Near-infrared emission and optical temperature sensing performance of Nd3+:SrF2 crystal powder prepared by combustion synthesis

Abstract

Nd3+:SrF2 crystal powder prepared by combustion synthesis technique was analyzed for potential use in thermal sensing of biological systems. Near-infrared emission was observed under CW laser excitation at 532 nm. The near-infrared fluorescence spectrum consisting of two emission bands, corresponding to the 4F5/2 →4I9/2 and 4F3/2 →4I9/2 transitions, was recorded over a temperature range of 298–573 K. A noticeable change on the relative intensities of those transitions with temperature was observed as a consequence of the thermal coupling induced by the small energy bandgap between the electronic states 4F5/2 and 4F3/2. Using the fluorescence intensity ratio approach, we obtained the relative sensitivity of ∼1.7% K−1 at 300 K, which is among the highest values reported for this class of optical thermometer. We also performed the experiment using pulsed (5 ns) near-infrared excitation (750 nm) in a solution containing the Nd3+:SrF2 powder dispersed in water aiming to use this system for temperature sensing in the first near-infrared biological transparency window. The same sensor sensitivity, within experimental error, was obtained for different excitation wavelengths (532 and 750 nm) and surrounding media (air and water).