The Impact of Cr Doping on Temperature Sensitivity Modulation in Cr Doped and Cr, Nd Co-doped YAlO, YAlGaO, and YGaO Nanothermometers.

A new approach to enhance the sensitivity of transition metal ion based nanocrystalline luminescent thermometer is presented. It was shown that the increase of Cr concentration in three types of garnet host namely YAlO, YGaO, and YAlGaO allows for significant enhancement of their performance in non-contact thermometry. This phenomenon is related to the weakening of the crystal field strength due to enlargement of average Cr-O distance at higher Cr concentrations. By increasing Cr concentration from 0.6 to 30%, the sensitivity increased by over one order of magnitude from = 0.2%/°C to = 2.2%/°C at 9°C in YAlGaO nanocrystals. Moreover, it was found that due to the Cr → Nd energy transfer in the Cr, Nd co-doped system, the usable Cr concentration, for which its emission can be detected, is limited to 10% while the sensitivity at -50°C was doubled (from 1.3%/°C for YAlGaO:10%Cr to 2.2%/°C YAlGaO:10%Cr, 1%Nd nanocrystals).