Two-photon spectroscopy of MgO:Ni2+

Abstract

We report polarized two-photon excitation spectra of the 'A2~'T&, 'E, and a 'T, transitions of Ni -doped MgO measured by detecting the T2~' A 2 infrared luminescence with a Ge photodiode. Two-photon excitation spectra of the 'A2~'T2 and b'T& transitions were measured by monitoring the visible emission from the T2 state. Hidden zero-phonon lines have been revealed as well as even-parity vibrational features. Additionally, the assignments of the well-known onephoton, odd-parity vibronic spectra have been confirmed by comparison with the two-photon spectra. The two-photon polarization ratios were measured for the T2(E) and 'T2( T i ) zero-phonon lines and an intensity calculation using only the d electrons was performed. The failure of this calculation demonstrated that the ligands significantly contribute to the overall two-photon intensity.

Alternative configuration interaction expansions for transition metal ions with intermediate oxidation states in crystals: The structure and absorption spectrum of Cs2GeF6:Mn4+

“…In particular, a recent calculation of the vertical absorption spectrum of the MnF 6 2Ϫ cluster embedded in the Cs 2 GeF 6 host 4 using the averaged coupled pair functional ͑ACPF͒ 7 led to very large discrepancies with accurate oneand two-photon spectra, [8][9][10] even though the same multireferences and truncated expansions had previously been used successfully in similar systems involving transition metal impurities in lower oxidation states. On the other hand, the Mn͑IV͒ impurity could not be handled as in the high oxidation state limit ͓e.g., Fe͑VI͒ in tetraoxo complexes in the solid state and aqueous solution 3 ͔ where the quasidegeneracy effects are more important than dynamic correlation and long multiconfigurational self-consistent field ͑MCSCF͒ wave functions are indicated.…”

Ab initio model potential calculations on the electronic spectrum of Ni2+-doped MgO including correlation, spin–orbit and embedding effects

“…We should mention now that the analysis by Campochiaro et al 13 of the results of the two-photon excitation measurements, whose selection rules for single frequency experiments allow to observe spin-orbit components of all of the excited states as well as to distinguish different components by means of their different polarization, was able to interpret the long-known spectrum in much detail. In consequence, we do not comment here on all the previous studies facing the assignment problem, and we rather refer only to Campochiaro's et al work, 13 which represents the present status of the assignments of the ligand field states in MgO:Ni 2ϩ .…”

“…In effect, the importance of electron correlation in order to understand the electronic structure of transition metal impurities in ionic crystals is out of the question. 19 Also, the spin-orbit splittings are a relevant part of the electronic spectra of Ni 2ϩ impurities in ionic crystals 13 and, although in this case the spin-orbit effects could probably be handled by perturbation techniques, they could hardly be neglected. Finally, evidences are being accumulated that embedding effects are important for a reliable description of the electronic spectra of this kind of doped solid state materials, both because of their direct effect on the transition energies and because of their indirect effect through the ground and excited states equilibrium structures.…”

“…Electron paramagnetic resonance, 1 optical absorption and emission, [1][2][3][4][5][6][7][8][9] magnetic circular dichroism, 10 excited state absorption and excited state emission, 8,11,12 and two-photon excitation 13 experimental studies have been conducted in this material. Theoretical models based on empirical data exist as well.…”

“…The Ni 2ϩ -doped MgO lasing material has been extensively studied using spectroscopic techniques, [1][2][3][4][5][6][7][8][9][10][11][12][13] mainly because the Ni 2ϩ substitutional defect is in a rigid, highly symmetrical site, which reduces the complications of the spectral analysis and makes it an ideal prototypical system for testing interpretative models of the spectroscopy of Ni 2ϩ impurities in sixfold coordination in ionic crystals. Electron paramagnetic resonance, 1 optical absorption and emission, [1][2][3][4][5][6][7][8][9] magnetic circular dichroism, 10 excited state absorption and excited state emission, 8,11,12 and two-photon excitation 13 experimental studies have been conducted in this material.…”