Optical behaviors of Mn4+-modified cubic type ZnTiO3:Eu3+nanocrystals: Application in optical thermometers based on fluorescence intensity ratio and lifetime

Cubic type ZnTiO3 nanophosphors were fabricated by using hydrothermal method. The photoluminescence behaviors of Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+-modified ZnTiO3:Eu3+ crystals were investigated. The red and near-infrared emissions assigned to Eu3+ and Mn4+ were observed at the excitation wavelength of 465 nm for Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+ modified ZnTiO3:Eu3+ crystals. Eu3+/Mn4+ co-doped ZnTiO3 crystals revealed the most intense near-infrared emission assigned to Mn4+. For Mn4+-modified ZnTiO3: Eu3+ crystals, the red emissions assigned to Mn4+ revealed an obvious enhancement with the concentration of Mn4+ increasing from 0.01 mol% to 0.1 mol%, and then revealed a concentration quenching behavior at the Mn4+ concentration of 0.5 mol% and 1 mol%. Under 465 nm excitation wavelength, the emission assigned to 2Eg -> 4A2g of Mn4+ in ZnTiO3 revealed stronger temperature dependence compared with that assigned to 5D0 -> 7F2 transition of Eu3+. Based on the fluorescence intensity ratio between Eu3+ and Mn4+, the maximum relative sensitivity of 3.15 %/K at 305 K for the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+ was achieved, which was higher than that of 2.9 %/K for Eu3+/Mn4+ co-doping ZnTiO3 nanocrystals. Based on the lifetime of the emission of Mn4+, the highest relative sensitivity of 1.4 %/K was obtained in the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+, which was lower than that based on fluorescence intensity ratio. It indicated that the surface modification by transition metals should improve the temperatures sensing performance and had potential applications in optical thermometers.