Enhancement of photoluminescence emission and anomalous photoconductivity properties of Fe3O4@SiO2 core-shell microspheres

In this manuscript we report the successful synthesis of both pristine Fe3O4 and the Fe3O4@SiO2 core@shell structure. From SEM images we observe that each Fe3O4 microsphere is composed of a large number of smaller nanoballs. We have extensively studied the photoluminescence and photoconductivity properties of both pristine and SiO2 coated Fe3O4 particles for the first time. An enhancement in photoluminescence emission is observed in the Fe3O4@SiO2 core@shell samples, whereas a reduced and negative photoconductivity is observed in the same sample. SiO2 coating reduces the concentrations of non-radiative trap levels at the interfaces of the core and shell, thereby resulting in the enhancement of photoluminescence intensity in the core-shell particles. An exponential rise and decay in photocurrent is observed upon UV irradiation in the ON and OFF state, respectively, for Fe3O4, whereas for Fe3O4@SiO2, we observe a transient rise in the photocurrent and this photocurrent is not stable. We have explained this unusual behavior of photocurrent.