Abstract:By using pressure to vary the extent of nontetrahedral distortions of the Cr4+ site in Mg2SiO4, we reveal the important influence of the 3T1 state on the emission properties of the 3T2 state. We find that 3T1-3T2 mixing has a pronounced effect on the line shape and radiative decay rate of emission from the 3T2 state and that the extent of mixing depends critically on the magnitude of nontetrahedral distortions. The results provide an explanation for the wide variation of Cr4+ emission properties in different h… Show more
“…Similarly, the evolution of α zz as a function of energy for the Mn-Mg The energy diagram for the 3d 2 configuration of specific ions in GaN was already reported for Ti 2+ [36], V 3+ [37][38][39], and Cr 4+ [37,40]. Here, for the particular case of 3d 2 Mn 5+ , we follow the Tanabe-Sugano approach -based on the occupancy of the d-shell of the transition metal and on symmetry considerations-accounting for the splitting of the energy levels, due to the crystal field [41].…”
Section: Nature Of Infra-red Emission a Resonant Excitationsupporting
By combining experimental photoluminescence excitation spectroscopy and calculations based on density functional theory and many-body Green's functions, the most efficient excitation channels of infra-red (IR) emission from Mn-Mg k paramagnetic complexes stabilized in GaN:(Mn,Mg) are here identified. Moreover, a Tanabe-Sugano energy diagram for 3d 2 Mn 5+ is reconstructed and Mn-Mg 3 are singled out as the predominant configurations responsible for the IR emission. The correlation of intensity of the individual emission lines as a function of temperature and excitation energy, allows assigning them to well defined and specific optical transitions.
“…Similarly, the evolution of α zz as a function of energy for the Mn-Mg The energy diagram for the 3d 2 configuration of specific ions in GaN was already reported for Ti 2+ [36], V 3+ [37][38][39], and Cr 4+ [37,40]. Here, for the particular case of 3d 2 Mn 5+ , we follow the Tanabe-Sugano approach -based on the occupancy of the d-shell of the transition metal and on symmetry considerations-accounting for the splitting of the energy levels, due to the crystal field [41].…”
Section: Nature Of Infra-red Emission a Resonant Excitationsupporting
By combining experimental photoluminescence excitation spectroscopy and calculations based on density functional theory and many-body Green's functions, the most efficient excitation channels of infra-red (IR) emission from Mn-Mg k paramagnetic complexes stabilized in GaN:(Mn,Mg) are here identified. Moreover, a Tanabe-Sugano energy diagram for 3d 2 Mn 5+ is reconstructed and Mn-Mg 3 are singled out as the predominant configurations responsible for the IR emission. The correlation of intensity of the individual emission lines as a function of temperature and excitation energy, allows assigning them to well defined and specific optical transitions.
“…Shen and Bray recently mentioned that controlling the local distortion around the transition-metal centers would lead to the design of new optical materials. 44 We support their direction. However, we consider that the meaning of the ''distortion'' should also include the recombination of the wave functions that change the covalency.…”
The multiplet structure of the tetrahedrally coordinated Cr 4ϩ in Y 3 Al 5 O 12 ͓yttrium aluminum garnet ͑YAG͔͒ was calculated by the ab initio electronic-structure calculation method. The authors examined the dependence of the multiplet structures on the size of cluster models, with the use of (CrO 4 ) 4Ϫ ͑without point charges͒, (CrO 4 ) 4Ϫ ͑with point charges͒, (CrY 6 Al 4 O 44 ) 54Ϫ , and (CrY 18 Al 42 O 148 ) 112Ϫ models. The covalency of the impurity-level molecular orbitals was analyzed, and it was revealed that the wave functions of the atoms outside the CrO 4 tetrahedron should not be neglected. The validity of the assignment of the peaks in the absorption spectrum written in the literature was evaluated by the calculated magnitude of the spin-orbit splittings and the oscillator strengths of the transitions, which were obtained by the fully relativistic many-electron calculation. The effect of the codopant on the transition probability was also estimated by (CrCaY 5 Al 4 O 44 ) 55Ϫ models. It was indicated that the nearest Cr-Ca pairs would reduce the symmetry, and could produce some satellite peaks. The mixing of the wave functions of the triplet states was numerically analyzed, and the results were correlated with the transition probability. The traditional nephelauxetic parameter was estimated, and the value 0.51 was obtained. It was confirmed from first principles that the magnitude of the nephelauxetic parameter in some literature was appropriate.
“…Thus, sudden changes in phenomenological CFPs as those observed mainly around 30 kbar could be attributed to an emerging dominant axial component of the pressure-induced volume compression of the unit cell of Eu(SO 4 ) 2 ‚NH 4 . 8,11,28,41,42 In other words, changes in the main axial component of the nonhydrostatic induced compression at a given pressure can account for important modifications of trends in CFPs.…”
Section: Resultsmentioning
confidence: 99%
“…Moreover, these calculations indicate that the evolution of the crystal field interactions in Eu(SO 4 ) 2 ·NH 4 is highly anisotropic, and only the effect of the compression along c is close to the effect of the hydrostatic compression. Thus, sudden changes in phenomenological CFPs as those observed mainly around 30 kbar could be attributed to an emerging dominant axial component of the pressure-induced volume compression of the unit cell of Eu(SO 4 ) 2 ·NH 4 . ,,,, In other words, changes in the main axial component of the nonhydrostatic induced compression at a given pressure can account for important modifications of trends in CFPs. 8 Variation of simulated (a), (b), and (c)Eu 3+ crystal field parameters vs hydrostatic H (▪), a (·) , b (▴) and c (▾) volume compressions of Eu(SO 4 ) 2 ·NH 4 .…”
The possibilities of the use of Eu3+ in extracting information of the pressure effects on the nature of its crystal site in the NH4.Eu(SO4)2 catalytic host are closely inspected through the study of emission spectra for applied pressures up to 87 kbar. The phenomenological crystal field analysis of these spectra reveals clear discontinuities, at approximately 30 kbar, the sharper ones, and then at approximately 70 kbar, in crystal field strength trends, which taken together with structure-based simulations of crystal field interactions indicate well-defined pressure-induced anisotropic distortions in Eu3+ local environments.
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