Nanoparticle (NP) and photosensitizer (PS) conjugates capable of X-ray photodynamic therapy (X-PDT) are a research focus due to their potential applications in cancer treatment. Combined with X-PDT, appropriate imaging properties of the nanocomposite will make it suitable for theranostics of deep lying tumors. In this work, we describe the development of magnetic-luminescent Gd2.98Ce0.02Al5O12 nanoparticles (GAG) coated with mesoporous silica (mSiO(2)) and loaded with rose bengal (RB) to yield a nanocomposite GAG@mSiO(2)@RB capable of X-PDT. GAG nanoparticles were synthesized using the sol-gel method. The synthesized GAG nanoparticles showed a strong visible yellow emission with a quantum yield of similar to 32%. Moreover, the broad emission spectra of GAG nanoparticles centered at 585 nm showed a good overlap with the absorption of RB. Upon irradiation with X-rays (55 1(V), the GAG@mSiO(2)@RB nanocomposite produced significantly higher singlet oxygen compared with RB alone, as confirmed by the 1,2-diphenylisobenzofuran (DPBF) assay. The developed GAG@mSiO(2)@RB nanocomposite significantly reduced the viability of human breast cancer (MDA-MB-231) cells upon irradiation with blue light (lambda = 470 nm). The calculated LC50 of GAG@mSiO(2)@RB nanocomposites were 26.69, 11.2, and 6.56 pg/mL at a dose of similar to 0.16, 0.33 and 0.5 J/cm(2), respectively. Moreover, the nanocomposite showed paramagnetic properties with high magnetic mass susceptibility which are useful for high contrast T-1 weighted magnetic resonance imaging (MRI). Together with X-PDT, the paramagnetic properties of the proposed GAG@mSiO(2)@RB nanocomposite system are promising for their future application in simultaneous detection and treatment of deep-lying tumors. (C) 2018 Elsevier Inc. All rights reserved.