Two photon thermal sensing in Er3+/Yb3+ co-doped nanocrystalline NaNbO3.

We investigate the potential use of two-photon absorption of Er3+/Yb3+ co-doped NaNbO3 nanocrystals for nanothermometry as well as thermal imaging, based on the thermally coupled green Er3+ emission lines. In fact, thermal sensor in the range of 20-80 degrees C with -0.1 degrees C accuracy using excitation powers readily obtained from commercially available semiconductor laser was achieved. The pump-intensity induced local heating was also investigated upon femtosecond laser excitation and 0.55 K/kW x cm(-2) was achieved. The highly efficient green emission together with two-photon dependence and femtosecond laser excitation should increase the brightness of thermal imaging. Additionally, the high temperature-sensitive fluorescence, when compared to previous literatures, should increase the resolution of nanothermometers.