Temperature-dependent upconversion luminescence multicolor tuning and temperature sensing of multifunctional β-NaYF4:Yb/Er@β-NaYF4:Yb/Tm microcrystals

Abstract

Temperature is one of the physical parameters that affects the emission luminescence properties of upconversion (UC) materials. Temperature-dependent emission color tuning and good temperature sensitivity in multifunctional β-NaYF₄:Yb/Er@β-NaYF₄:Yb/Tm microcrystals were achieved under 980 nm excitation. Based on the different emission bands (blue, green and red bands) and spectral sensitivities of the core–shell structured microcrystals to temperature, intense white-light emission was obtained at room temperature and a real-time naked-eye recognizable emission color change from white to the purplish-pink region was realized with the temperature increasing from 300 to 500 K. Furthermore, optical temperature sensing properties of the sample with good sensitivity (from 0.0034 to 0.0044 K⁻¹) were investigated by using a fluorescence intensity ratio between 521 nm (²H_11/2 → ⁴I_15/2 transition) and 540 nm (⁴S_3/2 → ⁴I_15/2 transition) in the temperature range from 300 to 500 K. The results indicate that the sample has high sensitivity in a relatively wide range of temperature intervals, especially in the low temperature region. We believe that the multifunctional core–shell structured microcrystals exhibit promising applications in white-light emitting diodes, the anti-counterfeiting field, and temperature sensing.