Thin films of thulium-active ZnS have been deposited on ITO coated glass substrates by a low-pressure vertical metalorganic chemical vapor deposition (MOCVD) system. Dimethylzinc (DMZn) and hydrogen sulfide (H2S) are used as reactants, and Tris(hexafluoroacetonato-thulium) (Tm(HFAA)(3), molecular formula Tm(C5HF6O2)(3)) is used as dopant source. Energy dispersive spectrometer (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectra (AES), and secondary ion mass spectra (SIMS) were used to determine the elemental composition, surface morphologies and depth profiles. Optical properties of ZnS:Tm thin films were characterized by photo-luminesence (PL). The best growth conditions are substrate temperature at 225 degrees C, DMZn bubbler temperature at - 8 degrees C, Tm(HFAA), bubbler temperature at 70 degrees C, growth pressure at 30 Torr, flow rate of DMZn 2.5 x 10(-5) mol/min, flow rate of H2S 5 x 10(-4) mol/min, flow rate of Tm(HFAA), 0.1 SLM, and VI/II molar ratio of 20.