High Performance Optical Temperature Sensing Via Selectively Partitioning Cr4+ In The Residual Sio2-Rich Phase Of Glass-Ceramics

Quadrivalent Cr4+ theoretically exhibits great potential to achieve higher photo-luminescence (PL) lifetime based temperature sensitivity than the commonly utilized trivalent Cr3+, but the problem is how to stabilize the anomalous quadrivalent chemical state of Cr4+. Here we propose a type of glass-ceramic phase structure with a precipitated ZnAl2O4 crystalline sub-phase and a residual ZnO-SrO-SiO2 glassy sub-phase, where Cr4+ can be well stabilized in the residual glassy sub-phase. From PL spectra, Cr4+ or Cr3+ was found to be located at T-d (tetrahedral crystal filed) or O-h (octahedral crystal filed) sites with a relatively high crystal field strength. The thermally coupled E-1(D-1)/T-3(2)(F-3) states of Cr4+ or the E-2((2)G)/T-4(2)(F-4) states of Cr3+ were revealed as competitive energy level pairs suitable for PL lifetime based temperature sensing. Quadrivalent Cr4+ had a particular PL lifetime ratio of E-1(D-1)/T-3(2)(F-3) up to 10(3), which was much higher than that (10(1)) of trivalent Cr3+:E-2((2)G)/T-4(2)(F-4). This supported Cr4+ to eventually achieve a higher temperature sensitivity (1.72% K-1) one order of magnitude higher than that of Cr3+ (0.83% K-1). This provides the possibility of utilizing Cr4+-doped glass to develop a type of temperature sensor with high precision and sensitivity.