A method of increasing the luminescence efficiency of titanium-doped oxide crystal, used as a laser material, is disclosed. This is accomplished by tempering the crystal at a temperature from 1750° C. to 50° C. below the melting point of the oxide crystal in a hydrogen protecting atmosphere with a constant partial pressure of the aluminium suboxide Al.sub.2O gas. By applying the method of the present invention, its luminescence efficiency of titanium-doped oxide crystal increases by 10 to 50 percent, and possibly by as much as 100 percent or more compared to previous technological treatments.

Provided is a high-density lithium-containing garnet crystal body. The lithium-containing garnet crystal body has a relative density of 99% or more, belongs to a tetragonal system, and has a garnet-related type structure. A method of producing a Li.sub.7La.sub.3Zr.sub.2O.sub.12 crystal, which is one example of this lithium-containing garnet crystal body, includes melting a portion of a rod-like raw material composed of polycrystalline Li.sub.7La.sub.3Zr.sub.2O.sub.12 belonging to a tetragonal system while rotating it on a plane perpendicular to the longer direction and moving the melted portion in the longer direction. The moving rate of the melted portion is preferably 8 mm/h or more but not more than 19 mm/h. The rotational speed of the raw material is preferably 30 rpm or more but not more than 60 rpm. By increasing the moving rate of the melted portion, decomposition of the raw material due to evaporation of lithium can be prevented and by increasing the rotational speed of the raw material, air bubbles can be removed.

The application relates to fluorescent powder which has a garnet structure and can be effectively excited by ultraviolet light or blue light, a method for preparing the fluorescent powder, and a light emitting device, an image display device and an illumination device comprising the fluorescent powder. A chemical formula of the fluorescent powder is expressed as: (M.sup.1a-xM.sup.2x)ZrbM.sup.3cOd, where M.sup.1 is one or two elements selected from Sr, Ca, La, Y, Lu and Gd, Ca or Sr being necessary; M.sup.2 is one or two elements selected from Ce, Pr, Sm, Eu, Tb and Dy, Ce being necessary; M.sup.3 is at least one element selected from Ga, Si, and Ge, Ga being necessary; and 2.8≦a≦3.2, 1.9≦b≦2.1, 2.8≦c≦3.2, 11.8≦d≦12.2, and 0.002≦x≦0.6.

The application relates to fluorescent powder which has a garnet structure and can be effectively excited by ultraviolet light or blue light, a method for preparing the fluorescent powder, and a light emitting device, an image display device and an illumination device comprising the fluorescent powder. A chemical formula of the fluorescent powder is expressed as: (M.sup.1a-xM.sup.2x)ZrbM.sup.3cOd, where M.sup.1 is one or two elements selected from Sr, Ca, La, Y, Lu and Gd, Ca or Sr being necessary; M.sup.2 is one or two elements selected from Ce, Pr, Sm, Eu, Tb and Dy, Ce being necessary; M.sup.3 is at least one element selected from Ga, Si, and Ge, Ga being necessary; and 2.8≦a≦3.2, 1.9≦b≦2.1, 2.8≦c≦3.2, 11.8≦d≦12.2, and 0.002≦x≦0.6.

A Group III nitride substrate contains a base material part of a Group III nitride having a front surface and a back surface, the front surface of the base material part and the back surface of the base material part having different Mg concentrations from each other.

A Group III nitride substrate contains a base material part of a Group III nitride having a front surface and a back surface, the front surface of the base material part and the back surface of the base material part having different Mg concentrations from each other.

A method for producing a Group III nitride crystal, includes: preparing an RAMO.sub.4 substrate containing a single crystal represented by the general formula RAMO.sub.4 (wherein R represents one or a plurality of trivalent elements selected from a group consisting of Sc, In, Y, and a lanthanoid element, A represents one or a plurality of trivalent elements selected from a group consisting of Fe(III), Ga, and Al, and M represents one or a plurality of divalent elements selected from a group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd) and having a notch on a side portion thereof; growing a Group III nitride crystal on the RAMO.sub.4 substrate; and cleaving the RAMO.sub.4 substrate from the notch.

A Group III nitride substrate contains a base material part of a Group III nitride having a front surface and a back surface, the front surface of the base material part and the back surface of the base material part having different Mg concentrations from each other.

A Group III nitride substrate contains a base material part of a Group III nitride having a front surface and a back surface, the front surface of the base material part and the back surface of the base material part having different Mg concentrations from each other.

According to an embodiment of the present invention, a method for preparing a graphite-titanium oxide composite comprises (S1) a surface-modifying graphite with benzyl alcohol or a cellulose-based material using a sol-gel method, (S2) distributing the surface-modified graphite in a solvent, adding a titanium precursor to the solvent, and mixing the titanium precursor with the surface-modified graphite to obtain a graphite-titanium mixture, and (S3) thermally treating the graphite-titanium mixture to grow a titanium oxide on a surface of the graphite.