Kenichiro Iwasaki

White light emission of Mn-doped SnO-ZnO-P_2O_5 glass containing no rare earth cation

The authors have demonstrated white light emission of rare earth (RE)-free Mn-doped SnO-ZnO-P(2)O(5) glass. The RE-free glass shows white light emission with a high value of quantum efficiency (QE) comparable to conventional crystalline phosphor. It is notable that the high QE value is attained for RE-free transparent glass, and the broad emission can be continuously tuned by both the amount of activator and the composition of the glass. Since this glass possesses low-melting property, we emphasize that the glass phosphor will lead to the development of a novel inorganic white-light-emitting device in combination with a solid state UV light-emitting source.

Interdiffusion and interfacial reaction between an YBa2Cu3Ox thin film and substrates

Interdiffusion and interfacial reaction between a sputter‐deposited YBa2Cu3Ox thin film and substrates (MgO, sapphire, quartz, and Si) have been investigated by 2.7 MeV 4He+ Rutherford backscattering spectrometry. The diffusivities of Cu in the substrates and of the substrate elements (Mg, Al, and Si) in the Y‐Ba‐Cu‐O thin films have been determined over the annealing temperature range from 876 to 1226 K in an oxygen atmosphere. Among three metallic elements of Y, Ba, and Cu, Cu diffuses the fastest into the substrates. Copper silicide is observed in the interfacial region between the film and the Si substrate. Among these substrates, MgO is suggested to be the most stable on annealing.

Blue photoluminescence, greenish-blue afterglow and their Ti-concentration dependence in rare earth-free bazirite-type BaZr 1- xTixSi 3 O 9

We synthesized Ti-bearing bazirite (BaZr(1-x)Ti(x)Si(3)O(9), x=0-0.2) and examined their spectroscopic features comprehensively, in order to elucidate the photoluminescent properties in the bazirite phase. Strong emission around 2.79 eV was observed in the synthetic bazirite phase with x=0.01 by UV excitation, which exhibited an internal quantum yield of 72% at room temperature. In addition, the bazirite phases also showed clear afterglow with peak around 2.62 eV in the range of x=0.005-0.03, whereas no afterglow property was confirmed in Ti-bearing pabstite (BaSnSi(3)O(9)) phases, in spite of being isostructural of bazirite. It was demonstrated that presence of Zr-related center is a necessary condition for evolution of the afterglow property in the bazirite structure.

Defect activation in willemite-type Zn2GeO4 by nanocrystallization

We demonstrated the selective introduction of interstitial Zn defects (Zni•) into willemite-type semiconductive Zn2GeO4 by nanocrystallization of 15Li2O–15ZnO–70GeO2 glass. The resulting nanocrystallized glass consisting of Zn2GeO4 exhibited a long-lasting photoluminescence (LLP). It is suggested that the Zni• is produced by capturing a zinc ion through six-membered rings of the Zn2GeO4 phase during nanocrystallization and the excess Zni• acts as an electron trap for the LLP. This defect activation through nanocrystallization is a promising new approach to functionalization.

High efficient white light emission of rare earth-free MnO–SnO–ZnO–P2O5 glass

White light emission of rare earth (RE)-free Mn-doped SnO–ZnO–P2O5 glass is demonstrated. Glass transition temperature of the obtained glass is below 440°C, which assures the application to sealant of solid state light emitting devices. The RE-free transparent glass shows white light emission with a high value of quantum efficiency (QE) comparable to conventional crystalline phosphor by excitation of deep UV light. The broad emission of RE-free transparent glass can be continuously tuned by both the amount of activator and the composition of the glass without decrease of the QE value.

High thermal stability of red emission in Mn-doped benitoite-type strontium silicogermanate

We assessed the photoluminescence performance characteristics of Mn4+-doped tetragermanate and silicogermanate phases with a benitoite-type structure. We observed a visible red emission based on the 2E → 4A2 transition in the doped benitoite-type tetragermanate. The partial substitution of Si for Ge, resulting in SrGe3.495Mn0.005Si0.5O9, improved the internal quantum efficiency and thermal stability of the red emission. A possible explanation of the substitution effect was reasonably presented on the basis of the connectivity of luminescent polyhedral units and the decrease in the Franck–Condon off-set value in the benitoite structure.

Precipitation of Pt nanocrystallites from BaO-TiO2-GeO2 remelted glass

We have examined the correlation between the thermal and optical properties of 30BaO-15TiO2-55GeO2 glass and its mode of preparation, i.e., the different temperatures at which the glass melts were held in a molten state (melt temperature). The changes in the absorption coefficients and the refractive indices, which increased with the increasing melt temperature, were reversible, and temperature-dependent structures were formed in the glass. In the remelted glass with short remelting duration, a black coloration and the precipitation of Pt nanocrystallites were observed. The precipitated Pt nanocrystallites acted as nucleation sites to induce crystallization by heat treatment at 10 °C below the glass transition temperature.

Fabrication and Photoluminescent Property of Transparent Nanocrystallized-Glass in Li2O-ZnO-GeO2 System

We investigated crystallization behaviour of several glasses in ternary Li2O-ZnO-GeO2 system in order to fabricate the glass-ceramics consisting of Zn-related compound showing photoluminescent property. Nanocrystallized glass with willemite-type Zn2GeO4 could be prepared from the 15Li2O-15ZnO-70GeO2 glass, and revealed a long-lasting photoluminescence (LLP). Origin of the LLP in the nanocrystallized glass is also discussed.

Photoluminescence in Bazirite Crystal by Addition of Impurity Ions

We examined photoluminescent (PL) and afterglow properties in bazirite (BaZrSi3O9) phases with Sr2+-, Sn4+-, Ge4+-, and Ti4+-impurities, in order to elucidate effect of the impurity-addition on these properties. The bazirite phases studied showed blue PL and afterglow regardless of sort of the impurities. Origin of PL and afterglow emission in the bazirite phase is also discussed.