The present invention relates to a method for growing a gallium oxide single crystal and an apparatus for growing a single crystal, and according to one aspect of the present invention, the method includes providing a gallium oxide raw material in a crucible containing iridium, injecting carbon dioxide so that a preset carbon dioxide partial pressure is formed to suppress the loss of iridium, melting the gallium oxide raw material provided in the crucible, and producing a gallium oxide single crystal from the melt.

Multi-component rare-earth garnet optical materials comprising at least three different rare-earth elements and an optional activator ion are described. The optical materials include rare-earth garnet scintillators. Methods of preparing powders, ceramics, and single crystals of the optical materials are also described. In addition, radiation detectors comprising the rare-earth garnet scintillators are described.

Multi-component rare-earth garnet optical materials comprising at least three different rare-earth elements and an optional activator ion are described. The optical materials include rare-earth garnet scintillators. Methods of preparing powders, ceramics, and single crystals of the optical materials are also described. In addition, radiation detectors comprising the rare-earth garnet scintillators are described.

This crystal material is an oxide single crystal represented by the chemical formula M.sub.3(Ta.sub.1-xNb.sub.x)O.sub.7 . . . (1), having a cubic crystal structure and a density of 8.0 g/cm.sup.3 or more. Here, M in the chemical formula is at least one element selected from rare earth elements, and 0x1 is satisfied. The crystal material is a high-melting-point material having a melting point of 2000 C. or more. A radiation detector can be formed of a scintillator formed of the crystal material and a photodetector that receives scintillation light from the scintillator.