Determination of near-infrared downconversion emission of Yb3+ and optical temperature sensing performances in Nd3+-sensitized SrF2 nanocrystals

Abstract

In this work, a series of Nd3+ and Yb3+ codoped SrF2 nanocrystals (NCs) were synthesized by the hydrothermal method. The TEM results show that the average size of these NCs is approximately ∼50 nm. The structure of SrF2 NCs and its optical properties of near-infrared (NIR) downconversion luminescence (DCL) are systematically characterized. Under the excitation of 808 nm laser, intense NIR DCL centered at 976 nm from Yb3+ ions is experimentally determined. The mechanism of the DCL is further interpreted based on the efficient energy-transfer (ET) processes from Nd3+ to Yb3+. In addition, utilizing the fluorescence intensity ratio (FIR) technique, the temperature sensing behaviors of SrF2:Nd3+/Yb3+ (15/4 mol%) are also investigated through the heterogeneously coupled states between Nd3+ (4F3/2 → 4I11/2) and Yb3+ (2F5/2 → 2I7/2) in a temperature range of 298–573 K. The results confirm that the maximum thermal sensitivity is up to 0.00346 K−1 at 473K. The excellent thermal sensitivity of these NCs, particularly the DCL located at the NIR region, have the potential for biological applications and temperature measurement at the nanoscale.