Luminescent thermometry with YVO4:Er/Nd: Achieving high sensitivities within the 1st and 2nd biological windows

YVO4:Er3+, Nd3+ powders were prepared by the modified sol gel synthesis route using glucose as chelating agent and characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Under 660 nm excitation, four infrared emission bands located between 790 and 845 nm, 870 and 930 nm, 950 and 1030 nm, and between 1050 and 1100 nm were observed, and were assigned the transitions 4F5/2 - 4I9/2 (Nd) and 4I9/2 - 4I15/2 (Er), 4F3/2 - 4I9/2 (Nd), 4I11/2 - 4I15/2 (Er), and 4F3/2 - 4I11/2 (Nd), respectively. The performance of these powders as optical temperature sensors using the luminescence intensity ratio (LIR) technique between thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs) was studied within the temperature range of 293-373 K. Using different combinations of the emission intensities at 809, 880, 914 and 1003 nm, three distinct (LIR) temperature sensors schemes were built, with both excitation and emission within the first and second biological window. These LIRs relative sensitivity (Sr) and temperature uncertainties (delta T) were investigated for samples with different Er and Nd concentrations. Sr values up to 2.08 +/- 0.03%. K-1 and delta T smaller than 1 K, were obtained. Repeatability and reproducibility tests demonstrated the reliability of the proposed LIRs.