The present invention provides an organic/inorganic composite containing a
rare earth metal or/and Period IV transition metal in which the
aforementioned rare earth metal or/and Period IV transition metal is
doped at a high concentration, and control of quenching and optical
transparency are assured thereby; and an optical amplifier, a light
control optical element, and luminescent device utilizing the same. The
organic/inorganic composite containing a rare earth metal or/and Period
IV transition metal is one in which at least one species of rare earth
metal or/and Period IV transition metal is dispersed in an organic
polymer, with the aforementioned composite containing an optically
transparent organic polymer and an inorganic dispersion phase comprising:
(1) a rare earth metal and (2) another element coordinated thereto via an
oxygen atom(s). The inorganic dispersion phase in which another metal
coordinates to rare earth metal or/and Period IV transition metal via an
oxygen atom(s) preferably has an average particle size ranging from 0.1
to 1000 nm. Preferably, the ratio of rare earth metal or/and Period IV
transition metal when mathematically converted to solid content is 90
mass % or less of the total mass of the organic polymer and the rare
earth metal dispersion phase.