Análise teórica das propriedades térmicas das matrizes de Y2O3, YF3 e Y7O6F9, dopadas com Nd3+ via modelagem computacional

Abstract

In this work, classical atomistic computational modeling techniques and crystal field theory studies were applied to the case of yttrium oxide (Y2O3), yttrium fluoride (YF3), and yttrium Voxyfluoride (Y7O6F9) matrices doped with neodymium lanthanide ions (Nd3+) from the perspective of thermometric variations within the temperature range of 273 K to 373 K, whose applications are based on thermometry in the biological window. The study was initially based on the interatomic potential model and the lattice energy minimization method. For the set of potentials used to simulate the crystal structures studied, an agreement above 97.9% was obtained for Y7O6F9, 98.7% for Y2O3, and 98% for YF3 within the proposed thermal scales. From this, the incorporation of the Nd3+ ion was carried out following the Mott-Littleton method, through isovalent substitution, in which the neodymium ion directly replaces the Y3+ ion in the matrices. For the Y2O3 and Y7O6F9 lattices, the Y3+ sites with the highest probabilities of neodymium incorporation into the matrix were evaluated. From these results, it was possible to note that the first Y3+ site (Y1) will have the lowest solution energy in the Y2O3 matrix, while for the Y7O6F9 matrix, the Y1 and Y2 sites have similar probabilities of neodymium incorporation. YF3 has only one available Y3+. From the atomistic modeling study, it was possible to perform crystal field theory calculations for the crystalline matrices studied. The calculation performed consists of applying two models found in the literature to obtain the results of the crystal field parameters, the PCEM and SOM models. In these calculations, it was possible to observe the electrostatic interaction in each matrix, and, after that, calculations of crystal field forces were performed. Crystal field forces were calculated from the rotational invariants. From these calculations, it was possible to define the limits of the spectroscopically active coordination spheres of neodymium at each site in the three crystalline matrices. Starting from the crystal field parameters, the energy levels of the ground state of Nd3+ , 4 I9/2, and the excited state, 4F3/2, were calculated. From the results obtained for the energy levels, it was possible to evaluate the thermal sensitivity from the variation between the energy levels of the excited state, correlating them to Boltzmann statistics.