ZnS:Sm and ZnS:Cu,Sm electroluminescent phosphors

Electroluminescent ZnS: Sm and ZnS: Cu, Sm phosphors have been prepared and their electroluminescent (el) characteristics have been studied. The time-averagedel brightness follows the Alfrey-Taylor relation over a wide range of frequencies. The constants of this relation have been determined. Theel emission shows one main and one auxiliary peak during each half cycle of the applied voltage. Variation of current with applied voltage has also been investigated.     

Characterization of ZnS:Cu, Br electroluminescent phosphor prepared by new route

Synthesis of electroluminescent ZnS:Cu, Br phosphor by a number of routes has been presented along with their brightness-voltage, brightness-frequency, brightness-waveform and spectral energy distribution studies. The sample fired in N₂ atmosphere with aluminum and bromine shows predominantly green emission with a peak around 530 nm whereas the sample prepared under H₂S and HBr shows the broadest emission spectrum with multiple peaks. These peaks may arise out of different possible bands of copper, self-activated luminescence of ZnS and association of copper with some of the donor levels formed because of the higher reactivity of HBr. All the samples have been found to obey the relation B=B₀ exp.(−b/V^0.5) which has been discussed using bipolar tunnel emission model. The frequency variation of brightness is linear. Samples containing bromine show multiple secondary peaks indicating that bromine helps in formation of multiple shallow traps.     

Effect of magnesium on the performance characteristics of ZnS:Cu,Mn phosphors

We have studied the effect of magnesium added to the starting mixture as MgS or MgCl₂ on the performance characteristics of synthesized ZnS:Cu,Mn phosphor powders. It has been shown that the incorporation of certain amounts of magnesium into the ZnS:Cu,Mn phosphor leads to an increase in photo- and electroluminescence brightness and is favorable for Mn incorporation into the structure of the phosphor. In particular, additional doping of a dc electroluminescent ZnS:Cu,Mn phosphor with 30 mol % Mg ensured not only a shift of its luminescence spectrum to shorter wavelengths, thereby extending the color range of light sources, but also a twofold increase in its brightness.     

Switch-off relaxation of the parameters of ZnS:Mn thin-film electroluminescent emitters

We have experimentally studied the decay of a current transferred via a phosphor layer in ZnS:Mn thin-film electroluminescent emitters. It is established that this decay is controlled by a bimolecular process of electron trapping on the surface states at the anode phosphor-insulator interface. The rate of the surface trapping, the trapping cross section, and the electron lifetime at the onset of current decay are determined. Dependences of these parameters on the polarity, amplitude, and frequency of the triangular voltage pulses have been studied.     

Mn,Cu掺杂对ZnS∶Mn,Cu电致发光材料亮度的影响

采用水热法制备了ZnS∶Mn,Cu电致发光材料,利用透射电镜对发光材料的结构和形貌进行表征,并且探讨了Cu2+、Mn2+掺杂量和反应温度对ZnS∶Mn,Cu发光材料亮度的影响。结果显示,随着Cu2+、Mn2+掺杂量的增加,发光材料的亮度也随之增加,但对于Cu2+、Mn2+掺杂都存在最佳值,当Cu2+掺杂量0.2%,Mn2+掺杂量4%,温度150℃时,得到的电致发光材料亮度较高,粒径约10nm左右。     

ZnS:Cu polymer nanocomposites for thin film electroluminescent devices

Copper-doped zinc sulphide nanoparticles with varying copper content were synthesized via a coprecepitation method and embedded in polymer thin films by phase transfer technique to examine direct current electroluminescence (DC-EL) properties. A single layer structure (ITO/ZnS:Cu@ polymer/Al) was chosen to examine the influence of film thickness, copper content and polymeric matrix. Two types of devices were investigated based either on an insulating polymethylmethacrylate (PMMA) matrix or a semiconducting poly(9-vinylcarbazole) (PVK) matrix. The resulting DC-EL differs in spectral characteristics showing a broad EL emission over the whole visible range for PMMA based devices and EL with narrow full width at half-maxima values (FWHM) and maxima positions close to those observed in photoluminescence (PL) spectra of particle dispersions.     

Preparation and properties of thin ZnS:Cu films phosphors

Thin films of ZnS and ZnS:Cu were prepared by an original metalorganic chemical vapour deposition (MOCVD) method under atmospheric pressure onto a glass substrate heated up to 230–250 °C. The film thickness varied from 0.6 to 1 μm. The thin films were doped with Cu and Cl by the thermal treatment during 1 h at 600 °C at atmospheric pressure in the blend composed of a ZnS powder with Cu and Cl compounds. These films were used for fabrication of the thin film electroluminescent (TFEL) devices with a conventional double insulating structure. The structural properties were investigated by use of X-ray diffraction (XRD) techniques and atomic force microscopy (AFM). Electroluminescent (EL) spectra, electrical and EL characteristics were investigated. The EL spectra and characteristics as well as structural parameters depend on the growth conditions and significantly modified after the annealing. Blue color emission with brightness of 10 cd m^− 2 under a sine wave excitation at 60 V and 5 kHz was obtained. The degradation behavior of the TFEL devices with ZnS:[Cu, Cl] films fabricated using an original non-vacuum methods of deposition and annealing is the same as that of commercial thin film phosphor.     

Effect of shock wave treatment on luminescence of ZnS:Cu,Cl phosphors

It is shown that shock wave treatment of ZnS:Cu phosphor between synthesis and annealing steps by placing phosphor powder into preservation ampoule and subjecting to the effect of explosion has positive effect on photo- and electroluminescence brightness due to increase of activator (copper) solubility in phosphor matrix and formation of additional Cl_S–Cu_Zn and Cl_S–V_Zn luminescent centers.     

Characteristics of surface states at the insulator-semiconductor interface of ZnS:Mn thin-film electroluminescent emitters

The energy distribution of the density of occupied surface states (N _ss) at the cathode insulatorphosphor interface in ZnS:Mn electroluminescent thin-film (ELTF) emitters has been modeled on the basis of experimental data. Changes in this distribution depending on the parameters of exciting voltage pulses have been studied. It is established that the energy distribution of N _ss shifts toward deeper levels upon a decrease in the frequency of the exciting signal and the resulting increase in the pause between the adjacent switch-on states. This behavior corresponds to a cascade relaxation mechanism of electrons trapped on the surface states. Maximum values of the N _ss (∼2.5 × 10¹³ cm⁻²) and the specific density of surface states per unit energy (2 × 10¹⁴–10¹⁵ cm⁻² eV⁻¹) are determined for the cathode insulator-phosphor interface from which electrons are tunneling. Positions of the equilibrium (∼1.25 eV below the conduction-band bottom) and the quasi-equilibrium (0.6–1.25 eV) Fermi levels during the ELTF emitter operation are estimated.     

Luminescence characteristics of ZnS:Cu thin film electroluminescent devices fabricated by sputtering

A ZnS:Cu electroluminescent (EL) device was fabricated by sputtering and its luminescence properties were examined. The structure of the fabricated device was glass/Si_xN_y/ZnS phosphor/Si_xN_y/Al. The luminescence spectrum of the device showed two peaks, one blue and the other yellow. The blue peak is created by excitation and recombination of Cu atoms, and can be used for creating blue EL devices.     

Surface electrical conductivity in ZnS(Cu,Cl, Mn) thin films

The surface electrical conduction in an In₂O₃(Sn)/ZnS(Cu, Cl, Mn)/Al thin film system was investigated by measuring the dependence of the current through the ZnS(Cu, Cl, Mn) film on the application of a sinusoidal voltage to two electrodes on the surface of the film. The measurements were carried out in an arrangement with an additional d.c. voltage applied between one of the upper electrodes and the lower electrode. The results obtained are discussed on the basis of a proposed theoretical model.     

Effect of activator distribution on photo- and X-ray excited luminescence properties of ZnS:Cu,Cl phosphors

ZnS:Cu,Cl phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux. The copper activator was introduced into the phosphor precursors by three different methods: co-precipitated with ZnS (CP), wet-coated onto ZnS powders (WC), and simply mixed with ZnS in a mortar (SM). The samples were characterized by X-ray powder diffraction, photoluminescence spectra and X-ray excited luminescence spectra. The results show that both photo- and X-ray excited luminescence intensities of the as-prepared ZnS:Cu,Cl phosphors are in the decreasing order of CP > WC > SM. The different copper activator distribution in the phosphors resulting from the different methods was the main reason responsible for the different luminescence intensity, and uniform distribution is beneficial to the luminescence of the phosphors.     

介孔ZnS:Mn2+的制备及其电致发光性能的研究

采用共沉淀法,以P123表面活性剂为模板剂,以无水乙醇为溶剂,分别制备了介孔ZnS前躯体和ZnS:Mn2+电致发光材料.选择合适的退火温度,对退火后的样品进行了电致发光性能的研究.结果表明,介孔前躯体具有较高的比表面积、较窄的孔径分布和较高的孔隙率;煅烧后的ZnS:Mn2+较纯ZnS的电致发光性能有了显著的改善.     

Photoelectroluminescence of ZnS:Mn crystals

Data on the room-temperature photoelectroluminescence of Mn-activated zinc sulfide crystals are presented. The differential luminescence spectrum demonstrates that the combined excitation leads to a strong buildup of the Mn-related emission.     

Comparative study of the crystal phase,crystallite size and microstrain in electroluminescent ZnS:Mn films grown by atomic layer epitaxy and electron beam evaporation

The crystallite size, the microstrain and their dependence on the thickness of the active layer in electroluminescent ZnS:Mn thin films were studied by X-ray diffraction line profile analysis. The average crystallite size in the films grown by atomic layer epitaxy (ALE) is about 100 nm, which is larger than that for films deposited by electron beam evaporation (EBE) by a factor of 5–10. In addition, the relative microstrain in the films prepared by EBE was about six times that in the films grown by ALE. The comparison is made using the average crystallite size values for both types of sample. Also the crystal phase and dislocation density were clearly different in the two types of the thin film. It is suggested that the large crystallite size and therefore the low density of crystallite boundaries are very probably causes of the observed increase in electroluminescent efficiency.     

Electron tunneling in ZnS:Mn thin-film emitters

Experimental kinetics of the current and charge transferred via a phosphor layer in ZnS:Mn electroluminescent thin-film emitters have been numerically simulated using a model time dependence of the current of electrons tunneling from the surface states at the insulator-semiconductor interface. It is found that, as the field strength increases, the depth of the surface states changes from ∼0.6 to 1.3 eV, the electron tunneling probability increases from 10–15 to 300–400 s⁻¹, and the potential barrier width decreases from 9 to 5.7 nm.     

Luminescent properties of ZnS:Mn2+/ZnS core/shell nanocrystals

High-quality ZnS:Mn2+/ZnS core/shell nanocrystals (NCs) with a core crystal diameter of 6.1 nm and 1.15 nm thick shells were synthesized via a high-boiling solvent process. The energy levels of the conduction band and valance band are estimated to be -3.2 eV and -6.8 eV by cyclic voltammetry and ultraviolet-visible (UV-vis) absorption spectra. The ZnS:Mn2+/ZnS NC emission peak is primarily located at 580 nm under 310 nm light excitation, originating from the charge transition from 4T1 to 6A1 within the 3d5 configuration of the Mn2+ ion. Based on ZnS:Mn2+/ZnS NCs as the active layer electroluminescent devices, the emission peak mainly locates at 460 nm with one shoulder emission peaking at 580 nm. The photoluminescence and electroluminescence properties of ZnS:Mn2+/ZnS NCs are investigated in the view of charge carrier injection and energy level alignment.