Enhanced Temperature-Sensing Behavior of Ho3+-Yb3+-Codoped CaTiO3 and Its Hybrid Formation with Fe3O4 Nanoparticles for Hyperthermia

In the present work, we describe the synthesis of (Ca0.99-xHo0.01Ybx)TiO3 (x = 0.05, 0.10, and 0.15) perovskite nanoparticles with a cubic structure by using a sol-gel method. As-synthesized particles have been found to be spherical in shape, as analyzed by transmission electron microscopy and scanning electron microscopy. Fourier transform infrared spectra of the product perovskite consist of distinct featured vibrational modes of Ti-O. Upconversion as well as power-dependent (500-4000 mW) spectra have been investigated at 980 nm excitation. It exhibits emission peaks at 547, 655, and 759 nm owing to F-5(4)/S-5(2) -> I-5(8), F-5(5) -> I-5(8), and F-5(4)/S-5(2) -> I-5(7) transitions of Ho3+ ions, respectively. Optical thermometry behavior has been evaluated using fluorescent intensity ratio (FIR) of thermally and electronically coupled levels of Ho3+ ions. It reports a good sensitivity with 0.0229 and 3 X 10(-3) K-1 as estimated through thermally and electronically coupled FIR, respectively, at room temperature (303 K). Upconversion nanoparticles of (Ca0.89Ho0.01Yb0.1)TiO3 have further been coupled with Fe3O4 as hybrid magnetic nanoparticles for hyperthermia study. It attains hyperthermia temperature (42 degrees C) in 3 min under ac magnetic field, with a specific absorption rate of 35 W/g. Therefore, it could be interpreted that the present hybrid upconversion nanoparticles may be very useful and paves the path for cancer therapy (hyperthermia) and in likewise biomedical applications.