Thermal enhancement of up-conversion luminescence in Lu2W2.5Mo0.5O12: Er3+, Yb3+ phosphors

Lu2W2.5Mo0.5O12: Er3+/Yb3+ phosphors were synthesized through high temperature solid state method. Under 980 nm laser excitation, the Lu2W2.5Mo0.5O12: Er3+/Yb3+ compounds show thermal enhancement of up-conversion luminescence (UCL), which is attributed to the lattice contraction and distortion from negative thermal expansion (NTE) of Lu2W2.5Mo0.5O12 host enhancing the energy transfer of Yb3+ to Er3+, eliminating the energy transfer of Er3+ to Er3+ through Er3+ single-doped Lu2W2.5Mo0.5O12 phosphors without thermal enhancement of UCL. The green luminescence intensities at 693 K of the Lu1.98-xW2.5Mo0.5O12: 0.02Er3+, xYb3+ (x = 0.2, 0.3, 0.4) samples are 4.6, 4.3 and 7.0 times as that of 302 K, respectively. And through fluorescence intensity ratio (FIR) technique, the corresponding maximum absolute sensitivities are 0.00741, 0.00744 and 0.00723, respectively. The green monochromaticity of UCL spectra in Er3+/Yb3+ co-doped samples increase with the increasing of temperature, and the possible UCL mechanism with temperature was discussed. The results indicate that the Lu2W2.5Mo0.5O12: Er3+/Yb3+ phosphors can be applied at a high temperature as optical thermometer with a good green monochromaticity.