Ação do íon de CE3+ na luminescência do LILAP4O12 : BI

Abstract

Lithium lanthanum phosphate (LiLaP4O12) is a material with a crystalline structure that has desired characteristics that make it useful in the application as a luminescent material. Although there are studies that analyze properties of LiLaP4O12 doped with Ce3+ and Bi3+ ions separately, it is still not known how the mechanism of interaction between Ce3+ and Bi3+ works in LiLaP4O12 and what is emission properties behav ior. There are reports that, in some structures, Ce3+ can transfer electrons to Bi3+ ion, indicating a possible increase of Bi3+-related emission yield. Furthermore, in some phosphate structures doped with Bi3+, it has already been observed that X-rays can in duce red emission related to the Bi3+ reduction to Bi2+ due to the interaction of X-rays. Therefore, in this work, the emission properties of the LiLaP4O12 doped and codoped with Ce3+ and Bi3+ ions were studied to identify the mechanism of interaction between the ions and the possibility of potentiation in the bismuth luminescence of due to Ce3+ codoping. The structural characterization was done through X-ray diffraction, which confirmed the formation of LiLaP4O12 as the majority phase. Using photoluminescence (PL) measurements, was possible to identify the characteristic emission and excitation spectra for both ions, Ce3+ and Bi3+, in addition, based on excitation spectrum, a pro cess of electron transference from Ce3+ to the Bi3+. Radioluminescence (RL) was used to analyze the ability to convert X-ray into light. The RL spectra showed a new emis sion region, in addition to the one related to Ce3+ and Bi3+, centered at 650 nm, related to Bi2+ emission, which increases in intensity as the concentration of cerium increases, while that of Bi3+ decreases. To analyze the secondary effects due to the sample expo sure to X rays, the thermoluminescence (TL) technique was used. In samples codoped with cerium and bismuth, for cerium concentration above 0.5%, the Ce3+ ion seems to act as a recombination center. The HRBE model was applied to estimate the positions of the energy levels of the dopant ions in the LiLaP4O12 band structure. The 4f level for Ce3+ was estimated to be 1.2 eV below the conduction band, similar to the energy values obtained by TL for the main peak.