Experimental determination and modeling of structural, vibrational and optical properties of the ZnAl2_xCrxO4 (x=0 and 0.05) spinels
JOURNAL OF LUMINESCENCE, vol.263, 2023 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 263
- Publication Date: 2023
- Doi Number: 10.1016/j.jlumin.2023.119968
- Journal Name: JOURNAL OF LUMINESCENCE
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, PASCAL, Chemical Abstracts Core, Chimica, Communication Abstracts, Compendex, INSPEC
- Istanbul Kültür University Affiliated: No
Abstract
The structural, vibrational and optical properties of the ZnAl2_xCrxO4 (x = 0 and 0.05) spinels (Fd 3 m space group), prepared by a conventional solid-state reaction, have been addressed in this work. The room temperature Raman and infrared (ATR-IR) spectra have been obtained and interpreted. The optical band gap Eg has been determined from reflectance and absorption UV/vis. spectra. Tauc's law confirmed the direct transition behavior. The observed increase in the Urbach energy Eu for ZnAl1.95Cr0.05O4 suggests that disorder and defects concen-tration are larger than in the undoped ZnAl2O4 spinel. From the absorption and photoluminescence excitation (PLE) spectra, the electronic structure of Cr3+ was determined by a crystal field study in the Oh symmetry site. The theoretical study led to a precise attribution of the Cr3+ d-d transitions. Using Group Theory and the notion of potential energy surface (diabatic and adiabatic), the origin of the spin-forbidden transitions in the studied materials was also investigated. The PLE spectra show the presence of vibronic progressions of about 485 cm_ 1, which were attributed to an O-Al-O asymmetric stretching vibration detected in the ATR-IR study. The contribution of a non-totally symmetric mode to the PLE spectrum proves the occurrence of the Jahn-Teller effect leading to a distorted CrO6 octahedral site. A detailed crystal field study is also presented for the D3d distorted symmetry site.