Role of the host matrix on the thermal sensitivity of Er3+ luminescence in optical temperature sensors

The influence of the local matrix environment on Er3+ luminescence properties is a key factor in the development of optical temperature sensors. The high sensitivity of Er3+ luminescence to the local structure, where the optically active ions reside, was analyzed along with the ligands type and bond character within the framework of the Judd–Ofelt theory. This model shows that the best thermalized emissions to use as optical temperature sensors are those in which the high energy emitting level is hypersensitive to the local structure, since the more disordered the local environment of the active ion, the better the ratio of emission intensities and the thermal sensitivity. These conclusions are experimentally supported using the fluorescence intensity ratio technique to analyze the relative variations of the luminescence intensities of the 2H11/2 and the 4S3/2 thermalized levels of the Er3+ ion in the green and the near-infrared spectral ranges from room temperature up to 720 K in two different matrices: an oxyfluoride glass and a nanocrystalline fluoride-type glass-ceramic. As expected, the best results were found in visible green emissions in oxyfluoride glass, for which a maximum thermal sensitivity of around 66 × 10−4 K−1 is obtained at around 570 K. This result can be understood as due to the higher radiative probabilities of Er3+ ion transitions in the disordered glass, which has higher values for the Ω2 and Ω4 and lower values of the Ω6 Judd–Ofelt parameters than the nanocrystalline glass-ceramic. The potential application of Er3+ ions as optical temperature sensors in these host matrices is also discussed.