Up-conversion luminescence and optical thermometry properties of transparent glass ceramics containing CaF2:Yb3+/Er3+ nanocrystals

A series of Yb3+/Er3+ codoped transparent oxyfluoride glass ceramics with various amounts of Yb3+ have been successfully fabricated and characterized. Under 980 nm laser prompting, the samples produce intense red, green and blue up-conversion emissions, and the emission intensities increase with Yb3+ concentration and heat treatment temperature. Before losing good transparency in the visible region, optimum emission intensities are obtained for the sample with 25 mol% of Yb3+ at a heat treatment temperature of 680 °C. A possible up-conversion mechanism is proposed from the dependence of emission intensities on pumping power. The fluorescence intensity ratio between the two thermally coupled levels 2H11/2 versus 4S3/2 was measured with the laser output power of 57 mW to avoid the possible laser induced heating effect. The fluorescence intensity ratio values in the temperature range from 295 K to 723 K can be well fitted with the equation: A exp (−∆E/kBT), where A = 6.79 and ∆E=876 cm−1. The relative temperature sensitivity at 300 K was evaluated to be 1.4% K−1. All the results suggest that the Yb3+/Er3+ codoped CaF2 glass ceramics is an efficient up-conversion material with potential in optical fiber temperature sensing.