Temperature sensor based on the UV upconversion luminescence of Gd3+ in Yb3+-Tm3+-Gd3+ codoped NaLuF4 microcrystals

Optical temperature sensing characteristics based on the ultraviolet (UV) upconversion luminescence (UCL) of Gd3+ ions are reported here for the first time. Under 980 nm excitation, the temperature dependence five-photon UV UCL from the P-6(J) and I-6(J) levels of Gd3+ ions in NaLuF4:Yb3+, Tm3+, Gd3+ microcrystals were investigated systematically. The fluorescence intensity ratios (FIR) of two pairs of thermally coupled levels (P-6(5/2), P-6(7/2) and I-6(9/2), I-6(7/2)) were studied as a function of temperature in a range of 298-523 K. The maximum sensor sensitivities were found to be about 0.0004 K-1 (333 K) and 0.0029 K-1 (298 K) by exploiting the UC emissions from the P-6(J) and I-6(J) levels, respectively. This suggests that the Gd3+-based UCL materials are promising prototypes for application as multi-mode probes for use in bio-separation, MRI imaging, optical thermometers, etc.