NOVELTY - A wavelength conversion material comprises resin particles containing acrylic resin containing organic rare-earths complex. The acrylic resin is a polymer obtained by reacting a composition containing a (meth)acrylate monomer, a crosslinking agent, and an azo polymerization initiator. The composition does not contain organic peroxide (a) containing carboxyl-containing group (I) as polymerization initiator, and contains organic peroxide (b) having 1-minute half life temperature of 145 degrees C or less as polymerization initiator.    USE - Wavelength conversion material is used for forming sealing film for solar cell (all claimed). Can also be used for electric equipment, optical instrument, display apparatus, and agricultural material.    ADVANTAGE - The wavelength conversion material has excellent wavelength conversion effect for long period of time and suppressed deterioration of the organic rare-earth complex.    DETAILED DESCRIPTION - A wavelength conversion material comprises resin particles containing acrylic resin containing organic rare-earths complex. The acrylic resin is a polymer obtained by reacting a composition containing a (meth)acrylate monomer, a crosslinking agent, and an azo polymerization initiator. The composition does not contain organic peroxide (a) containing carboxyl-containing group of formula: R-C(=O)O- (I) as polymerization initiator, and contains organic peroxide (b) having 1-minute half life temperature of 145 degrees C or less as polymerization initiator.    R=optionally substituted hydrocarbyl.    INDEPENDENT CLAIMS are included for the following:    (1) sealing film (13A,13B), which contains the wavelength conversion material and olefin (co)polymer; and    (2) solar cell, which consists of a solar cell element sealed using the sealing film.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of solar cell.    Surface side transparent protection material (11)    Back surface side protection material (12)    Sealing films (13A,13B)    Cell (14)