High-contrast green luminescence was obtained from molybdenum (Mo)-doped beta-phase gallium oxide (β-Ga2O3) by a sol-gel spin coating method. The X-ray diffraction, atomic force microscopy, and ultraviolet–visible–near infrared transmission results revealed that the Mo dopants did not significantly affect the fabricated films’ crystal structure, surface morphology, and energy bandgap (Eg). All spin-coated Mo-doped films formed a beta phase structure and exhibited smooth surface morphology with a root-mean-square surface roughness of less than 7 nm. The thickness of the coated film increased gradually with Mo doping concentration. In the photoluminescence measurements, a green luminescence band associated with the Mo ion dxz-dyz band transition slowly appeared, which hindered the original emission from the recombination of electron–hole pairs in β-Ga2O3 but increased overlapped green color luminescence. Compared with the undoped β-Ga2O3, the CIE chromaticity diagram showed that luminescence changed from blue to green, and the contrast of the green luminescence significantly improved from 0.33 to 0.73.