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Heavy metal oxide (PbO and BiO) glasses doped with transition metal (TM) ions (TiO, VO, CrO, and MnO) and having low content of common glass formers (BO, SiO, or PO) were prepared by the conventional melt annealing method. Ultraviolet, visible absorption, and photoluminescence properties of these glasses were measured, and the data were employed to investigate the prepared glassy samples. The optical absorption spectra of TiO and VO exhibited three bands centered at about 240, 305, and 380 nm, followed by a broad asymmetrical near-visible band centered at 425-432 nm, while CrO and MnO exhibited an extended visible peak at 517-548 nm. Results showed that the luminescence intensity changed with different transition metal oxides. From the absorption edge data, the values of the optical band gap E and Urbach energy (ΔE) were calculated. The calculated values of the optical energy gap were found to be dependent on the glass composition. The changing values of optical band gap and band tail can be related to the structural changes that are taking place in the glass samples. The variations of the luminescence intensity, values of optical band gap, band tail, and refractive index gave an indication of the potential use of the prepared glasses to design novel optical functional materials with higher optical performance. [ABSTRACT FROM AUTHOR]

A pump-probe method is used to study the dynamics of the destruction of color centers in KYF:Ce and KYF:Ce,Yb crystals by continuous UV radiation and to measure its parameters. The effect of Yb ions in crystalline KYF:Ce,Yb on the rate of bleaching of color centers in it under exposure to the probe light is studied. Irradiation of KYF:Ce and KYF:Ce,Yb crystals at a wavelength corresponding to an absorption band of a color center accelerates the destruction of the color centers and the reduction of Yb ions to the trivalent state in proportion to the density of the radiation. A model is constructed for the bleaching mechanism that can be used to estimate the ionization cross section of the color centers. [ABSTRACT FROM AUTHOR]

A method is developed for determining the mean lifetime of anion vacancies in dielectric crystals following irradiation. This method is used to study the temporal kinetics of the concentrations of vacancies and F color centers in lithium fluoride crystals irradiated by ionizing radiation. It is then possible to study the dependences of the vacancy lifetime on the concentration of F1 color centers, temperature, and impurity content of a crystal. Vacancy and F color lifetimes determined by this method are given. [ABSTRACT FROM AUTHOR]

New bands within the ranges of 1900–2200 and 700–1000 cm–1 have been discovered in the IR absorption spectra of crystalline alkali-earth fluorides. It is found that the defects responsible for the high frequency bands facilitate the formation of color centers during crystal growth. These bands are presumably caused by valence vibrations of CO molecules. The low frequency bands are attributed to molecular complexes which contain oxygen-vacancy dipoles. [ABSTRACT FROM AUTHOR]

The diffuse reflection spectroscopy technique was used to investigate the color centers (CC) in the products of thermolysis and photolysis of disperse Al(OH)3 in a vacuum. The spectra were recorded in situ in the region of 2.5–6.0 eV and 4000–12,000 cm−1. It was found that in thermolysis of Al(OH3) production of Al is accompanied, by transformation of the IR spectra of the compound and overtone vibrations of OH groups and by the appearance of an absorption band (AB) at 4.0 eV with a shoulder at 4.4 eV. A similar AB is induced by UV irradiation of Al(OH)3 in a vacuum. In the position of the maximum and shape, the AB at 4.0 eV in aluminum oxide produced by thermolysis of Al(OH)3 coincides with the AB of CC responsible for light- and temperature-stimulated degradation of white anode oxide coatings on Al(Al-AOC). This suggests that in Al-AOC, CC are formed in decay of structural OmHn groups. In Al oxide and in Al-AOC, their nature is discussed with the use of data on optical absorption of radiation-induced defects in Al2O3. [ABSTRACT FROM AUTHOR]

Photostimulated degradation of the reflectivity of white anodic-oxide coatings on Al alloy (Al-AOCs) that are used as thermal-regulating coatings of space vehicles is investigated by spectroscopy of diffuse reflection in the region of 0.5–6 eV. It is established that irradiation in vaccum when λ≤300 nm leads to the appearance in diffuse-reflection spectra of the absorption bands at 4.0 and ∼4.6 eV that are similar to these induced by vacuum heating for T≥350 K. A growth in the absorption bands is accompanied by gas release from the coatings. These processes have a common excitation spectrum, basic kinetic regularities, and a thermoactivated character. UV irradiation in vacuum is assumed to initiate Al-AOC destruction with the formation of color centers. This process is accompanied by the desorption of molecular products. [ABSTRACT FROM AUTHOR]

Using the spectroscopic method of diffuse reflection in the region between 0.5 and 6 eV, we investigate the degradation of reflectivity in thermal vacuum treatment of white anodic-oxide coatings on an Al alloy (Al–AOC) that are used as thermoregulating coatings of space vehicles. It is established that at T≥350 K absorption bands at 4.05 and ∼4.7 eV resembling those induced by UV irradiation in vacuum appear in the diffuse reflection spectra of Al–AOC. The kinetics of the increase of absorption in heating Al–AOC with a constant rate correlates with the rate of gas liberation from specimens. We assume that a thermally activated reaction with the formation of color centers identical to those produced by the photoeffect occur in Al–AOC in vacuum at T≥350 K. This process is accompanied by desorption of molecular products. [ABSTRACT FROM AUTHOR]