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The electrical properties of SrS:Ce thin-film electrolum inescent (TFEL) devices were studied. Photo-irradiation effects on capacitance-voltage and charge-voltage characteristics of SrS:Ce TFEL devices were measured and compared with those of ZnS:Mn devices. For the SrS:Ce device, the polarization charge due to the positive space charge was estimated to be 0.94 μC/cm 2 . This polarization charge was remarkably reduced by photo-irradiation. For the ZnS:Mn TFEL device, the polarization charge due to the positive space charge was 0.66 μC/cm 2 . However, the reduction of the polarization charge by photo-irradiation was small compared to that of the SrS:Ce device. The unique electrical and optical characteristics observed in the SrS:Ce TFEL devices such as relaxation of phosphor field and leading- and trailing-edge emissions are considered as functions of the large amount of space charge and also due to the electron emission from electron traps and electron recapture by the traps.

Transparent Y 2 O 2 S:Eu 3+ phosphor thin films have been grown by a reactive evaporation method. Y metal vaporized by electron-beam irradiation was allowed to react with SO 2 gas molecules. Eu was simultaneously supplied from a resistively heated crucible containing EuCl 3 powder. By employing a heated W filament and an ac plasma cell to excite (crack) the SO 2 molecules, Y 2 O 2 S:Eu 3+ thin films and thin films containing both Y 2 O 3 and Y 2 O 2 S phases which showed intense red photoluminescence were obtained. These results suggest that the films obtained are crystallized and Eu 3+ ions substitute for Y ions in the Y 2 O 3 and Y 2 O 2 S lattices and hence form luminescent centers.

Significant progress in the performance and commercialization of color thin-film electroluminescent (EL) displays has been achieved. This is due to the remarkable progress made in the performance of existing EL phosphors, development of new phosphor materials, and design of new EL phosphor structures. The physics of materials and luminescent centers of current EL phosphors (ZnS:Mn 2+ , ZnS:RE 3+ , SrS:Ce 3+ , and SrGa 2 S 4 :Ce 3+ ) are reviewed. As potential EL phosphors, metal oxides, yttrium oxides, oxysulfides, fluorides, and mixed-crystal-based phosphors are discussed. Multilayered and superlattice-structured EL phosphors are also discussed. The basic physics of the materials, host lattices, and luminescent centers is important in the development of novel EL phosphors.

The electroluminescent (EL) and cathodoluminescent (CL) characteristics of ITO-ZnS:Cu,Mn(Tb)-Al DC EL thin films were investigated. The experimental results showed that efficient resonant energy transfer takes place from self-activated ZnS and Cu centers to Mn ions resulting in high luminance of ZnS:Mn,Cu cells. EL properties of ZnS:Cu,Tb cells can be explained on the basis of the direct impact excitation model, while the energy transfer mechanism makes a negligible contribution to the excitation process. This accounts for the comparatively low EL luminance of Tb-doped cells.

The quenching mechanism of blue Tm3+ luminescence in Y2O2S phosphors due to residual Pr3+ ions has been studied. Results of photoluminescence and excitation spectra measurements and selective excitation measurements of Y2O2S:Tm3+, Pr3+ phosphors show that there is no energy transfer between Tm3+ and Pr3+ centers. The quenching of the blue Tm3+ emission by Pr3+ ions can be ascribed to the large electron-hole capture cross section of Pr3+ centers.

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 direction. Tb doped Y2O2S thin films show an efficient green photoluminescence. The growth process of Y2O2S:Tb thin films is also discussed.

An (Y2O2S:Tb/ZnS) n multilayered thin-film electroluminescence (TFEL) device has been fabricated by the multisource deposition method. The multilayered TFEL device has shown a maximum luminance of 124 cd/m2 at 5 kHz. It is also seen that the EL characteristics strongly depend on the structure of phosphor layers, and the TFEL device with the Y2O2S:Tb single layer showed nominal EL emission. The excitation mechanism of the (Y2O2S:Tb/ZnS) n multilayered TFEL devices is discussed.

The spectral response of the photo-induced transferred charge in Eu2+- or Ce3+-doped CaS and SrS thin-film electroluminescent (EL) devices has been studied. It is found that excitation spectra of the photo-induced transferred charge agree with those of photoluminescence. This result implies that the Eu2+ or Ce3+ luminescent centers are ionized by electric field when the centers are excited to the (4f) n-1(5d) excited state. The dynamics of the EL emission are controlled by field-dependent ionization of the luminescent centers and by field-dependent trapping at the ionized centers, rather than by impact excitation of the luminescent centers.

The picosecond time dependence of the optical gain due to high density electron-hole plasma (EHP) in GaAs is studied by means of time-resolved luminescence spectroscopy. The carrier temperature T e and the concentration N e-h of the EHP are determined from the spectral shape analysis of the optical gain. Our result shows that in 160 ps, T e decreases from 60 to 34 K, and N e-h decreases from 1.5×10 17 to 0.7×10 17 cm -3 . The decrease in T e results from the energy loss process of hot carriers due to the polar LO-phonon scattering, and the decrease of N e-h is mainly dominated by the bimolecular recombination process. Time variation of the optical gain spectra and time response of its maximum value are clearly ascribed to the time change of T e and N e-h in the EHP.

The dependences of brightness, emission efficiency η, average electric field EA, conduction current JA, and emission lifetime τ upon the device parameters such as film thickness, substrate temperature during evaporation, and Mn concentration have been systematically investigated in ZnS:Mn thin‐film electroluminescent devices. The value of η increases rapidly with film thicknesses below 3000 A but EA decreases slowly. These results can be explained by the increase of the crystallinity of the ZnS:Mn films. The value of η increases with the Mn concentration and reaches its maximum at about 0.45 wt %. At above this Mn concentration, η and τ decrease rapidly, EA increases, and JA decreases slowly. These results may be attributed to a decrease of hot electron energy and/or an increase of the nonradiative transition probability of the excited Mn centers. The brightness‐voltage (B‐V) hysteresis characteristic is observed in this Mn concentration region. This memory effect is also discussed.

Electroluminescence has been observed in rare earth-doped Y2O3 powder layers with various emission colors spanning a spectrum from red in case of Eu3+ to blue in case of Tm3+. The brightness of about 1 fL and efficiency of about 2×10-4 were obtained for Y2O3 : Tb3+ with dc excitation under the electric field of 3−5×104 V/cm. Samples were also responsive to ac excitation. To investigate the emission mechanism, the transient behaviour of the emission has been measured.

Electroluminescence(EL) and photoluminescence(PL) experiments have been carried out on the ZnS: Nd, ZnS: Cu, Cl and ZnS: Cu, Cl, Nd films. The EL emission spectra show two peaks due to Cu-Cl and Nd centers, while the PL emission spectra show only one peak due to Cu-Cl centers. By comparing the efficiencies and the emission spectra of the EL with the PL measurements, it has been clearly shown that the excitation mechanism of the Nd ions in the electroluminescent ZnS: Nd film is via direct impact excitation by hot electrons.

The growth behavior of evaporated CaS thin films has been investigated to achieve bright electroluminescence. The crystallinity of CaS films is improved with substrate temperature and for temperatures higher than 300°C, the films orient to the (200) plane. Sulfur coevaporation further helps to form a more perfect film even at lower temperatures. A CaS: Ce,Cl electroluminescent thin film device has been fabricated with a brightness of 650 cd/m2.

Electroluminescent mechanisms of ZnS:Mn and ZnS:TbF 3 devices have been investigated systematically by measuring the concentration dependences of the brightness, the emission efficiency, the emission lifetime, the electric field and the conduction current. From these dependences, the mechanisms, which optimize Mn and Tb concentrations, are proposed to obtain the highest brightness. The properties of the Tb emission centers and memory mechanism of ZnS:Mn are also discussed.

A theoretical approach to the growth mechanism of evaporated thin films of ZnS, CaS and SrS electroluminescent materials has been developed. The effect of surface energy on the thin-film orientation of the II–VI compounds of ZnS, CaS and SrS has been investigated. The dependence of the thin-film orientation of CaS (SrS) on the substrate temperature can be well explained by re-evaporation and atomic vibration of adsorbed atoms taken into account. We conclude that the growth rate of CaS (SrS) thin films seems to be related to the number of dangling bonds per atom rather than the number of bonds, which are in binding states.

We have investigated the operational parameters of a passively mode-locked Rh-6G dye laser, having a cavity with five mirrors and two jet streams, in order to generate stable subpicosecond pulses. The optimum concentration of saturable absorber (DODCI) was found to be 6.0×10-6M. The ratio of pumping power Pp to the threshold power Pth (Pp/Pth) falls in a range of 1.08±0.01, in order to obtain good mode-locking. The optimum value Pp/Pth is independent of the DODCI concentrations. Under this optimum condition, the narrowest pulses of 0.69ps were generated at 614nm. The time-bandwidth product of the pulse was calculated to be 0.78 indicating that the pulse was close to being transform-limited. The lasing-wavelength was tunable in the range of 604-613nm by using a Lyot filter. A nearly transform-limited pulse of 1.54ps with the time-bandwidth product of 0.40was obtained at 605.5nm.

A microcomputer-controlled multichannel analyzer system using a television camera equipped with a high sensitivity image-orthicon has been developed to perform spectral measurements of rather weak picosecond light pulses emitted or scattered by materials with sufficient sensitivity and accuracy. The features of the system are, 1) the mode-locked laser, the television camera and the microcomputer-controlled multichannel analyzer are operated synchronously, 2) the background noise of the television camera is eliminated by the subtraction process, 3) the improvement of the signal-to-noise ratio is achieved by the accumulation process of the spectral data obtained by repetitive laser operation, and 4) by monitoring laser output power, only suitable data are selected. To demonstrate the performance of the system developed, results of measurements for picosecond time-resolved luminescence spectra of CdSe are presented.

多色発光を示すCaS, SrS薄膜エレクトロルミネッセンス (EL) 素子の作製と評価を行った.まず, 電子線蒸着法を用いて作製したCaS, SrS薄膜の特性をX線回折, 走査電子顕微鏡, X線光電子分光法により調べた.良質の薄膜を作製するためには, 蒸着時の基板温度を400～550℃程度の高温にする必要があり, 蒸着時にイオウを共蒸着することによっても膜質を改善できることが明らかになった.希土類発光中心を添加することにより, CaS : Euで赤色EL, CaS : Ceで緑色EL, SrS : Ceで青緑色ELを得た.これらのEL素子の輝度は, 駆動周波数5kHzの際に, それぞれ430,650, 1100cd/m2である.従来のZnSを母体とする多色発光EL素子と比較すると, CaS : Eu赤色ELでは, より色純度の良い発光を得ることができた.また, SrS : Ce青緑色ELでは100倍以上の輝度の向上を達成することができた.

Variations of the brightness and efficiency of Ta-Ta2O5-ZnS: Ln3+-Au (M-I-S-M structure) thin film devices with the applied voltage across the ZnS layer doped with rare-earth ions have been investigated precisely. From the analysis of the experimental data, the operating regions of the devices can be classified into the follwing three separate regions: (1) the low voltage region where no light emission is observed, (2) the intermediate voltage region where the light emission occurs and the brightness B is given by the form B∝exp (-V0/Vp) and (3) the high voltage region where the electric field is clamped at a certain constant value and the brightness is expressed as B∝(Vp-Vb). The field clamping is attributed to the avalanche of the ZnS lattice electrons.

Spontaneous luminescence and optical gain of high density electron-hole phasma (EHP) in GaAs are observed at 4.2 K under nanosecond pulse excitation. Time-resolved luminescence spectra are observed under picosecond pulse excitation. The chemical potential and reduced band-gap energy of the EHP are obtained from the spectral shape analysis. These values and also their time changes are explained qualitatively by the calculation of the EHP ground-state energy. After picosecond pulse excitation, hot carriers cool down rapidly to 50 K within the first 150 ps, but the thermal equilibrium with the lattice is not attained up to 400 ps. The observed gaseous EHP is considered to exist only in a transient state and the electron-hole liquid state is not realized.

In order to investigate the energy transfer process and the mechanism of the sensitization effect of copper and sodium tons on Er luminescence in ZnS: Cu, Er, Na phosphors, emission spectra, time-resolved emission spectra, transient behavior and dependence of intensities of green copper (G-Cu) and Er luminescence have been measured, It is confirmed that the excitation of Er ions is caused by the nonradiative energy transfer from the G-Cu centers to the Er centers. The experimental results show that (i) the copper-ions, which form the G-Cu centers, act as the sensitizor of Er luminescence, (ii) but the sodium ions do not act as the sensitizor, but act as the charge compensators for the trivalent erbium ions.

A systematic investigation of the electroluminescent (EL) ZnS thin film devices doped with rare earth centers, SmF3 (red), TbF3 (green), and TmF3 (blue), is made to examine the possibility of multicoloring. Various characteristics, such as brightness, emission efficiency, decay time, EL spectra, and their concentration dependences are measured. The number of photons emitted from these devices is also estimated to discuss quantum efficiencies. For SmF3 and TmF3 activators, it is found that concentration quenching of EL emission takes place through non-radiative crossrelaxation process. No such quenching is observed for TbF3 activators. In TmF3 activators, most of the radiative energy is found to be emitted in the infrared region. The impact excitation cross-section for these rare earth compounds is also inferred to be lower compared with that of Mn2+ ions.

Electroluminescent (EL) characteristics in alkaline-earth sulfides thin-film EL devices doped with rare-earth activators for red (CaS:Eu 2+ ), green (CaS:Ce 3+ and blue (SrS:Ce 3+ ) are presented. The dominant excitation mechanism is that the Ce 3+ and Eu 2+ luminescence centers are first ionized due to impact ionization and/or hole trapping changing into Ce 4+ and Eu 3+ ions, subsequently the centers capture electrons and are converted into the Ce 3+ or the Eu 2+ excited state, and finally the centers give rise to luminescence.

The role of interfacial states in the electroluminescence process for Ta-Ta2O5-ZnS: Tb3+-Au and Ta-Ta2O5-ZnS: Tb3+-SiO2-Au structures has been studied. A similar electroluminescence has been observed for both types of cells. This indicates that electron injection via tunneling from the Au contact is not necessarily required to produce electroluminescence. The relaxation times of electrons related to the injection process from interfacial states are measured to be 10–100 ms. These values are the same for three interfacial states of interest (ZnS-Au, ZnS-SiO2 and ZnS-Ta2O5). Their temperature and electric field dependences are also presented. It can be concluded that field emission from the interfacial states is essential to the electron injection process for these types of cells.

A bright white‐light electroluminescence (EL) is obtained in a SrS:Pr,K thin‐film EL device. The device shows a luminance level of 500 cd/m2 with 1 kHz drive (1500 cd/m2 at 5 kHz), which is five times as high as that obtained for a ZnS:Pr,F thin‐film EL device. The dominant EL excitation mechanism in the SrS:Pr,K device responsible for a higher EL efficiency is ascribed to a process wherein the ionization of the luminescent center occurs first. Subsequent recombination with an electron follows in which the Pr3+ center reaches a (4 f )2 excited state through a (4 f )(5d) excited state. Finally, luminescence due to the relaxation of the (4 f )2 electron configuration of the Pr3+ ion arises.

The photoquenching effect of electroluminescence (EL) has been observed for the first time in thin‐film ZnS:TbF3 EL devices. The luminescent intensity and the conductive charge are quenched, when the device is exposed to a visible light of energy between 1.75–2.75 eV. The maximum photoquenching rate of 45% is observed at a voltage slightly higher than the EL threshold voltage. The recovering time from the photoquenching is of the order of several seconds. This photoquenching effect is likely to be due to deep hole traps.

Mn2+ ions and rare-earth ions (Ln3+) such as Tb3 + ions are most commonly used as luminescent centers in ZnS thin film electroluminescence (EL) devices.1) Luminescence of Mn2+ and that of Ln3 + ions are due to parity-forbidden (d-d) and (f-f) transitions, respectively. We report here, a greenish-white EL due to parity-allowed 5d-4f transition of Ce3+ ions in a double insulated ZnS:CeF3 thin film device, for the first time.

Recently, thin-film electroluminescent (EL) devices with rare-earth activated CaS and SrS phosphors have been investigated extensively to realize multi- and full-color thin film EL displays. Very recently, we have developed two types of bright white-light emitting thin film EL devices with new phosphors, SrS:Pr,K and SrS:Ce,K,Eu [1–3], White-light EL devices have the following important characteristics; White-light EL displays with a reverse mode are superior from an ergonomics point of view, because characters and/or figures are drawn in black on a white screen in this mode, just as in printed matter. In addition, full-color displays can be realized by combining a white thin-film EL with color filters.

Novel BaFBr:Eu2+ phosphor films were fabricated, for the first time, by an electron beam evaporation method by using mixtures of BaF2 and BaBr2 powder and EuBr3 ( or EuF3) salt. They show efficient photostimulated luminescence (PSL). To obtain highly efficient PSL, Tsub should be increased above 400°C, and a mole fraction x of (BaF2)x(BaBr2)1-x source should be chosen in a range from 0.3 to 0.7.

A real‐time subpicosecond‐pulse monitor with a simple new circuit is described. The autocorrelator consists of an usual audio speaker and the electronic circuit, which can detect the displacement of the interferometer.

We report a double insulated CaS:Ce thin‐film electroluminescent (EL) device which emits a bright green EL due to Ce3+ luminescent centers, being characteristic of parity allowed 5d–4f transitions. A brightness level of 500 cd/m2 and emission efficiency of 0.11 lm/W have been obtained under 5‐kHz sinusoidal voltage excitation. The CaS:Ce thin film has been fabricated by coevaporation of CaS and sulfur.

Luminescence of GaAs under excitation by two femtosecond pulses with equal intensity separated by a time delay Δ T demonstrates a peak at Δ T =0, which has a correlation width no more than the autocorrelation width of the escitation pulses. This peak is caused by the bimolecular recombination of electrons and holes and by the absorption saturation effect due to state filling.

The luminance‐applied voltage hysteresis characteristic, so‐called memory effect, has been found in the SrS:Ce,K blue‐emitting electroluminescent thin‐film device. The hysteresis voltage width is about 38 V with 1 kHz pulse drive. The origin of the memory effect is attributable to native defects of the SrS phosphors.

The electroluminescence (EL) and photoluminescence (PL) characteristics of SrS:Eu, F thin-films have been studied. It is found that valence of the Eu luminescent centers is affected by the presence of F- ions. At lower Eu concentration less than 0.3 mol%, Eu2+ centers exist, but at higher concentration over 0.6 mol%, both Eu2+ and Eu3+ centers coexist in the films. The Eu2+ centers are efficient for both EL and PL. The excitation process of Eu2+ centers is attributable to the energy transfer from the SrS lattice to Eu2+ centers. On the contrary, Eu3+ centers are efficient for EL only through the direct impact excitation by hot electrons.

Tunable near-infrared picosecond pulses with ∼25 ps duration and ∼10 MW peak power are produced by a mode-locked dye laser synchronously pumped by second harmonic train from a passively mode-locked Nd:YAG laser. The lasing wavelength can be tuned from 720 to 830 nm using several polymethine dyes. It is found that the most important characteristic for picosecond lasing dye is a fast rise of an amplified spontaneous emission rather than higher fluorescence efficiency.

Picosecond temporal character of high-density electron-hole plasma (EHP) in GaAs/AlAs multiple quantum well structure has been studied by means of time-resolved luminescence spectroscopy. The EHP with carrier density N QW of 3–4×1017 cm-3 is formed, where carrier induced band-gap shrinkage of 10–20 meV takes place. Temporal character of luminescence due to the EHP is well explained by time variation of N QW. Increase of N QW results from carrier trapping with trapping time of ∼60 ps, and subsequent decrease of N QW results from radiative recombination with bimolecular recombination coefficient of 4.5×10-8 cm3s-1.

White light emitting thin-film electroluminescent devices have been fabricated. The devices consist of double phosphor layers of a greenish-blue light emitting SrS:Ce, Cl and a yellowish-orange light emitting ZnS:Mn. A brightness level of 1100 cd/m2 at 5 KHz drive has been obtained.