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Ca3TaAl3Si2O14 (CTAS) single crystal is attracting much attention for high temperature sensor applications due to its high electrical resistivity and excellent piezoelectric properties. However, it is a big challenge to grow high quality CTAS single crystals. In this work, its growth conditions are optimized. Crack- and inclusion-free crystals are grown, achieving even a high quality single crystal with a width over 2 in. In addition, the temperature dependence of electro-elastic properties is systematically studied. This crystal presents a high thermal stability of structure and electro-elastic properties. The dielectric loss is less than 3% from room temperature to 650 °C. Therefore, CTAS single crystal is promising for high temperature sensor applications.

Microvoids are well-known crystal defects, usually exhibiting a rounded and/or irregular shape, which act as undesired scattering centers in optical applications. Here, for the first time, residual microvoids in the shape of perfect regular hexagonal-prisms are observed in apparently scattering-free CeF3 bulk single crystals. These microvoids reflect exactly the natural crystal habit in “negative” form: the prisms stand along the c-axis and the hexagonal sides are parallel to the six equivalent planes perpendicular to the a-axis. They distribute randomly with sizes up to 13 µm and heights in the submicron order with a maximum around 500 nm. The microvoids are formed by the embedding of bubbles during the crystallization process. The bubbles’ gas is possibly caused by the high vapor pressure of CeF3 itself at the high melting point.

SrAlF 5 has recently become one of the most promising candidates for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase-matching technique. It has been shown that it is highly transparent down to the cutoff wavelength at about 150 nm, optically uniaxial and ferroelectric. The refractive index of SrAlF 5 from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first-order quasi-phase-matching is estimated as a function of the wavelength. The effective nonlinear coefficient is similar to that of quartz, d eff ≈ 0.3 –0.4 pm/V, and the poling periodicity for 193 nm SHG from 386 nm is 4.1 μ m .

The growth characteristics of large size SrAlF 5 and BaMgF 4 single crystals by the Czochralski technique are described and compared. Transmission spectra in the vacuum ultraviolet wavelength region indicate a high transparency of SrAlF 5 (about 90% without considering surface reflection loses) down to 150 nm, in contrast to the optical loses observed for BaMgF 4 . The ferroelectric character of SrAlF 5 is evidenced by the reversal of the spontaneous polarization in a hysteresis loop. The higher potential of SrAlF 5 in comparison with BaMgF 4 for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase matching technique is pointed out. SrAlF 5 , besides a higher grade of transparency, shows a nonlinear effective coefficient similar to that of quartz and uniaxial nature, in contrast to the one-order smaller nonlinear coefficient and biaxial character of BaMgF 4 .

Large-size single crystals of β-Ga 2 O 3 with 1 inc in diameter have been grown by the floating zone technique. The stable growth conditions have been determined by the examination of the crystal structure. Wafers have been cut and fine polished in the (1 0 0), (0 1 0) and (0 0 1) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga 2 O 3 as a substrate for optoelectic devices operating in the visible/near UV and with vertical current flow.

The potential use of β -Ga 2 O 3 wafers as transparent conductive substrates for compounds with hexagonal structure, in particular the GaN-system, is shown. Nitridation of the main cleavage plane under high temperature and NH 3 gas results in the substitution of O by N on the surface, and a simultaneous surface reconstruction. The 2-fold symmetry of the initial (1 0 0) plane changes to a 6-fold symmetry, keeping the [0 1 0] azimuth as a symmetry direction. The RHEED pattern suggests the formation of GaN on the β - Ga 2 O 3 surface, with the b-axis of β - Ga 2 O 3 parallel to the 〈 11 2 ¯ 0 〉 direction of GaN, so that β - Ga 2 O 3 can be used as a substrate with no lattice mismatch to GaN.

CeF 3 , PrF 3 and NdF 3 single crystals with 1 inch in diameter have been grown under CF 4 atmosphere by the modified Czochralski technique. PrF 3 exhibited a single sharp emission at about 400 nm, with a light intensity comparable to that of BGO and a decay time of 510 ns. Lu-doping was effective to increase the luminescence efficiency of CeF 3 .