Quenching of cathodoluminescence from Eu3+-doped La2O2S

Quenching of the cathodoluminescent (CL) efficiency of La2O2S:Eu3+ prepared by combustion reaction was investigated by measuring the temporal dependence of the CL intensities. While the emission intensity corresponding to the D05⇒F27 electronic transition of Eu3+ did not change at a low current density (e.g., 65 μA/cm2), it decayed over the first 5 s of irradiation at a high current density (e.g., 500 μA/cm2). In addition, the difference between the initial and steady-state emission intensities increased as the current density increased. Based on thermal quenching data for the D05⇒F27 transition, the quenching observed at high current densities was only partially explained by electron-beam heating. In addition to changes in intensity, the ratio of the CL intensities from the D15 transition (D05⇒F27) and the D05 transition (5D0⇒7F2) (designated D15/D05) also decreased with increasing current density during the first ∼5 s of electron irradiation. Based upon measurement of the Auger electron peak energies, it is suggested that surface voltage changes due to charging cannot explain these changes. Instead, it is postulated that local redistribution of charge carriers over the range of the primary electron beam result from induced internal electron field. The effects of these internal electric fields on the magnitude and classification of interactions of the excited Dj5 state of Eu3+ are discussed.