Luminescence and temperature properties of Y2O3: Ho3+/Yb3+ millimeter crystals obtained by laser annealing

FIR temperature measurement based on thermally coupled levels of rare earth ions has been widely studied, but its sensitivity is limited by the thermal coupling levels' spacing. In this letter, a transition from non-thermally coupled levels of Ho3+ to thermally coupled levels is reported for the first time. It can effectively improve the sensitivity of temperature measurement based on thermal coupling levels. The Ho3+/Yb3+ co-doped Y2O3 millimeter crystals have been prepared by laser annealing. The fluorescence properties of laser-annealed Ho3+/Yb3+ co-doped Y2O3 millimeter crystals were investigated as a function of temperature. It was found that the I-667nm/I-549nm show non-thermal coupling below 453K, but changes to thermal coupling above 453K. The maximum relative sensitivity of I-667nm/I-549nm in thermal coupling is greater than the relative sensitivity of any known thermal coupling energy levels of Ho3+. It provides a new way to improve the sensitivity of thermally coupled FIR temperature measurement.