Multiple temperature effects on up-conversion fluorescences of Er3+-Yb3+-Mo6+ codoped TiO2 and high thermal sensitivity

We report multiple temperature effects on green and red up-conversion emissions in Er3+-Yb3+-Mo6+ codoped TiO2 phosphors. With increasing temperature, the decrease of the red emission from F-4(9/2) -> I-4(15/2), the increase of green emission from H-2(11/2) -> I-4(15/2) and another unchanged green emission from S-4(3/2) -> I-4(15/2) were simultaneously observed, which are explained by steady-state rate equations analysis. Due to different evolution with temperature of the two green emissions, higher thermal sensitivity of optical thermal sensor was obtained based on the transitions with the largest fluorescence intensity ratio. Two parameters, maximum theoretical sensitivity (S-max) and optimum operating temperature (T-max) are given to describe thermal sensing properties of the produced sensors. The intensity ratio and energy difference Delta E of a pair of energy levels are two main factors for the sensitivity and accuracy of sensors, which should be referred to design sensors with optimized sensing properties. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.