Optical behaviors of Mn-modified cubic type ZnTiO:Eu nanocrystals: Application in optical thermometers based on fluorescence intensity ratio and lifetime.

Cubic type ZnTiO nanophosphors were fabricated by using hydrothermal method. The photoluminescence behaviors of Eu/Mn co-doped ZnTiO crystals and Mn-modified ZnTiO:Eu crystals were investigated. The red and near-infrared emissions assigned to Eu and Mn were observed at the excitation wavelength of 465 nm for Eu/Mn co-doped ZnTiO crystals and Mn modified ZnTiO:Eu crystals. Eu/Mn co-doped ZnTiO crystals revealed the most intense near-infrared emission assigned to Mn. For Mn-modified ZnTiO:Eu crystals, the red emissions assigned to Mn revealed an obvious enhancement with the concentration of Mn increasing from 0.01 mol% to 0.1 mol%, and then revealed a concentration quenching behavior at the Mn concentration of 0.5 mol% and 1 mol%. Under 465 nm excitation wavelength, the emission assigned to E → A of Mn in ZnTiO revealed stronger temperature dependence compared with that assigned to D → F transition of Eu. Based on the fluorescence intensity ratio between Eu and Mn, the maximum relative sensitivity of 3.15 %/K at 305 K for the 0.05 mol% Mn modified ZnTiO:Eu was achieved, which was higher than that of 2.9 %/K for Eu/Mn co-doping ZnTiO nanocrystals. Based on the lifetime of the emission of Mn, the highest relative sensitivity of 1.4 %/K was obtained in the 0.05 mol% Mn modified ZnTiO:Eu, 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.