Orthorhombic and Trigonal Electron-Spin-Resonance Spectra ofCe3+Ions in CaF2

Abstract

ISING CHAIN WITH SPIN IMPURITY 311given in Sec. 2, it follows from inspection that a ± 2 +b ± 2 =a + 2 +aJ= b + 2 +bJ= 1, and a + a-+b + b^.= a + b + +a-b-.=0.With the above information one obtainsBy using the fact that in the bulk limit (coV^-f)^""^2"""^ for positive temperatures and t=2, 3, • •, 2V/2-1, one findsFrom (Al) and (A2) ar 1 i(^)/d^| t , t=1 = w+^( a + 2 -~6 + 2 ), dri2(t?)/dt;| v=a i=co + Z"^(a + a_--& + 5_),rn(l) = w + , ri 2 (l) = r 21 (l) = 0, and (d/dv) (rn (») T21 (») + T12 (t>) T 2 2 (») ) | v**l = 2a) + oo-J[h (a + a^-b+bJ).After referring back to (1), (30, and the derivation of (2) one arrives at (9) by differentiating with respect to X in (A3) and substituting Z=(2S+l)ai+x-2 D,Two new electron-spin-resonance spectra, one having trigonal and the other having orthorhombic symmetry, have been observed in CaF 2 doped with small amounts of Ce0 2 . The x and y axes of the orthorhombic spectrum lie in the (110) plane and are tilted by an angle 5= 13.8±0.2° from the [110] and the [001] axes, respectively, and the z axis lies along the [110] axis. The components of the g tensor for the two spectra are: orthorhombic, fo-0.844dz0.001, & = 0.22=1=0.05, g*=3.286±0.001; trigonal, g u =3.673±0.002, £i<0.3,

Understanding of the oxygen activation on ceria- and ceria/alumina-supported gold catalysts: a study combining 18O/16O isotopic exchange and EPR spectroscopy

“…The EPR study was first performed over CeO 2 and Au/CeO 2 . Again, the pretreatments had to be ; however, according to the literature, such paramagnetic ion could be observed at very low temperature only (T <20 K) [41,42]. Some authors proposed that this signal originated from Ce 3+ in peculiar geometry/ symmetry [43,44], while other authors proposed that it arises from quasi-free electrons with some orbital mixing with the empty f-orbitals of Ce 4+ ions [23,45].…”

EPR Investigations ofCe3+in Cubic Sites of CaO, SrO, and BaO

“…Although it is impossible on the basis of the g value alone to distinguish between the two values of cp, they can be related to the cubic-crystal-field parameters. The cubic-crystal-fie Id Hamiltonian is given by the expression" 7 C = B 0 (4) [C 0 < 4) +(A) 1/a (C. 4 < 4 > +C +4 (4 >)] + B 0 < 6 >[C 0 < 8 > -(^) 1/2 (C. 4 (8) +C +4 < 8 ')]…”

“…For Er 3+ in MgO, CaO, and SrO and for Nd 3+ in CaO, 19 " 21 the experimentally determined ratio J3 0 (6) /B 0 (4) i s larger than that computed from the simple point-charge model by a factor of approximately 1.5-2.0. Therefore, a ratio of B 0 (6) /B 0 (4) = 0.1 is probably a more accurate estimate for all the oxide hosts. The values of f* 0 (4) resulting from the latter ratio are shown in the last column of Table I (i.e., the alternate model).…”

“…For either value of cp, the crystal-field splittings computed from these parameters are anomalous- ly large. Figure 1 shows the computed splittings of Ce 3+ in CaO using both choices of £ 0 (4) and the B 0 iG) /B 0 (4) ratio given by the point-charge model. The splittings calculated for each J manifold can be compared to the splittings observed previously in other hosts and given in Table II.…”

Optical, infrared and EPR spectroscopy of CaF2:Ce3+ crystals co-doped with Li+ or Na+

“…For the parent CaF 2 :0.09%Ce 3+ crystal, the measured g values of g || =3.026 and g > =1.386 are those of the well-established C 4v (F À ) centre [6]. Annealing this CaF 2 :Ce 3+ sample in an O 2 atmosphere at 900 C, yields a trigonal Ce 3+ centre [C 3v (O 2À )], with charge compensation by O 2À along the [1 1 1] direction, whose observed g values are g || =3.67 and g > =0.31 [7].…”