Otimização das propriedades ópticas e estruturais do fósforo YF3: Nd3+ usando excesso de flúor e tratamento térmico

Abstract

In this work, we have investigated the optical and structural properties of Nd:YF3 phosphor synthesized through precipitation reaction using ethylene glycol as solvent. The molar ratio of the yttrium per fluorine (Y:F) precursors was varied in an attempt to prevent oxygen contamination during nucleation of the crystalline particles. The NH4F compound was used as the fluorine source, and its amount played a crucial role in the crystalline phase formation and crystallinity. For samples without thermal treatment (TT), those ones prepared without and with 15% of excess of this precursor in relation to the stoichiometric proportion, orthorhombic YF3 was obtained as majority phase, while exceeding the precursor t 30, 45, and 60%, the samples presented the NH4Y2F7 single crystalline phase. However, all the samples were successfully crystallized into orthorhombic YF3 phase after TT (annealing) at 400 ºC for 1 h. The structures were investigated before and after TT by means of X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Energy Dispersive X-ray (EDX). The results from these techniques are complementary and indicated that, indeed, the use of fluorine excess reduces oxygen contamination, but it leads the matrix to a new phase: from orthorhombic YF3 to cubic NH4Y2F7. Neodymium emission spectra were measured under excitation at 797 nm for all the samples and in a comparative way. As a result, a continuous reduction in the emission intensity with the increasing of fluorine excess for the samples as prepared was observed. After TT the emission intensity increased by over 50 times in comparison with the samples without annealing, being the most efficient and thus the indicated to use, that one with fluorine excess at 15%. In summary, the results show that the use of fluorine excess together annealing at the temperature and time applied, result in crystalline particles of YF3 phase with improved characteristics.