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 R0, critical concentration C0, energy transfer parameter Cda, and energy transfer probability Wda were found to be 4.9 Å, 2×1021 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.