As-grown Crystals Research Articles

Scattering-free Ce:LYBO single crystals for thermal neutron detection

Ce:Li6Y(BO3)3 (LYBO) is a well-known candidate for thermal neutron detection with a very high Li concentration (3.06 × 1022/cm3). So far, as-grown crystals exhibit a milky appearance that compromises their performance as scintillators. Current work demonstrates, for the first time, the growth of scattering-free undoped and Ce-doped LYBO by a thermal quenching process. The origin and features of the scattering centers are investigated in detail. Furthermore, the annealing treatment for the scintillation activation is studied, finding that the reduction in oxygen vacancies is mandatory. Under thermal neutron irradiation, the annealed scattering-free Ce:LYBO single crystal achieves a record-high light yield of 6200 ph/n in a single decay with a lifetime as short as 24 ns.

Solution-grown millimeter-scale Mn-doped CsPbBr3/Cs4PbBr6 crystals with enhanced photoluminescence and stability for light-emitting applications.

Metal halide perovskites are particularly emerging for optoelectronic applications in light-emitting diodes, photodetectors, and solar cells due to their flourishing photophysical properties. However, the poor stability of three-dimensional (3D) lead halide perovskite nanocrystals (NCs) significantly hampers their optoelectronics and photovoltaics applications. Embedding 3D perovskites into zero-dimensional (0D) perovskite crystals and doping ions of appropriate elements into host lattices provide effective approaches to improve the stability and optical-electronic performance. In this study, millimeter-scale Mn-doped and undoped CsPbBr3/Cs4PbBr6 perovskite crystals were successfully fabricated by a one-step slow cooling method. We systematically investigated the effects of Mn2+ ion doping on the PL performance and stability of CsPbBr3/Cs4PbBr6 crystals. Compared with undoped crystals, the existence of Mn2+ ions not only blue-shifted the PL peak but also improved the luminescence performance and stability of the prepared millimeter-sized crystals. Moreover, doping Mn2+ ions can increase the proportion of radiative recombination at low temperature, which may be because Mn2+ ions can effectively accelerate the decay of a dark exciton by the magnetic mixing of bright and dark excitons. In addition, green LED devices with high efficiency packaged as-grown crystals are explored, which promises further application in display backlights.

Single Crystal Growth and Nano-Structure Study in a Topological Dirac Metal, CoTe2-δ

A single crystal of a topological material, CoTe2-δ, has been grown via the chemical vapor transport method for a structural and electronic transport study. Single-crystal X-ray diffraction, powder X-ray diffraction, and high-resolution scanning electron microscope measurements confirm the high quality of the as-grown single crystals. In a high-resolution scanning electron microscopy study, a clear layered feature of the trigonal CoTe2-δ crystal was observed. Fractal features and mosaic-type nanostructures were observed on the as-grown surface and cleaved surface, respectively. The trigonal CoTe2-δ demonstrates a metallic ground state in transport measurements, with a typical carrier’s concentration in a 1021 cm−3 magnitude and a residual resistivity ratio of 1.6. Below 10 K, trigonal CoTe2-δ contains quite complicated magnetoresistance behavior as a result of the competing effect between Dirac states and possible spin fluctuations.

Broadened and enhanced ∼ 2.9 μm mid-infrared emission in Dy3+/Er3+: Na5Y9F32 single crystals by Gd3+ co-doping

A series of Er3+, Dy3+ and Gd3+ doped Na5Y9F32 single crystals for laser output at ∼ 2.9 μm have been fabricated via a reformative Bridgman technique. The impacts of optically active ions of Dy3+ and Er3+ and non-optically active ion of Gd3+ on the emission spectra at ∼ 2.9 μm were investigated. The patterns of X-ray diffraction (XRD) of the obtained crystals indicated that the doping level of rare earth (RE) ions had inconspicuous effects on the lattice structure of Na5Y9F32. The emission spectra at ∼ 2.9 μm of the as-grown single crystals as change of various Er3+/Dy3+/Gd3+ contents were measured systematically excited by 974 nm light. A strong and wide emission band at ∼ 2.9 μm could be obtained in Er3+/Dy3+ co-doped crystal by utilizing Er3+ as sensitizer for Dy3+ ions. Meanwhile, the introduction of Gd3+ ions into Er3+/Dy3+ doped Na5Y9F32 single crystal could further widen the emission band at ∼ 2.9 μm due to the lattice distortion and variation of the crystal fields around Er3+ and Dy3+. Furthermore, the effective ∼ 2.9 μm emission bandwidth (Δλeff) of the Er3+/ Dy3+/ Gd3+ triply incorporated crystal was approximately 255.65 nm, which was nearly 3.4 times that of the 0.5 mol% Er ion singly doped sample (74.86 nm) and 1.4 times that of the 0.5 mol% Er/0.3 mol% Dy ions doubly incorporated sample (182.25 nm). The results unveiled that the introduction of Gd3+ was conducive to the generation of level population inversion of 6H13/2 and 6H15/2 of Dy3+ ions to help the output of ∼ 2.9 μm laser.

Optical and scintillation properties of modified LSO crystals with different ions doping grown by a rapid CZ system

LSO:Ce is a well-known scintillation crystal that is widely used in nuclear medicine, security checks, and high-energy physics. The scintillation properties of LSO can be modified by doping to meet the ever-growing requirements of radiation detection. However, exploring new doping techniques for LSO crystals with self-designed scintillation features remains time-consuming, especially by the Czochralski (CZ) method. In this paper, we established a high-efficiency crystal growth system based on the CZ method for the rapid growth of LSO crystals. The system is regulated by a high-accuracy auto-diameter controller to grow small boules of ϕ 20 mm × 100 mm. By incorporating an arc bottom crucible and optimizing the temperature field, the crystallization fraction of the as-grown crystal can be increased to 95% with the growth period compressed to 48 h. With the aid of the growth system, LSO crystals with Lu3+ partially substituted by optical inertia RE ions (Sc3+, Y3+, La3+, Gd3+), metal cations co-doping (Ca2＋, Li1+, Yb3+), and different luminescent ions doping (Pr3+, Nd3+, Eu3+, Tb3+, Dy3+, Yb3+) are grown. Comparative analysis shows that the Ca co-doped LSO:Ce exhibits the best scintillation performance, taking into account both light output and decay time, among our samples. Moreover, Tb-doped LSO features relatively good scintillation efficiency with various wavelengths of visible light emission.

Effects of processing parameters and grinding direction on the material removal mechanism of (100) surface single crystal diamond in self-rotating mechanical grinding

The current commonly used method for diamond processing is mechanical polishing using the cast iron grinding wheel (Scaife). However, this method is challenging to meet the processing requirements of semiconductor applications. This study proposes a more efficient grinding method that employs a high-speed self-rotating grinding device, coupled with a bonded abrasive diamond grinding wheel with high self-sharpening properties, to achieve high precision grinding of single crystal diamonds. Different cutting depths, grit sizes, and linear velocities are employed in the processing, and the material removal mechanism is studied through morphology characterization, element content, and other detection methods. The experimental results indicate that the material removal method of diamond (100) crystal surface is influenced by the cutting depth. It is a collaborative removal process in the 〈110〉 and 〈100〉 directions, and the brittle-ductile transition in the <110> direction significantly affects the machining quality. Surface fractures and subsurface cracks primarily occur through cleavage along the (111) plane, so a method to distinguish the orientation of the (100) crystal plane is proposed. Additionally, this study demonstrates the influence of different processing directions on the surface of the diamond within the same plane. By using this method, the surface roughness of the 7 × 7 mm as-grown crystal can be reduced to Ra 0.523 nm within 10 min, with a material removal rate of 32.4 μm/h.

The Growth and Spectroscopic Properties of Er, Nd: YSGG Single Crystal Fibers

Single crystal fiber (SCF) is a novel solid gain medium and technique which combines the advantages of glass fiber and single crystal, showing great potential in the field of high-power lasers. In this paper, Er, Nd: YSGG single crystals with diameters of 2 mm and lengths of 80 mm were successfully grown using the micro-pulling-down method for the first time. Then, the measurements of Laue spots and Er3+ distribution indicated that the as-grown crystals were of a high quality. The effect of co-doped Nd3+ on the Er: YSGG was systematically discussed, which demonstrated that Nd3+ can decrease the fluorescence lifetime of Er: 4I13/2 that solve the self-termination bottleneck accordingly. These results demonstrate that Er, Nd: YSGG SCFs are promising materials for the further 3 μm laser generations.

Influence of heat treatment on the structure and mechanical properties of zirconium dioxide crystals partially stabilized by samarium oxide

The effect of high-temperature treatment in different media on the phase composition, microhardness and fracture toughness of (ZrO2)1-х(Sm2O3)х crystals with x = 0.02÷0.06 has been studied. The crystals have been grown using direction melt crystallization in a cold skull. The crystals have been heat treated at 1600 °C for 2 h in air and in vacuum. The phase composition of the crystals has been studied using X-ray diffraction and Raman scattering. We show that samarium cations enter the ZrO2 lattice mainly in a trivalent charge state and do not change their charge after air or vacuum annealing. The as-annealed phase composition has changed in all the test crystals except for the (ZrO2)0.94(Sm2O3)0.06 composition. After air or vacuum annealing the (ZrO2)1-x(Sm2O3)x crystals with 0.002 ≤ x ≤ 0.05 contain a monoclinic phase. The (ZrO2)0.94(Sm2O3)0.06 crystals contain two tetragonal phases (t and t´) with different tetragonality degrees. After air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals the lattice parameters of the t and t´ phases change in opposite manners, suggesting that the tetragonality degree of the t phase increases whereas the tetragonality degree of the t´ phase decreases. The microhardness and fracture toughness of the as-annealed crystals depend on the Sm2O3 concentration in the solid solutions. The formation of the monoclinic phase in the (ZrO2)1-х(Sm2O3)х crystals with 0.037 ≤ x ≤ 0.05 significantly reduces the microhardness and fracture toughness of the crystals. Annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals triggers more efficient hardening mechanisms and thus increases the fracture toughness of the crystals. We show that air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals increases the fracture toughness of the crystals by 1.5 times as compared with that of the as-grown crystals.

A flux growth technique for high quality cubic boron arsenide bulk single crystals

The growth of single crystal cubic boron arsenide (c-BAs) has attracted considerable interest due to its high room-temperature thermal conductivity and high ambipolar electrical mobility. However, currently the only growth technique reported for c-BAs crystals is the chemical vapor transport (CVT) method, which exhibits several drawbacks with regard to size scalability and crystal quality control, thereby hindering the further advancement of this semiconductor material. Herein, we report a flux growth technique using liquid arsenic (l-As) as a reaction medium at high pressures for the growth of high-quality c-BAs crystals with several millimeters size. The outstanding properties, including high uniformity, lower defect density, and lower carrier concentration of the as-grown c-BAs single crystals from flux growth, have been verified via a combination of techniques including x-ray diffraction, Raman scattering, photoluminescence spectroscopy, and electrical transport measurements, in comparison with the CVT-grown crystals.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals were studied. Two absorption bands with the low-photon-energy threshold at 1.35 and 1.73 eV (T = 300 K) appeared in the transparency region of GaSe after the high-energy-electron irradiation. The observed absorption bands were attributed to the defect states induced by Ga vacancies in two charge states, having the energy positions at 0.23 and 0.61 eV above the valence band maximum at T = 300 K. The optical pump-terahertz probe technique (OPTP) was employed to study the dark and photoexcited terahertz conductivity and charge carrier recombination dynamics at two-photon excitation of as-grown and 9 MeV electron-irradiated GaSe crystals. The measured values of the differential terahertz transmission at a specified photoexcitation condition were used to extract the terahertz charge carrier mobilities. The determined terahertz charge carrier mobility values were ~46 cm2/V·s and ~14 cm2/V·s for as-grown and heavily electron-irradiated GaSe crystals, respectively. These are quite close to the values determined from the Lorentz–Drude–Smith fitting of the measured dielectric constant spectra. The photo-injection-level-dependent charge carrier lifetimes were determined from the measured OPTP data, bearing in mind the model injection-level dependencies of the recombination rates governed by interband and trap-assisted Auger recombination, bulk and surface Shockley–Read–Hall (SRH) recombination and interband radiative transitions in the limit of a high injection level. It was found that GaSe possesses a long charge carrier lifetime (a~1.9 × 10−6 ps−1, b~2.7 × 10−21 cm3ps−1 and c~1.3 × 10−37 cm6ps−1), i.e., τ~0.53 μs in the limit of a relatively low injection, when the contribution from SRH recombination is dominant. The electron irradiation of as-grown GaSe crystals reduced the charge carrier lifetime at a high injection level due to Auger recombination through radiation-induced defects. It was found that the terahertz spectra of the dielectric constants of as-grown and electron-irradiated GaSe crystals can be fitted with acceptable accuracy using the Lorentz model with the Drude–Smith term accounting for the free-carrier conductivity.

Upconversion luminescence and optical thermometry behaviors of Yb3+ and Ho3+ co-doped GYTO crystal

Optical thermometry based on the upconversion (UC) luminescence intensity ratio (LIR) has attracted considerable attention because of its feasibility for achievement of accurate non-contact temperature measurement. Compared with traditional UC phosphors, optical thermometry based on UC single crystals can achieve faster response and higher sensitivity due to the stability and high thermal conductivity of the single crystals. In this study, a high-quality 5 at% Yb3+ and 1 at% Ho3+ co-doped Gd0.74Y0.2TaO4 single crystal was grown by the Czochralski (Cz) method, and the structure of the as-grown crystal was characterized. Importantly, the UC luminescent properties and optical thermometry behaviors of this crystal were revealed. Under 980 nm wavelength excitation, green and red UC luminescence lines at 550 and 650 nm and corresponding to the 5F4/5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+, respectively, were observed. The green and red UC emissions involved a two-photon mechanism, as evidenced by the analysis of power-dependent UC emission spectra. The temperature-dependent UC emission spectra were measured in the temperature range of 330–660 K to assess the optical temperature sensing behavior. At 660 K, the maximum relative sensing sensitivity (Sr) was determined to be 0.0037 K−1. These results highlight the significant potential of Yb,Ho:GYTO single crystal for optical temperature sensors.Graphical abstract

Elucidating the role of oxygen vacancies on the electrical conductivity of β-Ga2O3 single-crystals

The contribution of oxygen vacancies (VO) to the electrical conductivity of unintentionally doped β-Ga2O3 has been a topic of recent debate. Here, we use a combination of Hall measurements and Raman spectroscopy on as-grown and O2-annealed β-Ga2O3 crystals to investigate the role of VO on electrical conductivity. The annealed samples show a significant decrease in carrier concentration. By comparing the relative Raman shift of individual modes with theoretically calculated contributions of oxygen sites to these modes, we verify the marked reduction of VO in annealed β-Ga2O3 crystals. Furthermore, the IR modes in β-Ga2O3, usually hidden by free carrier absorption, are clearly seen in the annealed sample. The reduction of band tail states as well as free carrier absorption in the annealed samples provides additional evidence for reduced carrier concentration related to VO, making them a key determinant of electrical conductivity in β-Ga2O3.

Correlation between thermal properties, growth parameters and low segregation coefficient in (K, Na)NbO3-based growth by Bridgman-Stockbarger route

In order to achieve optimized growth conditions to reduce the compositional segregation in (K,Na)NbO3-based crystals produced by the vertical Bridgman-Stockbarger (VB-S) method, both a complete previous analysis of the thermal properties of the precursor oxides and a suitable choice of the dimensions of the crucible were made based on theoretical models proposed in the literature. By following this approach, chemical analysis of the as-grown crystals revealed very small effective segregation coefficients in the radial and longitudinal directions of the as-grown crystals. The obtained results revealed that is possible to grow single crystals by VB-S even for incongruent compounds, through a suitable establishment of the growth parameters adjusted according to the thermal properties of the piezoelectric oxide and the relative dimensions of the crucible.

Growth, structural, optical, thermal and terahertz time-domain spectroscopy of l-alanine single crystal: A potential amino acid based nonlinear optical material

In our present work, we focused on the terahertz (THz) based characterization of a very efficient organic nonlinear optical (NLO) single crystal of l-alanine (LA). Using the well-known slow evaporation solution growth method (SEST), an optically transparent amino acid-based LA crystal was effectively grown at room temperature. The structural information of the titled crystal was analyzed using powder X-ray diffraction (PXRD) which confirms the space group P212121 and orthorhombic structure of the crystal. Chemical etching of an as-grown single crystal was analyzed to identify the growth patterns. Fourier transform infrared (FTIR) and FT-Raman spectrometry were used to figure out the major functional groups that were present in the ingot crystal. The optical behaviour of LA crystal was observed through UV–Vis and Photoluminescence (PL) spectroscopies. The single crystal was found to have high transmission values over a wide range of wavelength. The PL results revealed that the main emission happens at 474 nm. Thermal stability of the titled compound was acquired by thermo-gravimetric and the differential thermo-gravimetric (TG-DTG) analysis. Open and closed aperture Z-scan measurements were used to analyze the third order nonlinear behavior of the as-grown sample using a femtosecond Ti-sapphire laser. To analyze the absorption peaks behavior Terahertz time-domain spectroscopy (THz-TDS) was also performed in the range 0.2–2.0 THz. The above study shows variation in absorption coefficient and refractive index at THz frequencies.

Investigating the effect of H+-ion irradiation on layered α-MoO3 flakes by defect engineering

Ion irradiation is a versatile and convenient tool for modifying the optical, electrical, and catalytic properties of two-dimensional (2D) materials through controlled induction of impurities and defects. The behavior of 2D materials under ion irradiation is interesting, which needs to be explored in the contest of their optoelectronic applications. In the present work, we have reported the effect of H+-ion irradiation on layered α-MoO3 flakes by defect engineering. Initially, the α-MoO3 crystals were synthesized using the physical vapor deposition technique followed by mechanical exfoliation of an as-grown crystal to obtain α-MoO3 flakes of different thicknesses. Then, the exfoliated flakes were exposed to H+-ion/proton irradiation with a fluence of 1 × 1016 ions/cm2 using a 30 keV source. After irradiation, new photoluminescence (PL) emission peaks were observed at different positions in the range of ∼2.4–1.9 eV, which was found to be absent in pristine flakes. Raman studies revealed non-uniform oxygen vacancy distribution in H+-ion irradiated α-MoO3 flakes, which affected the PL peak positions. Additionally, first-principle calculations and Bader charge analysis were performed to identify the origin of the new PL peaks. Our findings indicate that oxygen vacancies positioning at different locations of the α-MoO3 lead to the emergence of new absorption peaks within the range of ∼2.2–1.25 eV, which is consistent with our experimental findings. The present study gives insight into exploring the use of ion-irradiated α-MoO3 in optoelectronics applications with tunable properties.

Synthesis, Structural, Spectroscopic, Fluorescence, and Dielectric Studies of Bis-(4-Aminopyridine)-Zinc(II) Acetate: A Metal-Organic Crystal.

The advancement of crystalline growth and characterization tools allows us to investigate novel nonlinear optical substances suitable for photonic applications. Bis-(4-aminopyridine)-zinc(II) acetate (B4AZA), a metal-organic crystal was produced in this study using the slow evaporation procedure at room temperature. Analytical studies such as X-ray crystallography, Fourier transform infrared (FT-IR), UV-visible (UV-Vis), fluorescence, second harmonic generation (SHG), and dielectric tests were used to characterize the as-grown B4AZA crystals. According to the solubility data, the sample has a positive temperature coefficient of solubility. The crystallographic findings show that the B4AZA crystallized in a monoclinic structure with the P21/n space group. Molecular vibrations and functional groups in the substance were determined using the FT-IR technique. The UV-Vis absorbance and transmittance spectra have shown the wide transparency and minimum absorbance of the B4AZA in the near UV and entire visible regions of the electromagnetic spectrum. The bandgap of the B4AZA has been calculated using the Tauc relation and found to be 4.32eV. The fluorescence spectra have shown a prominent emission peak at 584nm with an excitation wavelength of 280nm. The larger Stokes shift found in the fluorescence spectra is advantageous for practical applications. The SHG study revealed that the powdered B4AZA samples generated a second harmonic output. The dielectric test revealed frequency-dependent changes in the dielectric constant and loss factor. Both the dielectric constant and the loss factor decrease exponentially as frequency increases, reaching low values at higher frequencies. The experimental results illustrate the suitability of the B4AZA crystals for photonic applications.

Controllable synthesis of monolayer WSe2 crystals by Copper-Assisted chemical vapor deposition

In this work, we demonstrate the controllable synthesis of high-quality WSe2 monolayers via a copper-assisted chemical vapor deposition method. The structure characterizations confirm that the as-grown WSe2 crystals by introducing Cu powder exhibit monolayer thickness and high crystalline quality. Most importantly, theoretical calculation reveals that Cu atoms could easily occupy the active sites above the monolayer WSe2 surface, consequently forming a self-limited growth. The Cu-assisted growth method broadens the scope of the 2D growth of other TMD materials, and also provides more application potential in 2D electronics.

Synthesis, experimental and theoretical studies of morpholinium bromide single crystal for NLO application

Due to the electronic applications, non-linear optical (NLO) materials are receiving research attention. A non-linear optical material, morpholinium bromide (MBr) single crystal with dimensions of 14 × 9 × 3 mm3 was grown successfully by slow evaporation solution growth technique. The synthesized crystal belongs to monoclinic crystal with space group P21/c, which was confirmed through single crystal XRD (SXRD) analysis. Further, powder XRD analysis was used to record several dispersion peaks and the presence of dispersion peak positions for the as-grown material is correlated with the scattering peak state. The optimised molecular structure, HOMO-LUMO, NBO, MEP and Mulliken atomic charges of MBr crystal were theoretically investigated using B3LYP with a 6–311 G ++(d, p) basis set. FTIR studies revelas the functional components present in the grown material. The optical band gap was found to be 3.3 eV with a transmittance cut-off wavelength of 362 nm. TG-DTA analysis was done to understand the as-grown MBr crystal's temperature withstanding capability by assessing the weight loss associated with the corresponding decomposition peak. The potential of the crystal to stand up to laser power is investigated using laser damage threshold (LDT) studies. The Z-scan study is implemented to the polished MBr crystal to assess its nonlinear refractive index (n2), absorption coefficient (β) and susceptibility χ(3) for its usefulness in optoelectronic applications.

Investigation of Planckian behavior in a high-conductivity oxide: PdCrO2

The layered delafossite metal PdCrO[Formula: see text] is a natural heterostructure of highly conductive Pd layers Kondo coupled to localized spins in the adjacent Mott insulating CrO[Formula: see text] layers. At high temperatures, T, it has a T-linear resistivity which is not seen in the isostructural but nonmagnetic PdCoO[Formula: see text]. The strength of the Kondo coupling is known, as-grown crystals are extremely high purity and the Fermi surface is both very simple and experimentally known. It is therefore an ideal material platform in which to investigate "Planckian metal" physics. We do this by means of controlled introduction of point disorder, measurement of the thermal conductivity and Lorenz ratio, and studying the sources of its high-temperature entropy. The T-linear resistivity is seen to be due mainly to elastic scattering and to arise from a sum of several scattering mechanisms. Remarkably, this sum leads to a scattering rate within 10[Formula: see text] of the Planckian value of k[Formula: see text]T/[Formula: see text].

Growth of millimeter-sized high-quality CuFeSe2 single crystals by the molten salt method and study of their semiconducting behavior

An eutectic AlCl3/KCl molten salt method in a horizontal configuration was employed to grow millimeter-sized and composition homogeneous CuFeSe2 single crystals due to the continuous growth process in a temperature gradient induced solution convection. The typical as-grown CuFeSe2 single crystals in cubic forms are nearly 1.6 × 1.2 × 1.0 mm3 in size. The chemical composition and homogeneity of the crystals was examined by both inductively coupled plasma atomic emission spectroscopy and energy dispersive spectrometer with Cu:Fe:Se = 0.96:1.00:1.99 consistent with the stoichiometric composition of CuFeSe2. The magnetic measurements suggest a ferrimagnetic or weak ferromagnetic transition below TC = 146 K and the resistivity reveals a semiconducting behavior and an abrupt increase below TC.