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A novel thermoelectric type hydrogen gas sensor based on exothermic reaction of hydrogen storage alloy is proposed and fabricated. First, an exothermic reaction of a hydrogen storage alloy at room temperature has been studied for a hydrogen gas sensor application. Next, a copper (Cu) constantan thermocouple painted a palladium (Pd) past on surface was fabricated as a hydrogen gas detector. The response characteristic of the fabricated hydrogen gas detector was evaluated under hydrogen gas flow. The exothermic reaction of Pd and hydrogen gas was successfully observed using fabricated gas detector. It was clarified that the fabricated hydrogen gas detector using Cu constantan thermocouple with Pd is potentially useful for hydrogen gas sensor material.

The surface microtopography of rough basal faces and internal inhomogeneities of amethyst crystals from Four Peaks, Arizona were investigated by means of optical, scanning electron microscopes and cathodoluminescence tomography. Rough interface overgrowth was shown to have taken place along the c-axis on mechanically broken surfaces and the present rough basal surfaces were demonstrated to have formed because of later heavy dissolution.

Sr3Al2O6, SrAl2O4, SrAl4O7, and SrAl12O19 that have been doped with Eu2+ and Dy3+ ions have been grown by a floating-zone technique for application as long-duration phosphors. Long-duration phosphorescence with a variety of colors has been observed in SrAl2O4, SrAl4O7, and SrAl12O19 crystals that have been doped with Eu2+ and Dy3+ ions. The peak wavelength of the phosphorescence is 520 nm for SrAl2O4, 480 nm for SrAl4O7, and 400 nm for SrAl12O19. The phosphorescence is characterized by decay times that have been analyzed by a curve-fitting technique.

Erbium-doped ZnO (ZnO:Er) thin films were fabricated by the KrF excimer laser ablation technique, which is a useful and simple technique to dope Er atoms on the order of 1020 cm−3 into a host material. As-prepared ZnO:Er films showing strong c-axis orientation with a hexagonal crystalline structure indicate a low electrical resistivity of 6.4×10−3 Ω cm. The sharp and intense photoluminescence (PL) at 1.54 μm originating from the intra-4f transition in the Er3+ ions as well as PL in UV region from the ZnO host were observed even at room temperature. Significant distinction arising from the different Er emission centers responsible for the 1.54 μm emission cannot be found in the temperature dependence between the ZnO:Er and Si:Er film as a reference, except for the PL spectrum feature and main PL peak position. This result suggests the existence of Er emission centers in ZnO:Er and Si:Er films that are different from each other. The details of Er-related 1.54 μm emission dynamics of ZnO:Er films have been i...

The spin lattice relaxation rates and the absorption spectra of 7Li in both LiB3O5 crystal and glass samples were measured from room temperature up to 800 K. At low temperatures the dominant contribution to the relaxation rates was due to the spin–phonon interaction in both samples. For the crystal the relaxation caused by the diffusion of Li ions became significant above 580 K, and the narrowing of the absorption line started at about 540 K. For the glass the narrowing of the line started at room temperature and the effect of the diffusion of Li ions on the relaxation rate appeared above 400 K. From these results the correlation time τc of the fluctuating field at Li nuclei was obtained. Each value of the activation energy of τc deduced from the relaxation rate and the narrowing of the line, respectively, agreed well.

Erbium-doped TiO2 (TiO2:Er) thin films with the anatase structure have been prepared on Si substrate by laser ablation. Sharp and intense Er-related emission in the visible region as well as in the IR region has been observed under over-band-gap excitation. The broad photoluminescence (PL) peaking at about 530 nm newly appears at low temperature. It has been understood that the broad PL is induced by an optically assisted reduction effect that is caused by both the H2O adsorption and the reduction process of TiO2 to Ti2O3 by UV illumination. In the IR region, Er-related emission consisted of one main peak located at 1.534 μm and many subpeaks located at around 1.54 μm can be observed even at room temperature. The drastic thermal quenching of the Er-related 1.54 μm emission is also considered due to the optically assisted reduction effect.

Sr3Al2O6, SrAl2O4, SrAl4O7, and SrAl12O19 that have been doped with Eu2+ and Dy3+ ions have been grown by a floating-zone technique for application as long-duration phosphors. Long-duration phosphorescence with a variety of colors has been observed in SrAl2O4, SrAl4O7, and SrAl12O19 crystals that have been doped with Eu2+ and Dy3+ ions. The peak wavelength of the phosphorescence is 520 nm for SrAl2O4, 480 nm for SrAl4O7, and 400 nm for SrAl12O19. The phosphorescence is characterized by decay times that have been analyzed by a curve-fitting technique.

Erbium-related 1.54 μm emission dynamics of Er-doped ZnO thin films has been investigated for the different excitation conditions. The excitation was achieved either by exciting indirectly Er3+ ions due to an electron–hole-mediated process or exciting directly discrete energy levels of Er3+ ions. There is no change in the 1.54 μm emission spectrum feature in spite of the different excitation conditions, whereas dramatic change can be seen in the rise time of 1.54 μm emission. The shorter rise time of 1.54 μm emission observed for indirect excitation implies an excitation efficiency superior to direct excitation of Er3+ ions.

Decay of the band-edge photoluminescence (PL) from semi-insulating GaAs wafers and two-dimensional maps of the PL decay time and PL intensity of a wafer on a picosecond time scale were measured at room temperature using systems which consist of a synchronously pumped dye laser, a laser diode and a streak camera. The temporal trace of the PL was separated into at least two different decay components with decay times of about 40 and 150 ps, respectively. Two-dimensional maps of the band-edge PL decay time for semi-insulating GaAs wafers have been successfully obtained using a streak camera combined with a laser diode driven by a short pulse current. PL decay time gradually varied over the wafer in reasonable association with the PL intensity. Most significant changes in decay time and PL intensity were seen around the scratch on the wafers.

Er-doped nanocrystalline Si thin films have been controllably prepared over the Er density of 1019–1021 cm−3 using a prescribed amount of Er in a bulk target by laser ablation. Intense photoluminescence at 1.54 μm originating from intra-4f shell transitions in Er3+ ions has been observed. The increase of Er density cannot immediately result in a linear increase in Er3+-emission intensity. The time response measurement indicated that the change in the rise time of the Er3+ emission directly shows that Er3+ ions are excited by the energy transfer associated with the recombination of electron–hole pairs generated optically in the Si host. We found that the decrease of the excitation efficiency of Er3+ ions was responsible for the suppression of the Er3+-emission intensity in highly Er-doped nanocrystalline Si thin films.

Fiber-optic thermal radiation thermometry was studied using Er end doped silica fiber sensor. Visible light radiation peaks were clearly observed at lambda=522 nm and, 655 nm, 800 nm and 984 nm from Er end doped silica fibers sensor. Theses peaks increase greatly with temperature of the sensor. Intensity ratio of thermally excited luminescence peaks at lambda=522 nm and 984 nm, I522/984, is suitable for the high temperature measurement. Two dimensional (2-D) temperature distributions in a flame are successfully visualized by X-Y scanning technique using Er end doped silica fiber sensor

A fiber-optic fluorescence thermometer is a useful technique for temperature measurement in extraordinary conditions. However, high temperature measurement is hard for the fluorescence thermometer due to thermal quenching of fluorescence. To develop the wide range thermometer, a hybrid fiber-optic thermometer which combines the fluorescence thermometry and the thermal radiation thermometry has been fabricated using Cr ion doped phosphor crystal. In this paper, temperature dependence of fluorescent lifetime and blackbody radiation from Cr ion doped phosphor crystal is reported for wide range temperature measurement.

Temperature dependences of peak intensity and peak intensity ratio of photoluminescence from Cr doped spinel sensor are evaluated for fluorescence thermometer applications. Peak intensity and intensity ratio of PL from Cr doped spinel sensor varies with temperature. Peak intensity ratio of PL at ?=699 and 688 nm, I699/I688, which increases linearly with temperature from 298 to 473 K, is found to be suitable for temperature measurement instead of PL lifetime. Spinel thermo-sensor is proposed successfully based on temperature dependence of PL intensity ratio instead of PL lifetime.

Tb4O7 doped YAlO3 (YALO) crystals have been grown and evaluated for application in the temperature sensing device. Photoluminescence (PL) peaking at lambda=492 and lambda=545 nm are seen the crystal. Excitation peaks at lambda=360 nm are also seen in PL spectra. PL intensity increases with Tb concentration up to 3 at%, it then decrease with Tb concentration due to concentration quenching. PL intensity decreases gradually with temperature from 300 K to 900 K. Intensity ratio of PL peaks at 492 and 545 nm also varies depending on temperature. From these results, Tb4O7 doped YALO crystals are found to be useful as the sensor material in fluorescence thermometer

Non-destructive evaluation technique of rice developed based on photoluminescence is examined with various temperatures. The visible PL with broad peak at wavelength of lambda=462 nm are observed from various foods including starches under illumination of ultra-violet (UV) light at lambda=365 nm. Peak intensity is found to b extremely sensitive to the temperature of specimens. Peak intensity of PL decreases exponentially with temperature. Starches is suggested to be used as a sensor material in fluorescence thermometer. Temperature must be controlled in non-destructive quality control of starches using photoluminescence

Temperature dependence of peak intensity and peak intensity ratio of photoluminescence (PL) from garnet crystal sensor is evaluated for fluorescence thermometer application. Peak intensity of PL from YAG sensor decreases exponentially with temperature. Intensity ratio of PL peaks at 690nm, 688nm and 688nm, I678 / I689, I707 / I689, I725 / I689, increases linearly with temperature from 299 to 473K. Cr doped YAG is potentially useful sensor material in fluorescence thermometer based on temperature dependences of PL intensity, and PL intensity ratio.

Variations in the photoluminescence (PL) spectra from porous silica gel containing the luminous organic pigments, which is sensitive to organic vapors, were evaluated at various temperatures. PL intensity from rhodamine and fluorescein contained silica gel decreases with temperature. Temperature coefficient of peak intensity from rhodamine and fluorescein contained silica gel is found to be different. In order to evaluate using rhodamine and/or fluorescein contained silica gel sensors, temperature must be controlled during measurement. Fluorescence thermometer is also suggested to be developed based on temperature dependence of photoluminescence from rhodamine and fluorescein contained silica gel sensors.

Al-Si Schottky diodes doped with Cu were made. The I–V characteristics showed good rectification.

The electrical conductivity and the atomic diffusion of 7 Li in the molten lithium borates have been evaluated for studying transport phenomena in the melt. The dc electrical conductivity of melt with high viscosity shows exponential temperature dependence, σ=σ o exp for the specimens with various compositions, x=Li 2 O/(Li 2 O + B 2 O 3 ). The activation energy of dc conductivity estimated are 1.47eV for x equals 0.2, 1.10eV for x=0.25, 1.23 eV for x=0.34 and 0.77eV for x=0.5, respectively. The thermal activation energy for the atomic diffusion of 7 Li in the melt evaluated by nuclear magnetic resonance technique, 0.37eV for x=0.07 and 0.69eV for x=0.67. Activation energy of Li diffusion is much smaller than those of the electrical conductivity in boron rich specimens. These are comparable in Li richer specimens. It may be suggested that small motive Li + cations dominate the electric conduction in the molten borates in Li rich specimens. While, the anionic group, boric oxides, which are large in size and difficult to move in the melt may be responsible for the thermal activation of electrical conduction in boron rich specimens.

The 7Li NMR spectra and spin lattice relaxation rates in crystalline LiBO2 sample were measured. The spectra exhibit a broad single line at low temperature and start to show a new narrow peak at the expense of the original peak as the temperature increases, i.e., in addition to a broad line, a narrow line is observed to grow as the temperature increases.

The spin lattice relaxation rates and the absorption line shapes of 7Li in both Li2B4O7 single-crystal and glass samples were measured from room temperature up to 900 K. At lower temperatures the dominant contribution to the relaxation rate was the spin-phonon interaction in both samples. For the single crystal the relaxation caused by the diffusion of Li ions became significant above 760 K, and the narrowing of the absorption line started at about 650 K. For glass the narrowing of the line started at room temperature and the effect of the diffusion of Li ions on the relaxation rate was dominant above 400 K. From these results the correlation time τ c of the fluctuating field at Li sites in the crystal and glass of Li2B4O7 was obtained.

The effect of a magnetic field on crystal quality and impurities was investigated in detail by growing LEC GaAs crystals under a strong magnetic field of up to 3000 Oe. The infrared absorption coefficient, α, at a wavelength of 1 μm, which is related to the native defect EL2, increased or decreased, depending on the melt composition, as the magnetic field strength increased from 1500 to 3000 Oe. When the arsenic mol fraction of the melt was 0.503, no significant change in α was obtained for the same increase in the magnetic field strength. It has been confirmed that the effective segregation coefficient of carbon in GaAs approaches unity and striations can be eliminated completely as the magnetic field becomes stronger. The homogeneity of both α and the resistivity in magnetic field applied LEC (MLEC) crystals was far superior to that of LEC crystals grown without a magnetic field.

The relationship between the infrared absorption coefficient and the resistivity was examined experimentally in undoped and In‐doped liquid‐encapsulated Czochralski grown semi‐insulating GaAs. The resistivity increases from ∼106 to 5×108 Ω cm with an increase in the infrared absorption coefficient at 1 μm from 0.6 to 1.0 cm−1 in Ga‐rich GaAs, and decreases from about 5×108 to 5×106 Ω cm with an increase in the infrared absorption coefficient from 1.0 to 3.0 cm−1 in As‐rich GaAs. This fact provides a physical basis for the use of infrared transmission topography as a nondestructive, rapid characterization technique for the evaluation of the two‐dimensional uniformity in resistivity of semi‐insulating GaAs.

A new IR transmission topograph apparatus in which video image contrast is enhanced greatly by digital processing is developed for fast and nondestructive evaluation of GaAs wafers. Clear topographs of IR (1 μm) absorption in 2‐in.‐diam GaAs wafers, resulting from the distribution of the native defect EL2, and birefringence, resulting from residual stress, are obtained with good contrast and high signal/noise ratio.

The longitudinal distribution of midgap native donor concentration was investigated in detail using semi‐insulating liquid‐encapsulated Czochralski GaAs crystals grown from various melt compositions. The midgap native donor concentration was found to decrease with fractional solidification under Ga‐rich conditions, to increase under As‐rich conditions, and not to change under stoichiometric conditions. Moreover, it varied with the magnetic field intensity and the crystal‐pulling speed depending on the melt composition. These phenomena were consistently explained by assuming that the midgap native donor acts like a dopant with a certain segregation coefficient k, where k 1 under Ga‐rich conditions. This is in good agreement with the expected segregation of As atoms determined from a phase diagram with a narrow solid‐solution region.

Influence of melt composition on uniformity of resistivity and mobility in semi-insulating, undoped GaAs grown by liquid encapsulated Czochralski technique was investigated in detail. Microscopic two-dimensional resistivity distribution was measured using the three-electrode guard method, and Hall mobility was measured by the van der Pauw method. Relatively uniform, four fold symmetric resistivity distribution was observed in crystals grown from stoichiometric or slightly As-rich melt, whereas very significant fluctuations in resistivity were found in crystals grown from Ga-rich or heavily As-rich melt. High and rekatively uniform mobility along both axial and radial directions is obtained at near stoichiometric melt compositions.

We have grown undoped GaAs single crystals by magnetic field applied LEC (MLEC) technique and measured their electrical and optical properties. The most striking result was that the electrical resistivity of undoped GaAs changed from being semi-insulating (108 ohm-cm) to semi-conducting (10 ohm-cm) by increasing the magnetic field (0 to 1300 Oe). PL, DLTS and SIMS measurements suggest that the decrease of resistivity is mainly due to the decrease in concentration of the deep level defects.

A systematic analysis of heat treatment experiments on a large number of melt-grown GaAs crystals with different concentrations of carbon revealed that the carbon concentration strongly affects thermal conversion. That is, the crystal with a higher concentration, larger than 1.5×1016 cm-3, showed a greater tendency to convert during the 20 min anneal at 850°C with a Si3N4 cap than the crystal with a concentration of carbon less than 1.5×1016 cm-3. This is further evidence of outdiffusion of the main electron trap, EL2, during the anneal.

A new vertical magnetic field applied LEC apparatus has been developed for volume production of large size GaAs single crystals. The apparatus consists of a superconducting magnet with compact refrigerator systems and an in-house modified high pressure puller. Temperature fluctuation through the molten GaAs was suppressed to less than 0.3°C by the application of more than 1000 Oe. The vertical magnetic field effects on GaAs melt are described in comparison with the results of a transverse magnetic field.

Effect of magnetic field on impurity concentration incorporated into an LEC GaAs crystal has been studied. The contamination from crucibles and/or B2O3 has been found to tend to be reduced by application of a magnetic field during puling. The residual or intentionally doped carbon concentration decreased and doped chromium concentration increased under the magnetic field. These results are explained by assuming that the GaAs melt convection is suppressed and the effective viscosity of the melt is increased under the magnetic field.