Estudo teórico-computacional das propriedades estruturais, eletrônicas, de defeitos e ópticas do Na2MSiO4 (M2+ = Mg e Zn) puro e dopado com Európio

Abstract

The orthorhombic silicates Na2MSiO4 (M = Mg and Zn) have attracted interest as host matrices for rare-earth ions due to their structural stability and potential applications in optoelectronic devices, solid-state lighting phosphors, dielectric materials, and energy storage systems. In this work, classical computational modeling was employed to investigate structural defects and the effects of Eu3+ doping in these matrices. The parameterized interatomic potentials satisfactorily reproduced the experimental structural parameters, validating the adopted methodology. The solution energies of intrinsic defects indicated that sodium vacancies and Frenkel defects are the most favorable. For extrinsic defects, Eu3+ was found to preferentially occupy the divalent cation site (Mg2+ or Zn2+), with charge compensation occurring through antisite defects. The crystal-field analysis revealed that Eu3+ occupies a distorted C3 local-symmetry environment in both matrices, a characteristic directly related to the intensity of the 5D0-7Fj transitions and, consequently, to the luminescent performance. Furthermore, doping was found to reduce the elastic moduli and Debye temperature while preserving the overall thermal stability, maintaining these compounds as suitable candidates for optoelectronic applications. Complementarily, first-principles calculations based on Density Functional Theory (DFT) were employed to investigate the structural, electronic, vibrational, and optical properties. The results indicate a dielectric character, with energy gaps in the visible-toultraviolet region, mainly associated with electronic transitions involving O-2p states in the valence band and Na-2p and M-s,p states in the conduction band. The optical properties reveal broad transparency in the visible region and a moderate dielectric response, consistent with insulating materials. Overall, the classical and ab initio results contribute to a comprehensive understanding of the mechanisms governing Eu3+ incorporation and the structural, electronic, and optical effects of doping, reinforcing the potential of Na2MSiO4 as a promising host matrix for applications in luminescent phosphors, optoelectronic devices, and other technologies based on dielectric materials.