Chang-Hong Kim

Phosphors for plasma display panels

Excitation and emission characteristics were reviewed for phosphors which were reported, applied, or suggested for the plasma display panel (PDP). Correlation of luminescence characteristics to the host crystal structure and the activator of the phosphor was explained. Improvements of the PDP phosphor for the practicality were considered.

Vacuum ultraviolet optical properties of (La, Gd)PO4 :RE3+ (RE = Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO4:RE3+ (RE = Eu or Tb) and X-ray photoelectron spectra of LaPO4 and GdPO4 are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO4:RE3+ is enhanced with the increasing of Gd3+ content, which implies that Gd3+ plays an intermediate role in energy transfer from host absorption band to RE3+. When Gd3+ is doped into LaPO4:Eu, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd3+ doped into LaPO4. These results suggest that the dopant (Gd3+) gives an important influence on energy transfer efficiency. The top of LaPO4 valance band is formed by the 2p level of O2-, whereas that of GdPO4 valance band is formed by the 2p level of O2- and the 4f level of Gd3+, showing the differences in band structures between LaPO4 and GdPO4.

Infrared spectra and VUV excitation properties of BaLnB9O16:Re (Ln=La, Gd; Re=Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius

Structure and luminescence of SrY{sub 2}O{sub 4}:Eu

Powder samples of SrY{sub 2(1{minus}x)}O{sub 4}:Eu{sub 2x} were prepared at 1,000 C by the combustion method. The emission spectrum of SrY{sub 2}O{sub 4}:Eu{sup 3+} showed two kinds of Eu{sup 3+} emissions, which could be assigned to Eu{sup 3+} ions in the Sr site and the Y site. Reducing SrY{sub 2}O{sub 4}:Eu brought a broad band emission around 470 nm, which could be attributed to crystal defects introduced by the reduction. The energy transfer from defects to Eu{sup 3+} ions was observed to be more effective to the Sr site than to the Y site.

VUV excitation properties of LnAl3B4O12:Re (Ln=Y, Gd; Re=Eu, Tb)

Abstract Vacuum ultraviolet excitation spectra of LnAl 3 B 4 O 12 :Re (Ln=Y, Gd; Re=Eu, Tb), along with X-ray photoelectron spectra, were measured. The spectra are tentatively interpreted in terms of the optical properties of the rare earth ions and the band structure. It was found that there is an energy transfer from the hosts to the rare earth ions. It was also found that the top of the valence band in the Gd compound is mainly formed by the 2p levels of O 2− and the 4f levels of Gd 3+ , and in the Y compound mainly by the 2p levels of O 2− .

Control of size and morphology in Ni particles prepared by spray pyrolysis

Recently, dielectric layers are made thinner and the number of these layers has been increased in order to meet the needs for MLCCs (multi layer ceramic condenser) being smaller in size but providing large capacitance [1]. MLCCs consist of alternately thin dielectric layers and internal electrode layers in one body. One of the disadvantages of this trend is the set-up cost, due to the increased use of noble metals to form internal electrodes. For example, the majority of MLCCs have employed a Pd internal electrode, an Ag external electrode, and barium titanate based dielectric material, all of which are too expensive. In order to decrease the electrode cost, Pd-Ag alloy is also used. Recently, other electrode materials like Ni (melting point 1455 ◦C) and Cu (melting point 1083 ◦C) have been receiving increasing attention because of their good electric conductivity, relatively high melting point and low cost. Ni will replace noble metal to become the most important electrode material [2]. Metallic Ni has been prepared by liquid and gas reaction methods [3, 4]. However, Ni particles with spherical shape and non-agglomeration are very difficult to obtain by these methods. Spray pyrolysis is a useful method for the preparation of spherical metal, and metal oxide particles [5]. In a typical spray pyrolysis process, an aqueous solution of precursors is atomized and the stream consisting of droplets suspended in a carrier gas is passed through a tubular furnace. In the furnace, the precursor reacts in the solid phase, forming the final product powder. In spray pyrolysis, the average size and size distribution of the final particles can be roughly determined from the size of atomized droplet and initial concentration of starting solution. However, rapid evaporation of solvent and dramatic evolution of decomposition gases from the droplets make it very difficult to control the particle structure [6]. In many cases hollow or irregular shaped particles are formed. The most important operating factors include the properties of the starting material, the concentration of the solution, the drying and pyrolysis temperatures, the residence time and heating rate of the droplets/particles. Complex precursors are used for spray pyrolysis method [7–10] and Xia et al. [11] showed that Ni particles could be prepared by spray pyrolysis using Ni(NO3)2·6H2O precursor containing ammonia. In this work, we prepared the Ni powders directly from Ni(NO3)2·6H2O (Aldrich) aqueous solution containing EDTA by spray pyrolysis on a pilot scale under reducing atmosphere. The EDTA was introduced

AFM image visualization of layered dichalcogenides, 1T-MTe2(M = V, Ta)

Abstract The surface structures of the layered chalcogenide VTe 2 , TaTe 2 were probed by atomic force microscopy (AFM). The observed AFM images at the atomic level were analyzed by calculating the total electron density maps. The title compounds adopt double zigzag CDWs (Charge Density Waves) resulting in three unique tellurides. Thus, the brightness of the AFM image on the corrugated surface decreases in the order of Te (3) > Te ( l ) ⪢ Te (2). Also, metal in the VTe 2 system is more localized than that of TaTe 2 .

The Effect of a Metal Electrode on the Electroluminescence of Poly(p-phenylenevinylene)

The effect of metal on the emission characteristics of a ITO-poly(p-phenylenevinylene)-M (M: Al, In, Mg, or Ca) electroluminescence device was studied. The emission peak at 550 nm is substantially smaller than that at 515 nm for devices with metals which have a larger work function. In the case of photoluminescence, the thinner the poly(p-phenylenevinylene) (PPV) film the smaller is the 550-nm peak observed using an Al electrode. These results are discussed in terms of the interaction of metal with PPV at the PPV-metal interface.

Blue Electroluminescence Mechanism of Polyester Derivative Blend Films

A new polymer of polyester derivative (PE) blend with poly(N-vinycarbazole) (PVK) and compound of PBD at various weight ratio were used as emitter in unilayer electroluminescence (EL) devices with indium cathode. Analyses of fluorescence and EL spectra imply common emission energy states are formed in the blend films, by which to explain the possibility of maximum EL efficiency in blend films higher than that in either of PE and PVK. The PL and EL spectra show the maximum emission band shifts red slightly between 430 nm and 450 nm as increasing the ratio of PE, meanwhile the half width increases and a new peak around 525 nm appears. The new peak is confirmed originating from the dimer formed by coupling of interchains in polymer PE. Both of PE and PVK can give rise to PL emission under UV light. The origin of PL and EL emission is analysed.

Digital and analog measurements of HTS SFQ RS flip-flops and shift register circuits

We fabricated reset-set (RS) flip-flops and shift registers by using YBCO bicrystal junctions and tested their operations by using a computer-controlled digital measurement set-up and an analog measurement set-up. The RS flip-flop circuits operated successfully at temperatures up to 71 K. The RS flip-flop circuit was observed over 600 computer-generated clock cycles with nearly no errors. The circuits were reset or set during each clock cycle. By using an analog measurement technique, we operated the RS flip-flop circuits at frequencies of up to 500 Hz. Since our probe was not designed for high speed operation, the test speed was limited to this frequency. Although we could not operate the shift register completely, we observed flux propagation in the shift register.