^aDepartment of Materials Science and Technology, Faculty of Science,

Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand

^bDepartment of Chemistry and Applied Chemistry, Faculty of Science,

Lampang Rajabhat University, Lampang 52100, Thailand

^cElectron Microscopy Research and Service Center, Faculty of Science,

Chiang Mai University, Chiang Mai, 50200, Thailand

^dMaterials Science Research Center, Faculty of Science,

Chiang Mai University, Chiang Mai 50200, Thailand

^eDepartment of Chemistry, Faculty of Science, Chiang Mai University,

Chiang Mai 50200, Thailand

^fDepartment of Physics and Materials Science, Faculty of Science,

Chiang Mai University, Chiang Mai 50200, Thailand

ZnO nanoparticles with different Sm doping contents were prepared by tartaric acid solution combustion method and followed by calcination at 600 oC for 2 h. The XRD patterns of ZnO and Sm-doped ZnO samples were indexed to the pure phase of hexagonal wurtzite ZnO structure. TEM images of ZnO and Sm-doped ZnO samples show that the samples contained nanoparticles with different particle sizes. Their particle sizes were decreased with increasing in the weight contents of Sm dopant. Their photocatalytic properties were also investigated through the photodegradation of methylene blue (MB) under visible light irradiation. The 3% Sm-doped ZnO nanoparticles have the highest photodegradation of MB under visible light irradiation because Sm3+ as an electron accepter played the role in inhibiting the recombination of charge carrier pairs and enhancing the photocatalytic performance of ZnO under visible light irradiation.