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

In this work, a series of Nd 3+ and Yb 3+ codoped SrF 2 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 SrF 2 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 Yb 3+ ions is experimentally determined. The mechanism of the DCL is further interpreted based on the efficient energy-transfer (ET) processes from Nd 3+ to Yb 3+ . In addition, utilizing the fluorescence intensity ratio (FIR) technique, the temperature sensing behaviors of SrF 2 :Nd 3+ /Yb 3+ (15/4 mol%) are also investigated through the heterogeneously coupled states between Nd 3+ ( 4 F 3/2  →  4 I 11/2 ) and Yb 3+ ( 2 F 5/2  →  2 I 7/2 ) 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 .