Rare-earth-free phosphors based on vanadate compounds were investigated, where the vanadates included chloride vanadates (M II 2 VO 4 Cl), pyrovanadates (M II 2 V 2 O 7 ), orthovanadates (M II 3 (VO 4 ) 2 ) with divalent cations M II of Mg, Sr, Ba, and Zn, and oxofluorovanadates (A I VOF 4 ) with an alkali metal A I . A chloride pyrolysis method and a liquid phase precipitation method were proposed for preparing the chloride vanadates and pyro-and orthovanadates, respectively. These vanadate compounds showed self-activated photoluminescence (PL) based on the VO 4 clusters against the ultraviolet (UV) light irradiation. The colors of PL covered almost the whole visible-light region from blue to yellow as Sr 2 VO 4 Cl (deep blue), Ca 2 VO 4 Cl (sky blue), Ba 2 V 2 O 7 (green), Sr 2 V 2 O 7 (yellowish green), Zn 3 (VO 4 ) 2 (yellow), and Mg 3 (VO 4 ) 2 (yellow). A correlation was suggested from these compounds between the luminescent colors and the structural feature as the longer V-O distances in the VO 4 tetrahedra in the crystal structures led to the longer wavelength in PL. This seemed to be also applicable for the oxofluorovanadates A I VOF 4 (A I = K and Cs) which contain the VOF 4 polyhedra with one O 2ion and four Fions as the ligands, as they exhibited the reddish PL.

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To develop a human-friendly driver support system, it is essential to detect the driver's status such as consciousness levels and looking aside. We have developed a driver monitoring system, which detect the driver's consciousness reduction and gaze direction change by image processing techniques. Furthermore, we have proposed a new warning method with this driver monitoring system. The effectiveness in this method has been verified using a driving simulator.

Directcurrent (dc)driven inorganic electroluminescent (EL) devices were fabricated with rareearth (RE) doped ZnO as the light emitting layer (RE = Tm, Eu). The suitability of several polycrystalline materials for the substrate was examined. Among the examined materials of yttriastabilized zirconia (YSZ), alumina (Al 2 O 3 ) and magnesia (MgO), YSZ was preferable with respect to the similarity of the thermal expansion coefficient and the chemical inertness with ZnO. On the other hand, the chemical affinity of zirconia with RE 3+ became a problem. When RE = Eu, a byproduct phase of Eu 2 Zr 2 O 7 was formed during heattreatment at a high temperature. Coating a MgO thinlayer on YSZ (MgOcoated YSZ) did not alleviate the formation of Eu 2 Zr 2 O 7. The dcdriven EL devices fabricated on the YSZ and MgOcoated YSZ substrates successfully revealed EL from the bare REdoped ZnO layers between the electrodes. A sharp line emission due to Tm 3+ and Eu 3+ was obtained from Tm 3+  and Eu 3+ doped ZnO on YSZ, respectively, whereas the REdoped ZnO layers formed on MgOcoated YSZ emitted a broad luminescence due to the luminescent defects in ZnO.