GaN:ZnO solid solution nanoparticles and films were synthesized by using ZnGa 2 O 4 nanoparticles with a particle size of below 25 nm obtained hydrothermally as a precursor. Nitridation of powder ZnGa 2 O 4 nanoparticles led to the formation of GaN:ZnO nanoparticles. The nitrided samples have higher specific surface area than those obtained by conventional method, which induces higher photocatalytic NO x decomposition activity. In addition, a transparent coating film with ZnGa 2 O 4 nanoparticles was converted to GaN:ZnO film after nitridation. The nitrided film absorbs UV and blue light and is [a]