Development in compact solid-state lasers requires extensive study of highly efficient single crystals and crystalline layers to be used, for example, as miniature disk lasers and active waveguides with different pumping configurations including laser and amplifier applications. In this connection, borate crystals with general formula RAl₃(BO₃)₄ (R=Y, Pr - Lu) can be considered as polyfunctional solids having device potential due to their possibility of wide isomorphous substitutions, good mechanical hardness, and thermal conductivity. Of them, NdAl₃(BO₃)₄ (NAB) possess above mentioned requirements for weaker luminescence quenching micro-lasers [1]. Recently, excellent laser performance of (Er,Yb):YAl₃(BO₃)₄ (Er,Yb :YAB) crystal has been demonstrated. Diode-pumped (Er,Yb):YAB laser exhibit a slope efficiency as high as 35 % and output power of 0.8-1 W at several wavelengths between 1531 and 1602 nm [2]. Mode-locked regime has been realized with pulse duration of about 4 ps and average output power of 270 mW [3]. Among the waveguide fabrication methods, liquid-phase epitaxy (LPE) was found to be reliable, simple and low-cost technique allowing to produce the waveguides of low propagation losses and high crystalline quality [4,5]. In this report, experimental results on the LPE of (Er,Yb):YAB and NAB low-dimensional layers and their growth kinetics peculiarities are summarized.

Single crystal layers of (Er,Yb):YAl₃(BO₃)₄, Er:YAl₃(BO₃)₄ and NdAl₃(BO₃)₄ were grown from K₂Mo₃O₁₀-B₂O₃ based fluxed melts by the LPE method. For LPE growth of the R:YAB (R=Er,Yb) layers, (10`11) – oriented YAB plates were used. NAB films were obtained on (11`1) and (001) substrates with and without Pt buffer layer. YAB and NAB single crystals were grown using dipping seeded solution growth (DSSG) technique.

The observed growth rates were similar for all the investigated R:YAB layers, because a small amount of dopant does not change the nucleation and formation of the layers. The linear growth rates were estimated to be within the ranges of 1.5-12 μm/h. Growth steps with almost flat terraces cover the epitaxial film surface. Also, the growth hillocks were particularly typical for the corners and edges of the substrate. Most of the grown R:YAB layers were crack-free without visible inclusions of the mother solution.

The NAB layers thickness was typically 120-260 μm after 24 h- growth period depending on the fluxed melt supersaturations. These values give a mean linear growth rates of 5-11 μm/h. Growth steps and hillocks were also observed on the surfaces of almost all NAB grown layers.

These results were compared with previous investigations of growth kinetics of YAB, NAB and YFe-borate single crystals in K₂Mo₃O₁₀ based high-temperature solutions. A major problem which awaits clarification concerns controlled growth of these layers with optimal composition and thickness.

This research was supported in part by the RFBR grants ## 12-05-90010-Bel_а and 12-05-00912_a.

[1] Sh. Amano, S. Yokoyama, H. Koyama, et al, Rev. Laser. Eng. 17, 48 (1989)

[2] N.A. Tolstik, S.V. Kurilchik, V.E. Kisel, et al, Opt. Lett. 32, 3222 (2007)

[3] A.A. Lagatsky, V.E. Kisel, A.E. Troshin, et al, Optics Letters 33, 83 (2008)

[4] Y. Romanyuk, C. Borca, M. Pollnau, et al, Opt. Lett. 31, 53 (2006)

[5] M. Pollnau, Y. Romanyuk, C. R. Physique 8, 123 (2007)

[6] S.-T. Jung, J.-K. Kang, S.-J. Chung. J. Crys/ Growth, 149, 207 (1995)

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1. Growth, spectroscopic and laser properties of (Er³⁺,Yb³⁺):GdAl₃(BO₃)₄ crystals