This letter reports blue oxynitride phosphors of La1−xCexAl(Si6−zAlz)(N10−zOz) (z∼1) (termed JEM crystal phase) and their application for the white light-emitting diodes (LEDs). The JEM phosphor can be excited by 405nm light efficiently, and its spectrum can be tuned widely by changing the Ce concentration. The emission spectrum of this phosphor is as wide as 110nm in full width at half maximum, which is convenient to solid state lighting. The preparation of white LED was attempted by using a 405nm InGaN chip and oxynitride phosphors in this work. High color rendering index >95 was achieved in white LED with various correlated color temperatures, indicating the suitability of the JEM phosphor in solid-state lightings.

The photoluminescence (PL) and PL excitation (PLE) spectra of Si Al O N (β-sialon):Eu phosphors with small values (=0.025-0.24) were studied at room temperature and 6 K. The PL and PLE spectra exhibit fine structure with the PL lines being as sharp as 45-55 nm even at room temperature; this fine structure was enhanced by decreasing the value. These results can be used for expanding the color gamut of liquid crystal displays, particularly in the blue-green region. From low-temperature measurements, the fine PLE structure was ascribed to discrete energy levels ofF states. The 4f5d excited states of Eu are considered to be localized near the 4f orbital. This is because the bonding of Eu with surrounding atoms is ionic rather than covalent. Lattice phonon absorptions were also observed in the PLE spectrum, revealing that the optically active Eu ions are located in the β-sialon crystal. The PL spectrum of the sample with the smallest value (0.025) consists of a sharp zero-phonon line and lattice phonon replicas, which results in a sharp and asymmetric spectral shape.

Metalorganic molecular beam epitaxial growth and characterization of CdSe/ZnSe strainedlayer single quantum wells and superlattices on GaAs substrates

No abstract

In order to search a possibility to prepare Ohmic contacts to p-ZnSe by depositing a single metal element, the electrical properties and thermal stability were studied by a current–voltage (I–V) method for a variety of metals (In, Cd, Nb, W, Cu, Ag, Au, Ni, Pt, and Se) contacting to nitrogen-doped ZnSe layers grown by the molecular beam epitaxy technique. All the metals were deposited on the ZnSe substrates which were chemically cleaned prior to metal deposition in order to remove the native oxide layers. The turn-on voltages (V T) and differential resistances were determined by the I–V curves for these contacts before and after annealing. The contacts were divided into three groups by the V T values: (1) In, Cd, Nb, and W contacts with V T∼16 V, (2) Au and Pt contacts with V T larger than 9 V, and (3) Cu, Ag, Ni, and Se contacts with V T∼3 V. The lowest V T value of 2 V was achieved by the Cu contact. However, this Cu contact deteriorated during storage at ambient temperature. The V T value of ∼3 V was routinely obtained for the Ag and Ni contacts. The Ni contact is the most promising materials for the device application among the contact materials studied in the present experiment, although the linear relation in the I–V behavior was not obtained. The electrical properties of these contacts during annealing at temperatures below 300° C were studied, and no significant reduction of the V T value was obtained in the present contacts. The present study suggests that the deposition of a single metal element to p-ZnSe with doping level of 1×1018 cm-3 would not provide low resistance Ohmic contact.