Photodynamic therapy systems comprising a nanoparticle that emits electromagnetic radiation having a first wavelength when irradiated with electromagnetic radiation, a photosensitizer which absorbs electromagnetic radiation of said first wavelength and a biocompatible mesoporous material are disclosed herein. In some examples, the photodynamic therapy system comprises a core comprising the nanoparticle, a first shell comprising the biocompatible mesoporous material, and a photosensitizer embedded in the first shell. Upon irradiation by, for example, X-rays, the nanoparticle can function as a transducer, converting X-ray photons to visible photons, and in turn, activating the photosensitizers. Methods of using the photodynamic therapy system are also disclosed.