Exploiting High-Energy Emissions of YAlO₃:Dy³⁺ for Sensitivity Improvement of Ratiometric Luminescence Thermometry

The sensitivity of luminescence thermometry is enhanced at high temperatures when using a three-level luminescence intensity ratio approach with Dy³⁺- activated yttrium aluminum perovskite. This material was synthesized via the Pechini method, and the structure was verified using X-ray diffraction analysis. The average crystallite size was calculated to be around 46 nm. The morphology was examined using scanning electron microscopy, which showed agglomerates composed of densely packed, elongated spherical particles, the majority of which were 80-100 nm in size. The temperature-dependent photoluminescence emission spectra (ex = 353 nm, 300-850 K) included Dy³⁺ emissions in blue (458 nm), blue (483 nm), and violet (430 nm, T 600 K). Luminescence intensity ratio, the most utilized temperature readout method in luminescent thermometry, was used as the testing method: a) using the intensity ratio of Dy³⁺ ions and ⁴I_15/2→⁶H_15/2/⁴F_9/2→⁶H_15/2 transitions; and b) employing the third, higher energy ⁴G_11/2 thermalized level, i.e., using the intensity ratio of ⁴G_11/2→⁶H_15/2/⁴F_9/2→⁶H_15/2 transitions, thereby showing the relative sensitivities of 0.41% K^-1 and 0.86% K^-1 at 600 K, respectively. This more than doubles the increase in sensitivity and therefore demonstrates the method's usability at high temperatures, although the major limitation of the method is the chemical stability of the host material and the temperature at which the temperature quenching commences. Lastly, it must be noted that at 850 K, the emission intensities from the energetically higher levels were still increasing in YAP: Dy³⁺.