Search

TeO2 single crystal has drawn much attention in recent years due to its excellent acousto‐optic (AO) performance in the field of spectral imaging and optical processing. The optical properties of TeO2 single crystal are critical for the fabrication of AO devices. To improve the optical properties of the TeO2 single crystal, Mn4+ ions were doped into the TeO2 lattice. Herein, bulk TeO2 single crystal and TeO2:0.02Mn4+ single crystal have been successfully grown by a Bridgman method. Compared with the TeO2 single crystal, a 30% transmittance increase was observed in the TeO2:0.02Mn4+ single crystal. Furthermore, the TeO2:0.02Mn4+ single crystal shows a smaller extinction coefficient (≤0.01) in the Vis–NIR region, indicating less optical loss. The bandgap energy of TeO2:0.02Mn4+ was broadened from 3.360 to 3.635 eV. In addition, TeO2:0.02Mn4+ single crystal exhibits a higher refractive index (about 2.244), which indicates that TeO2:0.02Mn4+ single crystal is a potential medium for high‐efficiency AO devices. [ABSTRACT FROM AUTHOR]

Thermally stimulated current (TSC) spectroscopy was used to characterize electronic trap states in the perovskite CsPbCl3 bulk single crystals which are promising for gamma ray detection. The TSC spectra indicate the presence of multiple traps over the temperature range from 80 K to above room temperature. The possible analytical defects identified were VCs and VCl vacancies and Pbi interstitials that have concentrations of the order of 1011−1016 cm−3 and capture cross sections of ∼10−18 cm2. A comparison of crystals grown from different ingots reveals that the concentration of defects in the crystal with an improved growth procedure is about one to four orders of magnitude less than those of a crystal from an earlier growth process. A further reduction and elimination of trap states within the perovskite ingot should lead to crystals with improved mobilities, carrier lifetimes, and detector response characteristics. [ABSTRACT FROM AUTHOR]

Recently, there has been considerable interest in x-ray and gamma ray detectors with large volume and high energy resolution that operate at room temperature. To improve detector energy resolution, the carrier mobility-lifetime product needs to be increased, and the electronic trap state concentration needs to be minimized. Defect concentrations in the part per billion range can alter the charge transport and carrier recombination lifetime. In this work, thermally stimulated current spectroscopy measurements were systematically carried out in bulk halide perovskite single crystals of CsPbBr3 over a temperature range of 80–320 K. The origins and trap parameters of CsPbBr3 crystals from the solution growth and melt growth procedures were determined and compared. Trap concentrations were ranged from 1 × 1011 to 1 × 1016 cm−3. Appreciable detector performance was observed for CsPbBr3 crystals with trap concentrations less than 1 × 1014 cm−3. The comparison of spectral responses of crystal samples grown using two different methods shows that, after purification, solution-grown crystals are comparable to melt-grown crystals in terms of low defect concentration and improved detector performance. For an improved mobility-lifetime product and enhanced spectral response to high energy radiation from fissile materials, trap states in either type of a crystal ingot must be reduced closer to 1011 cm−3. [ABSTRACT FROM AUTHOR]

Room temperature semiconductor detector (RTSD) materials for γ‐ray and X‐ray radiation are in great demand for the nonproliferation of nuclear materials as well as for biomedical imaging applications. Halide perovskites have attracted great attention as emerging and promising RTSD materials. In this contribution, the material synthesis, purification, crystal growth, crystal structure, photoluminescence properties, ionizing radiation detection performance, and electronic structure of the inorganic halide perovskitoid compound TlPbI3 are reported on. This compound crystallizes in the ABX3 non‐perovskite crystal structure with a high density of d = 6.488 g·cm–3, has a wide bandgap of 2.25 eV, and melts congruently at a low temperature of 360 °C without phase transitions, which allows for facile growth of high quality crystals with few thermally‐activated defects. High‐quality TlPbI3 single crystals of centimeter‐size are grown using the vertical Bridgman method using purified raw materials. A high electrical resistivity of ≈1012 Ω·cm is readily obtainable, and detectors made of TlPbI3 single crystals are highly photoresponsive to Ag Kα X‐rays (22.4 keV), and detects 122 keV γ‐rays from 57Co radiation source. The electron mobility‐lifetime product µeτe was estimated at 1.8 × 10–5 cm2·V–1. A high relative static dielectric constant of 35.0 indicates strong capability in screening carrier scattering and charged defects in TlPbI3. [ABSTRACT FROM AUTHOR]

The heavy element semiconductor compound Cs2Hg6S7 is of interest as a potential wide gap semiconductor for gamma ray detection. To determine electrically active defects and their energy levels, photoconductivity (PC) spectroscopy was carried out over the temperature range of 90-295 K. The low temperature spectrum exhibits photoconductive transitions at 1.495, 1.61, 1.66, and 1.68 eV. The optical transitions are tentatively attributed to defects with levels located at energies of 50, 70, 120, and 240 meV from the band edge. A superlinear dependence of photocurrent on illumination intensity is observed that is attributed to a two-center recombination process that involves shallow traps and recombination centers. Near band edge photoluminescence (PL) was observed over the temperature range of 24-80 K. The spectrum revealed three defect related emission bands located at 1.68, 1.66, and 1.62 eV, whose ionization energies are 57 meV, 78 meV, and 115 meV, respectively. From the temperature and excitation dependencies of the observed peak intensities and energies, the radiative recombination mechanisms of the bands were attributed to transitions involving excitons bound to neutral and ionized acceptors. Good agreement of the defect level energies determined by PL and PC were noted, indicating that they were of the same origin. The defects were tentatively attributed to metal vacancies that form shallow acceptor levels. [ABSTRACT FROM AUTHOR]

Abstract Here we report the first spectroscopic alpha particle detection based on CsPbBr 3 detectors with asymmetric contacts. The CsPbBr 3 single crystal was grown from the melt using Bridgman method and then fabricated into detectors with different contacts. The In/CsPbBr 3 /Au detector presented a low dark current density (∼ 100 nA/cm2) and temporal stable performance under high electric field (1000 V/cm). Such detector demonstrated excellent gamma ray resolving capability with a full-width at half maximum (FWHM) of ∼ 5.9 keV for the 57Co 122 keV γ ray. The CsPbBr 3 detector was capable of simultaneously resolving both the alpha particle (5.5 MeV) and γ ray (59.5 keV) peaks from 241Am radioactive isotope. The transport properties of CsPbBr 3 were then determined based on the alpha particle spectra and corresponding rise time distributions. The equivalent values of electron and hole mobilities were indicated as 63 and 49 cm2/(V ⋅ s) respectively. The calculated electron and hole mobility-lifetime products were 4.5 × 10−4 and 9.5 × 10−4 cm2/V, respectively, demonstrating superior transport properties of holes over electrons in CsPbBr 3. This work widens the scope of perovskite detectors to encompass charged radiation as well as high energy X/ γ rays, and will significantly promote and guide further studies on perovskite materials for radiation detection applications. Highlights • The first α particle spectroscopy by CsPbBr 3 detectors was clearly demonstrated. • In/CsPbBr 3 /Au detector was fabricated and exhibited low and stable dark current. • In/CsPbBr 3 /Au detector resolved both α particle and γ ray peaks from 241Am isotope. • The nearly balanced e and h mobilities of CsPbBr 3 were 63 and 49 cm2/(V s), respectively. • The μ τ products for e and h were 4.5 × 10−4 and 9.5 × 10−4 cm2/V, respectively. [ABSTRACT FROM AUTHOR]

Thermally stimulated depolarization current (TSDC) measurements were applied to investigate BaTiO3 single crystals with <100>, <110>, and <111> orientations, and annealed under different atmospheres, respectively. The TSDC peaks related to ferroelectric domain, ferroelectric–paraelectric phase transition, T i T i ′ − V Ö dipole relaxation and oxygen vacancy migration were observed from the TSDC spectra. The formation of oxygen vacancy clusters in BaTiO3 single crystals leads to a high dipole activation energy. The <111> crystalline face of BaTiO3 is more stable under external field than others. [ABSTRACT FROM AUTHOR]

We analyzed low-temperature photoluminescence (PL) and the band edge excitonic emission in bulk halide perovskite CsPbCl 3 single crystals. Strong near band edge excitonic emission is observed at 420 nm and a series of excitonic states was observed. Temperature-dependent PL measurements on cesium lead chloride over a wide temperature range from 13 K to 295 K revealed significant electron phonon coupling with a Huang-Rhys parameter ranging from 1.34 to 3.38. A primary experimental finding is that the near band edge PL emission shows existence of multiple sharp features at low temperatures that are attributable to free excitons, bound excitons, and their phonon replicas. The PL also shows evidence of band tailing effects due to disorder. We investigated the recombination mechanism of photogenerated charge carriers by means of time-resolved PL (TR-PL) spectroscopy at low temperatures and various excitation powers and observed competing mono- and bimolecular recombination processes. A dynamic model is proposed to describe the TR-PL. We observed both long-lived and short-lived recombination where the short-lived time decay is attributed to free exciton recombination, whereas the long-lived decay to bound exciton recombination involving traps due to intrinsic disorder. • CsPbCl 3 single crystal samples are grown with the Bridgman method. • The exciton - LO phonon coupling becomes dominant for temperature above 120 K. • PL dependence on excitation power shows that the PL emission is excitonic in nature. [ABSTRACT FROM AUTHOR]

The new layered compound CsHgInS3was synthesizedusingsolid state and flux synthesis techniques. The compound is a semiconductorand shows promising properties for X-ray and γ-ray detection.It features a layered structure that crystallizes in the monoclinicspace group C2/cwith cell parameters: a= 11.2499(7) Ǻ, b= 11.2565(6)Ǻ, c= 22.146(1) Ǻ, β= 97.30(5)°, V= 2781.8(4) Ǻ3, and Z= 8. CsHgInS3is isostructuralto Rb2Cu2Sn2S6, wherethe Hg, In, and Cs atoms occupy the Cu, Sn, and Rb sites, respectively.Large single crystals with dimension up to 5 mm were grown with avertical Bridgman method as well as a horizontal traveling heatermethod. CsHgInS3has a γ-ray attenuation length comparableto commercial Cd1–xZnxTe and a band gap value of 2.30 eV. The electricalresistivity of CsHgInS3is anisotropic with values of 98GΩ cm and 0.33 GΩ cm perpendicular and parallel to the(001) plane, respectively. The mobility-lifetime product (μτ) of electrons and holes estimated from photoconductivitymeasurements on the as-grown crystals were (μτ)e= 3.6 × 10–5cm2V–1and (μτ)h= 2.9 × 10–5cm2V–1, respectively. Electronic structure calculations at the DensityFunctional Theory level were performed based on the refined crystalstructure of CsHgInS3and show a direct gap with the conductionband near the Fermi level being highly dispersive, suggesting a relativelysmall carrier effective mass for electrons. [ABSTRACT FROM AUTHOR]

The terahertz (THz) dielectric constant (ε r ') and dielectric loss tangent (tan δ) of the commercial LTCC materials (Ferro A6M and DuPont 951), Al 2 O 3 (ceramic and single crystal), AlN and β-Si 3 N 4 ceramics were measured using a vector network analyzer (VNA) over the frequency range of 140–220 GHz and a time-domain spectrometer (TDS) from 0.2 to 1.0 THz. The results from the two instruments are compared with the literature and show good agreement and consistency. For Ferro A6M, ε r ' = 6.06, tan δ = 0.012 at 1.0 THz. For DuPont 951, ε r ' = 7.67, tan δ = 0.097 at 1.0 THz. For Al 2 O 3 ceramic and single crystal, the measured THz dielectric properties are consistent with the reported works. The dielectric constant of AlN (ε r ' = 8.85) and β-Si 3 N 4 (ε r ' = 8.41) ceramics in the THz region is a little lower than those reported for the MHz to GHz region. These results provide valuable and much needed reference information for device designers and material scientists. [ABSTRACT FROM AUTHOR]

Two new compounds CsCdInQ3(Q = Se, Te) have been synthesizedusing a polychalcogenide flux. CsCdInQ3(Q = Se, Te) crystalsare promising candidates for X-ray and γ-ray detection. Thecompounds crystallize in the monoclinic C2/cspace group with a layered structure, which is relatedto the CsInQ2(Q = Se, Te) ternary compounds. The cellparameters are: a= 11.708(2) Å, b= 11.712(2) Å, c= 23.051(5) Å, β= 97.28(3)° for CsCdInSe3and a=12.523(3) Å, b= 12.517(3) Å, c= 24.441(5) Å, β = 97.38(3)° for CsCdInTe3. Both the Se and Te analogues are wide-band-gap semiconductors withoptical band gaps of 2.4 and 1.78 eV for CsCdInSe3andCsCdInTe3, respectively. High-purity polycrystalline rawmaterial for crystal growth was synthesized by the vapor transfermethod for CsCdInQ3. Large single crystals up to 1 cm havebeen grown using the vertical Bridgman method and exhibit photoconductiveresponse. The electrical resistivity of the crystals is highly anisotropic.The electronic structure calculation within the density functionaltheory (DFT) framework indicates a small effective mass for the carriers.Photoconductivity measurements on the as grown CsCdInQ3crystals gives high carrier mobility-lifetime (μτ) productscomparable to otherdetector materials such as α-HgI2, PbI2, and CdxZn1–xTe (CZT). [ABSTRACT FROM AUTHOR]