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In this study, high purity n-type Mg2Ge single crystals are grown in graphite crucibles under nitrogen atmosphere using a facile growth process. X-ray diffraction proves that the grown crystal consists of only Mg2Ge single phase without any other additional impurity peaks. The clear symmetrical Laue diffraction pattern of the cleaved substrate demonstrates the single crystalline nature of the grown Mg2Ge crystal ingot. The Hall Effect measurement of the polished Mg2Ge wafer shows that the latter had a moderate carrier density (5.66 * 1016 cm−3), mobility (253 cm2/V) and electrical resistivity (0.5 Ω. cm) at room temperature. Detailed analysis of the temperature dependence of the carrier density demonstrates that the shallow donor level, which gives rise to the n-type conduction of grown Mg2Ge crystals is due to the unintentional Al impurities from Mg source material. Mg2Ge pn-junction photodiodes are also manufactured for the first time by thermal diffusion of silver thin layer into n-Mg2Ge at 550 °C for 5 min in an argon atmosphere. The results reveal that the fabricated p-n photodiodes had a clear rectifying behavior and a remarkable spectral response in the wavelength range from 0.8 to 1.7 μm with a maximum room temperature zero-biased photoresponse of 7 mA/W at 1.2 μm. These outcomes indicate that the fabricated Mg2Ge photodiodes are promising to detect short-wavelength infrared (SWIR) light in the above-mentioned wavelength domain.

N-type Mg2Si single crystal ingot has been successfully grown by the Vertical Bridgman technique. The Hall Effect measurement at RT revealed a moderate Hall mobility (~ 446 cm2/Vs), electrical resistivity (~ 1.4 Ω. cm) and carrier density (~1016 cm−3) for the grown crystal. The J-V characteristics of the fabricated Au/n-Mg2Si Schottky junction and Au/Ag-doped-p-type-Mg2Si/n-type-Mg2Si/Ag pn-junction diode showed better diode behavior with higher rectifying ratio in comparison with the same reported junctions. Analysis of the experimental forward J-V characteristics of our fabricated diodes based on the thermionic emission (TE) model demonstrated that our Schottky and pn-junction Mg2Si diode exhibited much lower series resistance in comparison with the survey data, confirming that precise polishing of Mg2Si surfaces with an oil-based diamond greatly improved the contact with the evaporated metal, enabling lower interfacial resistance between the evaporated metal and Mg2Si wafer. In addition, the manufactured Mg2Si pn-junction photodiode showed a clear photoresponsivity in the wavelength range from 0.95 to 1.8 µm with a maximum zero-biased photoresponse of 14 mA/W at 1.4 µm and a photon energy threshold of approximately 0.66 eV. These results indicate that our diode is promising to detect the SWIR light in the wavelength range from 0.95 to 1.8 µm.

A thermal actuator based on thin flexible lamellas of Ga_2O_3 was designed in order to demonstrate the potential of this semiconductor for micro-opto-electro-mechanical applications (MOEMs). The working principle of these devices is based on the thermal expansion that induces a vertical movement resultant of the lamella elongation due the self-heating/Joule effect. Upon excitation with photons, electrons or ions, intrinsic luminescence bands associated with self-trapped excitons and donor-acceptor pair recombination dominate the emission spectrum. When a current passes through the device, simultaneously with the thermal expansion, this luminescence is strongly quenched. Based on systematic Photoluminescence and Raman studies as a function of temperature and as a function of the applied power it is demonstrated that the observed luminescence quenching is directly related with the Joule heating effect. This work presents for the first time a thermal actuator based on Ga_2O_3 and it intends to be a stimulus for future works on MOEMs applications based on this semiconductor.

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.

Remarkable optical/electrical features are expected in two-dimensional group-IV monochalcogenides (MXs; M = Sn/Ge and X = S/Se) with a uniquely distorted layered structure. The lone pair electrons in the group-IV atoms are the origin of this structural distortion, while they also cause a strong interlayer force and high chemical reactivity. The fabrication of chemically stable few-to-monolayer MX has been a significant challenge. We have observed that, once the SnS surface is oxidized, the SnOx top layer works as a passivation layer for the SnS layer underneath. In this work, the SnOx/SnS hetero-structure is studied structurally, optically, and electrically. When tape-exfoliated bulk SnS is oxygen-annealed under a reduced pressure at 10 Pa, surface oxidation and SnS sublimation proceed simultaneously, resulting in a monolayer-thick SnS layer with the SnOx passivation layer. The field-effect transistor of nine-layer SnS prepared via mechanical exfoliation exhibits a p-type characteristic because of intrinsic Sn vacancies, whereas ambipolar behavior is observed for the monolayer-thick SnS obtained via oxygen annealing probably owing to the additional n-type doping by S vacancies. This work on monolayer-thick SnS fabrication can be applied to other unstable lone pair analogues and can facilitate future research on MXs.

(Y1−xGdx)3Al5O12:Ce ((Y,Gd)3Al5O12:Ce) single crystal phosphors (SCPs) were successfully grown using the Czochralski method. The Gd segregation coefficient was determined. The lattice spacing, absorption and emission properties were systematically investigated as a function of Gd concentration in a wide temperature range. Gd incorporation red-shifts the SCP emission so that neutral white with correlated color temperatures in the range of 4098–6594 K can be achieved in conjunction with a blue light-emitting diode (LED). SCPs demonstrate high conversion efficiency (>90% above 150 °C) and better thermal stability compared to analogous ceramic powders. Additionally, SCPs are compatible with resin-free packaging, overcoming drawbacks associated with powder encapsulants. Therefore, (Y,Gd)3Al5O12:Ce SCPs are promising candidates for high-brightness neutral white sources based on intense blue LEDs and laser diodes.

For the full benefit of the silicon chip industry and to further extend the photoresponse cut-off wavelength of the current Si photodetectors beyond 1100 nm, high-performance silicon-compatible Mg2Si/Si n-p photodiodes are constructed on the bulk silicon wafer by magnetron sputtering and post-annealing sequential processes. The results show that the annealing period appreciably affects microstructure, crystallite size, and roughness of the Mg2Si film sputtered on glass substrates and silicon wafers. Meanwhile, the fabricated Mg2Si/Si n-p photodiodes demonstrate clear rectifying behavior and evident spectral response characteristics in the wavelength domain from 0.8 to 1.35 μm, with a maximum room temperature zero-bias response of 0.1, 0.15, 0.86, and 0.47 A/W at 1.05 μm for the annealing periods of 10, 20, 40, and 60 min, respectively. The photoresponse cut-off wavelength of the fabricated Mg2Si/Si n-p photodiodes is 1.35 μm; however, the photosensitive cut-off of the commercially available Hamamatsu Si photodiode is 1.25 μm. The fabricated Mg2Si/Si n-p photodiodes at RTA period of 40 min reveal spectral response of longer cut-off wavelength and higher intensity near the photon energy threshold compared to the Hamamatsu Si photodiode. In this context, the fabricated photodiodes in this study offer huge potentials to develop high-performance silicon-compatible photodiodes for efficiently sensing the infrared light in the wavelength domain from 0.8 to 1.35 μm.

We demonstrate the high-speed growth of β-Ga2O3 quasi-heteroepilayers on off-angled sapphire (0 0 0 1) substrates by halide vapor phase epitaxy (HVPE). (2¯01) oriented β-Ga2O3 layers were successfully grown using GaCl and O2 as source gases. The growth rate monotonically increased with increasing the partial pressures of the source gases, reaching over 250 μm/h. This rate is over two orders of magnitude larger than those of conventional vapor phase epitaxial growth techniques such as molecular beam epitaxy or metalorganic vapor phase epitaxy. X-ray pole figure measurements indicated the presence of six in-plane rotational domains, in accordance with the substrate symmetry, plus some minor (3 1 0) domains. By the use of off-angled substrates and thick layer overgrowth, one of the in-plane orientations was strongly favored and the (3 1 0) residuals effectively suppressed, so that quasi-heteroepitaxial growth was achieved. Therefore, these results indicate the high-potential of the HVPE technique for the growth of thick and thin β-Ga2O3 layers for the cost-effective production of β-Ga2O3 based devices.

Nanostructured photoanodes based on well-separated and vertically oriented WO3 nanorods capped with extremely thin BiVO4 absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO3 -NRs/BiVO4 photoanode modified with Co-Pi oxygen evolution co-catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm(2) at 1.23 V versus a reversible hydrogen electrode in a stable Na2 SO4 electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO4 layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO3 -NRs/BiVO4 photoanode effectively increases the optical thickness of the BiVO4 layer and results in efficient absorption of the incident light.

For the full benefit of the silicon chip industry and to further shift the photoresponse cut-off wavelength of the silicon photodetectors, high-performance Ag-doped Si p-n photodiodes with an extended infrared photoresponsivity are constructed on the bulk silicon wafer by a facile thermal diffusion process at 550 °C for different annealing periods of 5, 10, and 15 minutes under an argon atmosphere. These Si-compatible p-n photodiodes revealed an obvious zero-bias room temperature photoresponsivity with a threshold photon energy at a longer wavelength compared to the photoresponsivity cut-off wavelength of the commercial Si photodiode of the Hamamatsu Photonics Co (model: S2281/-04). The photoresponsivity has decreased with the annealing time increase however; the detectivity has been improved by the significant drop in leakage current and noise power. The outcomes indicate that this study paves the way for developing cost-effective Si-compatible p-n junction photodiodes, with an obvious zero-biased room-temperature photoresponsivity of a comparable intensity and longer cut-off wavelength compared to the commercial Hamamatsu Si photodiode.

This paper reports the results on fabrication methodology and photoresponse characteristics of Mg2Si0.53Ge0.47 pn-junction photodiode. At first, we have grown a Mg2Si0.53Ge0.47 single crystal with the Vertical Bridgman growth process. The grown crystal was characterized structurally and electrically by XRD, Laue, and Hall Effect measurements. XRD revealed the single-phase composition, Mg2Si0.53Ge0.47, of the grown crystal ingot. The clear Laue symmetrical diffraction pattern showed the single crystalline nature of the grown crystal. The Hall Effect measurement revealed the n-type conduction and the moderate Hall mobility (258 cm2/Vs), electrical resistivity (6.03E-02 Ω. cm), and carrier density (4.02E+17 cm-3) of the grown crystal. Such carrier density is low enough to allow depletion region formation in case of pn-junction diodes. In that sense, we have made up for the first time Mg2Si0.53Ge0.47 pn-junction photodiode by thermal diffusion of a thin Ag layer into n-Mg2Si0.53Ge0.47 substrate. The fabricated diode had an obvious rectification behavior and demonstrated a clear zero-biased photoresponse in the wavelength range from 0.95 to 1.85 μm, indicating its prominence for IR sensation in that wavelength domain.

High optical quality LiREF4(RE = Tb3+, Dy3+, Ho3+, Er3+and Yb3+), PrF3and CeF3single crystals have been grown by the Czochralski technique. Their magneto-optical properties have been measured and analyzed in detail in the ultraviolet-visible wavelength region, and their figures of merit as Faraday rotators have been determined. CeF3presents superior properties above 300 nm, showing a figure of merit higher than that of the reference material, terbium-gallium-garnet, which is nowadays used in the visible-near infrared. PrF3is the best rotator for the 220-300 nm range. Towards shorter wavelength and in the vacuum ultraviolet, it is shown that the LiREF4crystals are unique rotators.

Czochralski grown Ce and Gd-doped Y 3 Al 5 O 12 (Ce,Gd:YAG) single crystal demonstrated superior performance features in a new concept of white LED where it is used as thin single crystal phosphor plates (SCPPs). New SCPP-based white LED realizes epoxy resin free package, which allows to eliminate the photodegradation issue of the organic material. Optical, thermal and electrical properties of SCPPs and SCPP-based white LEDs are discussed with the powder phosphor and commercial LED reference. SCPPs showed significantly higher values and better stability under the high temperatures, irradiation and current. Quantum efficiency was found to be as high as 93%.

White light-emitting diodes (wLEDs) are the new environmental friendly sources for general lighting purposes. For applications requiring a high-brightness, current wLEDs present overheating problems, which drastically decrease their emission efficiency, color quality and lifetime. This work gives an overview of the recent investigations on single-crystal phosphors (SCPs), which are proposed as novel alternative to conventional ceramic powder phosphors (CPPs). This totally new approach takes advantage of the superior properties of single-crystals in comparison with ceramic materials. SCPs exhibit an outstanding conversion efficiency and thermal stability up to 300°C. Furthermore, compared with encapsulated CPPs, SCPs possess a superior thermal conductivity, so that generated heat can be released efficiently. The conjunction of all these characteristics results in a low temperature rise of SCPs even under high blue irradiances, where conventional CPPs are overheated or even burned. Therefore, SCPs represent the ideal, long-demanded all-inorganic phosphors for high-brightness white light sources, especially those involving the use of high-density laser-diode beams.

A novel garnet single crystal with a composition of Tb3(Sc, Lu)2Al3O12 (TSLAG) is designed and fabricated to realize a large-scale crystal boule. 50 mm-diameter single crystal boule is grown by Czochralski (CZ) method without macro cracks. High optical transparency in the wavelength range of 400–1100 nm, and relatively high Verdet constant compared with Tb3Ga5O12 (TGG) are confirmed for TSLAG(111) bulk crystal. An optical isolator module using the TSLAG is also demonstrated to apply fiber lasers.

Ferroelectric fluoride BaMgF 4 , β -Ga 2 O 3 and F-doped core-free Y 3 Al 5 O 12 single crystals for ultraviolet and vacuum ultraviolet (UV/VUV) applications, are introduced. 2-in. size BaMgF 4 single crystals have been grown. Subsequently, second harmonic generation (SHG) in different wavelengths was demonstrated by the quasi-phase matching (QPM) devices. 2-in. size β -Ga 2 O 3 single crystals, which have large bandgap, 4.8 eV, have been grown. Blue light emitting diodes (LEDs) on β -Ga 2 O 3 were demonstrated. F-doped core-free Y 3 Al 5 O 12 single crystals have been grown as a potential new lens material for UV/VUV.

β-Ga2O3 single crystals have the band gap energy of 4.8 eV. Luminescence spectra in β-Ga2O3 crystals excited above the band gap energy consist of UV and blue/green broad bands. Polarization of the optical absorption and luminescence spectra and decay curves of the luminescence observed in the temperature range from 14 to 300 K can identify the luminescent centres. The UV luminescent centre with a lifetime of 1.5 μs is assigned as self-trapped exciton, consisting of self-trapped hole in the form of GaO4 tetrahedral complex and bound electron. As the decay curves of the blue/green luminescence bands fit a power function of t-n (n∼0.8), the luminescence occurs through recombination of donors and acceptors in the crystal. The donor is coincident with a conduction electron trapped at single or coupled oxygen vacancies in the crystal estimated from electron-spin resonance (ESR) (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescent and structural properties of M1-xCexF2+x (M=Ca, Sr, Ba, 0.15

シービーム海底地形図およびJ-EGG500データをもとに日本列島海底谷系図を改訂した．大陸棚外縁から大洋底・海溝まで連続する谷線を持つ海底谷は天竜海底谷，富山海底谷および最上海底谷のみである．曲流を呈するのは釧路海底谷，広尾海底谷および谷末端水深が2000 m以浅の海底峡谷と深海チャネルに限られ，他の海底峡谷は屈曲を主とする適従谷である．ほとんどの海谷とガリ状海底谷および御蔵海底谷，黒瀬海底谷は必従的である．ガリ状海底谷は太平洋側の水深2000 m以浅に分布する．海底谷の縦断面形状は勾配の違いにより7区分される．縦断面は海域によらず1，2の傾斜変換点で連結した単斜谷の組合せからなる．海底谷地形は流動体による作用を示すが，海底谷の形成機構は堆積物重力流の作用だけでなく，海水準変動や地殻変動も併せて考慮するべきであろう．

We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.5 kHz by AFM-based acoustic microscopy The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7kHz to 10kHz, and reached maximum at 8.1kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.

Low-frequency (below 100 kHz, even down to several kHz) near-field acoustic probe microscopy for imaging ferroelectric microstructure was successfully developed based on the commercial atomic force microscope, which provides a subsurface depth profile information and as well as nanoscale spatial resolution up to 10 nm. The domain configurations of ferroelectric material were clearly visualized by this newly, non-destructive, low-frequency acoustic mode scanning probe microscopy technique with high resolution. The acoustic imaging origin is discussed in terms of interaction between the excited acoustic wave and ferroelectric domains. It is expected that the combination of the acoustic and piezoresponse mode probe microscopy in application to imaging domain structures undoubtedly enrich our understanding the nature of elasticity, piezoelectricity and ferroelectricity at submicro-, even nano-meter scale.

The oxide garnet {Tb3}[Sc2-xLux](Al3)O12 (TSLAG) is developed as alternative to Tb3Ga5O12 (TGG). TSLAG exhibits better transmittance, Verdet constant, and radiation resistance. Further, PrF3 and CeF3 fluoride crystals are investigated as unique Faraday rotators for the UV-visible region.

Ferroelectric domain phenomena and periodic domain patterning of orthorhombic as-grown BaMgF4 single crystal were investigated in the present study. An isolated ferroelectric domain shows a hexagonal form and exhibits a high domain-wall anisotropy. Periodic domain patterning was demonstrated on the polar surface by a periodic macropoling technique. In-plane polarization switching-induced microdomain patterning was tailored by the lateral component of the inhomogeneous electric field through a biased atomic force microscope tip. Such in-plane domain switching behavior exhibits potential promise for periodic domain engineered phonon devices.

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-Ga2O3 with 1 inch in diameter have been grown by the floating zone technique. Wafers have been cut and fine polished in the (100), (010) and (001) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga2O3 as a substrate for optoelectric devices operating in the visible/near UV and with vertical current flow. Epitaxial growth of nitride compounds by the metalorganic vapor phase epitaxy (MOVPE) technique is demonstrated on β-Ga2O3 single crystal substrates. High-quality (0001) GaN epi-layers with a narrow bandedge luminescence are obtained using a low temperature conductive buffer layer. InGaN multi-quantum well (MQW) structures were also successfully grown. The first blue light-emitting diode (LED) on β-Ga2O3 with vertical current injection is demonstrated.

The growth characteristics and properties of large size SrAlF5 single crystals are described and compared with those of BaMgF4. SrAlF5 shows a higher grade of transparency and a larger nonlinear effective coefficient as well as uniaxial and ferroelectric nature, on contrast to the one order smaller nonlinear coefficient and biaxial character of BaMgF4. The Sellmeier and Cauchy coefficients are obtained fitting the measured ordinary and extraordinary refractive indices, and the grating period for the first order quasi-phase matching (QPM) is estimated as a function of the wavelength. The higher potential of SrAlF5 in comparison with BaMgF4 for the realization of all-solid-state lasers in the ultraviolet wavelength region by the QPM technique is pointed out.

Energy storage in pure and Ce-doped LiCaAlF6 and LiSrAlF6 crystals has been investigated. X-ray irradiated samples were treated thermally to determine the number of color centers. The absorption spectra and thermostimulated luminescence were studied to establish a relation between coloration and glow curve peaks. The similarity of the induced absorption band positions in both crystals in contrast to energy storage efficiency was observed. The coloration of LiSrAlF6:Ce is much higher than of LiCaAlF6:Ce. The color center nature is discussed starting from intrinsic and activator defect structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

CeF3, PrF3 and NdF3 single crystals have been grown under CF4 atmosphere by the modified Czochralski technique. PrF3 exhibited a dominant sharp emission at about 400 nm (1S0→1I6), with a decay time of 510 ns. Photon cascade process as well as energy migration to RE-dopants were not observed. Light emission from CeF3 remarkably increased by Lu3+-doping, yielding to efficiencies over that of BGO.

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 creation of radiation defects in LiBaF 3 crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K . Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V K -centers at 105 and 130 K indicates that 60° and 90° migration hops occur.

Three-dimensional numerical simulations of oxide melt flow in a large-scale Czochralski crucible (200 mmφ×100 mmh) have been carried out to investigate the effects of various factors such as the thermal boundary conditions at the crucible sidewall, the Marangoni effect at the melt free surface and the rotation rate of the crystal on the surface patterns and bulk flow structures of oxide melt. The block-structured boundary-fitting-coordinate technique was employed. It was found that the wave and wave-spoke patterns appear on the melt free surface depending on the factors. The change of the thermal boundary conditions at the crucible sidewall, from a constant temperature to a constant heat flux, and the Marangoni effect tended to cause the disappearance of the wave patterns because of the acceleration of the inward flow along the free surface toward the crystal. Unlike the case in a small crucible, the melt flows were always completely three-dimensional even though the surface temperature distribution was approximately axisymmetric. The increase of the crystal rotation rate could suppress the inward flow, and lead to a wave-spoke pattern when the Marangoni effect was taken into account. The spokes in the wave-spoke patterns were generated by an identical mechanism revealed in J. Crystal Growth 252 (2003) 550.

The effect of internal radiative heat transfer on the spoke pattern observed on an oxide melt surface was investigated by means of a three-dimensional numerical simulation of LiNbO3 melt flow in an open Czochralski crucible. In the mathematical model, the assumptions that the melt was an incompressible Newtonian Boussinesq fluid, the flow was laminar and the melt free surface was flat were adopted. The crucible wall was assumed to be heated by a constant heat flux. The Marangoni effect on the melt free surface was taken into account. When the internal radiative heat transfer was ignored, i.e., the melt was assumed to be opaque, a spoke pattern was generated and the bulk melt flow was oscillatory; otherwise, the internal radiative heat transfer decreased the temperature gradient and hence suppressed the Marangoni instability, and consequently, the spoke pattern disappeared and the melt flow became steady and axisymmetric. The investigation provided one theoretical explanation for the experimental phenomenon observed by Okano et al. (J. Mater. Process. Manuf. Sci. 4 (1995) 41).

Three-dimensional numerical simulations of LiNbO3 melt flow in a Pt crucible (47 mmΦ×47 mmH×1.5 mmT) in the Czochralski oxide crystal growth configuration have been performed to investigate the effect of RF coil position on spoke patterns observed on the free surface of oxide melt. The crucible temperature field calculation was coupled with the numerical simulations of melt flow to provide a realistic thermal boundary condition for the melt/crucible interface. The melt was assumed to be an incompressible Newtonian Boussinesq fluid, and the flow was laminar. The free surface of melt and the crystal/melt interface were flat. The heat loss from the free surface was due to thermal radiation alone. The heat generation rate of the crucible was obtained by analyzing the electromagnetic field; the outside surfaces of the crucible were adiabatic. The Marangoni effect was taken into account. It was found that the appearance of the spoke pattern is dependent on the RF coil position. When the RF coil was set low relative to the crucible, the spoke pattern appeared easily; otherwise, the spoke pattern was difficult to be generated. The results of the investigation validated the mechanism of spoke pattern formation reported in J. Crystal Growth 200 (1999) 204.

Three-dimensional (3D) unsteady mixed thermal buoyancy, Marangoni and forced convection of LiCaAlF 6 (LiCAF) melts (Prandtl number Pr ≈1.4) are investigated numerically for model set up typically for Czochralski crystal growth. With increasing crystal rotation rate, convection evolves from steady axisymmetric to three-dimensional oscillatory convection with varying spatio-temporal features. The details of the oscillatory convection structures are presented.

Absorption, photo- and radioluminescence spectra have been investigated for as-grown and irradiated LiCaAlF6:Eu crystal. Eu2+ ions markedly over lap. Irradiation induces Eu3+→Eu2+ transition and F-centers formation. Color centers destruction in the process of crystal annealing is accompanied by thermostimulated luminescence (peaks at 340, 420 and 490 K) with the typical for Eu2+ ion emission (370 nm). Scintillation light output is defined by the thickness of sample, Eu2+ concentration and contribution of factors, controlling Eu3+⇋Eu2+ transformation in LiCaAlF6:Eu.

LiCaAlF6 (LiCAF) single crystals with an extended diameter were grown by the Czochralski (CZ) technique under CF4 atmosphere. Modifying the growth conditions enabled the growth of LiCAF single crystals with 3- and 4-inch diameters. After considering reflection loss, LiCAF showed transmittance over 95% at 157 nm. A precise measurement of the refractive index showed that the birefringence of LiCAF vanished at around 152 nm. The fabrication of a LiCAF lens was demonstrated.

A number of good quality thulium and holmium-codoped LuLiF/sub 4/ and YLiF/sub 4/ single crystals were successfully grown by the Czochralski crystal growth method under a CF/sub 4/ atmosphere. Using a novel diode-pumped, quasi-end-pump scheme incorporating two lens ducts, pulsed laser action is achieved in 5%Tm, 0.5% Ho:LuLiF/sub 4/ and 5%Tm, 0.5% Ho:YLiF/sub 4/ crystals, at various pulse repetition frequencies and temperatures. At 10 Hz and at an operating temperature of 273 K, slope efficiencies (optical to optical efficiencies) with respect to the incident pump energies of 12.9% (9.2%) and 7.4% (5.2%) were demonstrated in the grown Tm, Ho:LuLiF/sub 4/ and Tm, Ho:YLiF/sub 4/ crystals, respectively. Free running laser output energies in excess of 30 mJ (LuLiF/sub 4/) and 17 mJ (YLF) were measured.

A large Ce3+:LiCaAlF6 (Ce:LiCAF) crystal with 15 mm diameter was grown successfully by the Czochralski method. Owing to its large size, 60 mJ, 289 nm pulses were generated directly from a quasi-coaxially pumped Ce:LiCAF laser. In addition, a new noncollinear Brewster-angle-pumping disk oscillator scheme was demonstrated for further output-energy scaling. An ultraviolet solid-state Ce3+:LiLuF4 (Ce:LLF) laser which was pumped transversely by a KrF excimer laser with the repetition rate of 1 Hz produced a 27 mJ, 309 nm pulse using a large Ce:LLF crystal which was grown by the Czochralski method, and the slope efficiency was approximately 17%.

Lu 3 Al 5 O 12 single crystals codoped with thulium and holmium were successfully grown by the Czochralski technique. A highly strained central core region caused by facet formation on the growth interface was observed. The distribution of birefringence in the radial direction except in the core region was of the order of 10 −7 . The segregation coefficients of the dopants in these crystals were estimated to be 0.87 and 0.73, respectively. The measured thermal expansion coefficient of Tm,Ho : Lu 3 Al 5 O 12 single crystals was 8.48×10 −6 K −1 . Laser performance of Tm,Ho : Lu 3 Al 5 O 12 was measured.

β-Ga2O3 is the most transparent conductive oxide, well known since several decades for its large bandgap of 4.8 eV. Its potential as semiconductor material, however, is just emerging in recent years. Present work shows the development of βGa2O3 for semiconductor applications and its current state-of-the-art. The discussion is focused on three different aspects: (1) Advantageous growth from melt of large-size β-Ga2O3single-crystals. High-crystalline quality and carrier control make possible the production of conductive and semi-insulating wafers. (2) β-Ga2O3as substrate for homoepitaxy as well as for heteroepitaxial deposition of GaN-based devices. High-brightness blue-LEDs with vertical current injection are demonstrated. (3) Potential of β-Ga2O3for high-power devices with higher breakdown voltage than GaN and SiC counterparts. The first Schottky barrier diode is shown, as well as first transistors (MESFET and MOSFET) are indicated. Single-crystal phosphors are introduced as novel alternative to currently used powder phosphors. In connection with high-brightness white light-sources, based on LEDs or LDs plus phosphor converters, single-crystal phosphors possess advantageous features. These avoid the use of resins and exhibit a very high internal quantum efficiency, which remains stable with the temperature increase.

Ferroelectric patterning is often used in advanced photonics and optoelectronic devices to increase their operational bandwidth and functionality, providing novel and unique performances. However, the extension of the ferroelectric structures to two-dimensional geometries is currently limited to very few oxides and phosphates systems, which constrains its current and future applications. Here, careful processing based on e-beam lithography and poling is employed to fabricate the first example of a two-dimensional nonlinear photonic crystal in Barium Magnesium Fluoride, BaMgF4, a ferroelectric fluoride crystal with an extraordinary transparency ranging from the deep ultraviolet (≈126 nm) to the mid infrared (≈13 μm). The optical characterization shows the possibility of obtaining simultaneously up to three different Cerenkov-type second harmonic generation processes distributed in a conical geometry via χ(2)-quasi-phase-matching technique. Additionally, the remarkably high χ(3) nonlinear response of BaMgF4 crystal in the UV spectral region is exploited to demonstrate what is believed to be the highest direct UV-third harmonic generation conversion efficiency in a solid state system via pure χ(3) nonlinear process. Together, the results highlight the outstanding opportunities offered by nonlinear photonic structures as innovative avenues to manipulate the light generation and control with reliable multifunctional optical character. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work has been supported by FP7 NoE Nanophotonics4Energy EU grant No. 248855; the Spanish MICINN CSD2007–0046 (Nanolight.es), MAT2010–17443, MAT2012–31659 (SAMAP) and the Comunidad de Madrid S2009/MAT-1756 (PHAMA) projects.

The growth of undoped and Ce-doped LiSrGaF6 (LiSGF) single crystals was carried out in a Czochralski system under CF4 atmosphere. LiSGF and Ce-doped LiSrGaF6 (Ce : LiSGF) single crystals of 1 in diameter were obtained and characterized. The reasons for the limited size of crack-free crystals were investigated. The distribution coefficient of Ce was determined to be 0.22. Absorption and fluoresence under excitation by the fourth harmonic of Nd : YAG laser were measured and compared with those of other colquiriite-type fluorides such as LiCaAlF6 and LiSrAlF6. The absorption edge of LiSGF was determined to be 128 nm, making it a good candidate as an optical window material.