Herein, rare earth oxides-based nanoparticles were synthesized and characterized for the use in photodynamic therapy. In this approach, a photosensitizer material, when excited with ultraviolet-visible light, generates reactive oxygen species, such singlet oxygen, which is an important cytotoxic agent that destroys cancer cells. Therefore, our main objective is the synthesis of scintillating nanoparticles, capable of converting X-ray radiation into UV-Vis light, designed for further functionalization with the methylene blue photosensitizer and use in cancer treatment. Thus, nanoparticles of gadolinium oxide doped with europium and samarium ions were obtained by sol-gel synthesis. Hybrid nanoparticles of silica with europium(III)-doped gadolinium oxide were also obtained with different doping concentration through the impregnation method. They were characterized with various physicochemical techniques and structural determination involving following instrumentalities: scanning and transmission electronic microscopies, infrared spectroscopy and powder X-ray diffraction, confirming the formation of nanoparticles with crystallinity and morphological properties suitable for applications in the biological system desired. In addition, photoluminescence analyses were conducted, where was possible to record excitation and emission spectra, confirming the compatibility of these materials with the photosensitizer to be used. To ensure the clinical safety of these nanoparticles, cytotoxicity studies were also carried out; results have shown that these materials did not appear to be toxic in concentrations of 10-500 micrograms.mL(-1), presenting high cellular viability. Moreover, the reactive oxygen species generation assays are under investigation in the absence and presence of the photosensitizer. In summary, it is believed that the nanoparticles obtained have a great potential for application in photodynamic therapy as an alternative for cancer treatment.