Extreme ultraviolet (EUV) radiation can be converted to visible light using tetraphenyl butadiene (TPB) as a phosphor. 1 mu m films of TPB were prepared using thermal vapor deposition of the pure material and by spin coating suspensions of TPB in high-molecular-weight polystyrene/toluene solutions. Calibrated sources and detectors were used to determine the effective photon conversion efficiency of the films for incident EUV radiation in the wavelength range of 125 nm <= lambda <= 200 nm. After exposure to atmosphere, the efficiency of the vapor-deposited films decreased significantly, while the efficiency of the spin-coated films remained unchanged. The production of TPB films by spin coating offers the advantages of simplicity and long-term stability. (C) 2020 Optical Society of America