Sumiaki Ibuki

Photoluminescence of Eu-Doped ZnO Phosphors

Characteristic 4f photoluminescence of Eu3+ doped into ZnO was first observed on the red band luminescence. The intensity and fine structures of the Eu3+ luminescence and their temperature dependence are strongly influenced by the doping conditions. In particular, for the increase of the Eu3+ luminescence intensity Li codoping is not effective but stoichiometric control of Zn and O is essential. Moreover, the observed red band luminescence can be considered to be due to excess oxygen.

Photoluminescence on Li-Codoped ZnS:Tm Phosphor

Very strong sharp lines in luminescence of Tm3+ have been observed in Li-codoped ZnS:Tm phosphor. In particular, blue emission intensity was stronger as compared with that of infrared emission when the codoped Li concentration in ZnS:Tm was 0.1 at.%. As ZnS:Tm emits a broad band and very weak Tm3+ lines, the role of Li is proposed as follows: Li ions fill defects in the ZnS host, and hence excitation energy transfers from the ZnS host to Tm3+ very easily.

Electro-reflectance near the fundamental edge of GaSe

Abstract Electro-reflectance of GaSe single crystal has been investigated in the spectral region from 1·97 to 2·13 eV. By analyzing the electro-reflectance signals with Kramers-Kronig relation, the energies of the exciton levels and the fundamental edge are assigned both at 300 and 90°K. An additional new structure is observed below the ground state exciton. Electric field and temperature dependences of the structure have been explored and a possibility of the existence of some local states (defect or impurity state) is postulated and discussed.

Spectroscopic Study on Sputtering of PLZT Thin Film

An optimization of RF sputtering condition for preparation of high-quality PLZT thin film has been studied by use of spectroscopic analysis of vapor phase species and composition for deposited PLZT thin film. Relative amounts of the component elements in the sputtering vapor have been measured from optical emission spectra of the plasma. Distributions of the elements perpendicular to the surface in the deposited films have been obtained by use of ESCA. Results of the systematic analysis imply that fine control of Pb content is the key issue for higher quality film. PLZT films having a large dielectric constant of 5000 have been obtained under the sputtering condition of low RF power.

Investigation of rare earth ions in ZnSe

Abstract The electrical properties of rare earth ions (Er+3, Tm+3 and Eu2+) doped into ZnSe crystals have been investigated by observing their optical absorptions, luminescent spectra, their Zeeman effects and ESR. The rare earth ions in the crystal from some kinds of centers close coupled with codopants or lattice defects, and they have emitted strong luminescence of the rare earth ions in the set group of (Er3+, Cu), (Tm3+, Cu) and (Tm3+, Li). The electronic structures of the latter two sets are the same, and Tm3+ exists in a crystal field of cubic symmetry. Parameters of the crystal field have been determined to suit best to the spectra obtained. Magnetic field induced absorption was observed in the absorption lines of ZnSe: Er, P by the pulse magnetic field Zeeman effect. From the ESR results of Eu2+ ions in ZnSe, it has been made clear that Eu2+ ions also exist in the crystal field of cubic symmetry.

Photoluminescence of Eu3+ in CaS:Eu Phosphor

New emission lines from Eu3+ centers aside from the main broad-band emission from Eu2+ in CaS-doped EuF3 were found at 10 K. The intensity of these emission lines increases after annealing in a mixed gas of Ar and O2. The origin of the emission might be related to interstitial O2- or F-.

Infrared absorption and Raman scattering due to localized vibrational mode of Be in zinc-chalcogenides

Abstract The localized vibrational modes of Be in ZnS and ZnSe are observed by using the infrared absorption and Raman scattering. The concentration dependent shift of local mode line is found in ZnS: Be. For these systems, anharmonic potential constants are calculated up to the 4th order. Fundamental local mode of ZnTe: Be is also measured.

Anomalous electro-reflectance signals near the fundamental edge of zinc selenide

Abstract A new structure has been found in the low temperature (90°K) electroreflectance spectra of ZnSe. The energies of the L0 phonon assisted exciton creation process and of the fundamental edge including excitons are assigned.

High Field Zeeman Effect of Pr3+ Absorption Lines in CaF2

The Zeeman effect of the absorption lines of Pr 3+ in CaF 2 was investigated photographically using pulsed magnetic field up to 130kOe at 77°K and 4.2°K. Some strong absorption lines were determined to be associated with the transitions from the ground doublet to the singlets in the crystal field of C 3 v symmetry and the transitions were found to be of electric dipole origin.

Low‐Frequency Oscillations in CdS Single Crystals

Low‐frequency current oscillations in CdS single crystals were observed. One type of oscillations was a damped one, and the other type of oscillations was continuous and only observed under superposed infrared light which produces quenching. The retrapping rate of the free holes and the occupation probability among the traps control the free electron density oscillation.