Luminescence Of ZnSe Research Articles

Thermally Stimulated Luminescence in ZnSe:Ag and ZnSe:(Ag, Gd) Phosphors

AbstractWith a view to understanding the luminescence mechanism in ZnSe, a systematic study of thermally stimulated luminescence (TSL) of UV ray (3650 Å) irradiated ZnSe:Ag and ZnSe:(Ag, Gd) phosphors has been undertaken. TSL glow curves of these phosphors are recorded in the temperature range 110–340 K. The TSL parameters like trap depth, frequency factor, order of kinetics, and capture cross‐section of the glow peaks are evaluated employing Cutie's method, various heating method, and peak shape method.

The Influence of Annealing in Zinc Vapor on the Visible and Mid-IR Luminescence of ZnSe:Fe2+

The influence of annealing in zinc vapor on the impurity-defect composition and the IR cathodoluminescence (CL) of ZnSe:Te plates diffusion-doped with iron is studied. Formation of precipitates on twin boundaries is found. It is shown that annealing of structures with surface iron concentrations exceeding 1 at % in zinc vapor leads to a significant increase in the IR CL intensity. It is found that interband luminescence in the regions with high iron concentrations is partially restored as a result of annealing.

Optical an photoelectric properties odf ZnSe:Ti crystals

The photoconductivity and photoluminescence spectra of ZnSe:Ti crystals in the visible and infrared spectral regions are studied. It is established that the high-temperature impurity-induced photoconductivity of ZnSe:Ti crystals is defined by the optical transitions of electrons from the 3 A 2(F) ground state to highenergy excited states, with the subsequent thermal transitions of electrons to the conduction band. The efficient excitation of intracenter luminescence of ZnSe:Ti crystals is achieved by light from the region of the intrinsic absorption of Ti2+ ions.

Study of the impurity photoconductivity and luminescence in ZnSe:Ni crystals in the visible spectral region

The photoconductivity and photoluminescence spectra of ZnSe:Ni crystals in the visible spectral region are studied. It is established that the high-temperature impurity photoconductivity of ZnSe:Ni crystals is controlled by the optical transitions of electrons from the ground state 3T1(F) to high-energy excited states, with subsequent thermally activated transitions of electrons to the conduction band. A photoconductivity band associated with the photoionization of Ni impurities is revealed. The intracenter luminescence of ZnSe:Ni crystals is efficiently excited with light corresponding to the intrinsic absorption region of Ni2+ ions.

Energy efficiency of near infrared cobalt luminscence in ZnSe:Co determined by a photoacoustic method

AbstractThe paper presents results of computations of the energy efficiency of the cobalt luminescence in ZnSe:Co determined by the photoacoustic method. The transmission spectra, photoacoustic experimental and theoretical spectra, and the frequency dependence on the photoacoustic amplitude characteristics are presented. From them, the energy efficiency of Co2+ the near infrared luminescence (3200 nm) was computed in the frame of new proposed photoacoustic model of computations of the luminescence energy efficiency.

Visible nonlinear band-edge luminescence in ZnSe and CdS excited by a mid-infrared free-electron laser

Visible nonlinear band-edge luminescence in ZnSe and CdS bulk crystals was observed upon excitation by a mid-infrared free-electron laser (mid-IR FEL) at approximately 9 mm. The emission intensity is proportional to the 74th and 45th powers of the excitation intensity for ZnSe and CdS, respectively. For ZnSe, the temporal profile of the emission intensity does not follow the profile of the excitation macropulse of the FEL, but sharply rises and decays only at the maximum of the macropulse profile. These features are in marked contrast to those of a previous report, where the emission profile follows that of the macropulse, and the emission intensity scales with the 4th power of the excitation intensity. The experimental observations were reproduced by a numerical simulation based on impact ionization and avalanche ionization by electrons accelerated by the optical electric field of the FEL. The large nonlinearity in the bandedge emission comes from the macropulse temporal structure, which consists of micropulses densely spaced to allow excited carriers to survive when the next micropulse arrives. They work as seed carriers in the next carrier multiplication step.

Effect of Te on the self-activated emission of ZnSe

An interpretation of the optical properties of ZnSe is suggested. The interpretation is based on the anticrossing band theory, which specifies the oxygen-induced splitting of the conduction band. It is shown that the new approach provides a means for understanding the specific features of the self-activated luminescence in ZnSe:O and (ZnSe:O):Te. The effect of small (<1%) Te additives on the luminescence of ZnSe:Te in the edge spectral region is interpreted. The model of electronic transitions is presented.

Identification of near-infrared luminescence in ZnSe

A Cr-related near-infrared photoluminescence (PL) band in ZnSe with a main no-phonon line at is investigated. Zeeman splitting indicates a tetragonally distorted ground state. The experimental data agree well with calculations using a spin Hamiltonian with parameters obtained from the ground state of . This contradicts a former assignment of the PL band to a emission of . Crystal field calculations demonstrate that the observed no-phonon lines and the corresponding luminescence band can reasonably be interpreted in terms of a transition within the configuration of . Furthermore, the influence of unmodulated supplementary irradiation on transmission and PL excitation spectra is discussed.

Nonradiative recombination processes in wide band GAP II-VI phosphor materials

Abstract Transition metal ions limit the light emission from wide band gap II-VI phosphor materials. Nickel, iron and chromium deactivate the visible luminescence of ZnSe due to the bypassing and three center Auger processes. For ZnMnS the donor-acceptor pair (DAP) emission is deactivated by spin dependent energy transfer transitions from DAPs to Mn ions.

Nature of Blue Anti-Stokes Luminescence in ZnSe:Cr

Transition metal (TM) ions are efficient centers of nonradiative recombination in II-VI compounds [1]. In this paper we show that twostep ionization transitions of Cr result in the appearance of the donor-acceptor pair (DAP) photoluminescences (PLs) of ZnSe:Cr. Blue DAP PL of ZnSe is observed under photoexcitation with a photon energy lower than the emission energy. Such light emission is called anti-Stokes luminescence (ASL). Even though ASL was observed previously in several media [2-4] its mechanism is still disputed.

Relaxation process and luminescence of lattice defects in epitaxially grown [formula omitted] layers

In this work, we report on the dependence of strain relaxation in epitaxially grown ZnSe GaAs layers on the growth process. New investigations about luminescence signals are presented, which are caused by lattice defects in these layers. The strain is due to different lattice constants of layer and substrate material and is relaxed by the nucleation of misfit dislocations during growth. This relaxation process depends on layer thickness and growth conditions. We determine the residual strain for different layer thicknesses and growth processes with X-ray diffractometry. Furthermore, the created misfit dislocations give rise to a luminescence at 2.6 eV, the so-called Y line. We found that its behaviour in ZnSe is analogous to that of Y lines in epitaxially grown ZnTe GaAs layers. An excitation of the Y luminescence is only possible with photon energies higher than the recombination energy of free excitons. Its intensity decreases with increasing impurity concentration. It also decreases strongly for a steady state excitation at 2 K. A recovery effect of luminescence intensity is observed, if the sample is heated to room temperature. Furthermore, the strain dependence of the Y luminescence in ZnSe is compared with the maxima of bound exciton luminescence from shallow donors and acceptors.

Temperature dependence of luminescence in ZnSe and role of excitation transfer

Excitation transfer among localized states has often been neglected for semiconductor luminescence. We have recently shown that such transfer is far more prevalent in the low temperature luminescence in ZnSe than had been realized. In this work, we studied the temperature dependence of the luminescence, and observed the phonon-assisted transfer between two bound excitons at relatively high temperature. This observation correlates with the result of a theoretical model consisting of a two-level system. Our results also show that excitation transfer may well be playing a role in the origin of the blue room temperature luminescence in ZnSe.

Luminescence properties of MgxZn1-xSe crystals

The luminescence properties of ZnSe single crystals doped with isoelectronic substituent Mg by a simple diffusion procedure have been studied. It has been shown that Mg easily enters substitutionally on a Zn site forming MgxZn1-xSe mixed crystals with a bandgap energy considerably larger than that of 'pure' ZnSe. The photoluminescence spectrum of such crystals is dominated by blue and violet emission, the efficiency of which is much higher than the efficiency of blue luminescence in ZnSe. Low-voltage blue-violet electroluminescence with maximum emission at 2.98 eV at T=45 K and 2.875 eV at room temperature in MgxZn1-xSe mixed crystals has been demonstrated, which makes this material very promising for future application in constructing blue and violet light emitting diodes.

Decay time of the blue luminescence in ZnSe at room temperature

The decay time of the blue luminescence at room temperature in n-type ZnSe grown by metalorganic chemical vapor deposition has been measured, using a mode-locked laser as excitation source and a streak camera for detection. Over an uncompensated donor concentration range 1017–1018 cm−3 the decay time is of the order of 100 ps. The short time is a result of strong nonradiative recombination: it is argued that the concentration of Hall–Shockley–Read recombination centers is high.

Quenching Centers of Red Luminescence in ZnSe:Te

Quenching Centers of Red Luminescence in ZnSe:Te

Luminescent and nonlinear spectroscopy of recombination centers in isovalent doped ZnSe: Te crystals

The investigations of photoluminescence and of photoinduced absorption have been carried out in ZnSe:Te crystals. The parameters of series of deep centers of intrinsic defects and their associates have been determined, and their connection with luminescence in ZnSe:Te has been revealed. The formation of high stable centers of { V - Zn + Te 0 Se + D +} 0 with the compensation of local deformation and charge is caused by the Te doping. The annealing of ZnSe:Te crystals in halogen vapour leads to the creation of IR-radiative centers of rapid hole capture which quench a red luminescence.

Prospects of fabricating blue/green lasers using ZnSe based metal-insulator-semiconductor (MIS) heterostructures

Lasing has been reported in ZnSe by several investigators using optical and electron beam pumping. This paper discusses the prospects of lasing by injection luminescence in ZnSe based metal-insulator-semiconductor (MIS) heterostructures. Results on fabricated Au-SiO 2(CVD)-nZnSe devices are presented. The problems associated with chemical vapor deposition (CVD) of SiO 2 insulating layers on ZnSe and ohmic contact formation are discussed. Numerical computations on Au-SiO 2-nZnSe-nZnSSe/ZnSe structures involving carrier and photon confinement are reported. Results of modal analysis on MIS laser heterostructures are compared with (potential) p-n double heterojunctions. In addition, various quantum well structures (e.g., ZnSe-ZnSSe, ZnSe-ZnCdSe) are presented to investigate the operation of MIS quantum well lasers.

Excitation transfer in donor-acceptor pair luminescence

In the analysis of spectral and time dependencies of donor-acceptor pair (DAP) spectra, it has usually been assumed that the primary factors are the distribution of pair separations together with the dependence of the decay and of the emitted energies on these separations. We have measured the time decay of the DAP luminescence in ZnSe as a function of excitation wavelength and show that, instead, excitation transfer via localized states cannot be neglected. We also point out that such transfer appears very reasonable, based on transfer versus luminescence decay rates.

On the Tunneling Among Shallow and Deep Centers in ZnS

Radiative tunneling among randomly dstributed donors (D) and acceptors (A) is one of the most efficient processes responsible for the visible luminescence (VL) in many semiconductors (SCs). However, the quantum yield of these transitions may be strongly affected by presence of the other, usually deep, centers. The best known deactivators (killers) of VL in ZnS are transition metal (TM) impurities. In the previous papers [1, 2] two deactivation mechanisms were identified. Recently O,Donnel et al. [3] proposed a new one which can limit the donor—acceptor pair (DAP) luminescence in ZnSe:Fe. During this process an electron tunnels from a donor (D) to iron instead of acceptor (Α) (Fig. 1). In this paper we present the results of photoESR studies of recharging process in ZnS crystals. By selecting the experimental temperature and conditions we could obtain the metastably occupied D, A, Fe and Cr centers with their depopulation monitored via the studies of Fe 3+ and Cr+ ESR signal intensities. At low temperature this depopulation occurs only due to tunneling transitions of e.g. A Cr type. Hence, the decay kinetics of the Fe3+ and Cr+ ESR signals enables us to estimate the tunneling efficiencies among activator and killer centers. The effIciency of the DAP luminescence is usually characterized by two parameters: W0 and α. This comes from the fact that the tunneling rate W(r) between given donor and an acceptor located at a distance r is taken in the form:

Spin-polarisation effects in luminescence

A model of one-electron states is devised to describe within the strong-field limit the chromium states Cr 2+(d 4) and Cr +(d 5) in tetrahedral crystal fields. The proposed advancement is the inclusion of spin-correlation effects, i.e. a differentiation between the energies of spin-up and spin-down electron configurations. The method comprises the known spin-allowed 5E(D)⇆ 5T 2(D) transitions of Cr 2+ and, above all, spin-forbidden transitions. The 4T 1(G)→ 6A 1(S) luminescence of ZnSe:Cr + peaking near v=10 300 cm −1 is interpreted as a t 2↓→e ↑ transition of the d 5 configuration. A weak emission band of ZnSe:Cr peaking near 6100 cm − at cryo-temperatures and its analogues in ZnS and other II–VI materials are now assigned to the t 2↑t 2↓e ↑ 2→t 2↑ 2e ↑ 2 spin-flip process of the Cr 2+ (d 4) configuration whose Jahn-Teller-stabilised ground state had earlier been proved to participate in this luminescence. The described emission bands provide for the first time direct means to derive from an experiment the spin-flip energy within the one-electron limit.