ZnSe Samples Research Articles

Chiral LigandInduced Circular Dichroism in Excitonic Absorption of Colloidal Quantum Dots

AbstractA range of unique properties have been extensively studied in colloidal semiconductor nanocrystals (quantum dots, QDs). The possibility to manipulate the properties of these systems by controlling size and composition is attractive for many different applications, as well as for fundamental studies. Recently, the properties of chirality and chiroptical activity induced by surface ligands at QDs were considered. It was shown that chiroptical activity can be induced in the exciton transitions of quantum dots by capping them with chiral molecules. In this work, chiroptical spectroscopy (mainly circular dichroism) is used to study induced effects in CdS, CdSe and ZnSe QD systems. Some fundamental differences are encountered between CdS or CdSe samples and ZnSe samples. The results are analyzed to account for the mechanism of induction of chiroptical activity in the inorganic core by chiral capping molecules. Two electronic mechanisms of interaction are considered and discussed in light of the results. It is also suggested that chiroptical spectroscopy might serve as an efficient tool to characterize electronic (or electron‐hole) level spectra of nanocrystal systems by analyzing circular dichroism intensity and lineshape.

Mechanical properties of ZnSe : Cr2+ single crystals

The microhardness of single-crystal samples of ZnSe: Cr2+ with a chromium concentration in the range from 3.3 × 1017 to 4.0 × 1019 cm−3 has been studied. The microhardness as a function of the load on the indenter on the faces (111), (1\(\bar 1\)0), and (001) of the ZnSe: Cr2+ and ZnSe samples has been measured. It has been established that doping of zinc selenide with chromium leads to a decrease in the anisotropy of the mechanical properties and stabilization of the cubic sphalerite structure.

Effect of N5+ ion implantation in CVT grown ZnSe single crystals

The ZnSe single crystals were grown by chemical vapor transport (CVT) technique using iodine as a transporting agent. As grown ZnSe single crystals have been implanted by N5+ ion at 45keV energy in room temperature with various fluences of 1×1015, 5×1015, 1×1016 and 5×1016 ions/cm2. The lattice constants of the as grown and implanted ZnSe single crystals are 5.57 and 5.45Å respectively. The photoluminescence studies reveal that N5+ implanted ZnSe has the band edge emission at 468nm (2.64eV) and broad luminescence peak due to defect level green emission at 551nm (2.25eV) and yellow emission 592nm (2.09eV). The as grown ZnSe crystal has the absorption cut off at 483nm whereas the cut off increases from 489 to 524nm with an increase in ion fluences. The frequency of vibration for as grown ZnSe crystal is 504cm−1 and for implanted ZnSe samples, the frequencies are 657–677cm−1 (NZn bending mode) and 2337–2353cm−1 (NSe stretching mode) which are due to bond formation of N.

Influence of the Surface Mechanical Treatment on the Photothermal Piezoelectric Spectra of ZnSe Crystals

This paper presents experimental and theoretical piezoelectric photoacoustic spectra of ZnSe samples after different surface treatments: grinding, polishing, and etching. The modification of the Jackson and Amer theory, presented in the paper, enabled numerical interpretation of the spectra in the model of a mechanically damaged surface layer. The nature of the characteristic peak observed at E = 2.65 eV below the energy gap is explained as caused by the Urbach absorption tail and the damaged surface layer of a sample. The correlation between the microhardness of the Zn1-x Be x Se and ZnSe crystals and the thickness of the mechanically damaged surface layer was observed.

Temperature and concentration quenching of mid-IR photoluminescence in iron doped ZnSe and ZnS laser crystals

Concentration dependences of the mid-IR kinetic of luminescence at 5 E↔ 5 T 2 transition in Fe:ZnSe and Fe:ZnS laser samples were studied in 14–300 K temperature ranges. Radiation lifetime in Fe:ZnSe samples measured using low doped samples with iron concentration 0.1×10 18 cm −3 was estimated to be 57 μs. The magnetic susceptibility for higher doped ( C Fe=38 and 112×10 18 cm −3) Fe:ZnSe samples was found to consist of a paramagnetic Curie–Weiss behavior arising from the weakly interacting Fe 2+ ions and a diamagnetic ZnSe contribution plus a temperature-independent, field-dependent contribution possibly arising from very small amounts of aggregated Fe.

X-ray induced conductivity of ZnSe sensors at high temperatures

Measurements of intrinsic conductivity and X-ray induced conductivity were performed on specially undoped ZnSe samples. The measurements demonstrated that sensors made of ZnSe have minor intrinsic conductivity when heating up to the temperature of 180 °C, and significant X-ray induced conductivity. Dose dependence “dose rate – current” is described with simple power function which considerably simplifies calibration of sensors. This results can be used during the designing of high-temperature X-ray and gamma-radiation detectors for radiation hot rolling thickness gauges which are widely used in the metallurgy.

The influence of nickel concentration on photoluminescence spectra of ZnSe:Ni samples

Photoluminescence (PL) spectra of ZnSe samples grown by iodine transport method and doped with Ni during the growth process and grown from the melt and doped with Ni by diffusion from a gas phase are investigated in visible and infrared (IR) ranges at 77 and 300 K. It is shown that under sub-band excitation, the PL spectra for the undoped samples of both types are similar and may be attributed to self-activated luminescence with participation of iodine- and V Zn-based centres. The PL study for ZnSe samples doped with Ni carried out at various Ni concentrations, temperatures, and excitation intensities gives reason to ascribe the observed bands in near-IR and IR ranges to 3 T 2( F)→ 3 T 1( F) and 3 T 1( P)→ 3 T 1( F) intracentre transitions within the Ni Zn 2+(d 8) ion.

Ferromagnetism in Cu-doped ZnSe semiconducting quantum dots

The projection of integrating optical, magnetic and electronic functionalities into a single material have aggravated passionate attention in mounting wide band gap diluted magnetic semiconductor (DMS) in the midst of room temperature ferromagnetism. We report the evidence of ferromagnetism in Cu-doped ZnSe quantum dots (QDs) below room temperature, grown from a single source precursor by lyothermal method with the sizes of approximately 3.2–5.14 nm. QDs mainly exhibit paramagnetic behavior between 80 and 300 K, with a weak ferromagnetic/anti-ferromagnetic exchange at lower temperature as observed by superconducting quantum interference device (SQUID) magnetometer. From the Curie–Weiss behavior of the susceptibility, Curie temperature (T c) of Cu-doped ZnSe sample has been evaluated. From EPR, we obtain the Lande-g factor in the Zeeman interaction term as 2.060. Photoluminescence and EPR measurements support and confirm the view that Cu2+ substitutes for Zn2+ in Cu-doped ZnSe quantum dots.

Kerr-lens mode-locked femtosecond Cr^2+:ZnSe laser at 2420 nm

We describe a cw Kerr-lens mode-locked Cr(2+):ZnSe laser pumped by a 1800 nm thulium fiber laser. The astigmatically compensated asymmetric x cavity contained a 2.4-mm-long Cr(2+):ZnSe sample with a pump absorption coefficient of 11.6 cm(-1) and was operated with a 1% output coupler. The dispersion compensation was achieved by using a MgF(2) prism pair. During Kerr-lens mode-locked operation, we could generate 95 fs pulses at a pulse repetition rate of 94.3 MHz and with 40 mW of output power. The center wavelength of the pulses was 2420 nm. The pulses had a spectral width of 69 nm and a time-bandwidth product of 0.335, which is close to the transform limit for hyperbolic secant pulses.

Effects of photoacoustic measurements on a nanostructured ZnSe mechanicallyalloyed

Zinc-blende ZnSe powder, with particles containing nanometric grains, was prepared usingthe mechanical alloying technique, from an equiatomic mixture of elemental Zn and Sepowders. An important interfacial component was observed in the as-milled powder,which affects its thermal and optical properties. In order to obtain a high-qualityzinc-blende ZnSe powder an annealing process was applied. The structural properties ofboth as-milled and annealed powders were characterized by an x-ray diffractiontechnique. The effects of defect centers on the optical band gap of both as-milledand annealed zinc-blende ZnSe powders were studied through optical absorbancemeasurements. The results showed a substantial broadening and a shift of the band gapenergy to lower values in the as-milled powder, while for the annealed sample noeffects were observed. For the annealed sample, the measured band gap energyvalue is in good agreement with those reported in the literature. A sequence ofphotoacoustic absorption measurements of the as-milled ZnSe sample showed that theabsorbed energy promotes a structural relaxation. This relaxation causes a change inthe heat transfer mechanism from thermal diffusion to thermoelastic bendingand a reduction in the thermal diffusivity values. Similar measurements of theannealed nanostructured ZnSe sample showed the thermal diffusivity value to have ahigh degree of stability, and to be in good agreement with values reported in theliterature.

Fluorescence lifetime of Mn-doped ZnSe quantum dots with size dependence

Radiative lifetimes of high quality Mn:ZnSe nanocrystals synthesized by nucleation-doping method are experimentally measured at wavelength near 580nm. The slow decay rate in millisecond time scale is identified as the radiative decay from the T14 metastable excited state of Mn2+ ions embedded in the ZnSe nanocrystals. Also, two fast decay components are measured at this wavelength with much lower intensities, which can be attributed to the emission tails from the host ZnSe nanocrystals and from the surface-trap states or the self-activated luminescence due to Mn ion pairs, respectively. Size dependences of the radiative decay rates for the Mn:ZnSe samples are measured.

Synthesis of ZnSe nanocrystalline powders by mechanochemical reaction

The ZnSe nanocrystalline powders were synthesized by mechanochemical reaction method. The powders milled at air atmosphere have the second phase ZnO, but that milled above 2 h at high N2 atmosphere have not second phase ZnO. The phase structure of the ZnSe powder milled for 10 h at N2 atmosphere is sphalerite structure. The average size of the as-milled and annealed ZnSe nanocrystalline powders is 5.17 and 8.88 nm respectively. The TEM analysis demonstrated that the size of agglomerated ZnSe crystalline is less than 100 nm, but the electron diffraction pattern showed that ZnSe clusters were a polycrystalline structure. The absorption spectrum of ZnSe samples was measured by UV–VIS–NIR Photometer Spectrum. It showed that the absorption edge of the ZnSe nanocrystalline powders by mechanochemical reaction comparing to ZnSe bulk materials had a red-shift. This result can be attributed to the residual stress and lattice aberrance of ZnSe nanocrystalline powders in milling process. The absorption edge of the annealed ZnSe powders was recovered owing to the residual stress was eliminated by annealing for 2 h containing nitrogen.

Changes in donor and acceptor states in Au-doped ZnSe samples induced by ageing atroom temperature

Photoluminescence (PL) spectra of n-ZnSe single crystals doped with Au are investigatedat temperatures between 4.4 and 300 K immediately after doping and after storage forfour years at room temperature in darkness in air. The formation of donor-typeAui interstitial defects stimulated by time is found in ZnSe for the first time.Changes in the structure of the edge and long-wavelength PL spectra withthe course of time are observed. The long-wavelength band attributed to(AuZn-DIII,VII) acceptors is not found in the PL spectra of the stored samples. At the same time, a greenPL band with maximum at 527 nm (2.35 eV) appears. This band is ascribed to(VZn–Aui) acceptors formed as a result of displacement of theAuZn atoms into interstitial sites due to deformation forces. When the Au concentration in theZn + Au meltexceeds 1 at.%, an Aui-donor impurity band is formed and the intensities of all the PL bands are reduced.

A solvothermal method to novel metastable ZnSe nanoflakes

Novel flower-like pattern of radially aligned ZnSe nanoflakes were synthesized via a facile solvothermal method in a mixed solvent of ethylenediamine and hydrazine hydrate. XRD, FESEM and TEM characterizations showed that as-prepared ZnSe sample is metastable wurtzite phase and the nanoflakes have uniform thickness of about 60 nm. The PL spectrum of the as-prepared sample was investigated. The formation conditions of the flower-like pattern of radially aligned ZnSe nanoflakes were discussed and it was found that the ratios of the solvent components are of great importance for the final formation of the flower-like structures.

Direct Experimental Determination of the Optimum Chromium Concentration in Continuous-Wave Cr$^{2 + }$:ZnSe Lasers

We employed several experimental techniques to measure the concentration dependence of the important laser parameters, and directly determine the optimum ion concentration for continuous-wave (CW) operation in room temperature Cr2+:ZnSe lasers. By using diffusion doping, 40 polycrystalline Cr2+:ZnSe samples with ion concentrations in the range of 0.8 times 1018 to 66 times 1018 ions/cm3 were prepared and used in this paper. Based on the spectroscopic measurements, empirical formulae showing the concentration dependence of the passive laser losses, fluorescence lifetime, and the fluorescence efficiency were obtained. By using the fluorescence efficiency data, the optimum chromium concentration, which maximizes the 2400-nm fluorescence intensity at a fixed excitation power, was determined to be 6 times 1018 ions/cm3. The dependence of the optimum concentration on sample length was further discussed. The CW power performance of the samples was also evaluated. At an incident pump power of 2.1 W, the optimum concentration for lasing was determined to be 8.5 times 1018 ions/cm3 that was in good agreement with the fluorescence measurements. The predictions of the fluorescence analysis and laser power measurements were in good agreement at low chromium concentrations. The observed discrepancy at higher doping levels was attributed to thermal loading.

Effect of boron ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films were deposited onto well cleaned glass substrates using vacuum evaporation technique under a vacuum of 3×10 −5 mbar. The prepared ZnSe samples were implanted with mass analyzed 75 keV B + ions at different doses ranging from 10 12 to 10 16 ions cm −2. The composition, thickness, microstructures, surface roughness and optical band gap of the as-deposited and boron-implanted films were studied by Rutherford backscattering (RBS), grazing incidence X-ray diffraction, Atomic force microscopy, Raman scattering and transmittance measurements. The RBS analysis indicates that the composition of the as-deposited and boron-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and boron-implanted thin films is cubic. It is found that the surface roughness increases on increasing the dose of boron ions. In the optical studies, the optical band gap value decreases with an increase of boron concentration. In the electrical studies, the prepared device gave a very good response in the blue wavelength region.

Thermal depolarization of naturally polarized zinc selenide polycrystals

The properties of zinc selenide (ZnSe) polycrystals grown by chemical vapor deposition have been studied. Homogeneous heating of the samples gives rise to a thermal-depolarization-induced current in the external circuit. The appearance of polarization in polycrystalline ZnSe samples is related to the internal electric and elastic fields formed in the course of growth and orientation ordering of the crystalline grains.

Intracavity-pumped Cr2+:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm

We obtained, what is to our knowledge, record tuning from an intracavity-pumped gain-switched Cr2+:ZnSe laser. In the experiments, a polycrystalline Cr2+:ZnSe sample with an absorption of about 43% at 1570 nm was used to minimize reabsorption losses at the lasing wavelengths below 2000 nm. By placing the gain medium inside the cavity of a pulsed KTP optical parametric oscillator (OPO) operating at 1570 nm, smooth, continuous tuning was achieved in the 1880-3100 nm range with four different sets of cavity optics. As high as 145 mW of average laser output power was obtained at 2365 nm with 1.2 W of intracavity OPO power.

Continuous-wave broadly tunable Cr 2+:ZnSe laser pumped by a thulium fiber laser

We describe a compact, broadly tunable, continuous-wave (cw) Cr 2+:ZnSe laser pumped by a thulium fiber laser at 1800 nm. In the experiments, a polycrystalline ZnSe sample with a chromium concentration of 9.5 × 10 18 cm −3 was used. Free-running laser output was around 2500 nm. Output couplers with transmissions of 3%, 6%, and 15% were used to characterize the power performance of the laser. Best power performance was obtained with a 15% transmitting output coupler. In this case, as high as 640 mW of output power was obtained with 2.5 W of pump power at a wavelength of 2480 nm. The stimulated emission cross-section values determined from laser threshold data and emission measurements were in good agreement. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster cut MgF 2 prism and a single set of optics.

SIMS STUDIES OF Cl-DOPED ZnSe EPILAYERS GROWN BY MBE

Chlorine is one of the most used species to produce n-type ZnSe epilayers. In this paper, we present Secondary Ion Mass Spectrometry (SIMS) profiles of a series of Cl -doped ZnSe samples, which were grown by Molecular Beam Epitaxy (MBE) technique on GaAs substrates. These profiles have been used to examine the limitation of SIMS analysis of narrow Cl -delta layers. In order to convert SIMS raw data to quantified data, the depth profile from a Cl -implanted standard sample has been used to estimate the "useful ion yield" of chlorine and thus the instrumental sensitivity for chlorine in a ZnSe matrix. The "useful ion yield" and detection limit of chlorine in the ZnSe host matrix were calculated to be 4.7 × 10-7 and 5 × 1017 atoms/cm3, respectively.