Near-infrared absorption thermometry exploiting an anomalously large spectral line-shift for the Yb3+ cubic centre in CaF2:Yb3+/Er3+ nanoparticles

Abstract

Near-infrared absorption spectra of Yb3+ in Er3+ co-doped CaF2 upconverting nanoparticles have been measured. The Yb3+ ion 2F7/2→2F5/2 inter-multiplet optical absorption spectra show negatively charged preferential clusters and non-locally charge compensated cubic centers as the dominant centres. The temperature dependent absorption spectra measured between 10 K and 413 K for Yb3+ cubic centres exhibit an anomalously large blue-shift of 16.90 ± 0.02 cm−1. The CaF2:Yb3+/Er3+ nanoparticles show an absolute thermal sensitivity Sa of 0.044 ± 0.001 cm−1⋅K−1 and the maximum relative thermal sensitivity Sr of 2.290 ± 0.010%·K−1 at 413 K region based on the large cubic centre absorption line-shift and a value of Sr of 0.0723 ± 0.001%·K−1 at 10 K (0.0562 ± 0.010%·K−1 at 413 K) from the line-width. The observed absolute absorption thermal sensitivity is 10 times higher (and the relative absorption thermal sensitivity is 2 times higher) than that obtained using the fluorescence intensity ratio of the thermally coupled 2H11/2,4S3/2 energy levels of Er3+ in co-doped nanoparticles.