Ultrafast multi-photon excitation of ScVO₄:Bi³⁺ for luminescence thermometry

We demonstrate a multi-photon excitation (MPE) scheme for luminescence thermometry using ScVO₄:Bi³⁺. MPE is performed using a 37 fs Ti:sapphire laser pulse centered at 800 nm. Log-log plots of the phosphorescence intensity versus excitation power show that the 800 nm MPE of ScVO₄:Bi³⁺ involves a 2- and 3-photon absorption process in comparison with a single-photon excitation (SPE) process at 266 and 400 nm. Spectroscopic investigation shows that with the 800 nm MPE and 266 nm SPE schemes, the emission spectra of ScVO₄:Bi³⁺ are similarly characterized by emissions of the VO₄ ^3- groups and Bi³⁺. MPE is advantageous to suppress fluorescence that interferes with the phosphorescence signal. We demonstrate this aspect for a ScVO₄:Bi³⁺ coating applied on an alumina substrate. The luminescence lifetime is calibrated with temperature in the range of 294-334 K; the MPE scheme has an equally impressive temperature sensitivity (3.4-1.7%/K) and precision (0.2-0.7 K) compared with the SPE schemes. The MPE scheme can be applied to a variety of phosphors and is valuable for precise temperature measurements, even in applications where isolating interfering background emissions is challenging.