New Type of Nanocrystalline Luminescent Thermometers Based on Ti3+/Ti4+ and Ti4+/Ln3+ (Ln3+ = Nd3+, Eu3+, Dy3+) Luminescence Intensity Ratio

The spectroscopic properties of YAG:Ti and YAG:Ti,Ln nanocrystalline powders were examined as part of the search for new functional materials devoted to luminescent thermometry. Various temperature-dependent processes occurring in the studied systems were analyzed and the mechanism of absorption and emission of trivalent and tetravalent titanium ions was proposed. The first luminescent thermometer based on the Ti4+/Ti3+ luminescence intensity ratio with maximum sensitivity of 0.71% is shown. It was shown that the codoping with lanthanide ions enhances the relative sensitivity of YAG:Ti,Ln nanocrystalline luminescent thermometers because of the Ti4+/Ln(3+) energy transfer. The maximal relative sensitivities in the physiological range (2.26% C-1 at 50 degrees C) were found for YAG:Ti,Nd3+ nanocrystals and the value increases with temperature reaching 3.70% C-1 at 200 degrees C.