Investigation on the upconversion luminescence and ratiometric thermal sensing of SrWO(4):Yb(3+)/RE(3+) (RE = Ho/Er) phosphors

SrWO(4) phosphors doped with Ho(3+)(Er(3+))/Yb(3+) are successfully prepared by a high temperature solid-state reaction method. The upconversion (UC) luminescence properties of all the samples have been investigated under 980 nm excitation. Strong green emissions are obtained in the SrWO(4):Yb(3+)/Ho(3+) and SrWO(4):Yb(3+)/Er(3+) samples with the naked eyes. In a temperature range going from 303 K to 573 K, the UC emission spectra of the phosphors have been measured. Then the temperature sensing properties also have been discussed via fluorescence intensity ratio (FIR) technology. For the SrWO(4):Yb(3+)/Ho(3+) phosphor, the FIR technologies based on thermal coupling levels (TCLs)((5)F(4),(5)F(5)) and non-thermal coupling levels (non-TCLs)((5)S(2), (5)F(4)/(5)F(5)) are used for investigating the sensitivity. The results show that the maximum absolute sensitivity reaches 0.0158 K(−1) with non-TCLs. As for Yb(3+)/Er(3+) codoped SrWO(4) phosphor, the maximum absolute sensitivity reaches 0.013 K(−1) with TCLs ((2)H(11/2),(4)S(5/2)) at a temperature of 513 K. These significant results demonstrate that the SrWO(4):Ho(3+)(Er(3+))/Yb(3+) phosphors are robust for optical temperature sensors.