We report on the luminescence of rare earth (RE) (Sm, Er, Tm) ions doped ZnO films grown by the rf-magnetron sputtering technique. Samples were insitu doped with Sm ion or with Sm, Er, and Tm ions simultaneously without any intentional co-dopants and deposited on c-Si or quartz substrates at low temperatures. Selected ZnO:RE samples were thermally annealed in 200ºC-1000ºC temperature range in oxygen or argon gas at ambient pressure. As-grown and annealed samples were amorphous (a-ZnO) as was confirmed by the X-ray analysis. Furthermore, a-ZnO:RE samples were investigated by energy diffraction, photoluminescence and cathodoluminescence. In general, CL spectra of as-grown RE-doped a-ZnO films show characteristic emission lines due to 4f-shell transitions of RE3+ ions. Optical excitation of as-grown a-ZnO doped with RE ions using above the bandgap excitation resulted in strong host emission overlapped with weak RE3+ emission bands. It was observed that a thermal annealing process promotes changes of RE ions' environments resulting in significant 4f-shell transition luminescence intensity quenching.