Achieving tunable multicolor display and sensitive temperature sensing in self-sensitization of erbium-doped CaF 2 nanocrystals under 808, 980 and 1532 nm irradiation

Photon upconversion (UC) based on self-sensitization of lanthanide-doped nanocrystals is of great importance for biological and photonic applications. Here, we report tunable multicolor display and sensitive temperature sensing in the erbium-doped CaF2 upconversion nanocrystals (UCNCs) codoped with Tm3+ ions. Under the excitation of 980, 808 and 1532 nm lasers, the upconversion luminescence (UCL) color of these self-sensitized UCNCs can be manipulated from green to red efficiently and the red-to-green (R/G) UC intensity ratio is promoted remarkably as the doping Tm3+ ions vary from 0 to 4 mol%. Especially, we have successfully demonstrated the multicolor modulation of these UCNCs by changing the pulse width and repetition frequency under multi-wavelength excitation. The power dependence and decay lifetimes measurements of Er3+ ions under multi-wavelength excitation were carried out to clarify the UC color manipulation. In addition, the optical temperature sensing properties of CaF2:Er3+/Tm3+ (10/0.125 mol%) UCNCs are also studied thoroughly under 980, 808 and 1532 nm lasers excitation, and the results show that the UCNCs possess outstanding thermal sensitivity. The features enable these UCNCs to act as promising candidates for high-resolution biological imaging, multicolor display and nanoscale thermometer fields.