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

Nd-3: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 F-4(5/2) -> I-4(9/ 2) and F-4(3/ 2) -> I-4(9/ 2) transitions, was recorded over a temperature range of 298-573K. 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 F-4(5/2) and F-4(3/2). Using the fluorescence intensity ratio approach, we obtained the relative sensitivity of similar to 1.7% K-1 at 300K, 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 (750nm) 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 750nm) and surrounding media (air and water). Published by AIP Publishing.