Centimeter-size Crystals Research Articles

Incorporating an Aromatic Cationic Spacer to Assemble 2D Polar Perovskite Crystals toward Self-Powered Detection of Quite Weak Polarized Light.

Two-dimensional (2D) hybrid perovskites with intrinsic attributes of structural and optical anisotropy are holding a bright promise for polarization-sensitive photodetection. However, studies on self-powered detection to quite weak polarized light remain scarce in this 2D family. By incorporating an aromatic spacer into the 3D cubic prototype, we have successfully assembled a new 2D hybrid perovskite with a polar motif, (FPEA)2(MA)Pb2I7 (FMPI, where FPEA is 4-fluorophenethylammonium and MA is methylammonium). Its unique 2D quantum-well structure allows optical absorption dichroism with a large ratio of ∼3.15, and the natural polarity results in a notable bulk photovoltaic effect. Further, centimeter-size crystals (10 × 10 × 3 mm3) of FMPI were facilely obtained by the temperature cooling method, and its crystal-based detectors enable excellent self-powered detection of quite weak polarized light, showing a notable polarization-sensitive ratio (∼1.5), extremely low detection limit (∼100 nW/cm2), and antifatigued stability. The alloyed aromatic cationic spacers facilitate the polarity and enhanced phase stability. This study paves a way for further exploration of new 2D perovskite candidates toward optoelectronic device applications.

Thermochemiluminescent peroxide crystals

Chemiluminescence, a process of transduction of energy stored within chemical bonds of ground-state reactants into light via high-energy excited intermediates, is known in solution, but has remained undetected in macroscopic crystalline solids. By detecting thermally induced chemiluminescence from centimeter-size crystals of an organic peroxide here we demonstrate direct transduction of heat into light by thermochemiluminescence of bulk crystals. Heating of crystals of lophine hydroperoxide to ~115 °C results in detectable emission of blue-green light with maximum at 530 nm with low chemiluminescent quantum yield [(2.1 ± 0.1) × 10‒7 E mol‒1]. Spectral comparison of the thermochemiluminescence in the solid state and in solution revealed that the solid-state thermochemiluminescence of lophine peroxide is due to emission from deprotonated lophine. With selected 1,2-dioxetane, endoperoxide and aroyl peroxide we also establish that the thermochemiluminescence is common for crystalline peroxides, with the color of the emitted light varying from blue to green to red.

Design and Synthesis of the Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material Ba₃(ZnB₅O₁₀)PO₄.

Access to the elusive deep-ultraviolet by direct second harmonic generation (SHG) enabled by a new beryllium-free zincoborate-phosphate crystal is reported. Ba3(ZnB5O10)PO4, exhibits large SHG responses at 1064 and 532 nm and a short 180 nm absorption edge. Centimeter-size crystals are grown, and quantum mechanical calculations demonstrate the key role played by ZnO4 tetrahedra in the enhanced optical responses.

Centimeter-size BiFeO3 single crystals grown by flux method

A narrow part of Fe2O3–Bi2O3 phase diagram was re-investigated in order to elaborate single crystals of the multiferroic BiFeO3 (BFO). Centimeter-size single crystals were successfully obtained by flux method, and present a preferred growth direction. X-ray diffraction studied have highlighted that the growth direction is along the polar axis [111] r of the structure. The stability of BFO versus temperature (reversible ferroelectric transition followed by multiple irreversible decompositions) is discussed in the light of Differential Scanning Calorimetry (DSC) analysis performed between 25 and 1400°C.

The hydrothermal synthesis, growth, and optical properties of γ-LiBO 2

Large single crystals of the acentric, tetragonal lithium metaborate, γ-LiBO 2, have been grown using the hydrothermal method. Favorable conditions for the synthesis of γ-LiBO 2 were found over the course of a phase stability study of lithium borates in supercritical aqueous base. Hydrothermal synthesis was achieved by: (1) conversion of the α phase, (2) direct crystallization from B 2O 3 and LiOH or (3) recrystallization of previously crystallized γ-phase crystallites. Solubility of γ-LiBO 2 in dilute aqueous LiOH was found to be 2–5 wt% from 460 to 75 °C with a positive solubility coefficient. Crystal growth experiments were designed to take advantage of the favorable solubility conditions within this range. Seeded growth occurred at a maximum rate of 2.1 mm/day when the dissolution zone temperature was 535 °C and the growth zone temperature was 495 °C. This permitted the routine growth of centimeter-size crystals in less than 1 week. These crystals possess an interesting combination of optical properties, including a band gap of about 9 eV and high non-linear optical (NLO) susceptibility.

Melt-grown CuInSe2 and photovoltaic cells

The crystal structure, cleavage properties and phase relations of the ternary semiconductor CuInSe2 are first described. Then the growth of monocrystals of this chalcopyrite from the melt, with the elements as starting materials, is reviewed from a historical perspective. The procedures for a preferred Bridgman method of growth are described, which result in centimeter-size crystals within an ingot having uniform composition and conductivity-type. The ingot is also free of adhesion to the synthesizing ampoule and, in addition, is free of voids and microcracks. The electronic properties of CuInSe2 are briefly discussed and photovoltaic cells using p-type monocrystalline absorber substrates are reviewed. Finally, the progress made in thin film polycrystalline CuInSe2 based cells is briefly touched upon.

Impurities and dopants in vanadium doped CdTe

Vanadium doped CdTe (CdTe:V) behaves as an efficient photorefractive material due to its higher figure of merit (n3r41) than InP:Fe. It is a potential material for optoelectronic applications, in particular to manufacture telecommunication switching devices at 1.3–1.5 μm. Two laser beams interfering with an angle of 2 θ create an interference pattern of grating spacing Λ = λ/2 sin θ (λ the wavelength). Free carriers (electrons or holes) photoionized in the bright regions generate a spatially modulated electric field which, due to the electro-optic effect, gives a refractive index variation. The strength of the modulation depends on the quantity of redistributed charges according to the concentrations of deep levels, shallow carriers, and finally, the V3+V2+ ratio. So, the knowledge of the vanadium doping level and shallow carrier concentrations are of primary importance to understand the photorefractive behavior of CdTe:V. This paper describes the physico-chemical analyses of 27 different CdTe or CdZnTe centimeter-size crystals by secondary ion mass spectrometry (SIMS) which has been shown to be a powerful technique to quantify all kind of dopants in semiconductors. The low detection limits of the method, in the range of 1 × 1030 atom cm−3, for main p-type, n-type residual dopants, together with vanadium, in CdTe, allow to classify, qualitatively, the different crystals according to whether their V3+V2+ ratio is greater or lower than one. In particular, the high levels of lithium, copper, and phosphorus in certain crystals are clearly evidenced. Some hints about the origin of these residual dopants are given.

Crystal growth of PbTiO3 by the top-seeded solution-growth method

Centimeter-size crystals of lead titanate PbTiO3 have been grown by the top-seeded solution-growth (TSSG) method using two different solvents: PbO and a mixture of PbO and B2O3. The maximum dimensions of the as-grown crystal boules were 32 × 32 × 6 mm3. The PbO-rich side of the phase diagram of the PbO-TiO2 system has been derived by means of crystal-growth experiments. If there is more than 11 mol% of TiO2 in the PbO-TiO2 solution, single crystal of PbTiO3 are obtained. If there is 5–9 mol% or less than 4 mol%, PbO in the tetragonal or orthorhombic phase is formed, respectively.

Growth of Europous Oxide (EuO) Single Crystals

The desirability of having large sound single crystals of EuO for a number of physical measurements has been well established. Although crystals of EuO had previously been grown, they were either of poor quality, primarily because of container contamination, or too small for many measurements. We report here on a method of growing large, single-phase, mechanically sound crystals of EuO. The method is one where growth takes place from a solution containing an excess of europium metal. The solution, sealed in molybdenum crucibles, is cooled from 1950°–2000°C at the rate of about 25°/h. Centimeter-size crystals were grown and shown to be of extremely good quality by an examination of their Laue spots and their microstructure. The crystals have a lattice constant of 5.1451 ű0.0003 and a density of 8.180±0.002. The data from the crystal-growing experiments were used to propose a phase diagram in which EuO, when pure, is shown to be an incongruently melting compound.