Surface characterization of MgO:Al,N films with meta‐stable de‐excitation spectroscopy and x‐ray photoelectron spectroscopy

Abstract— It is shown that meta‐stable de‐excitation spectroscopy (MDS) is one of the most useful characterization methods to analyze the interaction between the discharge gas and the surface of the material and is applied to MgO:Al,N films. From the results of the measurement and analysis of helium MDS and the in‐situ discharge experiment, it is confirmed that the limited composition films of MgO:Al,N have potentially a larger secondary‐electron‐emission coefficient (γ) compared with that of MgO. The improvement in γ is caused by the electron‐occupied tailing state at around the top of the valence band which is generated by the introduction of Al,N to MgO films. Also, the O1s spectra measured by x‐ray photoelectron spectroscopy (XPS) shows that the stable surfaces are formed with the introduction of Al,N to MgO films.     

Measurement of exo‐electron emission from MgO thin film of ACPDPs

Abstract— Exo‐electron emission from MgO thin film was measured by attaching a high‐precision current sensor to the address electrode of the rear plate of an ACPDP test panel. The measured results revealed that the exo‐electron emission currents can vary very sensitively with the type of doping elements used in MgO film and the measuring temperature. The activation energy of the exo‐electron emission estimated from the emission curves indicated that the trap levels are between 0.05 and 0.32 eV below the bottom of its conduction band. This suggests that shallow electron‐trap levels within MgO film are mainly responsible for the exo‐electron emission.     

Improved discharge characteristics using MgO single‐crystal particles and advanced CEL structure

Abstract— Pioneer Corporation introduced plasma‐display‐panel (PDP) TVs in 2005, which achieved the highest dark‐room contrast ratio of 4000:1 at the time. These PDPs had a novel discharge cell structure consisting of a crystal emissive layer (CEL) on a MgO protective thin film. This cell structure is refered to as a CEL structure. Magnesium‐oxide single‐crystal particles, which have a unique luminance peak around 230–250 nm and a good exo‐electron‐emission property, were found to be an excellent material for CEL and were utilized in CEL panels. In 2007, newly developed PDP TVs in which CEL was formed on a phosphor layer, in addition to the previous CEL structure, were introduced, and this discharge cell structure is refered to as advanced CEL structure. By using the new cell structure, the opposed discharge characteristics have been drastically improved, and a stable reset discharge has been realized with only a weak opposed discharge. As a result, black luminance has been drastically reduced, and a dark‐room contrast ratio of over 20,000:1, the highest ever reported, has been achieved.     

Electronic structure and electrical conductivity of MgO protecting layer in plasma‐display panels: A tight‐binding quantum chemical study

Abstract— The tight‐binding quantum chemical molecular dynamics code, Colors, has been successfully applied to the electronic‐structure calculations of the MgO‐protecting‐layer model in plasma‐display panels (PDPs). The code succeeded in reproducing the band‐gap energy of the MgO crystal structure. The energy gap between the bottom of the conduction band (CB) and the top of valence band (VB) was 7.45 eV, which is in quantitative agreement with the experimental and previous theoretical results. The electronic structure of the undoped MgO model and Si‐doped MgO model was also calculated. The impurity level was 2.15 eV lower than that for the bottom of the CB. This result was in qualitative agreement with recent cathodoluminescence measurements. In addition, we have already succeeded in developing a novel electrical conductivity simulator using the spatial distribution of the probability density of wave functions obtained from the tight‐binding quantum chemical molecular dynamics code, Colors. The electrical conductivity of the MgO‐protecting‐layer model was estimated with and without an oxygen defect and a significant change in the electrical conductivity of the MgO‐protecting‐layer materials was observed with the introduction of oxygen defects.     

Physical interpretation of the characteristics of LCDs embedded with MgO and SiO2 nanoparticles

Abstract— The electro‐optical characteristics of TN‐LCD and ECB‐LCD cells, both of which were embedded with of MgO and SiO₂ nanoparticles at a low concentration of about or below 1 wt.%, were investigated. The threshold voltage and operating voltage of these LCD cells were found to decrease by 5–16%, depending on the materials and the concentration of nanoparticles. Measurements of the physical properties of nanoparticle‐embedded NLCs, such as the order parameter, clearing point, birefringence, dielectric anisotropy, elastic constants, and rotational viscosity on the nanoparticle‐doped NLC sample cells, were performed. Through these measurements, it is shown that the decrease in the threshold voltage and the operating voltage may be attributed to the decrease in the order parameter by 10–30% due to the existence of these nanoparticles.     

A MgF2/MgO multiple protecting layer in ac plasma‐display panels

Abstract— A MgF²/MgO multiple protecting layer coated on a MgO layer in ac plasma‐display panels (AC‐PDPs) was developed to obtain high brightness and low driving voltages. The material characteristics of this layer were examined by carefully changing the deposition conditions, and the display characteristics of AC‐PDPs using this protecting layer were studied. It was demonstrated that this new method is effective in lowering the firing and sustaining voltages of PDPs and enhancing the brightness of the panel as well.     

Numerical analysis of density of energy states for electron‐emission sources in MgO

Abstract— An analytical method to determine the density of energy states of electron‐emission sources (EESs) in chemical‐doped MgO is described using a discharge probability model and a thermal excitation and emission model. The density of energy states for multiple types of EESs is represented by using a linear combination of Gaussian functions of which parameters are determined by the theoretical emission time constant of an exoelectron and statistical delay time ts extracted from experimental stochastic distributions of discharge delay time in plasma‐display panels. When applied to Si‐doped MgO, the effective number of Si EES is calculated to be 1.8 × 10⁶ per cell. The average and standard deviations of activation energy have an energy level of 770 meV and a large value of 55 meV. In Si and H co‐doped MgO, the high peak density of [H^2?]⁰ appears at 550 meV. ts at the short time interval of 1 msec decreases and is independent of temperature due to exoelectron emission from the [H^2?]⁰. The dependence of ts at a time interval of 10 msec on temperature becomes weak because the energy structure of the Si EES broadens significantly attributed to the electrostatic effects of the doped H atoms.     

Electron‐beam deposition of MgO on plastic substrate and manufacturing flexible flat fluorescent lamp

Abstract— A flexible fluorescent lamp that utilizes the same plasma discharge mode as in PDPs has been manufactured. The structure of the flexible lamp is simple and easy to manufacture. All‐plastic materials including plastic substrates, barrier ribs (spacers), and sealants for low‐temperature manufacturing processing have been adopted except for the phosphor and MgO thin film. The MgO thin films were coated on the plastic substrates as a protection layer against the plasma discharge. The adhesion and biaxial texture of MgO thin film deposited on the plastic substrates, poly‐ethyle‐nenaphthalate (PEN) and polycarbonate (PC), at low temperature (100–180°C) has been characterized. The MgO film on PEN shows good adhesion under a repeated bending test. The manufactured flexible lamp consists of two plastic substrates of about 3 in. on the diagonal, barrier rib (spacer), and external ITO electrodes. The Ne‐Xe (5%) gas mixture at 100–200 Torr was used for the discharge gas. A maximum surface luminance of about 100 cd/m² was achieved for a 1 ‐kHz AC pulse.     

Discharge properties and chemical stability of SrZrO films

Abstract— MgO thin film is currently used as a surface protective layer for dielectric materials because MgO has a high resistance during ion sputtering and exhibits effective secondary electron emission. The secondary‐electron‐emission coefficient γ of MgO is high for Ne ions; however, it is low for Xe ions. The Xe content of the discharge gas of PDPs needs to be raised in order to increase the luminous efficiency. Thus, the development of high‐γ materials replacing MgO is required. The discharge properties and chemical surface stability of SrO containing Zr (SrZrO) as the candidate high‐γ protective layer for noble PDPs have been characterized. SrZrO films have superior chemical stability, especially the resistance to carbonation because of the existence of a few adsorption sites due to their amorphous structure. The firing voltage is 60 V lower than that of MgO films for a discharge gas of Ne/Xe = 85/15 at 60 kPa.     

Studies on a LaF3‐coated MgO protecting layer in AC‐plasma‐display panels

A new protecting layer, a LaF₃‐coated MgO layer, in color AC‐plasma‐display panels (PDPs) was studied in order to overcome the weakness of the conventional single MgO protecting layer. The material characteristics of the new layer were examined by using variations in the deposition process. The display characteristics were also examined by implementing their processes to actual PDPs. It was demonstrated that this method is effective in lowering the firing and sustaining voltages of PDPs and enhancing the brightness of the panel as well.     

Relationship between exo‐electron currents from MgO thin film and statistical delay time in ACPDPs

Abstract— The exo‐electron currents from a ACPDP test panel with or without MgO crystals sprayed on MgO film were measured directly after eliminating of the wall‐voltage effect. An inverse relationship was established between the statistical delay time and exo‐electron currentfrom the MgO cathode film. The spraying of MgO crystals on MgO thin film was observed to reduce the statistical delay time dramatically even for the same exo‐electron currents measured. The shift of the inverse curve may be attributed to an increased discharge success probability by the MgO crystals sprayed.     

High‐performance MgO thin films for PDPs with a high‐rate sputtering‐deposition process

Abstract— A high‐rate sputtering‐deposition process for MgO thin films for PDP fabrication was recently developed. The deposition rate of the MgO thin film was about 300 nm/min which shows the possibility of production‐line application. The MgO film deposited in this work has a higher density than that of other deposition processes such as electron‐beam deposition and shows good discharge characteristics including firing voltage and discharge formation. These were achieved by controlling the stoichiometry and/or the impurity doping during the sputtering process.     

Spectroscopic and photoluminescence properties of MgO:Cr3+ nanosheets for WLEDs

This work explores the synthesis of nanocrystalline MgO:Cr³⁺ (1–9 mol%) nanophosphors via solution combustion route at 400 °C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15 nm. Upon 356 nm excitation the emission profile of MgO:Cr³⁺ exhibits an emission peak at 677 nm due to ²E_g → ⁴A_2g transition. It was observed that PL intensity increases with increase in Cr³⁺ concentration and highest PL intensity was observed for 3 mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs).     

High‐contrast driving method for advanced CEL structure with magnesium oxide single‐crystal powder in ACPDP

Abstract— A new driving method for an advanced‐CEL‐structure panel has been developed. Picture qualities have been upgraded. Discharge time lags are drastically shortened by priming electron emission from magnesium oxide (MgO) single‐crystal powder, refered to as a crystal emissive layer (CEL). The advanced‐CEL‐structure panel has CEL material on the surface of not only the surface‐discharge‐electrode side but also on the address‐electrode side. This panel structure enables a stable opposed discharge when the address electrode functions as a cathode. By utilizing the opposed discharges in the reset and LSB‐SF sustain periods, the dark‐room contrast ratio has been drastically increased to over 20,000:1, which is higher than five times that of the conventional method, and the luminance of the least‐significant‐bit sub‐field (LSB‐SF) is as low as 0.1 cd/m², which is one‐fourth that of the conventional method. The high‐picture‐quality PDP TVs refered to as “KURO” that employs these technologies have been introduced into the marketplace.     

Reduction of permanent image sticking in ACPDPs using RF‐plasma pretreatment on MgO surface

Abstract— The characteristics of the MgO layer are known to be an important parameter that affects the permanent image sticking or lifetime of an ACPDP. In this paper, to reduce the permanent image sticking in ACPDPs, the effects of RF‐plasma pretreatments of the MgO layer on the permanent image sticking are investigated. The treatment was conducted by using several plasma‐forming gases, including Ar, Ar followed by O², and O² followed by Ar. Measurements of luminance, normalized luminance, V^t closed curve, haze, MgO hardness, and photoluminescence between the discharge and nondis‐charge regions under dark and bright backgrounds indicated that the plasma treatments of MgO using either Ar or Ar followed by O² gases reduce the permanent image sticking on dark and bright images in an ACPDP.     

Color‐by‐Blue: A novel method to achieve full‐color inorganic EL displays

Abstract— A new method for achieving full‐color capability for inorganic EL displays was developed, which combines electroluminescence with photoluminescence phenomena in the same device structure. In this display panel, the blue emission was obtained from the EL device by using the Eu‐doped barium thioaluminate phosphor material system, which was then used to generate green and red emission by the use of down‐conversion materials. The major advantages of the Color‐by‐Blue method (CBB) are the elimination of color‐balance control issues associated with the use of different electroluminescent phosphor materials for red, green, and blue with potentially different threshold voltages for the onset of luminance and the achievement of a low‐cost high‐yield manufacturing process.     

Aggregate‐induced emission in light‐emitting liquid crystal display technology

Nowadays, liquid crystal displays (LCDs) with light‐emission are considered as energy‐efficient devices and are promising alternatives to conventional LCDs. To realize such possibility, strong fluorescent materials with a dichroic properties are required. Aggregate‐induced emission (AIE) is an unusual photophysical phenomenon shown by some luminogenic materials that will be highly emissive in their aggregate state. In this work, we studied the AIE effect of a luminescent liquid crystalline molecule TPE‐PPE in our LC system as a luminophore dopant. The result showed the excellent AIE effect that higher concentration of luminogen in the nematic LC host induced stronger luminescent intensity. Through exposure of a photoisomeriable alignment material sulfonic‐dye‐1, the photopatterning of a light‐emitting LC device was achieved with the use of the TPE‐PPE/nematic LC mixture.     

Effect of gas pressure on permanent dark image sticking on a bright screen in AC plasma‐display panels

Abstract— The permanent dark‐image‐sticking phenomenon on a bright screen was examined under various gas pressures in a 42‐in. ACPDP with an He(35%)‐Xe(11%)‐Ne gas composition. Infrared‐emission observations reveal that the discharge characteristics related to the MgO surface are almost the same in both the discharge and non‐discharge cells, whereas luminance observations show a deterioration in the visible‐conversion characteristics related to the phosphor layer in both the discharge and non‐discharge cells. Consequently, the permanent dark‐image‐sticking phenomenon on a bright screen is found to be strongly related to the deposition on the phosphor layer to the Mg species sputtered from the MgO surface due to a repetitive strong sustain discharge. For a decrease in gas pressure, the permanent dark image sticking on a bright screen became worse due to a severe degradation of the visible‐conversion characteristics of the phosphor layer caused by the deposition of higher amounts of sputtered Mg species on the phosphor layer, as confirmed by various measurements, such as V_t closed curves, time‐of‐flight secondary‐ion mass spectrometry, photoluminescence, and atomic‐force‐microscope analyses.     

New oxide phosphors for FEDs: Ruddlesden—Popper phases synthesized with IIIB‐group elements

Abstract— A red‐emitting phosphor, SrTiO³:Pr³⁺, for low‐voltage‐type FEDs and VFDs was developed by Futaba Corporation in 1996. The addition of Al or Ga is essential in the preparation of this phosphor because it improves the luminescence efficiency dramatically. For this impurity effect, Futaba Corporation proposed a charge‐compensation mechanism, which was supported by a recent observation of emission lines due to Al³⁺‐Pr³⁺ pairs. In addition, it was found that Al also works as a scavenger of planar defects, presumably SrO thin layers interleaved in the SrTiO³ lattice, by forming strontium aluminates. The latter mechanism suggests the possibility that a similar impurity effect can be found in materials with crystal structures, including alkaline‐earth oxide layers (Ruddlesden‐Popper phases).     

Nonlinear properties of aluminum‐doped zinc sulfide under IR excitation

Abstract— Second harmonic generation (SHG) in ZnS‐based materials is reported. ZnS, ZnS:Cu, Br, and ZnS:Cu, Al, Br samples were studied. Phosphor powders were subjected to 30‐mJ pulses from YAG:Nd infrared laser. The wavelength of the generated green emission was 532 nm, exactly one‐half that of incident laser light (1064 nm). However, the non‐linear dependence of the emission intensity on pump intensity was observed only for the ZnS:Cu, Al, Br powder. It is concluded that aluminum co‐doping is crucial for the non‐linear properties.