Mechanism of photoluminescence in intrinsically disordered CaZrO3 crystals: First principles modeling of the excited electronic states

Abstract

CaZrO3 (CZO) powders were synthesized at different temperatures (400, 600, 800, and 1000 °C) and characterized by X-ray diffraction, Raman and ultraviolet-visible spectroscopic methods, along with photoluminescence (PL) emissions. First principle calculations based on the density functional theory (DFT), using a periodic cell models, provide a theoretical framework for understanding the PL spectra based on the localization and characterization of the ground and electronic excited states.Fundamental (singlet, s) and excited (singlet, s*, and triplet, t*) electronic states were localized and characterized using the ideal and distorted structures of CZO. Their corresponding geometries, electronic structures, and vibrational frequencies were obtained. A relationship between the different morphologies and structural behavior has also been established. Polarized structures were identified by the redistribution of the 4dz2, 4dyz, and 4dxy (Zr) orbitals at the conduction band and the 2pz (O) orbital in the valence band for s, s* and t*. Analysis of the vibrational eigenvector modes of these electronic states reveals a relationship between them via asymmetric bending and stretching modes that arise from Zr atom displacements due to polyhedral [ZrO6] distortion. Furthermore, the results provided an insight into the PL emissions of the as-synthesized CaZrO3 and led to the conclusion that the presence of electronically excited states is strongly related to the structural order-disorder effects (polyhedral distortion) at short range for both [ZrO6] and [CaO8] clusters.

Experimental and theoretical study of the energetic, morphological, and photoluminescence properties of CaZrO3:Eu3+

“…We link the excited states theory to the generation of electron-hole pairs, providing a deeper understanding of optical effects in the solid state. This new approach was proposed in previous studies and has been confirmed in the present work 25 . The proposed connection between excited states and optical properties is well established in quantum chemical approaches; however, the present quantum evidence of dangling bonds generating electron-trapping levels and localizing spin density is entirely new.…”

“…It is important to point out that in this study the Eu 3+ doping of the CZO matrix was modeled allowing lattice and atomic position relaxation for the singlet state, and calculations were carried out for both bulk and slab models, using the optimized cell for ordered and disordered models of CZO reported in our previous work 25 ; this enabled the computational treatment of the main electronic features associated with the doping process and the optical properties. well-defined peaks, denoting a high degree of crystallinity, without any secondary phases.…”

“…4(a-c) properties, in this study we investigated excited singlet (s*) and triplet (t*) states by combining the analyses mentioned above. The main purpose was to rationalize the PL emission of CZO:Eu 3+ following an approach similar to that employed in our previous study of pure CZO 25 .…”

“…From a theoretical viewpoint, the investigation of PL emissions is a challenging task because it requires a detailed understanding of the excited states involved in the optical phenomena 1, 24 . In our previous work, we presented a novel approach to explore ground (singlet) and excited (singlet and triplet) states involved in the experimental PL spectra of CZO nanoparticles 25 . This approach was successfully applied by our group to investigate the mechanism of PL emission in SrTiO3, SrTiO3:Sm, CaWO4, BaZrO3, and BaZr1-xHfxO3 solid solutions, based on the characterization of excited electronic states [26][27][28][29][30][31] .…”

Magnetism and multiferroic properties at MnTiO3 surfaces: A DFT study

“…The Wulff proposal refers to a simple relation between E surf and the distance in the normal direc tion from the center of the crystallite, which also allows this ideal morphology to be modified by tuning the surface energies of the different facets [62,63]. In recent years, this method was successfully applied for different kinds of materials, showing excellent agreement between theoretical predicted and experimental reported morphologies [45,[64][65][66][67].…”