•Zn1-xCoxO single crystals are successfully grown from molten hydrous LiOH and NaOH solutions.•The lattice parameters and bond lengths decrease with increasing cobalt concentration.•Cobalt doping leads to two new PL peaks and the disappearance of certain Raman active modes.•The Zn1−xCoxO crystals are typically paramagnetic.•The Zn1−xCoxO crystals have the same piezoelectricity as the un-doped ZnO.Transparent, olive-green single-crystal Zn1−xCoxO in the form of hexagonal lamellae grown from molten hydrous LiOH and NaOH solutions have been studied in terms of crystal structure, optical properties, Raman scattering, and magnetic and piezoelectric properties. Rietveld refinement shows that the lattice parameters and bond lengths decrease with increasing cobalt concentration. Cobalt doping results in slight changes to the piezoelectricity of ZnO, but leads to two new photoluminescence emission peaks at wavelengths of 443 and ∼510 nm, along with the disappearance of certain Raman active modes. Furthermore, the ferromagnetic state is absent in all Zn1−xCoxO crystals, and they are all typically paramagnetic instead.

MgO doped near stoichiometric LiNbO3 (MgOSLN) crystals have great potential for use in periodically poled structured LiNbO3 (PPLN) for doubling frequency lasers and optical parametric oscillation infrared lasers, because of their high optical damage threshold, single domain characteristics, and very low coercive field. However, few MgOSLN crystals are commercially available in the present market because of the great difficulty in growing them. This paper describes how a hanging crucible Czochralski technique with a newly-designed ship lockage type powder feeding system assisted by numerical simulation was developed for the successful growth of high quality near stoichiometric LiNbO3 (SLN) and MgOSLN (~1 mol%) crystals. The physical properties of the crystals were assessed by measuring their crystallinity, Curie temperature, optical properties, coercive field and thermal properties. These properties, including a coercive field of 1.4 kV mm−1 and a thermal conductivity of 6.61 W (m K)−1 demonstrated that the crystals meet the demands for manufacturing periodically poled crystal devices. This growth method has great potential in the mass production of SLN and other incongruently melting crystals.

•Nd3+:Ba3Gd2(BO3)4 single crystals have been grown by the Czochralski method.•Thermal properties were systematically researched as a function of temperature.•The polarized absorption and fluorescence spectra were detailed investigated.•Nd3+:Ba3Gd2(BO3)4 crystal could be a promising crystal for use in solid state laser.Nd3+:Ba3Gd2(BO3)4 single crystal of sized ∅20 mm × 20 mm was grown by the Czochralski technique. The effective segregation coefficient of Nd3+ in Ba3Gd2(BO3)4 crystals was measured to be 1.147. A series of thermal properties, including specific heat, the average linear thermal expansion coefficient, thermal diffusivity and thermal conductivity, were systematically determined as a function of temperature. The thermal conductivity along a, b and c-axes increases with increasing temperature. The room temperature polarized absorption spectrum was obtained over the range of 330–1000 nm, together with the room temperature fluorescence spectrum. The spectral parameters of the crystal were calculated by using the Judd–Ofelt (J–O) theory. The fluorescence lifetime is 80.58 μs and the fluorescence quantum efficiency is ηc = 43.8%. A large FWHM value, moderate absorption cross-section and high thermal conductivity show that Nd3+:Ba3Gd2(BO3)4 crystal holds promise as a useful solid state laser material.

Yb–Mg codoped LiNbO3 (LN) crystals have many applications in self-frequency doubling lasers. However, the great difficulty associated with growing this crystal is one of the obstacles for its application. In this work, Yb-, Mg-doped and Yb–Mg codoped (MgYb0.8 and MgYb1.2) single crystals were successfully grown by the Czochralski method from the congruent melt. Some basic physical properties have been measured to provide reliable reference for application of the crystals. Compared to its value in a singly doped crystal, the effective segregation coefficient of the Yb3+ ion in codoped crystals clearly decreases. When doping Yb into Mg-doped LN, the absorption edge of the crystal shifts to longer wavelengths, while the refractive index stays nearly the same. Yb3+ doping apparently decreases the Curie temperature Tc. The thermal conductivity of Yb–Mg codoped LiNbO3 was found to be identical to that of Mg-doped LN and greater than that of congruent LN (CLN), which is a benefit for laser applications. The occupation sites of the Yb3+ ions are discussed, and the distinct raised growth ridges observed are attributed to the change in the lattice structure due to Yb–Mg co-doping.Highlights► High quality Yb–Mg codoped LiNbO3 crystals in size of ∅50 × 40 mm were grown by the Czochralski method. ► Compared to that in Yb-doped crystal, the keff of Yb3+ ion in codoped crystals clearly decreases. ► The absorption edge of Yb–Mg codoped LiNbO3 shifts to longer wavelengths, compared to that of MgOCLN. ► The thermal conductivity of Yb–Mg codoped LiNbO3 was identical to MgOCLN and greater than CLN. ► The distinct raised growth ridges are attributed to the change in lattice structure due to Yb–Mg co-doping.

The room temperature phonon modes of trigallium phosphorus heptaoxide (Ga3PO7) single crystal have been determined by polarized Raman spectroscopy. The Ga3PO7 single crystal exhibits a trigonal structure belonging to the space group R3m   (C3v5) with three molecules per unit cell (Z=3). The framework structure of the Ga3PO7 crystal consists of PO4 tetrahedra and Ga3O10 clusters. Since the PO4 tetrahedra are more tightly bound than the GaO5 trigonal bipyramids, only the internal modes of the PO4 are observed. We observed 7A1(TO)+7E(TO) out of 7A1(TO)+10E(TO) vibrations predicted by the Group Theory.Graphical AbstractHighlights► The phonon modes of the trigallium phosphorus heptaoxide (Ga3PO7) single crystal have been determined by polarized Raman spectroscopy at room temperature. ► 7A1(TO)+7E(TO) was observed out of 7A1(TO)+10E(TO) vibrations predicted by the Group Theory. ► Since the PO4 tetrahedra are more tightly bound than the GaO5 trigonal bipyramids, the high wavenumber spectral region exhibits only the internal modes of the former. ► A tentative mode assignment is given based on correlations with other PO4-based compounds.

Deep-UV nonlinear optical material KBe2BO3F2 (KBBF), fabricated by flux and hydrothermal methods, are studied by single crystal and powder X-ray diffraction (XRD) and neutron diffraction (NPD). Based on the single crystal diffraction data, the standard R32 structure is confirmed for flux grown KBBF, while the Rc structure is identified for the hydrothermally grown KBBF. No clear evidence of hydrogen bonding is found in the crystals by single crystal neutron diffraction. From powder XRD and neutron diffraction, the hydrothermally grown KBBF under investigation is found to be a mixture of two components consisting of 19.8 wt% of the R32 structure and 80.2 wt% of the Rc structure. No phase changes as a function of temperature up to 775 °C are observed for both samples from temperature dependent powder XRD data. However, a large anisotropic thermal expansion of the lattice is shown in the temperature dependent data.

Ammonium sulfate has been widely used as a control agent in the preparation of yttrium-aluminium-garnet (YAG) transparent ceramics, however, research of its application in the preparation in transparent ceramic yttria has not been intensively studied. Neodymium–doped yttria (Nd:Y2O3) nanopowders with controlled morphology and size were synthesized via a urea precipitation method using ammonium sulfate as the additive. The effect of ammonium sulfate was intensively studied throughout the preparation process. Morphology of precursors was found to be evidently affected by the [(NH4)2SO4]/[Nd:Y2O3] ratio (measured by weight). Uniform spheres of Nd:Y2O3 precursor were obtained without the addition of ammonium sulfate. With increasing amounts of ammonium sulfate added, the scale of the Nd:Y2O3 precursors diminished which results in the aggregation of the Nd:Y2O3 precursor. Aggregates of coral like particles after precipitation and uniform well dispersed particles after calcinations were obtained as the dosage of ammonium sulfate reached 20 wt%. It was considered to be the optimum state for the preparation of highly sinterable Nd:Y2O3 nanopowders. Ammonium sulfate was proved to be a regulator that could mediate the nucleation and growth of the precursor as well as its decomposition behaviour. Results of this paper can contribute to the controllable synthesis of transparent ceramic yttria.

The room temperature phonon modes of both the alkali metal doped and pure CBN (CaxBa1−xNb2O6) crystals were determined using the Raman scattering technique. Owing to the intrinsic disorder of the tetragonal lattice we observe few and broad bands. The wavenumber of the internal modes observed shifts upwards when the volume of the unit cell increases. This blue shift is likely to be related to the closer packing of the NbO6 octahedrons. The Curie temperatures of the ferroelectric to paraelectric phase transition for the CBN-like crystals were obtained from DSC measurements. The Raman spectra of CBN32 in the temperature range from 300 to 568 K were also recorded in order to investigate the phase transformation.

A new crystal, BaNd2(MoO4)4, has been grown from the flux melt based on Li2Mo3O10 by a spontaneous nucleation method. The phase structure of the obtained crystals was determined by X-ray powder diffraction. The result shows that the as-grown crystals are well crystallized and indexed in a monoclinic crystal system with space group B2/b. The specific heat of BaNd2(MoO4)4 crystal at 20 °C is 0.485 J/g K. Absorption and fluorescence spectra were also measured at room temperature. There are several strong and broad absorption peaks from 200 to 1200 nm and three emission transition bands located at 890, 1060, and 1334 nm are detected.

The mechanical and thermal properties of single crystal Tb2(MoO4)3 have been systematically studied. The result of microhardness measurement indicates that the crystal belongs to the soft materials category. The thermodynamic parameters obtained from DTA analysis were used for determining the type of liquid–solid interface during crystal growth. Negative thermal expansion along the c-axis was observed, and this behavior was attributed to the bent Tb–O–Mo bonds. The specific heat of the crystal was measured to be 0.122 cal g−1 K−1 at 293.15 K. The thermal conductivity of Tb2(MoO4)3 at room temperature was found to be smaller than that of representative ferroelectric LiNbO3.Highlights► Tb2(MoO4)3 possesses a low hardness value and can be easily processed. ► The growth interface is a rough surface when Tb2(MoO4)3 is pulled from melt. ► The bent Tb–O–Mo bonds result in the negative thermal expansion along the c-axis. ► Abnormal behaviors are observed because of the phase transition.

The room temperature phonon modes of the isostructural (Nd,Yb):YxGd1−x(VO4) laser crystals were determined using the Raman scattering technique, and the observed wavenumbers follow the overall mode distribution expected for REVO4 (RE  =rare earth) compounds with the tetragonal zircon structure, D4h19. They were assigned according to the group theory in terms of the internal modes of the VO4 tetrahedron and the external modes of the YxGd1−x(VO4) lattice. No appreciable changes in the phonon wavenumbers were observed for Yb:GdVO4 (Yb=0.008, 0.015, 0.020, 0.025, and 0.035), indicating that the force fields in the GdVO4 lattice are not strongly altered by Yb doping at the Gd site. However, most of the phonon wavenumbers in the systems (Nd,Yb):YxGd1−x(VO4) shifts upwards (one-phonon-like behavior) when Y replaces for Gd.Graphical abstractPlot of the observed wavenumbers of Nd:YxGd1−x(VO4) versus Y content (x). The linear trend indicates that most of the observed wavenumbers exhibit a one-phonon-like behavior.Research highlights► Force fields in the GdVO4 lattice are not strongly altered by Yb doping at the Gd site when the doping content of Yb is below 3.5 at%. ► Most of the phonon wavenumbers in the systems (Nd,Yb):YxGd1−x(VO4) shifts upwards with x increasing. ► The upward shifting is related to the decrease of the RE–O distance due to the lattice contraction. ► Most of the observed wavenumbers exhibits a one-phonon-like behavior.

CdS thin films on LiNbO3 (1 0 4) and silicon (1 1 1) substrates were prepared through an atom substitution technique using cadmium nitrate as a reactant in an H2S atmosphere at 230 °C. X−ray diffraction, scanning electron microscopy and transmission microscopy results indicate that the CdS film grows on LiNbO3 oriented along the [0 0 1] axis in form of crystallized nanoplates, while that deposited on silicon forms randomly oriented nanoparticles. Investigation of the precursor thin film suggests that CdS forms from the O in the CdO precursor thin film being substituted by S from H2S in the surrounding environment, which is designated as an atom substitution process. This novel method involving an atom substitution reaction between the CdO precursor thin film and its environment can provide a new low cost approach to the preparation of chalcogenide or other compound thin films. A schematic illustration and corresponding mechanism describing the details of this method are proposed.Graphical abstractElemental O in CdO is substituted by elemental S from the atmosphere in the apparatus, which is designated as an atom substitution process. This novel method involving an atom substitution reaction between the CdO precursor thin film and its environment can provide a new low cost approach to the preparation of chalcogenide or other compound thin films.Research highlights► An atom substitution method for thin film preparation was demonstrated. ► Combination of the atom substitution and spin coating method was achieved. ► Well oriented CdS thin film was prepared on LiNbO3 substrate. ► The atom substitution method could be used for many compound systems.

NdxLu1−xVO4 (x = 0, 0.005, 0.02, 0.023, 0.03 and 0.05) series crystals have been grown by the Czochralski method. The results of X-ray powder diffraction experiments show that these crystals belong to the zircon-type structure. The cutoff wavelength of LuVO4 is 330 nm and the transmittance is about 80% in 540–3010 nm. The functional relation of absorption coefficient α at 808 nm on Nd3+-doped concentration Nd in units of atomic % is obtained to be α = 7.649 Nd. The results of Judd–Ofelt analysis show that there is no obvious concentration quenching effect below 3 at.% doped concentrations. The highest output power at 1.06 μm is 1090 mW for Nd0.02Lu0.98VO4 at the pumping power of 6.58 W of a laser diode, the optical–optical conversion efficiency is 16.6% and slope efficiency is 19.4%.Research Highlights► High-quality NdxLu1−xVO4 series crystals have been grown. ► Concentration quenching effect in 5 at.% Nd:LuVO4 is serious. ► Highly doped Nd:LuVO4 possesses appropriate output power level at 1.06 μm. ► Miniaturized microchip green laser would be realized in reasonable approach.

We report the laser output of transparent Nd:YAG (Nd:Y3Al5O12) ceramics fabricated from Nd:YAG precursors through the microwave-assisted homogenous precipitation (MAHP) method. Pure phase and uniform Nd:YAG nano-powders with average sizes less than 100 nm were obtained by heating treatment of the Nd:YAG precursor particles aged for 6 d in vessel with humidity of 30%–50% at 25°C. Transparent Nd:YAG ceramic pellets were obtained by vacuum sintering at 1730°C for 10 h. Laser output (305 mW) with a slope efficiency of 5.1% was realized through an end-pumped configuration. Our results indicate that the MAHP method could potentially be used for the fabrication of laser ceramic products.

Single crystal of LiBaB9O15 for the first time has been grown from a Li2Mo3O10 flux by the top-seeded growth method. Details on the preparation and growth procedures are discussed. The phase structure of the as-grown crystal was determined by X-ray powder diffraction (XRD). The frequencies of the vibrational modes of the crystal were obtained from Infrared and Raman spectrum measurements. The results show that the obtained crystal is well-crystallized and indexed as a trigonal crystal system with lattice parameters of a = b=10.95053 Å, c = 16.88215 Å, and V = 1753.19 Å3. The observed frequencies were assigned on the basis of the BO3 and BO4 vibrations, and correlations with previous data reported for the similar compounds. On the basis of the XRD data and interfacial angle measurements, the as-grown crystal was found to be bounded by the (110), (113), and (101) planes. The seed crystal used for producing the crystal was oriented along the [100] direction.

To improve the fire retardancy performance of polyamide 6 (PA 6), layered silicates are used in combination with multi-walled carbon nanotubes (CNTs) to address the issue of packing density and uniformity of the protective inorganic barrier formed at the burning surface of the nanocomposites during combustion. Benzimidazolium is used to modify the silicate layers instead of conventional alkyl ammonium surfactants to tackle the issue of thermal stability. However, the poor dispersion of the modified layered silicates in PA 6 has a significant negative effect on the fire performance of the materials and offsets the positive effect of CNTs. Also, the results point to the apparent contradictions with different fire exposure tests; that is, significant reductions in heat release and mass loss rates in the cone calorimetry test do not imply a higher rating in the UL 94 vertical burning test.

Reduced lithium tantalate (LiTaO3, LT) wafers were prepared by chemically reducing regular congruent LT wafers in mixed iron and lithium carbonate powders under a flowing nitrogen atmosphere. The electrical conductivity, Curie temperature, infrared spectrum, UV–vis transmittance, piezoelectric constants and dielectric properties of the LT wafers before and after reduction were measured. In comparison with regular LT wafers, it was found that both the electrical conductivity and the optical absorption in the visible region are greatly increased after reduction, which is beneficial for eliminating pyroelectric discharge and for high accuracy device processing. In addition, we also found that the piezoelectric and dielectric properties of the chemically reduced wafers remain almost the same, a prerequisite for fabricating SAW devices. The effects of mechanisms related to chemical reduction on the evolution of the physical properties of LT wafers are also discussed.

Functional crystals are the basic materials for the development of modern science and technology and are playing key roles in the modern information era. In this paper, we review functional crystals in China, including research history, significant achievements, and important applications by highlighting the most recent progress in research. Challenges for the development of functional materials are discussed and possible directions for development are proposed by focusing on potential strengths of these materials.

Neodymium phosphate single crystals, NdPO4, have been grown by a flux growth method using Li2CO3-2MoO3 as a flux. The as-grown crystals were characterized by X-ray powder diffraction(XRPD), differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques. The results show that the as-grown crystals were well crystallized. The crystal was stable over the temperature range from 26 to 1200 °C in N2. The specific heat of NdPO4 crystal at room temperature was 0.41 J/g °C. The absorption and the fluorescence spectra of NdPO4 crystal were also measured at room temperature.

•A millimeter-sized LiNd(MoO4)2 crystal has been grown by the flux method.•The thermal and spectral properties were measured for the first time.•A comparison of properties was made between LiNd(MoO4)2 and other laser crystals.A millimeter-sized LiNd(MoO4)2 crystal has been grown using the flux method. LiNd(MoO4)2 crystallizes in the scheelite-type structure with space group I41/a, lattice parameters: a=5.26090(10) Å, c=11.5395(3) Å, V=319.379(15) Å3, and Z=2. The full-matrix, least-squares refinement with R=1.64 % and Rw=4.34 % shows that the Li and Nd atoms are completely disordered at jointly occupied sites. The theoretical growth morphology with indexed (hkl) planes was developed from the Bravais–Friedel–Donnay–Harker (BFDH) theory and it is in good agreement with the morphology of the as-grown crystals. The chemical composition was analyzed using an inductively coupled plasma emission spectrometer. The full set of thermal properties, including specific heat, thermal expansion, thermal diffusivity, and thermal conductivity of LiNd(MoO4)2 are reported. The UV–visible diffuse reflectance spectrum contains many strong and broad Nd3+ absorption lines over the spectral range from 300 to 1000 nm. Three transition emission bands located at 890, 1064 and 1335 nm are observed in the fluorescence spectrum. The fluorescence lifetime is measured to be 2 μs at room temperature. LiNd(MoO4)2 possesses a large absorption cross section of 1.04×10−20 cm2 at 804 nm and an emission cross section of 4.8×10−20 cm2 at 1064 nm.