A composite material includes a core particle and a silane coupling agent including a double-bond or an epoxy group grafted onto the surface of the core particle. The core particle includes an oxide of zinc and titanium, and zinc and titanium have a weight ratio of 1:0.4 to 1:0.9. The composite material may react with a radical initiator or a crosslinker to form a film, and the film can be used to cover a light-emitting element of a light-emitting device.