Optical study of Yb³⁺/Yb²⁺conversion in CaF₂crystals

Abstract

Yb(3+) ions with various site symmetries have been observed in the absorption and emission spectra of Yb(3+):CaF(2) crystals, both γ-irradiated and annealed in hydrogen. The absorption intensity value is found to be much higher for the γ-irradiated crystal and strongly dependent on the gamma dose. The UV absorption spectra of γ-irradiated and H(2)-annealed CaF(2):5 at.% Yb(3+) crystals are quite similar. Yb(2+) absorption bands are observed at 360, 315, 271, 260, 227 and 214 nm, which are called A, B, C, D, F and G bands, respectively. For γ-irradiated CaF(2):30 at.% Yb(3+), an additional band at 234 nm can be seen. It is suggested that only a negligible amount of Yb(3+) ions are converted into Yb(2+) under the γ-irradiation. The presence of Yb(2+) is confirmed by the 565 and 540 nm luminescence under 357 nm excitation. It is also suggested that the excitation in the A, C, D and F absorption bands of Yb(2+) gives rise to photo-ionization of Yb(2+) ions and electrons in the conduction band to form the excited Yb(3+) ions which emit IR Yb(3+) luminescence.The UV absorption and emission spectra obtained for γ-irradiated and H(2)-annealed crystals have different structures. This suggests that different mechanisms are responsible for the creation of Yb(2+) ions. γ-irradiation favours Yb(2+) isolated centres by reduction of Yb(3+) ions located at Ca(2+) lattice sites, whereas annealing in hydrogen favours Yb(2+) centres neighbouring Yb(3+) ions when a Yb(3+) ion pair captures a Compton electron. Also, γ-irradiation does not change the position of Yb(3+) ions converted into Yb(2+) in the CaF(2) lattice. In the case of H(2) annealing, a Yb(3+) ion converted to Yb(2+) is shifted to the Ca(2+) position in the lattice.

Influence of Various Impurities on the Optical Properties of YbF3-Doped CaF2Crystals

“…These bands are consistent with other reported experiments and calculations [1,3,4,[6][7][8][9]12]. The UV region absorptions can be related to the 4f 14 −4f 13 5d transitions of the Yb 2+ ions [1,3,6,12].…”

“…For Yb 3+ ions the strongest absorption band peak appears around Y 4 = 979 nm and corresponds to C 2v or C 3v symmetries. The other peaks, called Y 1 , Y 2 , and Y 3 bands, are also observed by several investigators, but there are some discrepancies between their spectra [1][2][3][4]. The sharp Y 1 = 922 nm band has not been reported by [4] but has been observed by [3,9,11].…”

“…Several of RE ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF 2 . The change of valence has been attained by various methods [1][2][3][4][5]. There are a few reported results [6][7][8] about the properties of the Yb 2+ -ions, with high concentration in the as-grown crystals.…”

Gamma radiation effects in Yb-doped optical fiber

“…Some authors have speculated that decreases in Yb clustering might be the origin of the radiation hardness exhibited by some Yb-doped fibers 17 . A further possibility, which is known to occur in certain fluorides, is the presence of a Yb 2+ /Yb 3+ conversion process, which could effectively absorb energetic photons, thus diminishing the potential for gamma-induced color-center formation 18 .…”

Crystal growth and spectroscopic characterization of Yb-doped and Yb, Na-codoped PbF2 laser crystals

“…1 of Ref. [21], which may originate from the Yb 2+ ion accompanied by an impurity or a lattice vacancy and the 4f 14 -4f 13 5d transitions of isolated Yb 2+ ions (O h site), respectively [22,23]. For thorough testify the existing of Yb 2+ ions and the impact of Na ions, the room temperature emission spectrum of Yb-, and Yb, Na-doped PbF 2 crystals excited with the 338 nm wavelength are shown in Fig.…”