Study on Ultraviolet-A of CaSiO3:Ce3+ Film Phosphor

Abstract

The advancement of ultraviolet (UV) radiation is urgently required for various sanitation applications, for example, disinfection of water and fine particulate issues. UV-radiative electroluminescence (EL) has been demonstrated by using Ce3+-activated CaSiO3 film phosphor as an emitting oxide layer in electrolyte-oxide-silicon (EOS) structure. The phosphor film consists of CaSiO3: Ce3+ layer grown on N-type Si wafer as the bottom electrode. The phosphor layer was prepared through a sol based spin coating method, which was heat-treated through a rapid thermal annealing method at 1200 °C for 90 seconds in a vacuum atmosphere. The 250 nm-thick CaSiO3: Ce3+ film with perovskite crystal structure was uniformly grown on N-type Si wafer. The CaSiO3: Ce3+ film phosphor showed 370 nm-ultraviolet photoluminescence (PL) spectrum, which is attributed to 5d →4f (2F5/2 and 2F7/2) transition of Ce3+ in CaSiO3: Ce3+ phosphor. The UV EL in EOS structure was performed in NaCl-water electrolyte under AC and DC voltages, which was similar with PL spectrum with the main peak at 370 nm. The threshold (turn-on) voltage was measured as about 10 Vrms. The EL intensities versus voltages were exponentially increased, and the EL intensities versus frequencies were linearly increased and then rapidply quenched. However, the EL behavior of CaSiO3: Ce3+ film was short-lived with a lifetime of less than 100 seconds, which is attributed to severe redox reaction of CaSiO3: Ce3+ with NaCl electrolyte.