PURPOSE: To photo-cure a composition obtained by photopolymerizing photopolymerizable organic materials such as epoxy resins to a greater depth and thickness.

CONSTITUTION: Photopolymerizable organic resin compositions are comprised of (A) photopolymerizable organic materials and (B) photoinitiators comprising aryl ketone-containing diaryliodonium salts having the formula; R1-I+-RX- (wherein R is a 6-13C monovalent aromatic hydrocarbon group or halo substituted monovalent aromatic hydrocarbon group and R1 is a monovalent aryl ketone group which is attached to iodine by a nuclear carbon atom to form a carbon-iodine bond, and X- is a counter ion). The photoinitiators (B) having monovalent aryl ketone groups can effect deep section cure of (A) photopolymerizable organic materials and cure the materials to greater thickness, as compared to the diaryliodonium salts of the prior arts.