The effect of temperature on green and red upconversion emissions of LiYF4:20Yb3+, 1Ho3+ and its application for temperature sensing

Optical thermometry is a non-contact temperature detective technique that has high sensitivity and rapid response. In present work, we developed LiYF4:20Yb3+, 1Ho3+ (mol%) micro octahedrons obtained by a modified hydrothermal method. The temperature dependent up-conversion (UC) emission and luminescence decays for LiYF4:20Yb3+, 1Ho3+ under 976 nm LD excitation with various power density were studied systematically in the temperature range from 100 K to 500 K. The green and red UC emissions are sensitive to the sample temperature whereas the excitation power density in the studied temperature ranges plays a negligible role on the red to green UC emissions ratio. The non-contact optical temperature sensing behaviors were investigated based on the fluorescence intensity ratio (FIR) of red (R3 + R4) and green (G3) at temperature from 100 K to 500 K, which are ascribed to non-thermally coupled levels of Ho3+:5F5 and 5F4, respectively. The maximum absolute sensitivity (Sa) of 0.0477 K−1 and maximum relative sensitivity (Sr) of 0.0129 K−1 at the temperature range of 100–500 K based on FIR of (R3 + R4)/G3 were found. The mechanism of temperature effect on UC emission was discussed. The heating and cooling cycle test indicates the high thermal stability of LiYF4:20Yb3+, 1Ho3+. These results imply the LiYF4:20Yb, 1Ho has potential application in ratiometric thermometers and temperature sensing devices.