AVS 47th International Symposium
    Flat Panel Displays Tuesday Sessions
       Session FP-TuM

Invited Paper FP-TuM2
Enhanced Activator Interactions During Low Electron Energy Cathodoluminescence

Tuesday, October 3, 2000, 8:40 am, Room 313

Session: Luminescent Materials
Presenter: C.H. Seager, Sandia National Laboratories
Authors: C.H. Seager, Sandia National Laboratories
D.R. Tallant, Sandia National Laboratories
Correspondent: Click to Email
We have measured the time decay of spectrally-resolved, pulsed cathodoluminescence (CL) and photoluminescence (PL) in several phosphors activated by rare earth and transition metal impurities; These included Y@sub 2@O@sub 3@:Eu, Y@sub 2@SiO@sub 5@:Tb, and Zn@sub 2@SiO@sub 4@:Mn; typical activator concentrations ranged from ~ 0.25 to 10%. The CL decay curves are always non-linear on a log-linear plot - i.e. they deviate from first order decay kinetics. These deviations are always more pronounced at short times and larger activator concentrations and are largest at low beam energies where the decay rates are noticeably faster. PL decay is always slower than that seen for CL, but these differences disappear after most of the excited species have decayed. We have also measured the dependence of steady state CL efficiency on beam energy. We find that larger activator concentrations accelerate the drop in CL efficiency seen at low beam energies. These effects are largest for the activators which interact more strongly with the host lattice. While activator-activator interactions are known to limit PL and CL efficiency in most phosphors, the present data suggest that a more insidious version of this mechanism is partly responsible for poor CL efficiency at low beam energies. This "enhanced" concentration quenching is due to the interaction of nearby excited activators;these interactions can lead to non-radiative activator decay, hence lower steady state CL efficiency. Excited state "clustering" appears to enhance these interactions, and this may be caused by the large energy loss rate of low energy primary electrons. In support of this idea, we find that PL decays obtained at high laser pulse energies replicate the non-linear decays seen in the CL data. This work was supported by DARPA. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract #DE-AC04-94AL85000.