N.I. Leonyuk

Structural aspects in crystal growth of anhydrous borates

A crystallochemical interpretation of acid-base properties was developed for the numerous anhydrous borates. A quantitative estimation was made of the correlation between the ratio of the numbers of B 3+ /O 2- ions and the oxygen activity coefficient. The stability of borate structures depends on the delocalization of formal charges of the B n O m anions as a result of their polymerization. This analysis and experimental studies consistently explain the high activation energy of borate crystallization by the polymerization of BO 3 triangles and BO 4 tetrahedra in their melts and fluxed melts. It also sets forth the judicious choices of phase systems for the growth of borate crystals. In particular, in order to obtain the orthoborate crystals, a wide range of flux agents can be proposed which destroy boron-oxygen polymers and intensify mass transfer in the fluxed systems.

Flux growth and luminescence of Ho : YAl3(BO3)4 and PrAl3(BO3)4 crystals

Abstract HoxY1−xAl3(BO3)4 and PrAl3(BO3)4 crystals have been grown from high-temperature solutions. Holmium segregation coefficients ranged from 1.08 to 1.40. Strong visible and near-infrared luminescence from Ho3+ and Pr3+ was obtained in the crystals with only weak-concentration quenching. Spectral evidence of energy transfer among Ho3+ ions was also observed. The simultaneous observations of low-concentration quenching and Ho3+–Ho3+ energy transfer suggest that YAl3(BO3)4 is a suitable host lattice for high-efficiency rare-earth energy transfer and sensitization schemes.

Crystal growth of solid solutions based on the YAl3(BO3)4, NdAl3(BO3)4 and GdAl3(BO3)4 borates

Abstract Single crystals of NdxY1−xAl3(BO3)4 (NYAB) and GdxY1−xAl3(BO3)4 (GYAB) have been grown from fluxed melts based on the potassium trimolybdate by both the TSSG method and spontaneous crystallization. Neodymium and gadolinium are practically uniformly distributed over the entire volume of crystals. The effective segregation coefficients of neodymium and gadolinium were found to be 0.3–0.8 and about 1 for NYAB and GYAB, respectively. In the case of NYAB, this coefficient increases with an increase in crystallization temperature and a decrease in the crystal growth rate. Growth striations are developed on the trigonal prism faces of the NYAB and GYAB crystals enriched by NAB and GAB which tend to form the monoclinic structures.

High-temperature crystallization and X-ray characterization of Y2SiO5, Y2Si2O7 and LaBSiO5

The laser crystals of chromium-doped yttrium oxyorthosilicate (YSO) were grown from melts by Czochralski technique. The crystals of YSO, yttrium pyrosilicate and stillwellite-like lanthanum borosilicate were obtained from high-temperature solutions. Lithium and potassium di- and trimolybdates were used as fluxes for silicate systems. In the case of borosilicate crystals, the choice of fluxes was based on potassium trimolybdate with an excess of potassium fluoride. The composition of grown crystals was studied by electron microprobe analysis, and structural characteristics were determined for all the single crystals.

Passively Q-switched microchip Er, Yb:YAl3(BO3)4 diode-pumped laser.

We report, for the first time to our knowledge, a diode-pumped cw and passively Q-switched microchip Er, Yb:YAl(3)(BO(3))(4) laser. A maximal output power of 800 mW at 1602 nm in the cw regime was obtained at an absorbed pump power of 7.7 W. By using Co(2+):MgAl(2)O(4) as a saturable absorber, a TEM(00)-mode Q-switched average output power of 315 mW was demonstrated at 1522 nm, with pulse duration of 5 ns and pulse energy of 5.25 μJ at a repetition rate of 60 kHz.

Crystallization of solid solutions based on double borates with huntite structure

Abstract Single crystals of RE x Y 1− x Al 3 (BO 3 ) 4 (REYAB), where RE=Nd, Gd, Ho, Yb and Lu, have been obtained from fluxed melts based on potassium trimolybdate. The Nd x Gd 1− x Al 3 (BO 3 ) 4 (NGAB) ( x =0.2) have also been grown by top seeded solution growth (TSSG) method. Effective segregation coefficients of rare earth elements were found to be 0.3–1.03, depending on the type of dopant cations. In the case of Nd x Y 1− x Al 3 (BO 3 ) 4 (NYAB), it increases with increasing Nd 2 O 3 /Y 2 O 3 ratio in the initial mixture. The crystal structure of Nd 0.17 Gd 0.83 Al 3 (BO 3 ) 4 was refined.

Crystal Growth and Structural Refinements of the Y2SiO5, Y2Si2O7 and LaBSiO5 Single Crystals

The laser crystals of chromium doped yttrium oxyorthosilicate (YSO) were grown from the melt by Czochralski technique. The crystals of YSO, yttrium pyrosilicate and stillwellite-like lanthanum borosilicate were obtained from high temperature solutions. Lithium and potassium di- and trimolybdates were used as fluxes in the growth experiments on silicate crystals. In the case of borosilicate crystals, the choice of fluxes was based on the potassium trimolybdate with an excess of potassium fluoride. The composition of grown crystals was studied by electron microprobe analysis, and structural characteristics were determined for all the single crystals.

Eye-safe 1.55 μm passively Q-switched Er,Yb:GdAl3(BO3)4 diode-pumped laser.

We report for the first time, to the best of our knowledge, on a diode-pumped passively Q-switched Er,Yb:GdAl3(BO3)4 laser. By using a Co2+:MgAl2O4 crystal as a saturable absorber, Q-switched laser pulses with a duration of 12 ns and a maximum energy of 18.7 μJ at a repetition rate of 32 kHz corresponding to an average output power of 0.6 W were obtained at 1550 nm under continuous-wave pumping. In the burst mode of operation, Q-switched laser pulses with the highest energy up to 44 μJ were realized with a pulse repetition rate of 6.5 kHz.

Flux growth, composition, structural and thermal characteristics of (RxY1−x)Al3(BO3)4 (R=Nd, Gd; x=1, 0.6, 0.65, 0.7 and 0.75) crystals

(R x Y 1-x )Al 3 (BO 3 ) 4 (R = Nd, Gd; x = 1, 0.6, 0.65, 0.7 and 0.75) single crystals have been grown from fluxed melts. The segregation coefficients of neodymium and gadolinium were estimated to be 0.66-0.92 and 0.88-1.03, respectively. This coefficient increases with an increase of R 2 O 3 /Y 2 O 3 ratio in the initial mixture. The (Nd 0.63 Y 0.37 )Al 3 (BO 3 ) 4 structure was refined. The thermal behavior of the above borates was studied in the temperature range of 940-1030°C. Among the decomposition products, the crystalline aluminoborates Al 4 B 2 O 9 , Al 18 B 4 O 33 and rare earth borates RBO 3 were determined.

Volatility of potassium trimolybdate melt and solubility of yttrium-aluminium borate in it

Abstract The volatility and thermal stability of potassium trimolybdate melt was studied with the temperature range from 900 to 1150°C. The dependence of the melt volatilization rate on temperature has been found, the composition of the products of thermal melt dissociation has been determined, and the colatilization activation energies have been evaluated. The solubility in the melt of yttrium-aluminium borate has been investigated, with the volatility taken into account. All borate crystals have been produced on an inoculation.