Prof. Velin Nikolov Profile

Prof. Velin Nikolov

at Institute of General and Inorganic Chemistry

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Publications (2)

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Proceedings Article | 15 November 2007 Paper

Al2-X MeX (WO4)3 single crystal, Ме=Sc, Y, Ga and In, as a new tunable laser media

Donka Ivanova, Velin Nikiolov, Pavel Peshev

Proceedings Volume 6740, 67400N (2007) https://doi.org/10.1117/12.736831

KEYWORDS: Crystals, Aluminum, Gallium, Sodium, Solids, Lithium, Ions, Tunable lasers, Chromium, Laser crystals

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The crystallization conditions of Al₂(WO₄)₃ from Li₂O-WO₃ solvents (molar ratio 30.0:70.0, 32.5:67.5, 35.0:65.0, 45.0:55.0 and 55.0:45.0) as well as from Na₂O-WO₃ solvents (molar ratio 25.0:75.0, 27.5:72.5, 30.0:70.0 and 32.5:67.5) have been investigated. The concentration and temperature regions of crystallization of Al₂(WO₄)₃and the density, viscosity as well as the solution losses due to evaporation have been established. On the basis of the data obtained it has been concluded that the most suitable solvent for growing Al₂(WO₄)₃ single crystals is Na₂O-WO₃ with a molar ratio of 27.5:72.5. The temperature and concentration regions of crystallization of Al_2-xMe_x(WO₄)₃ solid solutions obtained by replacement of Al2O3 in the Na₂O-Al₂O₃-WO₃ system by Ga₂O₃, In₂O₃, Sc₂O₃ or Y₂O₃ have been investigated. The crystallization regions and concentration boundaries of existence of the solutions are found to depend strongly on the nature of the replacing element. Solid solutions containing Sc and In crystallize from high-temperature solutions with a lower concentration as compared to that of pure Al₂(WO₄)₃, this being accompanied by a high distribution coefficient of the substituting ion. On the contrary, Ga and Y containing solid solutions crystallize from high-temperature solutions with much higher concentrations, the distribution coefficient of the substituting ions being relatively low. The experimental obtained data are the basis for growing bulk single crystals with preset compositions from the Al_2-X Me_X (WO₄)₃, Me=Sc, Y, Ga or In, solid solutions.

Proceedings Article | 9 August 2007 Paper

Cr3+ doped NaAl(WO4)2 crystal as a new broadband laser material

V. Nikolov, I. Nikolov, P. Peshev

Proceedings Volume 6731, 67311Q (2007) https://doi.org/10.1117/12.752939

KEYWORDS: Crystals, Chromium, Sodium, Absorption, Aluminum, Laser crystals, Luminescence, Crystallography, Laser applications, Ions

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The growth conditions of single crystals of the new double tungstate of sodium and aluminum, NaAl(WO₄)₂ have been investigated. Data have been obtained on the concentration and temperature regions of crystallization of this compound in the system Na₂O-Al₂O₃-WO₃. Nontsoichiometric high-temperature solutions with very low crystallization temperatures, low viscosity and absence of volatility have been found and used for growing pure and differently Cr³⁺- doped single crystals of NaAl(WO₄)₂ by the top seeded solution growth (TSSG) slow cooling. technique. The main defects of the crystals obtained have been established, the reasons for their appearance analysed and single crystals free from inclusions were grown. Measurements of the optical characteristics of samples with chromium concentrations in the range 1.4x 10¹⁹-1.3x 10²⁰ atoms/cm³ were carried out. Absorption and luminescence spectra of Cr³⁺ : NaAl(WO₄)₂ were obtained at temperatures between 6 and 300 K and the temperature dependence of the Cr³⁺ luminescence lifetime was established. The Dq/B value found indicates that Cr³⁺:NaAl(WO₄)₂ belongs to the intermediate field site crystals. The results show that the new crystal is a good candidate for broadband laser applications.

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