Up-conversion luminescence properties and temperature sensing behavior of Nd3+/Yb3+/Tm3+ triply doped LaNbO4 phosphors under 808 nm and 980 nm excitations

LaNbO4: Nd3+/Yb3+/Tm3+ phosphors were synthesized via a solid-state reaction method. Under both 808 nm and 980 nm excitations, the effects of Tm3+ concentration and temperature on the up-conversion luminescence properties of Tm3+ were investigated. From the excitation power densities dependent up-conversion emission intensities, it was confirmed that the up-conversion luminescence process of Tm3+ was insensitive to sample temperature within the temperature range we studied. Under the excitations of 808 nm and 980 nm, both blue and red up-conversion emissions of Tm3+ kept two-photon and three-photon processes at various temperatures. And the near-infrared (NIR) up-conversion emission of Tm3+ was two-photon process when excited at 980 nm. Variation of the fluorescence intensity ratio (FIR) based upon the two thermally coupled energy levels 3F2,3 and 3H4 of Tm3+ with temperature was investigated and the temperature sensing behavior of Tm3+ was studied under 980 nm excitation. In the temperature range from room temperature to 663 K, the absolute temperature sensitivity of Tm3+ increases monotonously with the elevation of temperature, and the maximum value was obtained to be 3.702 × 10-4 K-1 at 663 K.