Optical temperature sensing with CaWO4:Yb3+/Er3+ phosphors driven by a 405 nm laser diode

Traditionally, the 980 nm laser is used as the excitation source for Yb3+/Er3+ codoped phosphors. Different from this conventional way, it is shown here that the as-prepared CaWO4:Yb3+/Er3+ (5/1 mol %) phosphors can be effectively triggered by the commonly used and cheap 405 nm laser diode. On such excitation, the Er3+ ion's characteristic green emission, which is ascribed to the H-2(11/2)/S-4(3/2)-I-4(15/2) transitions, is successfully detected with a good signal to noise ratio. The green emission's response to the temperature change is investigated in the 93-813 K range. It is confirmed that the H-2(11/2)-I-4(15/2) and S-4(3/2)-I-4(15/2) transitions obey the Boltzmann distribution well, which are thus suitable for optical ratiometric temperature measurement. Their maximum relative sensitivity is found to be 10.41% K-1 at 93 K.