Photon upconversion (UC) is a technique to convert long wavelength light into short wavelength light. UC fluorescence by triplet-triplet annihilation (TTA) follows a mechanism involving two kinds of molecules as sensitizer and emitter. In this study, we constructed the photon UC dyes system that was applicable to weak excitation light and convert the red light into yellow light in high efficiency. The present result will be useful for the purpose of application to optical elements and light medical care.