Chong-Hong Pyun

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− .

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.

The effect of a metal electrode on PPV electroluminescence processes

Abstract Two metal electrodes of aluminum (Al) and calcium (Ca), which have different work functions, were used to fabricate EL devices based on poly(p-phenylene vinylene) (PPV) with single-layer structure. A new experimental phenomenon is discovered. The electroluminescent (EL) spectra are different in EL devices with metal electrode of Al and Ca. The feature is expressed as a variation of the ratio of intensity from the peak at 550 nm to the peak at 510 nm. From this, we discussed the main type of carrier moving in PPV film with Al and Ca electrodes, respectively. By comparing the processes between EL and photoluminescence (PL), a reason for the difference in EL spectra with Al and Ca electrodes was analyzed.

Luminescence properties of Ca1−xSrxTiO3:Pr3+

The phosphor CaTiO 3 :Pr 3+ is highly regarded as a low-voltage red phosphor because of its good color quality and intrinsic conductivity. Under 330-nm excitation it shows red emission, which corresponds to the transition from 1 D 2 to 3 H 4 . This transition is a forbidden f-f electric dipole transition, but its fluorescence intensity is quite large in CaTiO 3 :Pr 3+ and decreases in Ca 1-x Sr x TiO 3 :Pr 3+ as X increases. In this study, luminescence properties of CaTiO 3 :Pr 3+ have been investigated in terms of crystal structure, using the Eu 3+ ion as a probe. The Pr 3+ ion site in the CaTiO 3 :Pr 3+ has no centrosymmetry, and the partial allowance of the 1 D 2 → 3 H 4 transition by the odd crystal-field terms due to the loss of centrosymmetry gives quite strong emission. With the increase of the Sr ion substitution in Ca 1-x Sr x TiO 3 :Pr 3+ prepared by heating at 1150°C, the fraction of the Pr 3+ ions at inversion centers increases and the emission intensity decreases as the result.