Cadmium Iodide Crystals Research Articles

Synthesis and Characterization of Single Crystals of Cadmium Iodide as Gamma-ray Radiation Sensor

Synthesis and Characterization of Single Crystals of Cadmium Iodide as Gamma-ray Radiation Sensor

Organometallic l-alanine cadmium iodide crystals for optical device fabrication

Single crystals of l-alanine cadmium iodide (LACI) were grown by adopting the slow evaporation technique at room temperature. A single-crystal X-ray diffraction (SXRD) model was used to evaluate the crystal structure of the as-grown LACI crystal. The energy dispersive X-ray (EDX) analysis and ultraviolet–visible–near infrared (UV-vis-NIR) transmittance studies were carried out, and the results reveal the presence of elements in the title compound. From the transmittance data, the optical bandgap as a function of photon energy was estimated, and the different optical constants were calculated. A fluorescence study was performed for the LACI crystal. Thermogravimetric and differential thermal analyses have also been studied to investigate the thermal property of the LACI crystal. The efficiency of the second harmonic generation (SHG) by the title crystal was investigated. The magnetic and electrical properties were estimated by the vibrating sample magnetometer (VSM) analysis and impedance study respectively.

Low-temperature luminescence of CdI2 under synchrotron radiation

Synchrotron radiation is applied to study visible and UV luminescence spectra and their excitation spectra of undoped as well as In and Sb doped cadmium iodide crystals at 10 K. The origin of principal luminescence bands and the role of impurities in the formation of emission centers are discussed. The luminescence properties have been explained based on the electronic structure of CdI2 crystals.

Investigations on surface and mechanical properties of bis-thiourea cadmium iodide – A non-linear optical crystal

The semi-organic non-linear optical crystals of bis-thiourea cadmium iodide (BTCI) were grown from slow evaporation of their aqueous solutions. The grown crystals were confirmed with XRD, FTIR, and DSC analysis. The as-grown (010) crystal faces reveal growth striations. The structural perfection was assessed by the wet chemical etching method; acetic acid and formic acid are the best etchants to reveal dislocations. The strength and deformation characteristics of the crystals were assessed through laser damage tolerance, Vickers, and Knoop hardness measurements. The change in hardness is approximately 26% for every 40–45° shift in the orientation of the crystal, indicating anisotropy in hardness. The work hardening index calculated from Meyer's plot helps in distinguishing the indentation size effect. The yield strength and Young's modulus calculated using the standard relations indicate that the crystal is suitable for desired applications.

In situ growth and physio-electrical characterization of bis-thiourea cadmium-iodide (BTCI) single crystal

The basic understanding of nucleation kinetics is very important for any useful material. In the present investigation, the solubility of BTCI (2:1 ratio) has been determined at various temperatures. The metastable zone width and induction period values were estimated in order to optimize the growth parameters. The Nucleation parameter such as interfacial energy has been determined using the experimentally determined induction period values. Various critical nucleation parameters like Gibbs free energy, radius of critical nucleus, and nucleation rate have also been investigated. It is observed that the nucleation rate increases with the increase of supersaturation. The growth parameters of the titled materials have been optimized for the growth of bulk size single crystals of BTCI. The single crystals of thiourea cadmium iodide have been grown by slow evaporation solution technique. The DSC study reveals that the melting point and the specific heat of BTCI have been found to be ~155.25 °C and 54.319 J/g °C respectively. The mechanical study has been carried out by Vickers method. DC conductivity study indicates NTCR–type behavior in BTCI single crystal and the activation energy was found to be 0.57 eV.

Points to Ponder in the Study of Cadmium Iodide

During the growth of cadmium iodide crystals from solution, it has been observed that sometimes the crystal suddenly rotates. Probably, the convection currents are providing the force for the rotation. Mathematically, this force can be estimated and it must be greater than the van-der Walls force acting between adjacent sandwiches of cadmium iodide and can give rise to polytypic phase transformations. Further, studies of vacancies and the density measurements of various polytypes can help in understanding the phenomenon of polytypism better.

Points to Ponder in the Study of Cadmium Iodide

During the growth of cadmium iodide crystals from solution, it has been observed that sometimes the crystal suddenly rotates. Probably, the convection currents are providing the force for the rotation. Mathematically, this force can be estimated and it must be greater than the van-der Walls force acting between adjacent sandwiches of cadmium iodide and can give rise to polytypic phase transformations. Further, studies of vacancies and the density measurements of various polytypes can help in understanding the phenomenon of polytypism better.

Observation of crystallization and characterizations on thiourea cadmium iodide: A semi-organic optical material

In this work, the single crystals of thiourea cadmium iodide were grown by slow evaporation solution technique in two different ratios 2:1 and 1:1. During the formation of their single crystals the morphological features and its live growth process were recorded with the help of inverted microscope. Structural studies of the grown crystals have been carried out by powder X-ray diffraction to confirm the crystal system and vibrational modes by Raman spectroscopy. The optical energy band gaps were investigated through UV–vis spectroscopy study. The surface morphology of the grown single crystals was analyzed by using Scanning Electron Microscope and thermal analysis was carried out by using thermogravimetric analysis. The electrical properties were also studied as a function of frequency and the obtained results are discussed.

Optical sensor protector using wide-bandgap semiconductors

Optical power limiting is the increase of optical absorption with light intensity. Optical absorption in dependences of the light intensity and thickness of single crystals of wide-bandgap semiconductor cadmium iodide was studied using laser light. The transmission of the crystals was found to increase with increasing light intensity. However, at higher light intensity, an increase of optical absorption with intensity was observed. This power limiting characteristics was also found to depend on the thickness of the crystals. The findings resulting from this investigation might have potential applications in optical sensor protector using wide-bandgap semiconductors.

Study of cracks and phase transitions in cadmium iodide crystals using X-Ray diffraction

Polytypism has been observed in a large number of materials where the nearest. Neighbour relationship between identical two-dimensional layers of atoms can be satisfied in more than one way. The phenomenon has posed interesting problem for the Scientists, since the nature of force that causes ordering over the scale ranging from few angstrom to few thousands of angstrom units is not known. The Cadmium iodide has been purified and single crystal grown using a zone-refining system. The frequent appearance of cracks in the grown crystals when exposed to N2 laser at room temperature has been explained on the structural considerations of CdI2. The crystals of cadmium iodide have also been grown from solution in two batches using unpurified and purified material. A comparative study has been made on these batches for polytypism using x-ray diffraction technique. Formation of small period polytype 2H is governed by both temperature and impurities contained in the starting material. 4H is the most stable polytype. Higher occurrence of unidentified polytype in crystals of purified material has been attributed to free movement of edge dislocations during growth. The results have been examined, keeping in view the empirical considerations of earlier investigations.

Optical power limiting and transmitting properties of cadmium iodide single crystals: Temperature dependence

Optical limiting properties of the single crystals of cadmium iodide are investigated using ns laser pulses. It is found that the transmissions in the crystals increase with increasing temperature. However, they limit the transmissions at high input powers. The limiting power is found to be higher at higher temperature. From the measured transmission data, the photon absorption coefficients are estimated. The temperature dependence of the coefficients shows a decrease in magnitude with increasing temperature. This might be due to the temperature-dependent bandgap shift of the material. The results demonstrate that the cadmium iodide single crystals are promising materials for applications in optical power limiting devices.

Recombination processes in europium-doped cadmium iodide crystals

Results of comprehensive research into optical and luminescent-kinetic characteristics of europium-doped cadmium iodide crystals excited by nitrogen laser radiation, α-particles, and x-rays are presented. Crystals under study have been grown by the Bridgman–Stockbarger method. The doping EuCl3 admixture was introduced into the charge in quantities of about 0.05 and 1.0 mol%. Impurity absorption detected in the near-edge region of the crystals is interpreted as part of the Eu2+ ion long-wavelength band associated with f–d-transitions. The cation impurity and matrix defects in CdI2:Eu2+ crystals create complex centers responsible for emission with a maximum in the 580–600-nm region. The short component in the luminescence decay kinetics of weakly-doped crystal excited by α-particles and x-ray photons is due to the exciton emission characteristic of CdI2. The slow component in the scintillation pulse results from recombination of charge carriers followed by creation of exciton-like states on the defect-impurity centers. Laser or x-ray excitation induces light-sum accumulation on the trapping levels at a depth of 0.2–0.6 eV that is mainly related to matrix microdefects. Trapping centers associated with the chlorine impurity are observed in the heavily-doped crystal. Photostimulated luminescence at 85 K arising at the electron stage of the recombination process is caused by recombination of electrons released from F-type centers with holes localized near the activator.

Growth and characterization of bis thiourea cadmium iodide: A semiorganic single crystal

Single crystals of bis thiourea cadmium iodide[CdI 2(CH 4N 2S) 2], abbreviated as BTCI, a semiorganic material has been successfully grown by both slow evaporation and slow cooling methods. Crystal of dimensions up to 3.3 × 1.0 × 1.5 cm 3 is reported. Single crystal X-ray diffraction analysis has been carried out to confirm monoclinic system and etching studies for their perfection. The morphology of the grown crystal was also identified by single crystal X-ray diffraction analysis. The powder X-ray diffractogram of the crystal has been recorded and the various planes of reflection are identified. The presence of functional groups and the coordination of metal ions to thiourea were confirmed by FTIR analysis. Transmission spectra reveals that the crystal has low UV cutoff of 324 nm and has a good transmittance in the entire visible region enabling its use in optical applications. The thermal behaviour of the crystal has been investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA), which indicates that the material does not decompose before melting. Studies of dielectric properties (dielectric constant and dielectric loss) both as function of frequencies (100 Hz to 5 MHz) for varying temperatures in the range 308–348 K suggests good candidate for electro optic modulators.

Luminescent properties of Pb2+- and Mn2+-activated CdI2 crystals

The luminescent properties of CdI2, CdI2:Pb2+, CdI2:Mn2+, and CdI2:Pb2+,Mn2+) crystals have been studied at temperatures from 85 to 295 K under optical and x-ray excitation. Analysis of new and earlier spectroscopic data suggests that the 560-nm luminescence of CdI2:Pb2+ and CdI2:(Pb2+,Mn2+) crystals under excitation on the long-wavelength component of the A absorption band of Pb2+ centers is due to Pb2+-bound anion excitons. The 640-to 660-nm emission of these crystals is attributable to α centers. The manganese luminescence in the codoped material originates from both intracenter Mn2+ excitations and a sensitized process due to energy transfer from the host and Pb2+-related centers. The mechanisms of recombination and energy transfer processes in cadmium iodide crystals codoped with Pb2+ and Mn2+ are discussed.

A combined optical, SEM and STM study of growth spirals on the polytypic cadmium iodide crystals

Some novel results of a combined sequential study of growth spirals on the basal surface of the richly polytypic CdI 2 crystals by optical microscopy, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) are presented and discussed. Under the high resolution and magnification achieved in the scanning electron microscope, the growth steps of large heights seen in the optical micrographs are found to have a large number of additional steps of smaller heights existing between any two adjacent large height growth steps. When further seen by a scanning tunneling microscope, which provides still higher resolution, sequences of unit substeps, each of height equal to the unit cell height of the underlying polytype, are revealed to exist on the surface. Several large steps also lie between the unit steps, with heights equal to an integral multiple of either the unit cell height of the underlying polytype or the thickness of a molecular sheet I–Cd–I. It is suggested that initially a giant screw dislocation may form by brittle fracture of the crystal platelet, which may gradually decompose into numerous unit dislocations during subsequent crystal growth.

Some novel results of scanning tunneling microscopy (STM) study of cadmium iodide crystals

A combined optical, SEM and STM study of growth spirals on the richly polytypic CdI 2 crystals has yielded some novel results. The STM photographs directly reveal the atomic arrangement in the unit cell, in exact conformation with the known structural data. The STM has also enabled an accurate measurement of the interstep spacings, which are all found to be an integral multiple of the unit cell a-dimension. The interstep spacing is found to be variable for steps of the same height, which apparently arise from differences in supersaturation during crystal growth.

Influence of weak atomic bonding on the height of growth spiral steps on cadmium iodide crystals

Step heights of growth spirals on CdI2 crystals, unambiguously measured for the first time by STM, do not turn out to be integral multiples of the unit cell height, as normally expected, unless enhanced by a constant value of 0.31nm. The discrepancy primarily arises from the weak van der Waals bonding between the neighbouring molecular sandwiches I–Cd–I constituting the structure and from the dangling bonds existing at the edge of a growth step and at the crystal surface. The result is significant for problems of surface physics and surface chemistry.

Band gap variation in laser irradiated polytypic crystals of cadmium iodide

Highly purified single crystals of cadmium iodide obtained through repeated zone refining have been subjected to laser beam exposure (Argon ion laser), both for various time durations and to various beam intensities, and then subjected to band gap determination by UV spectroscopy. The band gap has been found to decrease gradually with increase in the laser beam intensity, whereas its variation with increase in time of exposure shows an unusual behaviour such that it initially falls sharply followed by a gradual rise back to its original value. The results have been analysed and interpreted in terms of indirect band gap character of the material and an unusual variation in phonon frequency. The interpretation is well supported by X-ray diffraction and scanning electron microscopy (SEM) studies.

Variation in the polytypism of cadmium iodide crystals grown by different methods

Variation in the polytypism of cadmium iodide crystals grown by different methods

Growth and characterization of kdp-doped dendritic single crystals of cadmium iodide

Abstract Dendritic single crystals of KDP-doped cadmium iodide have been grown from vapour phase in vacuum. Polytypic behaviour of these crystals has been studied by X-ray diffraction. X-ray oscillation photographs have shown the occurrence of the most common CdI2 polytype 4H in 97% of cases. Streaking and arcing of reflections on the X-ray photographs are infrequent. Surface growth features on the basal faces have been studied by optical and scanning electron microscopy. It has been observed that doping with KH2PO4 has been found to result in marked changes in the surface features, as compared with doping with PbI2 and CdBr2.