Co-doped ZnSe Research Articles

Nano structural and opto-magnetic investigation of Co–Ni co-doped ZnSe for spintronics

Cobalt and Nickel co-doped ZnSe nanoparticles with fixed concentration of nickel and varying concentration of cobalt formulated as Zn0.95-xCoxNi0.05Se(where x = 0.0, 0.01, 0.03, 0.05) are synthesized by using wet-chemical route by co-precipitation method at 60 °C and calcined at 200 °C temperature. The structural study is carried out by applying X-ray diffractometer (XRD) characterization technique and found the synthesized material having crystallite size in nanometer range 08–37 nm with cubic zinc blende structure. Size increment of nanoparticles has been obtained as the concentration of cobalt was increased. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Diffractometer (EDX) and Transmission-Electron Microscopy (TEM) analysis of the nanoparticles are performed to study morphology and confirming presence of doped elements by forming Cobalt and Nickel co-doped ZnSe nanoparticles. Fourier-Transform Infrared (FTIR) study is carried out to detect presence of different functional groups, bending and stretching in molecules. Energy band gap is also calculated using UV–Visible spectroscopy and found increment in band gap due to quantum confinement effect. Ferromagnetism is recorded in these Co and Ni co-doped ZnSe nanoparticles using Vibrating-Sample Magnetometer (VSM) characterization technique at 300 K and 15 K.This inducted magnetism is due to the presence of exchange interactions between electrons of different elements. Electron spin resonance (ESR) spectra is also recorded at room temperature by the presence of paramagnetic defects in the samples.

Photoluminescence from Cu / Mn: ZnSe quantum dots and their phase transformation in silicate glass

To realize the polychromatic and tunable luminescence of ZnSe quantum dots (QDs) in glass, Cu and Mn co-doped ZnSe QDs (Cu/Mn: ZnSe QDs) glass were prepared by melt quenching and subsequent heat treatment method. For the ZnSe QDs glass without Cu and Mn dopants, there is only intrinsic luminescence from ZnSe QDs observed. For Cu/Mn: ZnSe QDs glass, the band edge emission from ZnSe QDs is quenched and the broadband emission from Cu2+/Mn2+ ions is observed, which is resulted by the effective energy transfer from ZnSe QDs to Cu2+/Mn2+ ions. With the increase of heating temperature, the emission spectra of Cu/Mn: ZnSe QDs glass change from green to orange light, which is characteristic luminescence wavelengths of Cu2+ and Mn2+ ions, respectively. For the ZnSe QDs glass without Cu2+ and Mn2+ dopants, ZnSe QDs undergo a phase transformation from the cubic to the hexagonal structure at higher heating temperature (≥610 °C) than those of Cu/Mn: ZnSe QDs glass at 600 °C and Cu-doped ZnSe QDs glass at 580 °C, in addition, For Cu/Mn: ZnSe QDs glass, the phase transformation temperature drops to 600 °C. For Cu-doped ZnSe QDs glass, the phase transformation temperature is further reduced to 580 °C. However, for Mn-doped ZnSe QDs glass, there is no phase transformation. It indicated that Cu2+ promotes the phase transformation of ZnSe QDs.

Excitation Transfer from Cr2+ to Fe2+ Ions in Co-doped ZnSe as a Pumping Scheme for Infrared Solid-State Lasers

We present the results of the photoluminescence behavior reflecting Cr2+ → Fe2+ excitation transfer in co-doped ZnSe:Cr2+Fe2+. This transfer can be seen as a possible promising pump mechanism to create short pulse lasers for the 3- to 6-µm wavelengths that can be excited using inexpensive 2-µm pump light sources. In addition to the kinetics, emphasis was put on comparing the intensities of both emissions, those of Cr2+ and Fe2+. With resonant excitation of Cr2+, the kinetics of the Fe2+ emission shows a very clear picture of the transfer with 60-ns rise time and the peak delayed by 200 ns. However, the evaluation of the PL intensities brought a surprise. With efficiencies above 80%, the observed Cr2+ → Fe2+ transfer is much more efficient than theoretically expected, and even the overall efficiency including the losses at the Fe2+ ions of almost 4% is still an order of magnitude higher than the theoretical values given for the Förster transfer alone. This leads to the suspicion that either the dopant atoms might not be uniformly distributed in the samples or that the transfer mechanism might be more effective than previously thought.

High Curie temperature and half-metallic ferromagnetism in Cr- and V-doped ZnSe in wurtzite phase: First-principles study

The electronic and magnetic properties of Cr-, V-doped, and co-doped ZnSe in the wurtzite structure have been calculated within LSDA + U method. The ab-initio calculations are carried out using Atomistic ToolKit code, based on the density functional theory. The band structure and density of states calculations showed the half-metallic behavior for 12.5%, 6.25%, 3.125%, 1.5625% concentrations in ZnSe:Cr, ZnSe:V and ZnSe:Cr,V. The magnetic moments of Zn1-xCrxSe and Zn1-xVxSe supercells are 4 and 3 μB, respectively. Co-doping greatly raises the ferromagnetism and the value of total magnetic moment of the supercell is 7 μB. The defect formation energies were calculated and obtained that ferromagnetic state is more stable than antiferromagnetic state. The Curie temperatures are estimated for Zn1-xCrxSe and Zn1-xVxSe supercells for all studies concentrations. The results indicate that these materials are high Curie temperature DMSs. First-principles studies show that Cr- and V-doped ZnSe are promising materials for spintronics.

Efficient Electronic Excitation Transfer via Phonon-Assisted Dipole-Dipole Coupling inFe2+:Cr2+:ZnSe

${\mathrm{Cr}}^{2+}$ - and ${\mathrm{Fe}}^{2+}$ -doped $\mathrm{Zn}\mathrm{Se}$ crystals are laser materials with phonon-broadened absorption and emission spectra, which provide broadband laser gain in the 2- to 5-$\text{\ensuremath{\mu}}\mathrm{m}$ wavelength range. While ${\mathrm{Cr}}^{2+}\text{:ZnSe}$ can be directly pumped with high-power Er, Ho, or Tm lasers, no such possibility exists for ${\mathrm{Fe}}^{2+}\text{:ZnSe}$. To this end, electronic excitation transfer between ${\mathrm{Cr}}^{2+}$ and ${\mathrm{Fe}}^{2+}$ ions in codoped ZnSe is investigated as an alternative excitation process in photo luminescence (PL) experiments with sub-10-ns temporal resolution. For a wide range of ion concentrations, we observe nonexponential decays of ${\mathrm{Cr}}^{2+}$ PL on a microsecond time scale, a 60-ns rise time of ${\mathrm{Fe}}^{2+}$ PL at high doping densities, and a prolonged decay of ${\mathrm{Fe}}^{2+}$ PL due to the temporal characteristics of excitation transfer over a range of interionic distances. Using a multirate equation model, the transfer process is analyzed on length scales up to 30 nm and compared to the established continuum model approach. The analysis reveals an unexpectedly efficient excitation transfer from ${\mathrm{Cr}}^{2+}$ to ${\mathrm{Fe}}^{2+}$ ions with an enhancement of the excitation transfer rates by up to a factor of 5 in comparison to resonant dipole-dipole coupling. The enhancement is assigned to (multi)phonon-assisted excitation transfer, in analogy to the phonon-mediated efficient radiationless decay of the excited ${\mathrm{Fe}}^{2+}$ state. As nonradiative losses and excitation transfer show different temperature scaling, a cryogenic temperature regime is found that promises overall efficiencies above 50%, making ${\mathrm{Fe}}^{2+}:{\mathrm{Cr}}^{2+}\text{:ZnSe}$ a much more viable alternative to parametric conversion schemes in the midinfrared range.

Passively Q-switched Pr:YLF laser with a Co,Fe:ZnSe saturable absorber

An iron-cobalt co-doped ZnSe polycrystalline (Co,Fe:ZnSe) was prepared by the thermal diffusion method, and its nonlinear optical response was characterized for the first time. Using the as-prepared Co,Fe:ZnSe as a saturable absorber (SA), the blue laser diode pumped Q-switched Pr:YLF laser at 607 nm (orange), and 639 nm (red) was successfully realized. For 607 nm, the Q-switched laser delivered the shortest pulse width of 59 ns with a repetition rate of 15 kHz. For 639 nm, the shortest pulse width and maximum repetition rate were 119 ns and 32 kHz, respectively. The experimental results indicate that the Co,Fe:ZnSe SA has a great potential for optical pulse generation in the visible region.

On the Absorption and Photoluminescence Properties of Pure ZnSe and Co-Doped ZnSe:Eu3+/Yb3+ Crystals

Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficiency and wide spectral range emission in the visible region. In this work, ZnSe and Eu3+/Yb3+ co-doped ZnSe crystals were grown by the chemical vapour transport method. Photoluminescence and optical measurements revealed the effect of trivalent rare earth Eu3+/Yb3+ ions on the emission of new lines with enhancement intensity. In the photoluminescence spectrum, some sharp and intense lines were observed that allow for the possibility of covering a broad emission range. Moreover, the optical measurement showed a lower bandgap compared to that of pure ZnSe bulk crystal. This material is suitable for developing optoelectronic devices, which can emit light in the visible and near infrared range with an improved emission efficiency and wide tunability.

Kinetics of excitation transfer from Cr2+ to Fe2+ ions in co-doped ZnSe.

The transfer of electronic excitations from Cr2+ to Fe2+ ions in co-doped epitaxially grown ZnSe is studied by time-resolved photoluminescence (PL) spectroscopy with unprecedented sub-10 ns time resolution. Upon excitation of Cr2+ ions by a picosecond pulse at 2.05 µm wavelength, PL from Fe2+ ions displays a delayed onset and a retarded decay in comparison to Fe2+ PL directly excited at 3.24 µm. We measure an extremely rapid 60 ns buildup of the Fe2+ luminescence, which is followed by a slower relaxation on the few micrometer scale. The experimental results are analyzed in the framework of Förster radiationless resonant energy transfer. Directly connecting to the work of Fedorov et al. [Opt. Mater. Express9, 2340 (2019)10.1364/OME.9.002340], the 60-ns buildup time of energy transfer is found to correspond to a Cr2+-Fe2+ distance of 0.95 nm, close to the length of the space diagonal of the ZnSe unit cell. This result demonstrates a significant density of spatially correlated Cr2+-Fe2+ ion pairs at short distance, in parallel to ions with a random distribution at a larger mutual separation.

Functional codoped ZnSe:Cu, Mn quantum dots(QDs): Microstructure, calorimetric and photoluminescence properties

In the present work, undoped ZnSe, and Zn1-x-y Cux Mny Se (x = 0.001, y = 0, 0.001, 0.010 0.015, 0.02 and 0.04 mol) codoped-quantum dots (cdQDs) of mean crystallite size within the range of 1.12 to 1.63 nm are synthesized employing the simple microwave irradiation (MWIR) assisted method; Different synthesis regimes of variable MWIR times and also Mn content are performed for ZnSe:Cu-Mn QDs. Structural, optical properties and melting point of the as-synthesized ZnSe QDs are studied by XRD, FESEM equipped with EDX and Map, TEM, Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analysis. XRD confirms the incorporation of Mn and Cu in ZnSe structure with the tunable size by changing the synthesize conditions; TEM results indicate spherical particles, most of which had a diameter of about 5 nm. Results of photoluminescence (PL) investigations show the synthesis condition dependence nature of the samples, suggesting their application in green-region sensors/biosensors; Mn doping causes more extent of PL in to the light wavelengths; doping with transition metals (TMs) impurities and employing MWIR cause an enhancement in the intensity and peak shift of PL band toward higher wavelengths, which influence on the optical properties of semiconductors. The FTIR absorption peaks for the understudied samples show the formation of ZnSe structure (the interaction between Se2− and Zn2+ ions) and insertion of Mn and Cu ions into their lattices; The Experimental and empirical melting temperature of synthesized nanomaterial are investigated; DSC analysis shows that nanoparticles melting point of the present nanoparticles are 600 °C lower than that of the bulk ZnSe owing melting point of 1520–1525 °C. Empirical size dependency of melting point shows that at lower than the Bohr radius of ZnSe (~8 nm), reasonable fast decrease in melting point occurs.

Anomalous nonlinear optical effect and enhanced emission by magnetic excitons in CVD grown cobalt-doped ZnSe nanoribbon

The magnetic excitons in diluted magnetic semiconductor (DMS) have varied formats due to the inhomogeneous phases out of doping concentration and/or structural relaxations or defects. Here the high quality cobalt-doped zinc blende ZnSe nanoribbons (NRs) were synthesized, showing bright and color-variable emissions from blue, yellow to a little mixed white colors. Their power and temperature dependent micro-photoluminescence (PL) spectra have been obtained in which two emission bands, one magnetic exciton band near the band-edge and a Co2+ high-level d–d transition emission band at 550 nm out of their ferromagnetic (FM) coupled aggregates in ZnSe lattice, both bands could also be reflected by a nonlinear optical absorption enhancement. The easy formed stacking fault defects in a chemical vapor deposition (CVD) grown ZnSe zincblende NR took part in the above optical processes out of magnetic polaronic excitons (PXs). The femtosecond (fs) laser pulse pumping on single ZnSe:Co NR produces obvious lasing behavior but with profile of a complicated magnetic exciton interactions with indication of a crossover from collective exciton magnetic polarons (EMP) to bound magnetic polaron (BMP) scattering in Co doped ZnSe NR. These findings indicate the complication of the magnetic coupling natures in varied DMS structures, whose optical properties have been found to be highly nonlinear, due to the involvement of the spin–spin, spin–exciton and spin–phonon interactions, verified by the theoretic calculation in Yang X-T et al (2019 Interstitial Zn-modulated ferromagnetism in Co-doped ZnSe Mater. Res. Express 6 106121).

Co-doped ZnSe: Mn, Cu quantum dots (QDs)—Eco-friendly synthesis, optical and structural properties besides lattice strain/dislocation density

Cu-Mn co-doped ZnSe quantum dots were eco-friendly synthesized at different synthesis conditions using water-based microwave-activated (MWIR) method. Energy band gaps $$E_{\text{gap}}^{\text{DASF}}$$ were determined using high-precision derivation of absorption spectrum fitting (DASF) method; the obtained results show that $$E_{\text{gap}}^{\text{DASF}}$$ values are within the range of 3.49–3.77 eV. Depending on the synthesis conditions, a decreasing trend of energy gap was observed with the increasing of MWIR time and ambient temperature. Morphologies and structural characterizations were done by XRD, EDX, FESEM, map and TEM, which revealed formation of ZnSe nanoparticles with mean crystallite size of ~ 2–5 nm. Also, Urbach energies were estimated, which their very small values in compare with $$E_{{{\text{gap}}}}$$ imply to the sharp band edges and so their good crystallinity nature. Moreover, refractive index, dielectric constant and nonlinear optical susceptibility of each sample were determined; results imply that these nanoparticles have a high potential in optoelectronic applications. Also, structural characteristics such as dislocation density, lattice strain and size of NCs were evaluated upon the Scherrer, Williamson–Hall and Williamson–Smallman methods. The results of structural features obtained from these approaches are highly inter-correlated and show same trends with the variation of synthesis conditions. Results show that the size of QDs is varied tunable by changing the MWIR time, ambient temperature and Mn dopant percentage and the as-synthesized ZnSe QDs and doped QDs have similar cubic zinc blend structure. Also, TEM result reveals that ZnSe nanoparticles are spherical in shape with an average grain size of about 5 nm. Upon the different performed opto-structural criteria, sample with Mn = 4% has the best crystallinity as good candidate in optical and mechanical applications. There were anomalies in different properties at Mn = 1.5 and 2% attributed to their higher density of lattice imperfections and surface trap centers related to how Mn ions incorporated to the ZnSe host lattice.

Broadband mid-infrared (2.5-5.5 µm) emission from Co2+/Fe2+ codoped chalcogenide glass ceramics.

Compact, mechanically robust, and cost-effective mid-infrared (MIR) light sources are key components in portable and field-deployable gas sensors. Capitalizing on an efficient energy transfer mechanism between Co2+ and Fe2+, we have demonstrated for the first time, to the best of our knowledge, that ultrabroadband 2.5-5.5 µm MIR emission can be achieved at room temperatures in chalcogenide (ChG) glasses that are pumped by a commercially available erbium-doped fiber amplifier emitting at 1.57 µm. These MIR-transparent ChG glass ceramics are embedded with Co2+/Fe2+ codoped ZnSe nanocrystals, and show sufficient MIR emission intensities and bandwidths to enable gas sensing for multiple target analytes such as butane and carbon dioxide. We also describe, to the best of our knowledge, the first observation of a unique "anomalous" increase in the MIR luminescence intensity as a function of temperature.

Optical properties of Co-doped ZnSe thin films synthesized by pulsed laser deposition

Effects of Co concentration on the properties of ZnSe:Co films were investigated. The amorphous and crystalline (ZnSe)1-x:Cox (x = =0.1, 0.3, 0.5) thin films were grown on sapphire (Al2O3) substrates with temperature of 25 °C and 800 °C respectively by pulsed laser deposition. The X-ray diffraction analyses indicate that, with increasing Co concentration, the average grain size decrease whereas the microstrain and dislocation density increase. Meanwhile, the further investigation for crystalline thin films shows that the crystalline phase transform from single cubic zinc blende structure to a mixture structure containing a small amount of hexagonal wurtzite phase. The Raman spectra and X-ray photoelectron spectroscopy reveal that the Co atoms were incorporated into ZnSe lattice and the samples reached an overdoping state when the x value surpassed 0.3. With increasing Co concentration, the average transmittance of films decreased due to the Co impurities un-incorporating into ZnSe lattice. Meanwhile, the band gap Eg values of films increased from 3.17 eV to 3.50 eV for TS = =25 °C and from 2.86 eV to 3.34 eV for TS = =800 °C. The large Eg values with regard to that of undoped bulk ZnSe (~2.7 eV) can be attributed to the Co doping and quantum confinement effect. Moreover, the refractive index of the films increased by improving Co concentration. The dispersion energy Ed, oscillator energy Eo, static refractive index n0, static dielectric constant ε0, oscillator strength So and oscillator wavelength λo are analyzed by a single oscillator model. All these parameters were found to be dependent upon the Co concentration in the (ZnSe)1-x:Cox thin films.

Interstitial Zn-modulated ferromagnetism in Co-doped ZnSe

A theoretical investigation on ground state magnetic order of Co-doped ZnSe was performed by using first-principles plane-wave pseudo potential method. Calculations verified the antiferromagnetic character of Co-doped ZnSe compounds. Defect calculations represented that the incorporation of one interstitial Zn could change the ground state of Co-doped ZnSe from antiferromagnetic to ferromagnetic order. The ferromagnetic mechanism was given based on a band structure model, according to which we speculated that two interstitial Zn would make the ferromagnetism more stable, while three interstitial Zn would not. First-principles calculations verified our speculation. In addition, the little formation energy of interstitial Zn shows that ferromagnetism of Co-doped ZnSe can be obtained easily in Zn-rich environment. The Curie temperature is up to 422 K by a rough estimation. Therefore Co-doped ZnSe is a prospective material for room temperature ferromagnetic semiconductor devices. Our theoretical results provide some guidances for experimental preparations and applications of ferromagnetic Co-doped ZnSe.

Energy transfer in iron-chromium co-doped ZnSe middle-infrared laser crystals

We report on the characterization of energy transfer in iron-chromium co-doped ZnSe middle-infrared laser crystals. The room temperature kinetics of the Fe:Cr:ZnSe sample under excitation of chromium ion at 1560 nm shows that energy transfer in Fe-Cr centers could be as fast as 290 ns. This rate is close to the non-radiative relaxation rate of Fe2+ ions in this host. The analysis of energy transfer rate in Cr-Cr; Fe-Fe and Cr-Fe pairs based on the resonance dipole-dipole interaction showed that energy transfer rate could be as fast as 109 s-1.

Theoretical investigation of electronic, magnetic and optical properties of ZnSe doped TM and co-doped with MnTM (TM: Fe, Cr, Co): AB-initio study

Based upon the first principal spin density functional calculation, the electronic, magnetic and optical properties of ZnTMSe and ZnMnTMSe where TM=Fe, Cr, Co are studied using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the local density (LDA)and the self-interaction-corrected(SIC) approximation. The purpose of this study is to determine the effect of different type of dopant and concentration on ferromagnetic and half metallic behavior of ZnSe. Therefore the magnetic disorder local moment (DLM) and the ferromagnetic state are investigated for different concentrations of Mn, Fe, Cr and Co; also the advantages of co-doped ZnSe with TM elements, behavior at room temperature are discussed. The electronic structure and optical properties are studied employing the local density (LDA) and the self-interaction-corrected (SIC) approximation. Moreover, the X-ray spectra modeling are in good agreement with the electronic and magnetic properties results.

Preparation, spectroscopic characterization and energy transfer investigation of iron-chromium diffusion co-doped ZnSe for mid-IR laser applications

The spectroscopic characterization and energy transfer mechanism of iron-chromium co-doped ZnSe polycrystalline (Cr,Fe:ZnSe) were reported with dimension of 15mm×15mm×2mm obtained by controlled post-growth thermal diffusion method. The infrared absorption is characterized by a strong broad-band centered at 1770nm which can be attributed to the only spin-allowed transition 5T2→5E within the 3d4 shell of Cr2+ ions. Photoluminescence spectrum shows a relatively strong broad emission band centered at 4.1μm with a width of 0.8μm (FWHM) under 1770nm excitation at room temperature and reveals effective Cr2+→Fe2+ energy transfer process. Room temperature photoluminescence decay about 8μs was measured. All the results indicate that Cr,Fe:ZnSe could achieve laser operation at 3.7–4.5μm via Cr2+→Fe2+ energy transfer using a more convenient laser pump source in the near IR region.

Electroluminescence of Zinc Selenium (ZnSe) Nanocrystals Co-Doped with Poly[2-methoxy-5-(2′-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV)

We have synthesized water soluble zinc selenium (ZnSe) nanocrystals by using mercaotoacetic acid (TGA) as the stabilizer. The synthesized ZnSe nanocrystals were co-doped with poly[2-methoxy-5-(2'-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) to fabricate an organic/ inorganic hybrid multilayer light-emitting device (LED). The structure of the device was indium-tin-oxide (ITO)/poly (ethylene-dioxythiophene):poly(styrenesul-fonate) (PEDOT:PSS)/MEH-PPV:ZnSe/bathocuproine (BCP)/tris-(8-hydroxylquinoline)-aluminum (Alq3)/Al. We demonstrate that the device has a lower driving voltage and increased current densities and power efficiencies owing to the co-doped ZnSe quantum dots. We obtained good efficiency of the devices when the quality ratio of MEH-PPV and ZnSe quantum dots was 1:1.

Preparation and optical properties of Co-doped ZnSe single crystals

ZnSe single crystals doped via Co diffusion are investigated. The diffusion was carried out from metal Co in He or Ar atmosphere. The spectra of optical density in the wavelength range 0.4–2 μm are investigated. It is found that the absorption edge shifts as the concentration of doping impurities increases. This shift is caused by the formation of the Zn1 − xCoxSe alloy. The diffusion profile of the Co dopant is determined via measurement of the relative optical density of the crystals in the visible spectral region. The Co diffusivities (D) in the ZnSe crystals at T = 1103–1273 K are calculated. The analysis of the temperature dependence D(T) made it possible to determine the coefficients in the Arrhenius equation, namely, D0 = 3.4 × 106 cm2/s and E0 = 3.8 eV.

Growth and characterization of codoping of ZnSe : Cl with Li grown by molecular beam epitaxy on GaAs

Codoping with Li and Cl of ZnSe grown on GaAs(0 0 1) substrate by using molecular beam epitaxy has been investigated. Complex formation between Li and Cl atoms by codoping has been demonstrated by photoluminescence measurements. A new approach to codoping in ZnSe, which involves Li and Cl deposition alternatively without spatially separated atomic planes (alternative-doping), has been attempted to obtain higher carrier concentration than that achieved by uniform-doping technique, and indeed confirmed the effectiveness of codoping. The growth rate of codoped ZnSe films was larger than that of ZnSe layer doped with Cl alone, and the electrical conductivity changed from n-type to p-type.