Electrochemical Luminescence of ZnGa2O4 and ZnGa2O4 : Mn Semiconductor Electrodes. —Emission Mechanism under Cathodic and Anodic Polarization—

Abstract

Abstract Electrochemical luminescence properties and mechanism of ZnGa2O4 and ZnGa2O4 : Mn (ZnGa2O4 doped with Mn) were studied. ZnGa2O4 disk showed an n-type semiconductor property after reduction in H2 atmosphere. Under cathodic polarization, the emission in a ZnGa2O4 electrode showed a broad peak at 485 nm in Na2S2O8 electrolyte solution. ZnGa2O4 : Mn exhibited a sharp emission peak at about 500 nm based on Mn2+, and a broad peak of ZnGa2O4 was also observed with increasing the cathodic bias. Under anodic polarization in Na2SO4 electrolyte, electrochemical luminescence was observed from the ZnGa2O4 electrode surface at +12.5 V (vs. Ag/AgCl) with two emission peaks at about 500 and 700 nm. The emission mechanism based on avalanche breakdown and impact excitation of emission centers by injected electrons is proposed. By adding K4[Fe(CN)6], KI, and KBr as reducing agents to the Na2SO4 electrolyte, the emission intensity was increased in the order KBr < KI < K4[Fe(CN)6]. Temperature dependence of the emission intensity suggests that electron transfer at the ZnGa2O4/electrolyte interface occurs equi-energetically from the occupied energy level of each reducing agent to the conduction band of ZnGa2O4.