Optical high temperature sensor based on enhanced green upconversion emissions in Er3+-Yb3+-Li+ codoped TiO2 powders

Enhanced Power Conversion Efficiency of Perovskite Solar Cells with an Up-Conversion Material of Er3+-Yb3+-Li+ Tri-doped TiO2

In this paper, Er³⁺-Yb³⁺-Li⁺ tri-doped TiO₂ (UC-TiO₂) was prepared by an addition of Li⁺ to Er³⁺-Yb³⁺ co-doped TiO₂. The UC-TiO₂ presented an enhanced up-conversion emission compared with Er³⁺-Yb³⁺ co-doped TiO₂. The UC-TiO₂ was applied to the perovskite solar cells. The power conversion efficiency (PCE) of the solar cells without UC-TiO₂ was 14.0%, while the PCE of the solar cells with UC-TiO₂ was increased to 16.5%, which presented an increase of 19%. The results suggested that UC-TiO₂ is an effective up-conversion material. And this study provided a route to expand the spectral absorption of perovskite solar cells from visible light to near-infrared using up-conversion materials.

Multiple Temperature-Sensing Behavior of Green and Red Upconversion Emissions from Stark Sublevels of Er³⁺

Upconversion luminescence properties from the emissions of Stark sublevels of Er(3+) were investigated in Er(3+)-Yb(3+)-Mo(6+)-codoped TiO₂ phosphors in this study. According to the energy levels split from Er(3+), green and red emissions from the transitions of four coupled energy levels, ²H11/2(I)/²H11/2(II), ⁴S3/2(I)/⁴S3/2(II), ⁴F9/2(I)/⁴F9/2(II), and ²H11/2(I) + ²H11/2(II)/⁴S3/2(I) + ⁴S3/2(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 energy levels 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, and luminescence intensity. Experimental results suggest that Er(3+)-Yb(3+)-Mo(6+)-codoped TiO₂ phosphor with four pairs of energy levels coupled by Stark sublevels provides a new and effective route to realize multiple optical temperature-sensing through a wide range of temperatures in an independent system.