Multiple wavelengths excitation of NaYF4:Tm/Er microcrystals for multicolor anti-counterfeiting and temperature sensing.

Multicolor luminescence and optical thermometry hold charming potential applications in many fields, which are likely to be achieved in one rationally designed unit. Herein, a triple-wavelength (980 nm, 1550 nm and 808 nm) responsive upconversion microcrystal, using Er3+ ions as sensitizers, is proposed, which can generate tunable emission color from red to yellow and then to green. The modulated population route and energy transfer process of Er3+ are perceived to be the reason for tunable luminescence color upon excitation-wavelength. In addition, based on thermally coupled energy levels (TCLs), i.e., 2H 11/2 /4S 3/2 and non-thermally coupled energy levels (NTCLs), i.e., 2H 11/2 /4F 9/2 of Er3+ ions, the temperature-dependent upconversion properties were investigated. The maximum relative sensing sensitivity (S r) of NaYF 4 :0.5%Tm/20%Er was found to be 1.373 % K−1 at 313 K, outperforming the majority of the same type thermometers. The results indicate that the NaYF 4 :0.5%Tm/20%Er microcrystals serve as a promising candidate for multicolor anticounterfeiting and optical thermometry applications. • Multicolor emission can be obtained from 0.5%Tm20%Er sample. • Based on triple-wavelength responsive, novel information encryption strategies are proposed. • 0.5%Tm20%Er microcrystals possess the maximum relative sensitivity of 1.373%K−1 at 313K under 980 nm excitation. [ABSTRACT FROM AUTHOR]