Efeito dos íons codopantes (Tb3+, Ca2+) nas propriedades luminescentes do Y3Al5O12: Eu3+

Abstract

The structural and luminescent properties of YAG compounds (Y3Al5O12) – pure, Eu3+ doped and Tb3+ or Ca2+ codoped were investigated, for applications as a light source through WLEDs. To study such materials, two sets of samples (YAG:Eu,Tb and YAG:Eu,Ca) were produced using the modified sol-gel method, which uses glucose as a polymerizing agent. For the characterization of these samples, different techniques were used, such as X-ray diffractometry (XRD), X-ray absorption spectroscopy (XAS), X-ray excited optical luminescence (XEOL), photoluminescence spectroscopy (PL), radioluminescence (RL) and luminescent decay time. The XRD results revealed the formation of the desired phase in all samples, without the formation of secondary phases, proving that the production method was quite efficient to obtain the desired compound. Through of the Rietveld refinement and the Scherrer equation, the lattice parameters and the medium size of the crystallite were determined, showing that the values changed with the variations of the concentrations of dopants/codopants. XAS measurements confirmed the predominantly trivalent oxidation state of europium ions, not having evidence of a possible reduction of this valence due to ionizing radiation or incorporation of these ions in the Y3+ site. The results of the PL emission measurements, obtained by exciting the samples YAG:Eu,Tb and YAG:Eu,Ca with wavelengths of 230 nm and 225 nm, respectively, showed the typical transitions of the ions involved, except for the ions of Ca2+, which transitions were not evidenced. Furthermore, through these spectra, the chromaticity diagrams were obtained, which made it possible to determine how the molar proportions of the dopants can influence the color coordinates emitted by the samples. Most of these transitions, observed in the PL spectra, were also observed in the XEOL and RL spectra. These corroborated the high stability of the compounds when subjected to high energy radiation, not showing transitions related to the Eu2+ ion. All emission spectra confirmed that their intensities were influenced by the concentrations of Eu, Tb and Ca ions, in addition, they allowed an investigation into the local symmetry around Eu3+ ions. Finally, the luminescent decay time was strongly influenced by the variation of dopants and codopants.