CdSe Crystal Research Articles

Study of Photoconductivity of Thin Films of Cadmium and Selenium Obtained by Chemical Deposition

In this work, the photoconductivity (PC) spectrum of thin CdSe films was studied. In the course of studies on glass substrates, thin films of cadmium and selenium with a thickness of h = 200 nm and h = 400 nm were selected. The thickness of the samples obtained by chemical deposition was determined by the gravimetric method. Since CdSe crystal is a light-sensitive semiconductor material, the photoconductivity of thin films has been studied. The spectra obtained during studies carried out at a wavelength λ = 600-1100 nm were analyzed. It has been established that the spectrum is chaotic, since in the h = 200 nm layers the phase is not completely formed. In the layers h = 400 nm, a maximum centered at the wavelength λ = 710 nm was recorded.

High-quality ZnO anti-reflective coatings for CdSe crystal in the infrared wavelength

The anti-reflective coating of infrared window materials plays an important role in infrared devices. In this paper, pure ZnO nanoparticles dispersion liquid was obtained by purifying and redispersing ZnO nanoparticles of about 4 nm prepared by the sol-gel method. High-performance ZnO coatings were prepared on CdSe crystals by the dip-coating method. Changing the thickness of the ZnO coating can change the position of the optimal anti-reflection. In the wavelength range of 1280–3000 nm, the lowest reflectance can reach 0.20 %, and the average reflectance is reduced from 26.36 % to 6.02 %. In the wavelength range of 3000–5000 nm, the lowest reflectance can reach 0.22 %, and the average reflectance is reduced from 26.91 % to 2.23 %. In the wavelength range of 8000–10,000 nm, the lowest reflectance can reach 0.20 %, and the average reflectance is reduced from 28.24 % to 1.28 %. Especially in the wavelength ranges of 3000–5000 and 8000–10,000 nm, the anti-reflection is significant in the whole band. In addition, the coating has excellent high-temperature stability and mechanical properties. This work is of great significance for preparing infrared anti-reflection coatings by chemical method.

Large-size high-quality CdSe-OPO component for far IR laser output prepared by directional crystal growth technique

Φ40 × 100 mm3 CdSe crystal was obtained using a capsuled Mo-crucible method combined with a seed directional technique.

High-gain broadband laser amplification of mid-IR pulses in Fe:CdSe crystal at 5 μm with millijoule output energy and multigigawatt peak power.

We report on a first of its kind, to our knowledge broadband amplification in a Fe:CdSe single crystal in the mid-IR beyond 5 µm. The experimentally measured gain properties demonstrate saturation fluence close to 13 mJ/cm2 and support the bandwidth up to 320 nm (full width at half maximum). Such properties allow the energy of the seeding mid-IR laser pulse, generated by an optical parametric amplifier, to be pushed up to more than 1 mJ. Dispersion management with bulk stretcher and prism compressor enables 5-µm laser pulses of 134-fs duration, providing access to multigigawatt peak power. Ultrafast laser amplifiers based on a family of Fe-doped chalcogenides open the route for wavelength tuning together with energy scaling of mid-IR laser pulses that are strongly demanded for the areas of spectroscopy, laser-matter interaction, and attoscience.

Cr-=SUP=-2+-=/SUP=-:CdSe-лазер с мощностью непрерывной генерации более 20 W

Strong thermal lensing limits cw power of Cr2+:CdSe laser about ~ 1 W level due to unfavorable active media properties: low thermal conductivity and high thermo optical coefficient. Shifting from conventional approach to moving active media scheme allowed us to achieve over 20 W of cw generation in Cr2+:CdSe crystal

Vibrational Signatures of Substitutional Oxygen in CdTe and CdSe

Vibrational modes of substitutional oxygen on the anion site in cubic CdTe and wurtzite CdSe are identified from infrared (IR) absorption measurements on single crystals codoped with 18O and 16O. The 16O isotope variety of the defect in CdTe gives rise to a local vibrational mode at 349.8 (10 K), whereas the corresponding species in CdSe results in a doublet structure at 370.6 and 372.5 (10 K). The latter two modes are fully polarized for light parallel and perpendicular to the c axis of the CdSe crystal, respectively, and belong to the nondegenerate and the twofold degenerate E representations of the C3v point group.

Ab Initio Investigation of Cooperativity in Ion Exchange

Ion exchange reactions are being increasingly employed for the templated synthesis of inorganic nanomaterials for plasmonics, topological quantum computing, and solid-state electrolytes. Some cation exchange reactions have been found to be cooperative akin to the nature of ligand binding processes in enzymes. What is the structural origin of this cooperative behavior? This question is answered here through computational simulations of Cd2+-to-Cu+ replacement reactions in a CdSe crystal. Density functional theory simulations show that the incorporation of Cu+, at the initial stages of exchange, induces a translocation of Cd2+ ions from their ideal tetrahedral sites to the otherwise unfavored octahedral sites. This reorganized structure has a lower energy cost for Cd2+-to-Cu+ replacement and is therefore much more amenable to further cation exchange. Thus, Cu+-insertion-induced reorganization of the cationic sublattice is at the origin of the cooperativity exhibited by the cation exchange reaction. This atomic-level understanding establishes a close link between solid-state chemical reactions and phase transitions and will lead to more precise transformations for accessing unusual material phases.

Jahn–Teller Cr2+ Centers in a CdSe Crystal

Impurity Cr2+ ions in the CdSe crystal are studied by tunable EPR spectroscopy in the frequency range of 70–320 GHz. The discovered Jahn–Teller tetragonal distortions of the nearest environment of the chromium ion confirm the results of recent ultrasound studies. The set of spectroscopic parameters that allows obtaining agreement between the calculates and experimental angular and field–frequency dependences of the EPR spectra is determined.

Dark current behavior of x-ray photoconductors based on CdSe crystal

In this work, the dark current behavior of the x-ray photoconductors based on CdSe crystal was investigated. The MSM planar structure was used to fabricate x-ray photoconductor with two orthogonal directions configurations which are the applied electric field parallel to the crystallographic c-axis (E//c) and perpendicular to the c-axis (E⊥c), respectively. The dark current density, relaxation time, stability and electrical asymmetry for two orthogonal directions configurations have been studied. The results show that the dark current density is still below 0.2 nA cm−2 at a high electric field of 1 × 103 V cm−1, the relaxation time under various bias voltages is about 40 s, the stability of dark current is good, the electrical asymmetry that negatively biased current larger than positively biased is about one order of magnitude. In addition, the anisotropy of dark current behavior is slight. This work provides a reliable basis for x-ray detector of CdSe crystal.

Growth and characterization of mid-far infrared optical material CdSe crystal

We investigated the decomposition conditions of CdSe crystal with the aid of thermodynamics analysis. We chose the optimized growth parameters (1 MPa, 1250°C) based on the numerical simulation, and obtained single crystal boule with 28 mm in diameter and 70 mm in length. Preliminary tests showed that the crystal had fine homogeneity in composition (CdSe0.975), high infrared transmission (68-70%, 2.0-16 µm) and large laser induced damage threshold value (LIDT, 56 MW/cm2). This crystal may be a good candidate for the 8-12 µm mid-far nonlinear optical (NLO) material.

Terahertz optical properties of nonlinear optical CdSe crystals

We investigate the optical properties of cadmium selenide (CdSe) crystals in a wide terahertz (THz) range from 0.2 to 6 THz by THz time-domain spectroscopy (THz-TDS) and Fourier transform infrared spectroscopy (FTIR). The refractive index, absorption coefficient and transmittance are measured and analyzed. The properties are characterized by several absorption peaks which represent the relevant phonon vibrations modes. The experimental results are in agreement with the theoretical results. The dispersion and absorption properties of CdSe crystal are analyzed in THz range. These properties indicate a good potential for THz sources and THz modulated devices.

Generation of 320 mW at 10.20 μm based on CdSe long-wave infrared crystal

CdSe single crystal, with the sizes of ∼54 mm in diameter and ∼25 mm in length, was grown by a high pressure vertical gradient freeze (HPVGF) technique using (0 0 1)-oriented seed. The CdSe crystal was characterized with transmission spectrophotometer. The transmission spectra showed that the infrared transmission was above 68% and the mean absorption coefficient was 0.041 cm−1 in the range of 2.5–20 μm. Using fabricated CdSe crystal with the dimensions of 6 mm × 10 mm × 44 mm, we demonstrated an optical parametric oscillator (OPO) pumped by a 2.05 μm Ho:YLF laser at a pulse repetition frequency of 5 kHz. Up to 320 mW output was obtained at the idler wavelength of 10.20 μm with a pump power of 18.06 W. 320 mW at 10.20 μm, to our knowledge, was the highest power obtained with a 2.05 μm laser-pumped CdSe OPO.

Photoluminescence characteristics of CdSe quantum dots: role of exciton–phonon coupling and defect/trap states

In this paper, we report temperature dependent photoluminescence (PL) characteristics of CdSe colloidal QDs with average diameter ~2.8 nm. Temperature dependence of strongly confined exciton PL peak position, linewidth and intensity were investigated in 30 K to 300 K temperature range. Our studies reveal nearly four times weaker exciton-LO phonon coupling than bulk CdSe crystal. Theoretically, it should be vanishingly small due to near identical electron and hole charge distributions in strongly confined QDs. On the other hand, exciton-acoustic phonon coupling is an order of magnitude larger than its bulk counterpart. Observed finite value of exciton-LO phonon coupling and enhanced exciton-acoustic phonon coupling are due to piezoelectric strain fields. PL intensity exhibits anomalous behavior in the temperature range 100–230 K. This has been explained by thermally activated detrapping of the charge carriers trapped in the potential wells formed at the interface adjoining dislocations/stacking faults developed during the synthesis process. Above 230 K, PL is partially quenched by thermal escape of charge carriers from luminescing exciton state to higher lying nonluminescing states.

Effect of the surface on the internal structure of CdSe crystal lattice based on molecular dynamics simulations

The results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-index atomic planes, (100), (110) and (111), are presented. The effect of the crystal termination on the atomic arrangement (interatomic distances) at the surface and underneath the surface is examined. It is shown that the crystal lattice is distorted in lateral and normal directions to the depth of up to about 2 nm from the surface. The exact characteristic of the changes of interatomic distances is specific to the type of the atomic plane terminating the crystal lattice. At some surfaces, the very last monoatomic layer loses the long-range ordering and becomes quasi amorphous. The atoms group into randomly distributed pairs or short linear groups.

Luminescent CdSe Superstructures: A Nanocluster Superlattice and a Nanoporous Crystal.

Superstructures, combining nanoscopic constituents into micrometer-size assemblies, have a great potential for utilization of the size-dependent quantum-confinement properties in multifunctional electronic and optoelectronic devices. Two diverse superstructures of nanoscopic CdSe were prepared using solvothermal conversion of the same cadmium selenophenolate precursor (Me4N)2[Cd(SePh)4]: the first is a superlattice of monodisperse [Cd54Se32(SePh)48(dmf)4]4- nanoclusters; the second is a unique porous CdSe crystal. Nanoclusters were crystallized as cubic crystals (≤0.5 mm in size) after solvothermal treatment at 200 °C in DMF. UV-vis absorption and PLE spectra of the reported nanoclusters are consistent with previously established trends for the known families of tetrahedral CdSe frameworks. In contrast to these, results of PL spectra are rather unexpected, as distinct room temperature emission is observed both in solution and in the solid state. The porous CdSe crystals were isolated as red hexagonal prisms (≤70 μm in size) via solvothermal treatment under similar conditions but with the addition of an alkylammonium salt. The presence of a three-dimensional CdSe network having a coherent crystalline structure inside hexagonal prisms was concluded based on powder X-ray diffraction, selected area electron diffraction and electron microscopy imaging. Self-assembly via oriented attachment of crystalline nanoparticles is discussed as the most probable mechanism of formation.

Optical Spectroscopy of Barium Fluoride Crystals under Simultaneous Pulsed Excitation

This paper reports optical absorption spectra and rapidly decaying luminescence of BaF2 crystals measured at 295 K under excitation pulse of accelerated electrons and excited simultaneous stimulated emission of CdSe crystal. It is shown that the simultaneous excitation of the crystals BaF2 pulse accelerated and SE semiconductors in electronic components STE absorption leads to a reduction efficiency of creation of STE and the appearance of fast decaying emission in the UV region of the spectrum.

Research on the optical band positions, spin-Hamiltonian parameters and atom-position parameter of Co2+ ion in CdSe crystal

The optical band positions and EPR (or spin-Hamiltonian) parameters (g factors g//, g⊥ and zero-field splitting D) of Co2+ ion in the trigonally-distorted tetrahedral Cd2+ site of CdSe crystal are calculated simultaneously from the complete diagonalization (of energy matrix) method (CDM) based on the two-spin–orbit-parameter model. This model contains the contributions to the spectral data from both the spin–orbit parameters of central dn ion (i.e., one-spin–orbit-parameter model) in the conventional crystal-field theory and that of ligand ions via covalence effect. The calculated 12 optical band positions and three spin-Hamiltonian parameters using four adjustable parameters show reasonable agreement with the experimental values. The local atom-position parameter uloc (where the corresponding parameter u in the host CdSe crystal is unlikely) in the Co2+ center is also estimated from the calculations. The calculations of these spectral data from the CDM based on the conventional one-spin–orbit parameter model are also made for comparison. It is found that the calculated optical band positions are also close to the experimental values, but the calculated spin-Hamiltonian parameters are in poor agreement with the observed values. So, for the unified and reasonable calculations of optical and EPR data of dn ions in crystals (in particular, in the cases of ligand with large spin–orbit parameter), the CDM based on the two-spin–orbit-parameter model should be applied.

Aqueous Processing CdSe/TGA Quantum dots For Potential Bio-Medical Applications

ABSTRACTThe size-dependent optical properties of CdSe nanoparticles are desirable in bio-imaging and cell sorting applications because of their tunable photoluminescence in the visible range. Previous studies have already suggested that CdSe QDs could be utilized for pathogen detection by using suitable capping agents to make it biocompatible; however, systematic works on the effect of crystallite size and composition of the nanocrystals are scarce. The present research will be focused on the effect of CdSe crystal size and composition (pure and doped systems) to systematically evaluate its applicability in detecting pathogens, like Escherichia coli (E. coli). Highly luminescent water-soluble CdSe QDs were firstly synthesized in the aqueous phase, in the presence of thioglycolic acid (TGA) as a capping agent. CdSe/TGA molar ratios, reaction temperature, time, and pH were evaluated in order to optimizer the QDs optical properties. X-Ray diffraction (XRD) measurements confirmed the formation of CdSe exhibiting hexagonal structure with an estimated averaged crystallite size in the 4-6 nm range. Transmission electron microscopy (TEM) analyses evidenced the formation of CdSe nanocrystals with particle sizes between 3-5 nm. UV-Vis measurements showed a strong exciton peak between 390-400 nm with an estimated band gap of 2.64 eV (bulk: 1.74 eV); additionally, a strong fluorescence peak was observed between 500-550 nm using an excitation wavelength of 400 nm. Fourier Transform Infrared Spectroscopy (FT-IR) analyses suggested the actual functionalization of the CdSe surface with TGA functional groups. Preliminary results of the CdSe/TGA coupling with the selected bacteria, E. coli, are presented and discussed.

Electronic Density of States in 0D, 1D, 2D and 3D structures of CdSe Crystal

Electronic Density of States in 0D, 1D, 2D and 3D structures of CdSe Crystal

Se 전구체 함량 따른 CdSe 양자점 형광체의 발광특성

The quantum dots (QD) have unique electrical and optical properties due to quantum dot confinement effect. The optical properties of QDs are decided by various synthesis conditions. In a prior QDs study, a study on the QDs size with synthesis condition such as synthesis time and temperature is being extensively researched. However, the research on QDs size with composition ratio has hitherto received scant attention. In order to evaluate the ratio dependence of CdSe crystal, synthesis ratio of Se precursor is changed from 16.7 mol%Se to 44 mol%Se. As the increasing Se ratio, the band gap was increased. This is caused by red shift of emission. We confirmed optical property of CdSe QDs with composition ratio.