Theoretical studies of theg-shift for Cr⁴⁺ions in GaN crystal from crystal-field and charge-transfer mechanisms

Abstract

The assignment of the 1.193 eV zero-phonon line of the 3d2 ion in GaN crystal to the internal luminescence of Cr4+ on the Ga3+ site is analysed. Based on this assignment, the g-shift Δg ( = g-gs) of the groundstate of this luminescence is calculated by considering not only the conventional contribution due to the crystal-field mechanism, but also the contribution due to charge-transfer mechanism. The calculated result shows good agreement with the observed value, suggesting that the assignment is reasonable. The calculated Δg due to the charge-transfer mechanism is opposite in sign and 62% in magnitude, compared with that due to the crystal-field mechanism, and so it cannot be neglected. It appears that for the 3d2 (or 3dn) ion with a high valence state in crystals (particularly, in the case of the ligand having small optical electronegativity), the reasonable explanation of the g-shift should consider the contributions from both the crystal-field and charge-transfer mechanisms.

Resonant optical spectroscopy and coherent control ofCr4+spin ensembles in SiC and GaN

“…Within GaN, similar measurements reveal that the ZPL energy is located at 1.193 eV (T = 1.8 K) [32]. While the identity of the impurity associated with the line at 1.193 eV is not universally agreed upon [32,34], the similarity of its optical and spin properties as compared to SiC:Cr and AlN:Cr [35], as well as recent computational results [37,38], suggest that chromium is the most likely candidate. Very weak phonon sideband emission is observed for all three species, with a small number of discrete phonon modes being clearly visible in the PL signature of each sideband [31,32].…”

Investigations of the electron paramagnetic resonance parameters and atomic positions for Co2 ions in 3C-, 2H- and 4H-ZnS

“…The small discrepancies cannot be removed by changing the values of the adjustable parameters δ(i) and ε(i), because the contributions to the g-shift g i come mainly from the second-order perturbation terms which are independent of the trigonal distortions and hence of δ(i) and ε(i). In fact, for the g-shifts g i of the d n ion in crystals, besides the above crystal-field mechanism, the contribution due to the charge-transfer mechanism has been pointed out by some authors [27][28][29]. The relative importance of the charge-transfer mechanism depends upon the energy differences between the charge-transfer energy levels and the ground state.…”