Optical Spectrum of Cr3+ Ions in Spinels

Abstract

The optical absorption and fluorescence spectra of two spinels, ZnAl2O4:Cr3+ and MgAl2O4:Cr3+ have been measured at various temperatures between 2°K and room temperature. The data have been fitted to a crystal-field theory which includes spin-orbit coupling and the trigonal field of the D3d site. The parameters for a best fit for both crystals were: Δ = 18 250 cm−1, B = 700 cm−1, C = 3200 cm−1, ζ = 250 cm−1, ν = −200 cm−1, ν′ = −1700 cm−1, and k = 0.7. The E2 splitting was directly observed optically for both spinels, and in the case of the ZnAl2O4:Cr3+, the A24 splitting was also observed. In addition to fitting the energies and zero-field splittings, the theory gave values of absolute R-line intensities and lifetimes which agree well with observed values. Vibrational sidebands and pair lines observed in fluorescence were identified.

Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar

“…These modes are attributed to translations of the Mg 2 + cation in its tetrahedral site. This assignment is corroborated by our new data on Fe and Zn aluminate spinels and by previous infrared and sideband spectra of Co and Zn aluminate spinels (Preudhomme and Tarte 1971;Wood et al 1968), because substitution of cations in the tetrahedral site produced significant decreases of frequency only for modes below 350 cm -1. In fact, for gahnite, the lowest Raman mode at 196 cm-1 is almost exactly equal to ]/~gMg/mz, x 312 cm-1 (= 190 cm-1),…”

“…Third, sideband fluorescence data (e.g. Wood et al 1968) provide direct measurement of the acoustic modes at the Brillouin zone edge. Thus, pressure dependence of the sidebands (Chopelas 1990a, b) can be related to pressure derivatives of sound velocities.…”

Structural relaxation around substitutionalCr3+inMgAl2O4Juhin1, Calas2, Cabaret3 et al. 2007Phys. Rev. B541340View full textAdd to dashboardCite

“…3a). This result is consistent with optical absorption 31 and Electron-Nuclear Double Resonance experiments 32 performed on MgAl 2 O 4 : Cr 3+ . Our firstprinciples calculations also agree with a previous investigation of the first shell relaxation, using Hartree-Fock formalism on an isolated cluster.…”

Near-infrared absorption properties of oxygen-rich stardust analogs

“…Additionally, two distinct absorption bands occur around 0.550 μm and 0.387 μm. The positions and shapes of these bands accordance well with the band positions in spectra of low-Cr Mg-Al-spinels -both natural and synthetic ones -published by Wood et al (1968), Taran et al (1994), and Ikeda et al (1997). These bands originate from crystal field electronic transitions, namely 4 T 2g ← 4 A 2g for the 0.550 μm maximum and 4 T 1g ← 4 A 2g for the 0.387 μm maximum.…”