Multi-source Deposition Method Research Articles

ChemInform Abstract: Characteristics of SrS:CeCl3 TFEL Device Prepared by Multisource Deposition Method with H2S and Sr Metal.

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Luminescent properties of SrGa 2S 4:Eu thin film phosphors deposited by two electron beam evaporation

SrGa 2S 4:Eu thin film phosphors have been deposited on quartz glass substrates at substrate temperatures of 350–450 °C by multi-source deposition method in which two electron beam (2EB) evaporation sources were used. The films were annealed between 750 and 850 °C for 30 min in H 2S atmosphere after the deposition. It was shown by XRD measurement that SrGa 2S 4 phase was not formed but crystalline GaS was included in an as-deposited film, therefore, PL and CL due to SrGa 2S 4:Eu were not observed. The SrGa 2S 4 phase was formed by the annealing. Photoluminescence (PL) and cathodoluminescence (CL) spectra of all annealed films showed green emission peaked at about 530 nm. CL luminance of all the films increased as the substrate temperature was increased. But the dependence on annealing temperature was not observed. So CL luminance depended only on substrate temperature during deposition. However, the CL luminance did not depend clearly on the annealing temperature between 750 and 850 °C. The SrGa 2S 4:Eu film deposited at 450 °C and annealed at 850 °C for 30 min showed a CL luminance and CIE coordinates of 1700 cd/m 2 and (0.27, 0.67), respectively under excitation with 3 kV and 60 μA/cm 2.

An X-Ray Photoelectron Spectroscopy Study of Elements' Chemical States in SrGa2S4:Ce Blue Electroluminescent Thin Films

SrGa2S4:Ce blue electroluminescent thin films with a (440) single orientation have been prepared by a multisource deposition method using a molecular beam epitaxy (MBE) apparatus. The elements' chemical states and the doped oxygen effects on them have been analyzed by X-ray photoelectron spectroscopy (XPS). A small variation in the elements' chemical state with depth indicates that the growth of the thin film is stable. Sr ions exhibit no chemical shift due to a Sr–O bond, but Ga ions exhibit a chemical shift due to a Ga–S bond and a larger shift due to a Ga–O bond, indicating that the oxygen ion does not substitute for a S site in which the S ion bonds with the Sr ion. No Ce4+ ions have been detected and no oxidation of Ce3+ ions occurs even if some of the S ligands of Ce3+ are replaced by doped oxygen ions. The trivalent state of Ce is stable in the SrGa2S4 crystal.

Investigations of the influence of halides on the properties of CeX3-doped (X = Cl, F) strontium sulphide thin film electroluminescence devices

Cerium activated strontium sulphide (SrS: Ce) phosphor layers for thin film electroluminescence (TFEL) devices have been prepared using a multi-source deposition method. CeCl3 has been used as dopant starting material for reference SrS: Ce,Cl samples. Additionally, CeF3 has been employed in several cerium concentration series to study the influence of the halides. The concentrations of cerium and of the halide in all layers have been determined by X-ray photoelectron spectroscopy (XPS). Cathodoluminescence (CL) and electroluminescence (EL) emission spectra of luminance-optimized phosphor films have been measured. Additionally, the effect of the halide containing codopants LiCl and LiF on the emission characteristics has been studied.The maximum EL luminances have been found at cerium concentrations of 0.26–0.28 at%. The cerium to halide ratio has been determined to 1:1 for all doping and codoping experiments. CL spectra of the corresponding active layers yield the C.I.E.1931 colors yellowish green in standard SrS: Ce,Cl and bluish green in SrS: Ce,F phosphors. Moreover, codoping with LiCl resulted in no mentionable spectral change, whereas the emission of SrS: Ce,Cl: LiF shifted to green. The measured blue shifts have been attributed to the Nephelauxetic Effect.

Effect of multilayered SrSSrS: CeSrS phosphor prepared by multi-source deposition method on the thin film electroluminescent devices

Single-layer SrS: Ce and multilayer SrSSrS: CeSrS thin films have been grown by multi-source deposition method. The X-ray diffraction patterns of the films showed the typical diffraction patterns of the cubic SrS powder. Single-layer SrS: Ce thin films exhibited sulfur deficiency and their fluorescence spectra showed a broad red emission peak. The multilayer SrSSrS: CeSrS electroluminescent device showed nearly stoichiometric composition and an electroluminescent device made of these layers displayed a green-emission intensified spectrum with peaks located at 493 and 523 nm. A distinct S-shaped pinching effect in the transferred charge versus applied voltage characteristics, similar to a hysteretic electroluminescent device, was observed in multilayer device. We interpret that the separation of the light-emitting SrS: Ce layer from the two interfacial SrS layers and the resulting nonuniform space charge in the middle SrS: Ce layer are responsible for the observed enhancement of luminance through the intensified hysteretic effect in the multilayer structure.

The role of ZnS in ZnS/SrS:Ce,Cl multilayered TFEL devices

AbstractDifferent ZnS/SrS:Ce,Cl multilayered electroluminescent devices have been prepared by a multisource deposition method. The highest luminance achieved in this investigation is 1540 cd m−2 at 1 kHz using a stack of nine alternating layers of ZnS and SrS:Ce,Cl; the highest luminance in the blue exceeds 14 cd m−2 at 60 Hz, 50 μs pulse excitation. The influence of the ZnS thickness on device performance and stability has been investigated. The electrical and optical behaviour of standard and multilayered devices in time‐resolved measurements is compared.

Y2O2S:Tb Phosphor Thin Films Grown by Multisource Deposition and Their Luminescent Properties

Y2O2S:Tb phosphor thin films have been grown by using a multi-source deposition (MSD) method. Y2O2S thin films grown by MSD method are highly crystallized with hexagonal structure and strongly oriented to <0001> direction. Tb doped Y2O2S thin films show an efficient green photoluminescence. The growth process of Y2O2S:Tb thin films is also discussed.

Characteristics of SrS : CeCl3 TFEL Device Prepared by Multisource Deposition Method with H 2 S and Sr Metal

A new preparation method is proposed for the phosphor layer for the use in blue‐emitting electroluminescent devices by advanced multi‐source deposition method using Sr metal, , and . This technique eliminates the problems due to sulfur coevaporation, i.e., serious damages to pumping system, difficulty of pressure control during deposition, and disconnection of leading wires. The stoichiometry of the film was determined using Rutherford backscattering spectroscopy (RBS). The volume density of the film which was calculated by RBS and optical ellipsometer measurements was confirmed to have a value close to that of bulk. pressure during the deposition affected the crystallinity of the film and the characteristics of luminance‐voltage (L‐V) curves of the device.

The Characteristics of a SrS:CeCl3 Thin-Film Electroluminescent Device Prepared by Multi-Source Deposition Method

A blue-emitting SrS:Ce EL device was developed by multi-source deposition method with strontium metal, sulfur and cerium chloride. The formation of SrSO4 in deposited films was confirmed by X-ray diffraction and a quadrupole mass spectrometer (QMS) analysis. The luminance-voltage (L-V) curve became steeper with increasing Ce concentration. In the light output waveform the first peak and the third peak at high Ce concentration were weaker than those at low Ce concentration. The light output when the aluminum electrode was biased positively was weaker than that when it was biased negatively. These optical characteristics are discussed on the basis of the proposed model.