Odd crystal field

Only three quantities, two odd crystal-field parameters B( and B and the energy distance E between the two configurations, were used as parameters in the calculations to describe the changes of the 5Do lifetime. Performing the fits, Shen and Bray (1998a) assumed a linear dependence of Bq, Bq/Bq, and Ed on pressure. As the result for the pressure dependence of these quantities they finally found (p in GPa, Ed and B in cm-1) ... 

Luminescence lifetime depends upon radiative and nomadiative decay rates. In nanoscale systems, there are many factors that may affect the luminescence lifetime. Usually the luminescence lifetime of lanthanide ions in nanociystals is shortened because of the increase in nomadiative relaxation rate due to surface defects or quenching centers. On the other hand, a longer radiative lifetime of lanthanide states (such as 5Do of Eu3+) in nanocrystals can be observed due to (1) the non-solid medium surrounding the nanoparticles that changes the effective index of refraction thus modifies the radiative lifetime (Meltzer et al., 1999 Schniepp and Sandoghdar, 2002) (2) size-dependent spontaneous emission rate increases up to 3 folds (Schniepp and Sandoghdar, 2002) (3) an increased lattice constant which reduces the odd crystal field component (Schmechel et al., 2001). 

The sign of M is clearly related to the symmetry of the coordination sphere around the rare-earth ion through the q value which appears in the odd crystal field terms ... 

Another view on the role of the odd crystal field terms in MCD... 

Thus the odd crystal field terms mix in the M ) excited states 2),... 

The energy diagram is considered in the rotation schemes x y z x and X y z X (Prather, 1961). Now the absorption of circularly polarized light is governed by the rotated odd crystal field terms. The relevant odd crystal field terms are given in Table 1. 

Odd crystal field terms acting between the wave function (M quantum number) of the f-configuration in the bra and the wave function of the mixing configuration in the ket. 

Fig. 19. Composite two-photon excitation spectrum of the 4f ->5d transition in 0.003% in CaF, at 6K. The transition is studied by monitoring the 5d— 4f, no phonon transition occurring at 313.1 nm. As noted in text this transition is normally two-photon forbidden because of parity selection rules, however, odd crystal-fields components admix parity to make the transitions partially allowed. The pure electronic transition of the state is labeled as 0 other excitations, 1 to 12, are identified as phonon or normal mode excitations of the lattice which couple to the pure transition. Selection rules for assisted transitions follow selection rules which differ from the one-photon case. After Gayen and Hamilton (1982).

The parity prohibition can be lifted only by the influence of the crystal lattice. Just as the spin prohibition was cancelled by mixing of the F state with the state as a result of spin-orbit coupling, so too can the parity prohibition be cancelled by mixing the 4 configuration with a state possessing a different parity. The interaction responsible for this is formed by the odd crystal-field terms, that is to say those terms that change sign on inversion with respect to the R ion. If the R ion is located at a site that is a centre of symmetry in the crystal lattice, the odd crystal field terms are absent and the parity prohibition cannot be lifted. 

Intensity parameters for the lanthanide ions Ce through Yb " " doped into singlecrystal Lap3 have been calculated by Leavitt and Morrison (1980). They used wave-functions generated by A = even crystal-field parameters determined from a point-charge model. The k = odd crystal-field parameters have been calculated on the basis of the same... 

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