in an orthorhombic phase with space-group Pbnm (62). The SEM images of the sample showed heterogeneous morphology and the average crystallite size was 0.7 μm. Luminescent spectra, typical for Nd3+ ions at low symmetry site (Cs), were observed in all samples excited at 266 nm and 808 nm. The highest emission intensity was obtained for the sample doped with 3% Nd3+. The emission lifetimes at 77 K and 300 K shorten with increasing Nd3+ concentration due to cross-relaxation processes. Noticeably, the lengthening of the decay times at 300 K, as compared to 77 K, resulted from the thermalization of the higher Stark component of the 4F3/2 level. In addition, the experimental data were analysed using the Inokuti – Hirayama model; the energy transfer between Nd3+ ions was predominantly regulated by the dipole–dipole interaction. The critical transfer distance R 0 , critical concentration C 0 , energy transfer parameter C d a , and energy transfer probability W d a were found to be 4.9 A , 2 × 10 21 ions∙cm−3, 5.67 × 10 - 41 cm6∙s-1, and 4004 s-1, respectively. Furthermore, the temperature–dependent luminescence exhibited good thermal stability with temperature quenching at 450 K. The temperature sensing ability of the sample doped with 5 % Nd3+, based on the emission of two thermally coupled 4F5/2 and 4F3/2 levels, was investigated. The highest value of the relative sensitivity was 0.81 and 0.83 % K-1 at 248 K and 275 K, respectively.