Estudo das propriedades luminescentes do LiBaPO₄:Er,Yb para aplicação em sensores ópticos luminescentes

Abstract

The present work highlights the synthesis and characterization of lithium barium phosphate (LiBaPO₄) doped with different concentrations of erbium (Er³⁺), while fixing the concentration of ytterbium (Yb³⁺) at 1 mol%. The samples were synthesized by a modified sol-gel route, using PVA as a chelating agent, with a calcination process at 1000 °C for two hours. Structural characterization of the samples was performed by X-ray diffraction, and the results were compared with the reference patterns ICSD No. 036801 and ICSD No. 198235. The analyses confirmed the formation of the monoclinic crystalline phase of LiBaPO₄, belonging to the space group C1c1 (Nº 9), with the presence of a secondary phase observed only when the dopant concentrations were increased. The average crystallite size was calculated using the Scherrer equation, ranging from 26 to 28 nm. The luminescent properties of the samples were investigated by photoluminescence (PL) spectroscopy under excitation from a 980 nm laser, with a temperature variation between 225 and 420 K. Codoping with erbium and ytterbium promoted the upconversion phenomenon. In this context, the characteristic emissions of erbium were analyzed, corresponding to the transitions (⁴H₁₁/₂ → ⁴I₁₅/₂), (⁴S₃/₂ → ⁴I₁₅/₂), and (⁴F₉/₂ → ⁴I₁₅/₂). To deepen this analysis, the luminescence intensity ratio (LIR) technique was used, allowing the investigation of thermally coupled energy levels (TCELs). Based on the results obtained by the LIR technique, the thermal sensitivities of each sample were calculated. The relative sensitivity reached a maximum value of 2.45% K⁻¹ at 225 K, and the absolute sensitivity reached a maximum value of 0.044 K⁻¹ at 420 K. Therefore, the formation of the material was confirmed, as well as its relative sensitivities, demonstrating its potential as an effective thermal sensing material.