Multiple Temperature-Sensing Behavior of Green and Red Upconversion Emissions from Stark

Abstract: Upconversion luminescence properties from the emissions of Stark sublevels of Er 3+ wereinvestigated in Er 3+ -Yb 3+ -Mo 6+ -codoped TiO 2 phosphors in this study. According to the energylevels split from Er 3+ , green and red emissions from the transitions of four coupled energy levels, 2 H 11/2(I) / 2 H 11/2(II) , 4 S 3/2(I) / 4 S 3/2(II) , 4 F 9/2(I) / 4 F 9/2(II) , and 2 H 11/2(I) + 2 H 11/2(II) / 4 S 3/2(I) + 4 S 3/2(II) ,were observed under 976 nm laser diode excitation. By utilizing the fluorescence intensity ratio(FIR) technique, temperature-dependent upconversion emissions from these four coupled energylevels were analyzed at length. The optical temperature-sensing behaviors of sensing sensitivity,measurement error, and operating temperature for the four coupled energy levels are discussed,all of which are closely related to the energy gap of the coupled energy levels, FIR value, andluminescence intensity. Experimental results suggest that Er 3+ -Yb 3+ -Mo 6+ -codoped TiO