A composition comprising: a first monomer comprising at least three thiol groups, each located at a terminal end of the first monomer, wherein the first monomer is represented by the following Chemical Formula 1-1: a second monomer comprising at least two unsaturated carbon-carbon bonds, each located at a terminal end of the second monomer, wherein the second monomer is represented by the following Chemical Formula 2: wherein in Chemical Formulae 1 and 2 groups R2, Ra to Rd, Ya to Yd, L1′ and L2, X and variables k3 and k4 are the same as described in the specification, and a first light emitting particle, wherein the first light emitting particle consists of a semiconductor nanocrystal comprising a Group II-VI compound, a Group III-V compound, a Group IV-VI compound, or a combination thereof, wherein the first light emitting particle has a core/shell structure having a first semiconductor nanocrystal being surrounded by a second semiconductor nanocrystal, and the first semiconductor nanocrystal being different from the second semiconductor nanocrystal.