Propriedades fotoluminescentes do YAG:Tb em baixa temperatura para aplicação em termometria óptica

Abstract

Yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) is a ceramic material with a cubic crystalline structure. Some of its characteristics include thermal stability, hardness, mechanical resistance, and high durability. The Y³⁺ ion is optically inactive but can be easily replaced by other rare-earth cations, granting YAG interesting optical properties and various applications. For instance, YAG:Nd is widely used in solid-state lasers, being popular in medicine (ocular surgery, dermatology) and industry (metal cutting and welding), with recent studies also exploring its use as a luminescent nanothermometer. Luminescent thermometry relies on the thermal dependence of luminescence to estimate temperature. Due to its non-contact nature, this measurement technique is particularly promising for temperature sensing in environments where conventional sensors are impractical, such as cryogenic systems, small biological structures, and miniaturized electronic devices. This study investigates the potential of YAG:Tb (yttrium aluminum garnet doped with terbium) as an optical thermometer for low temperatures, analyzing its spectroscopic properties via photoluminescence and Raman spectroscopy in the 20–320 K range. Samples with different Tb³⁺ concentrations (0.5%, 1%, and 2%, in mol) were examined. Various thermometric parameters were tested, including intensity ratios between peaks, areas, and peak-area combinations. From a total of 666 combinations per sample, nine were selected for a more detailed analysis. The results demonstrated good relative sensitivity, with emphasis on the intensity peak ratios. The maximum relative sensitivities for the 0.5%, 1%, and 2% Tb concentrations were 4.7, 2,.9, and 4.6% K⁻¹, respectively. Additionally, Raman spectroscopy revealed the presence of Nd³⁺ impurities, enabling the exploration of its luminescence as a secondary optical thermometer. The spectral analysis of Nd³⁺ led to the identification of 18 parameters with relative sensitivities exceeding 2 % K⁻¹, including a maximum value of 7.5 %K⁻¹ at 22 K. The findings indicate that both YAG:Tb and the luminescence of Nd³⁺ are promising for optical thermometry at low temperatures, providing viable alternatives for non-invasive and highly precise thermal sensors.