Complex metal oxide

Patent Pending PROBLEM TO BE SOLVED: To provide a method for efficiently and inexpensively producing a single-phase complex metal oxide having a small particle diameter and a homogeneous chemical composition by a liquid phase process using a smaller amount of an organic compound and more particularly, to provide a method for producing inexpensively with reduced environmental load a complex metal oxide phosphor having excellent crystallinity, a high luminance equivalent to that of a conventional large particle and realizing high-definition displays, high-luminance lighting elements or fixtures, or high-speed immunoassay systems.