A series of mixed borates of rare-earth elements and calcium with the composition R 2 CaB 10 O 19 (RCB) (R: rare-earth element) were synthesized by Wu et al., from the system of R 2 O 3 -CaO-B 2 O 3 in 1998 [1]. In 2001, the growth and structure of La 2 CaB 10 O 19 (LCB), one member of the RCB family, was reported [2]. LCB crystallizes in the monoclinic system and belongs to the C2 space group with two formula units per cell (Figure 4.1). Its lattice parameters were measured to be a ¼ 11.043 (3) The structure contains B 5 O 12 groups as the basic units. B 5 O 12 groups are linked together to form an infinite two-dimensional double layer by sharing O atoms with one another. The layer runs almost perpendicular to the caxis of the crystal. The La atoms are located in layers, while the Ca atoms are located between two layers. LCB crystal has a high transparency from ultraviolet (UV) to infrared range. The birefringence of LCB crystal at 1064 nm is 0.053, which allows to perform SHG and THG in LCB. The damage threshold was measured to be about 11.5 GW/cm 2 . An effective nonlinear optical coefficient d eff of LCB was measured to be 1.05 pm/V. In addition, LCB can be doped with other rare earth (RE) elements because of the existence of the La 3þ ions in LCB. So LCB is a promising nonlinear optical (NLO) and self-frequency doubling (SFD) crystal.
Synthesis and Crystal Growth of LCB and RE:LCBIn 1998, a series of compounds with the composition R 2 CaB 10 O 19 (R: rare earth) including the LCB crystals were synthesized from the stoichiometric melt. In 2000, the Nd 3þ -doped LCB (Nd:LCB) with a size of 20 Â 17 Â 7 mm 3 was grown from the Nonlinear Optical Borate Crystals: Principles and Applications, First Edition. Nd 3þ was used to replace the La 3þ in LCB using different Nd concentrations to form Nd:LCB. For LCB RE:LCB crystal growth, flux method is convenient because the crystal decomposes above 900 C before melting at 1200 C. In 2002, pure LCB was grown from its stoichiometric melt by the top-seeded pulling method (TSSG, topseeded solution growth) by Xu et al. [4]. The morphology of LCB grown by TSSG method was then studied [5]. In 2003, Wu et al. studied the phase diagram of the binary system LaB 3 O 6 -CaB 4 O 7 by X-ray powder diffraction and differential thermal (DSC) analysis, and they found that LCB phase exists between lanthanum borate and calcium borate, and melts congruently with a melting point of 1065 C [6]. Thereafter, a series of rare earth-doped LCB such as Er:LCB [7,8], Ce:LCB [9], Nd,Yb:LCB [10], and Pr:LCB [11,12] were successfully grown by flux and TSSG method. To further enlarge the size and improve the optical quality of LCB crystals, people made more efforts to improve the crystal growth equipment and the growth conditions. For example, in 2005, Jing et al. made efforts to search for the new flux to grow LCB crystals and successfully grew the LCB with size of 30 Â 25 Â 9 mm from a new flux CaO-Li 2 O-B 2 O 3 [13]. It was also found that the morphological faces are most effected by the direction of ...
