Formation of hydrogen-bonded complexes in alkali-halide crystals containing trace hydroxyl

Bryukvin, V. V.; Bryukvina, L. I.

doi:10.1007/bf00679257

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“…As is well known [4,5], molecular complexes with the hydrogen bond (H-bond) absorbing in the IR range of the spectrum from 500 to 3700 cm -1 can be formed in such crystals upon exposure to ionizing radiation. According to our data, there are no studies devoted to the formation of molecular complexes with the Н-bond in nonirradiated ionic crystals.…”

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Oxygen- and Hydrogen-Containing Impurity in Laser-Active Matrices of Alkali and Alkaline-Earth Metal Fluorides

2005

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Presence of oxygen-and hydrogen-containing impurities in alkali and alkaline-earth fluorides influences significantly the optical and thermal properties of both impurity and radiation-induced defects in laser crystals [1,2]. For alkali-halide crystals, for example, a number of models have been suggested, which include native (color centers) and impurity defects changing considerably thermal and photostability of color centers [3].In alkali-halide and alkaline-earth metals, infrared bands generated by valence vibrations of hydroxyl ions, both free and distorted by impurity cations, occupy the range 3400-3740 cm -1 . As is well known [4,5], molecular complexes with the hydrogen bond (H-bond) absorbing in the IR range of the spectrum from 500 to 3700 cm -1 can be formed in such crystals upon exposure to ionizing radiation. According to our data, there are no studies devoted to the formation of molecular complexes with the Н-bond in nonirradiated ionic crystals.In this regard, we have investigated alkali and alkaline-earth fluorides with oxygen-and hydrogen-containing impurities to study the formation of molecular complexes with the Н-bond (ν̃ = 3500-3700 cm -1 ) just after synthesis of crystals not subjected to irradiation or photo and thermal treatment.LiF:Co, LiF:Ni, NaF:Co, MgF 2 :Co, and MgF 2 :Ni crystals grown by the Czochralski method with addition of СoF 2 and NiF 2 in the melt were investigated. The absorption spectra were measured in the visible and infrared ranges of the spectrum with Specord UVVIS and IFS25 spectrophotometers at room temperature. Bands characteristic of bivalent Co and Ni ions [6,7] were observed in the spectra recorded in the visible range. In the IR spectra of the examined crystals, wide bands were observed in the range 2500-3750 cm -1 and no absorption bands corresponding to valence vibrations of single anion-substituting OH ¯ or OH ¯ ions distorted with impurity cations were detected in the range 3500-3740 cm -1 . Figure 1 shows the spectrum of the LiF:Co crystal (curve 1) in which the band between 2500 and 3700 cm -1 is well pronounced together with the spectrum of the LiF:Co crystal γ-irradiated with a doze of 10 8 R (curve 2). As already pointed out above, bands in the range 2500-3700 cm -1 were caused by molecular complexes with the Н-bond previously observed only in irradiated or irradiated and thermally treated crystals. From Fig. 1 (curve 2) it can also be seen that crystal complexes with the Н-bond absorbing in the range 2500-3700 cm -1 decompose after γ-irradiation .These complexes behave analogously when they are formed on irradiation of alkali fluoride crystals with hydroxyl ( Fig. 2) [8]. Curve 1 in Fig. 2 shows the spectrum of the initial LiF:ОН, Мg crystal, curve 2 shows the spectrum of the crystal irradiated with a doze of 10 7 R, and curve 3 shows the spectrum of the crystal γ-irradiated with a doze of 10 8 R. It can be seen that defects with the 2500-3700 cm -1 absorption band first are formed and then decay as the irradiation doze increases, and the 1900-2200 cm -1 ...

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