Суперсверхтонкая структура спектров ЭПР примесных ионов Nd-=SUP=-3+-=/SUP=- во флюорите CaF-=SUB=-2-=/SUB=-

EPR spectra of a CaF_2 single crystal that was grown from melt containing a small addition of NdF_3 were studied. Signals corresponding to tetragonal centers of Nd^3+ ions and cubic centers of Er3+ and Yb3+ ions were found. Superhyperfine structure (SHFS) in the spectra of the Nd^3+ ions was observed for the first time in this crystal; parameters of the superhyperfine interaction of the Nd^3+ ions with the nearest nine fluorine ions were determined. The dependence of the resolution of the Nd^3+ EPR spectrum SHFS on the incident microwave power at the temperature of T ≈ 6 K was studied. Obtained results are discussed and compared with the literature data.

CENTROS PARAMAGNÉTICOS EM ELBAÍTA ROSA NATURAL E IRRADIADA.

Estudos espectroscópicos em turmalinas rosas naturais e tratadas de Minas Gerais, Brasil, foram feitosusando ressonância paramagnética eletrônica (EPR), detecção óptica da ressonância magnética(ODMR), absorção óptica e espectroscopia Raman. Microanálises indicam que todas as amostras têmcomposições próximas às do membro final elbaíta. O espectro EPR indica a presença de Mn2+.Medidas de absorção óptica mostram três bandas de absorção dominantes centradas a 460, 520 e 680nm, atribuídas às transições ópticas do Mn2+. Diferentes defeitos foram identificados na elbaíta rosapor EPR, como Mn2+, Fe3+, H0 e O- produzidos por g-irradiação. O último é um centro do tipo buracodo tipo O- e mostra interação superhiperfina com dois Al. É considerado como um centro de coramarelo do tipo Al-O-Al. O átomo de hidrogênio H0 é um centro de aprisionamento de elétrons, aopasso que o Fe3+ é um precursor de elétrons. A partir dos dados obtidos após tratamento térmico eirradiação, conclui-se que Mn2+ é o principal centro cromóforo da cor rosa, favorecido por um certo grau de desordem presente na estrutura dessa espécie. A irradiação intensifica a cor rosa pálida,enquanto o aquecimento a 4500C descolore o rosa. ABSTRACT: pectroscopy study of natural and treated pink tourmalines from Minas Gerais, Brazil, using electronparamagnetic resonance (EPR), optical detection of electron paramagnetic resonance (ODEPR),optical absorption and Raman spectroscopy is reported. Electron-microprobe analyses indicate thatall samples are close elbaite end-member. EPR spectra of natural pink elbaite indicate the presence of Mn2+ in to distinct Y site. Optical absorption measurements show three dominant absorption bands centered at 460, 520 and 680 nm in the pink tourmalines, which can be related with opticaltransitions of Mn2+. Different defects have been identified by EPR like Mn2+, Fe3+, H0 and O- producedby g-irradiation in pale pink elbaite. The last one is a hole trap of O- and considered a color center.It shows mainly superhyperfine interaction with two Al nuclei. Atomic hydrogen H0 is as electrontrap whereas the Fe3+ is an electron precursor. From irradiation and heat treatments we conclude thatthe Mn2+ is the precursor of the pink color in elbaites. Irradiation intensifies the pink color whereas heat treatments at about 4500C decolorize the pink tourmaline.

Superhyperfine Interactions of the Nitrogen Donors in 4H SiC Studied by Pulsed ENDOR and TRIPLE ENDOR Spectroscopy

The nitrogen donors residing at quasi-cubic lattice site (Nk) in 4H SiC were investigated by field sweep electron spin echo (FS ESE), pulsed electron nuclear double resonance (ENDOR) and pulsed General TRIPLE ENDOR spectroscopy. The 29Si and 13C superhyperfine lines observed in the FS ESE and ENDOR spectra of Nk in n-type 6H SiC were assigned by pulsed General TRIPLE resonance spectroscopy to the specific carbon (C) and silicon (Si) atoms located in the nearest environment of Nk in 4H SiC. The superhyperfine interaction constants and their relative signs for Nk with 29Si and 13C nuclei located in the nearest-neighbor shells are found from the General TRIPLE ENDOR spectra to be positive for C atoms and negative for Si atoms.

Investigations on the Hyperfine and Superhyperfine Interaction Parameters for Cs2GeF6:Mn4+

The hyperfine structure constant A and the superhyperfine interaction parameters Aʹ and Bʹ of Cs2GeF6:Mn4+ are theoretically studied by the cluster approach. The orbital mixing coefficients and the unpaired spin densities in 2s, 2pσ and 2pπ fluorine orbitals are obtained from the optical spectra and the impurity-ligand distance of the studied system. Based on a uniform scheme, the parameters A, Aʹ and Bʹ (as well as the g factor) are reasonably explained. The results are discussed, and the unpaired spin densities of the 2s, 2pσ and 2pπ orbitals of the ligand F− are compared with those in previous works.