Undoped Crystals Research Articles

Achieving Giant Piezoelectricity and High Property Uniformity Simultaneously in a Relaxor Ferroelectric Crystal through Rare-Earth Element Doping.

The low uniformity in properties of relaxor ferroelectric crystals is a long-standing issue in the ferroelectric community, which limits the available volume of the entire crystal boule. The aim of this study is to develop a relaxor ferroelectric crystal with improvedproperty uniformity and excellent piezoelectricity. To this end, Pb(In1/2 Nb1/2 )O3 -Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 is doped with Nd2 O3 (Nd-PIN-PMN-PT) to improve the crystal performance. Along the crystal boule, the piezoelectric coefficient d33 varies from 2800 to 3500 pC N-1 , and the dielectric constant ranges from 8400 to 9800, with variations of 25% and 16%, respectively. Such high property uniformity results in over 75% available volume of the crystal boule, compared to 30-50% for undoped crystals grown by Bridgman method. At the electric field of 1kV cm-1 , the converse piezoelectric response is up to 4780 pm V-1 . In addition, its Curie temperature (TC ) and coercive field (EC ) are above 150°C and 3kV cm-1 , respectively. Compared with Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 crystal (d33 : 1500 pC N-1 , TC : 135°C, EC : 2.3kV cm-1 ), the larger piezoelectricity, the higher TC and EC , and improved uniformity make Nd-PIN-PMN-PT crystals promising candidates for advanced piezoelectric applications.

The Mu2e Crystal Calorimeter: An Overview

The Mu2e experiment at Fermilab will search for the standard model-forbidden, charged lepton flavour-violating conversion of a negative muon into an electron in the field of an aluminium nucleus. The distinctive signal signature is represented by a mono-energetic electron with an energy near the muon’s rest mass. The experiment aims to improve the current single-event sensitivity by four orders of magnitude by means of a high-intensity pulsed muon beam and a high-precision tracking system. The electromagnetic calorimeter complements the tracker by providing high rejection power in muon to electron identification and a seed for track reconstruction while working in vacuum in presence of a 1 T axial magnetic field and in a harsh radiation environment. For 100 MeV electrons, the calorimeter should achieve: (a) a time resolution better than 0.5 ns, (b) an energy resolution <10%, and (c) a position resolution of 1 cm. The calorimeter design consists of two disks, each loaded with 674 undoped CsI crystals read out by two large-area arrays of UV-extended SiPMs and custom analogue and digital electronics. We describe here the status of construction for all calorimeter components and the performance measurements conducted on the large-sized prototype with electron beams and minimum ionizing particles at a cosmic ray test stand. A discussion of the calorimeter’s engineering aspects and the on-going assembly is also reported.

Electrical and optical properties and defects of (100)- and (001)-oriented V-doped β-Ga2O3 crystals grown by EFG

Altering the n-type conductivity and optical properties of ultra-wide bandgap β-Ga2O3 by impurity doping has been a topic of research interest in the semiconductor field. Simultaneously, β-Ga2O3 with a monoclinic structure has exhibited interesting anisotropy. In this study, (100) and (001) V-doped β-Ga2O3 crystals were synthesized by the edge-defined film-fed growth (EFG) method, and their structural, electrical and optical properties, and defects were systematically investigated. V-doped β-Ga2O3 crystals with a (100) plane have a better crystalline quality and flatter surface than those with a (001) plane. Compared with undoped crystals (∼1016 cm−3), the carrier concentration of the (100) and (001) V-doped β-Ga2O3 substrates only increased to 4.30 × 1017 cm−3 and 1.92 × 1017 cm−3, respectively, which was related to the VxOy clusters formed by excess V as trapping traps and the carbon DX center as an electron capture trap formed by the relaxation of C atoms in the direction opposite to that of the C–O bond. The generation of absorption peaks and flat regions in the transmittance spectra was attributed to the introduction of V doping. The etch pit morphology and Raman peak intensity on the surfaces of the (100) and (001) V-doped β-Ga2O3 substrates were different owing to the anisotropy of the monoclinic lattice structure. These results contribute to the understanding of the influence of V and anisotropy on β-Ga2O3 crystals and expand their applications in electrical and optical fields.

Investigation of Sn Incorporation in β-Ga2O3 Single Crystals and its Effect on Structural and Optical Properties

Undoped and Sn-doped β-Ga2O3 single crystals were grown by optical floating zone technique by varying the doping concentration of Sn from 0.05 wt% to 0.2 wt%. Uniform distribution of the dopant ions was achieved by heat treatment. The crystalline quality and the expansion of the lattice were observed from the PXRD. Raman spectra reveals the incorporation of Sn atoms into the lattice by replacing Ga in the octahedral site. The interplanar distance (d) was calculated as 2.39 Å from the HR-TEM micrographs. The transmittance was found to be decreasing from 80% to 78% as the concentration of Sn increases. The absorption spectra shows a cut off edge around 260 nm for undoped and 270 nm for all Sn doped samples. The bandgap obtained for undoped β-Ga2O3 was 4.36 eV. The doping of 0.05 wt% of Sn decrease the value of bandgap to 4.08 eV, but, for 0.1 wt% and 0.2 wt% Sn an increase in the bandgap value of 4.13 eV and 4.20 eV was observed respectively. The refractive index was found to be 1.96 at 500 nm wavelength. The increase in Sn concentration results in increase of the roughness from 1.116 nm to 3.511 nm.

INVESTIGATIONS ON THE GROWTH AND CHARACTERIZATION OF MAGNESIUM SULFATE DOPED L-LEUCINIUM OXALATE CRYSTALS

Magnesium Sulfate-doped L-Leucinium oxalate (MSLO) single crystal was grown using slow evaporation method. Structure of the crystal was determined by single-crystal X-Ray Diffraction (XRD). Lattice parameters of MSLO crystal were determined. Optical transmittance study was done to find various linear optical parameters like band gap, reflectance, refractive index, absorption coefficient, extinction coefficient, optical conductivity. Vickers Micro hardness study was carried out to find mechanical properties such as hardness, work hardening coefficient, brittleness index and fracture toughness of the grown MSLO crystal. Kurtz-Perry powder technique with Nd: YAG laser was applied to study the second harmonic generation (SHG) competency. By using Z-scan technique, third-order NLO efficiency of MSLO crystal was calculated. LDT study was also done for MSLO crystal. It is observed that magnesium sulfate-doped L-leucinium oxalate (MSLO) crystal has the superior properties compared to that of undoped L-leucinium oxalate crystal. EDS studies were conducted for MSLO crystal to check the elements present in the crystal.

Ultrahigh Piezoelectric Strains in PbZr1-xTixO3 Single Crystals with Controlled Ti Content Close to the Tricritical Point.

Intensive investigations of PbZr1-xTixO3 (PZT) materials with the ABO3 perovskite structure are connected with their extraordinary piezoelectric properties. Especially well known are PZT ceramics at the Morphotropic Phase Boundary (MPB), with x~0.48, whose applications are the most numerous among ferroelectrics. These piezoelectric properties are often obtained by doping with various ions at the B sites. Interestingly, we have found similar properties for undoped PZT single crystals with low Ti content, for which we have confirmed the existence of the tricritical point near x~0.06. For a PbZr0.95 ± 0.01Ti0.05 ∓ 0.01O3 crystal, we describe the ultrahigh strain, dielectric, optical and piezoelectric properties. We interpret the ultrahigh strain observed in the region of the antiferroelectric–ferroelectric transition as an inverse piezoelectric effect generated by the coexistence of domains of different symmetries. The complex domain coexistence was confirmed by determining optical indicatrix orientations in domains. The piezoelectric coefficient in this region reached an extremely high value of 5000 pm/V. We also verified that the properties of the PZT single crystals from the region near the tricritical point are incredibly susceptible to a slight deviation in the Ti content.

Croconic Acid Doped Glycine Single Crystals: Growth, Crystal Structure, UV-Vis, FTIR, Raman and Photoluminescence Spectroscopy

Glycine (Gly) single crystals doped with croconic acid (CA) were grown by evaporation from aqueous solutions. Depending on the weight ratio of Gly and CA in solutions, the crystals take on a plate or pyramidal shape. Both powder and single crystal XRD analyses indicate that the crystal lattices of plates (α-Gly:CA) and pyramides (γ-Gly:CA) correspond to the lattices of pure α-Gly and γ-Gly polymorphs, respectively. Raman and FTIR spectra of Gly:CA crystals are very close to the spectra of undoped crystals, but include bands associated with CA impurity. Analysis of UV-Vis absorption spectra indicates that doping does not remarkably change bandgap value Eg~5.2 eV but results in appearance of strong absorption bands in the transparency region of pure glycine crystals, which result from local electronic transitions. Incorporation of CA molecules in Gly creates strong green photoluminescence in a wide spectral range 1.6–3.6 eV. Comparison of the optical spectra of Gly:CA and previously studied TGS:CA crystals indicates that in both cases, the modifications of the optical spectra induced by CA doping are practically identical and are related to the interaction between CA molecules located in the pores of the host Gly crystals and neighboring Gly molecules.

Influence of excitation nature on temperature attenuation of luminescence in ZnSe crystals

Experimental studies have shown that temperature attenuation of luminescence in undoped ZnSe crystals depends on the nature of the band-band excitation. It is determined that this attenuation differs from the attenuation at intracentric excitation of the 630 nm luminescence band.A comparative analysis of the results of the action of X-rays, N2 laser (337 nm) and LED-390 (390 nm) shows that the temperature dependence of luminescence depends on the density of generated free electron-hole pairs.The corresponding theoretical dependences for external luminescence attenuation and in the presence of simultaneous intracentric and external luminescence attenuation are obtained. Analysis of the shape of the curves of temperature luminescence attenuation shows that the increase in the excitation density increases the probability of radiative transitions from the excited state of the luminescence center in comparison with nonradiative transitions. This is confirmed by the lux-luminescent characteristics of X-ray and photoluminescence at different temperatures. It can be stated with high probability that the temperature position of the beginning of the temperature attenuation of luminescence is affected by forced transitions in the scintillation pulse.

Optically based dosimetry of high-energy radiation using the undoped lithium tetraborate crystals: Nonlinear features

The lithium tetraborate (LTB) optical characteristics studies, particularly the luminescence and phosphorescence after irradiation on the M − 30 microtron to create radiation defects, are presented. The investigation was conducted in a wide range of intensities of accelerated electrons, their energies within 7–15 MeV, and absorbed radiation doses.The threshold character and nonlinear influence of the radiation defects on the optical dosimetric characteristics of LTB were established when their concentration became comparable to that of intrinsic or structural defects. Undoped optical crystals LTB are a convenient target for this type of research. It is shown that the combination of optical data from the study of thermally stimulated luminescence and phosphorescence allows one to control the irradiation conditions: flux density and absorbed dose.The obtained results are important for radiation technologies that use high doses of radiation, and can also be taken into account when planning of dosimetric procedures in medicine using high-energy nuclear particles.

Investigations on the Growth and Characterization of L-Leucine Doped Rubidium Sulfate Nonlinear Optical Single Crystal

Objectives: To grow crystal of inorganic material Rubidium sulfate by doping with an organic material L-leucine. Methods: Crystal has been grown by solution method. Crystallographic studies were done. Mechanical studies were carried out to find the mechanical strength and other parameters. Dielectric studies of L-leucine doped rubidium sulfate crystals were carried out to evaluate dielectric constant, dielectric loss and activation energy. UV-visible- NIR spectral studies were done in the wavelength range 200-1100 nm. Second order Non Linear Optical (NLO) studies of the grown crystal of LLRS were carried out by Kurtz-Perry technique. Findings: The grown LLRS crystal is observed to be crystallizing in orthorhombic structure by single crystal XRD studies. The optical band gap of LLRS crystal was found to be slightly more than that of undoped rubidium sulphate crystal. The SHG efficiency of LLRS crystal is observed to be 0.61 times that of the reference KDP sample. Dielectric parameters are found to decrease with increase in frequency. Dielectric constant and dielectric loss factor increase when the temperature of the samples increases. AC conductivity increases with increase of temperature. Activation energy is increasing when the frequency increases. The band gap value is found to be 4.43 eV for undoped rubidium sulfate crystal. For L-leucine doped rubidium sulfate (LLRS) crystal, the optical band gap is 4.48 eV. From the Microhardness teat, it is observed that the hardness increases with increase of the applied load for both the samples and this is due to reverse indentation size effect. Novelty: In this study, as a novel work, a very first attempt has been made to combine an organic material L-leucine with an inorganic crystal viz. rubidium sulfate to alter its physical and chemical properties. Keywords: Inorganic Single Crystal; Crystal Structure; Mechanical Properties; Dielectric properties; Optical Properties; Spectral Properties

Mechanism of photo-ionic stoichiometry changes in SrTiO3

The impact of UV light (λ = 365 nm) on defect chemistry and composition of undoped SrTiO3 single crystals was investigated by means of impedance spectroscopy. In-plane conductivity measurements between 280 and 450 °C in air reveal a drastic increase of the bulk conductivity upon UV illumination. The measured time dependence of this increase is in accordance with oxygen chemical diffusion in SrTiO3. The corresponding photo-induced change in defect concentrations is caused by oxygen being pumped from the gas phase into the oxide under UV irradiation. This affects the entire SrTiO3 crystal rather than only the thin UV absorption zone and leads to very high oxygen chemical potentials with nominal oxygen pressures up to 106 bar. After switching the UV light off, the resulting conductivity increase relaxes extremely slowly due to slow surface exchange kinetics. A mechanistic model is introduced to explain the impact of UV light on the oxygen chemical potential as well as on the oxygen vacancy and hole/electron concentrations in semiconducting oxides, here SrTiO3. This model is based on the formation of oxygen quasi-chemical potentials in the illuminated region. It is discussed how the interplay of four kinetic parameters causes the observed time-dependent stoichiometry and thus conductivity changes.

Effects of Pr concentration on the structural, mechanical and optical properties of KCl0.5Br0.5:Pr3+ crystals

KCl0.5Br0.5:XPr3+ [X = 0.0 (pure KCl0.5Br0.5), 0.002, 0.004, 0.006, 0.008, 0.01, 0.02 and 0.04] crystals were successfully grown by Czockralski (Cz) pulling method and the structural, mechanical and optical properties of crystals were thoroughly investigated. X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) studies indicated that the Pr ions have been incorporated into the KCl0.5Br0.5 host lattice and existed mainly as trivalent Pr. UV–Vis absorption spectra showed that the presence of peaks at 211, 227, 293, 457, 479, 494 and 601 nm. Hardness was found to increase with increasing of in Pr3+ concentration and indentation load, the hardness of the Pr doped crystals were larger than the un-doped crystal and the reverse indentation size effect was observed. The intensity of photoluminescence (PL) peaks was strongly depended on the Pr3+concentration. thermo-luminescence (TL) glow curves exhibited one peaks at 63–76 °C, indicating that one kind of trap existed in the crystals. The optimal luminous (both PL and TL) properties the KCl0.5Br0.5:XPr3+ crystals were obtained at X = 0.006. These results indicated that the KCl0.5Br0.5:Pr3+ crystals could be considered as a promising candidate for their use in optical and dosimetry applications.

Diode-pumped CaGdAlO4 crystal-assisted Kerr-lens mode-locked all-solid-state Pr:LiYF4 laser at 639 nm

At present, direct generation of an ultrafast laser with a pulse width shorter than 10 ps in the visible spectral region has been very rarely demonstrated. In this work, we focus on this issue by operating an InGaN blue-diode-pumped Kerr-lens mode-locked Pr:LiYF4 laser. Using an undoped CaGdAlO4 crystal as an additional Kerr medium in the resonator for providing enhanced third-order nonlinearity, a stable mode-locked Pr:LiYF4 laser with red emission at 639 nm is achieved with the shortest pulse duration of 2.6 ps at a repetition rate of 49.7 MHz. The maximum average output power, single pulse energy, and peak power reach 68.4 mW, 1.38 nJ, and 530 W, respectively. To the best of our knowledge, this is the shortest pulse width that has ever been achieved in this specific emission line of Pr3+ ions.

CRYSTAL GROWTH IN SOLUTION AND CHARACTERIZATION OF RUBIDIUM SULFATE SINGLE CRYSTALS DOPED WITH L-LEUCINE

Rubidium sulfate crystal is an inorganic material and it is doped with an organic material viz. L-leucine to improve the various properties of the host crystal. L-leucine doped rubidium sulfate (LLRS) crystals have been grown by solution method. LLRS crystals have been harvested after the growth period of 30 days. The grown LLRS crystal is observed to be crystallizing in orthorhombic structure by single crystal XRD studies. Mechanical studies were carried out to find the mechanical strength and other parameters. Dielectric studies of L-leucine doped rubidium sulfate crystals were carried out to evaluate dielectric constant, dielectric loss and activation energy. UV-visible-NIR spectral studies were done in the wavelength range 200-1100 nm and linear optical properties like transmittance, absorption coefficient and extinction coefficient of samples have been evaluated. Second order Non Linear Optical (NLO) studies of the grown crystal of LLRS were carried out by Kurtz-Perry technique. The fundamental absorption was noted at 280 nm and at 278 nm for undoped and L-leucine doped rubidium sulphate crystals respectively. The optical band gap of LLRS crystal was found to be slightly more than that of undoped rubidium sulphate crystal. The SHG efficiency of LLRS crystal is observed to be 0.61 times that of the reference KDP sample.

Continuous-Wave Crystalline Laser at 714 nm via Stimulated Raman Scattering and Sum Frequency Generation

A compact high-power continuous-wave (CW) laser at 714 nm is originally developed via intracavity stimulated Raman scattering (SRS) and sum frequency generation (SFG). The fundamental wave at 1342 nm and the first-Stokes Raman wave at 1525 nm are generated by using a Nd:YVO4 and a undoped YVO4 crystals, respectively. Compared to the self-Raman laser, the separation of the gain media for generating the fundamental and Raman waves can effectively reduce the thermal lens effect in the Nd:YVO4 crystal and efficiently enhance the SRS in the undoped YVO4 crystal. Furthermore, the undoped YVO4 crystal is coated to act as a high-reflection mirror for minimizing the cavity losses. At a pump power of 40 W, the output power at 714 nm can reach 1.8 W. The present compact design for CW laser source at 714 nm is believed to be practically useful for laser cooling and trapping of radium.

Effect of the Indentation Load on the Raman Spectra of the InP Crystal.

Nanoindentations and the Raman spectroscopy measurements were carried out on the (001) surface of undoped and S-doped InP crystal. The samples were indented with the maximum load ranging from 15 mN to 100 mN. The phase transition B3→B1 was not confirmed by spectroscopic experiments, indicating a plastic deformation mechanism governed by dislocations activity. Increasing the maximum indentation load shifts and the longitudinal and transverse optical Raman bands to lower frequencies reveals a reduction in the elastic energy stored in the plastic zone right below the indentation imprint. Mechanical experiments have shown that a shift in Raman bands occurs alongside the indentation size effect. Indeed, the hardness of undoped and S-doped InP crystal decreases as a function of the maximum indentation load.

Continuous wave dual-wavelength Nd:YVO4 laser at 1342 and 1525 nm for generating a 714-nm emission

Continuous wave dual-wavelength lasers at 1342 and 1525 nm are developed by using separate Nd:YVO4 and YVO4 crystals to form compactly coupled cavities for fundamental and Raman waves, respectively. The design of the coupled cavity not only reduces the thermal lensing effect in the Nd:YVO4 crystal, but also improves the stimulated Raman scattering (SRS) efficiency in the undoped YVO4 crystal. In addition, the Raman crystal is coated to form a highly reflective mirror to minimize cavity losses. By using a plano-concave cavity with a pump power of 40 W, the output powers of the fundamental and Raman waves are 470 mW and 310 mW, respectively. Changed to a concave cavity, the output powers of fundamental and Raman waves are 220 mW and 510 mW, respectively. Basis on the dual-wavelength operation, the maximum output power at 714 nm can reach 2.0 W via the sum frequency generation. A light source at 714 nm can be used for laser spectroscopy of atomic and ionic radium isotopes.

Development of novel crystal scintillators for lunar surface science

The development of novel crystal scintillators for a lunar landed mission near future is reported. On that mission, we aim to assess the radiation dose, biological effect, water, and other resources on the lunar surface. To accomplish this, a Lunar Vehicle Radiation Dosimeter (LVRAD) made up of several radiation detectors has been proposed. New scintillation crystals are being developed for neutron and gamma measurements. Stilbene and undoped LaCl3 crystal were selected for fast neutron/gamma spectrometers. The mutual combination of organic and inorganic detectors benefits from direct fast neutron detection via 35Cl(n, p)35S reaction as well as the good gamma resolution of LaCl3 and the high detection efficiency of stilbene. LaCl3 crystals with the diameter of 38.1 mm were grown by a homemade modified Bridgman furnace. For epithermal neutron spectrometer, 6LiI:Ag crystal was selected due to its pulse shape discrimination capability and highest detection efficiency in terms of size for both thermal and epithermal neutron among scintillation materials. Enrich 6LiI was purified using the zone-refining technique. The crystal was then grown by the same Bridgman furnace.

Role of Magnetic Nanoparticles Size and Concentration on Structural Changes and Corresponding Magneto-Optical Behavior of Nematic Liquid Crystals.

The effect of magnetic nanoparticles size and concentration on nematic liquid crystal (NLC) behavior in a magnetic field was investigated. The magneto-optical investigation using measurements of the light transmission through the liquid crystal was used to study the structural changes induced by an applied weak magnetic field. Magnetic nanoparticles Fe3O4 of spherical shape with different size and volume concentration were added to NLC 4-cyano-40 -hexylbiphenyl (6CB) during its isotropic phase. In contrast to undoped liquid crystals, the distinctive different light transmission responses induced by a magnetic field in studied NLC samples were observed suggesting both structural changes and the orientational coupling between magnetic moments of nanoparticles and the director of the NLC. Experimental measurements were conducted, including investigation under linearly increasing and/or jumped magnetic field, respectively, as well as the investigation of time influence on structural changes to study their stability and switching time. The analysis of observed light transmission characteristics confirmed the role of concentration and size of magnetic nanoparticles on the resultant behavior of investigated NLC compounds. The obtained results showed the lowering of the threshold magnetic field with an increase in the volume concentration of nanoparticles and on the important role of nanoparticles size on stability and switching properties. Obtained results are discussed within the context of previous ones.

Luminescence in undoped and Nb-doped SrTiO3 crystals: Bulk and surface emission

The luminescenceof SrTiO3 depends on the sample type, either doped or stoichiometric, as grown or treated, the excitation conditions, and temperature. The origin of the luminescence emissions, blue, green, and infrared, remains controversial. In particular, the role played bydefects, mainly oxygen vacancies, impurities, and self-trapped holes and electrons on the different emissions are far to be elucidated. We present a cathodoluminescence (CL) and photoluminescence (PL) study of undoped and Nb-doped samples. The different excitation conditions of CL and PL permit to distinguish the luminescence emission from the bulk (CL) and from a surface skin region (PL). Significant differences between both techniques are seen for the undoped sample, while the Nb-doped sample presents less differences, highlighting the role played by the surface defects and the doped electrons. The study is complemented by the temperature dependence of the luminescence spectra and the emission due to defects generated by plastic deformation.