Optical, EPR, and ENDOR Studies of CdF2:V3+, V2+

Abstract

Single crystals of CdF2 containing either V3+ or V2+ ions have been prepared and studied by optical, EPR, and ENDOR techniques. As expected, the properties of V3+ in the eight-coordinated (cubal) environment closely resemble those of Ni2+ in octahedral sites. The ENDOR data show that Ms = ± 1, confirming the identification of the ion as V3+. The V2+ ions, produced by heating samples containing V3+ in Cd vapor, exhibit evidence for a large trigonal Jahn–Teller distortion of the cubal site. On the basis of the EPR and optical data it is suggested that the environment about the V2+ ions may be more nearly octahedral than cubal, thus reflecting the presence of a static trigonal field comparable in magnitude to the (undistorted) cubic field. Some optical and EPR data are presented for isoelectronic Cr3+ ions, which also display a strong Jahn–Teller effect.

Transition Metal Ions in Crystals with the Fluorite Structure

“…18): the 4T,g ground state is split by the trigonal component of the crystal field into an upper 4E and a lower 4A2 state where the latter exhibits a zero-field splitting of 2 0 so that two Kramers doublets I f 112) and I &3/2) result. The temperature dependence of the intensity of the EPR signal measured on CdF, :V2+ between 1.5 and 4.2 K gives the suggestion that the I &3/2) state is the lower one, i. e. D < 0 [50]. That the trigonal distortion is probably of the same considerable strength as for Ni2+, i. e. d, is of the same magnitude as 10 Dq, can be seen from the small anisotropy of the g-values ([2], p. 431).…”

“…The obtained parameters G and 2 which characterize the splitting of the spin levels and the hyperfine splittings are given in Table 6. But the experimental parameters must be corrected, because they were x em-l, [50] of the linewidth no other information strdng angular dependence 3 !i? the H F interaction of the electron magnetic moments with their own nuclear spin moments was determined by ENDOR measurements in the X-band a t 17 = 4.2 K more precisely ( Table 7).…”

“…The origin of the weak bands remains unexplained, their assignment to V2+ [50] is doubtful. No interpretation exists for the spectrum measured after heating of this crystals in Cd vapour, possibly it is due to precipitated VF,.…”

“…An interpretation of this spectrum as due to Cr3+ in cubic or axially distorted (likeNi2+) eightfold environment is not possible. It has been proposed [50] that the EPR and optical spectra of CdF3:Cr3+ can be consistently interpreted assuming octahedrally coordinated Cr3 + centres [CrF,I3-with a small trigonal distortion rather than eightfold cubically coordinated ones. Following this, the intensive bands are the 4A2, --f *Tzg(F) and + 4Tlg(F) transitions giving the reasonable parameters Dq = 1520 cm-l and B = 790 cm-l, and their splittings by about 700 cm-1 are due to the trigonal distortion.…”

Theoretical investigation of the optical spectra andgfactors for Cu2+in dioptase

“…The local structure of the Cu 2þ centre in the Cu 6 Si 6 O 18 Á 6H 2 O crystal is approximate D 4h symmetry. A number of methods [3][4][5], such as extended X-ray absorption fine structure (EXAFS), magnetic resonance (electron paramagnetic resonance (EPR) and electron-nuclear double-resonance (ENDOR)) and optical spectrum, are used to study the local structures of paramagnetic ions in crystals. The EPR and optical spectrum methods are powerful tools for establishing the local structure of the immediate environment of the paramagnetic ion in crystals [5][6][7][8].…”