Influência do teor de oxigênio nas propriedades estruturais e ópticas do sistema yf-yof aplicável em sensores ópticos sem contato

Abstract

In biomedicine, little local temperature variations in cells can indicate health disorders like growth and appearance of carcinogen cells, inflammations, and other pathologies. Nowadays, the development of new methodologies to detect and treat these illnesses causing less side effects are widely explored to minimize many invasive methods used in patients. So, the ability to infer the temperature of a cell with a non-contact thermometer is being very studied with inorganic compounds, where the techniques can be less invasive, with fast response and great stability. Based on inorganic materials highlighted in the literature, were studied is this work, the synthesis of two Yttrium-based materials: YF3 (YF) and Y7O6F9 (YOF). To improve the optical response of these materials, 1 mol% Nd3+ ions were inserted into the Y3+ site. The choice of Neodymium as dopant is due its excitation and emission in the first biological window (700–950 nm), very important to biological applications. The nucleation and growth of YF particles was performed by the microwave-assisted hydrothermal method, using a temperature of 140 ºC for 1h. This method is an eco-friendly route and very promising to synthesize materials due its low temperature and time of heat treatment, mainly on fluorides synthesis. To obtain YOF, a second step was used: after the hydrothermal reaction, the YF particles were thermally treated. After calcination, the final product obtained was a crystalline phase corresponding to YOF. The structural results were analyzed using XRD and XPS measurements. Diffraction patterns show successful formation of YF, and YOF with posterior increasing temperature. In XPS analysis, an increase of oxygen content was noticed within increasing thermal treatment temperature. The morphology and size of particles was analyzed by scanning electron microscopy (SEM), showing rod-like shape morphology particles and submicrometer sizes. Through optical absorption it was possible to observe the main transitions, typical of neodymium. Optical analyzes, based on Luminescence Intensity Ratio (LIR) methodology were used to investigate sensibility of samples to temperature, and how the insertion of oxygen influences the relative sensibility (Sr) of materials under study. It is important to highlight that the powers used in 800 nm (6.2 mW) and 660 nm (11 mW) CW lasers are considered low according to the MPE (maximum permissible exposure) for human skin, a parameter that defines the power density of the safe laser for biological applications without risk of damage. In addition, the low power of the lasers, combined with the sensitivity values obtained with a low doping concentration in the samples, with excitation and emission in the first biological window, suggest that the studied compounds, doped with neodymium, are promising in luminescent optical sensors field.