| AVS 57th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+EN-MoM |
| Session: | ALD: Energy Applications |
| Presenter: | O.M. Ntwaeaborwa, University of the Free State, South Africa |
| Authors: | O.M. Ntwaeaborwa, University of the Free State, South Africa P.D. Nsimama, University of the Free State, South Africa J.J. Dolo, University of the Free State, South Africa M.S. Dhlamini, University of the Free State and CSIR, South Africa E. Coetsee, University of the Free State, South Africa J.J. Terblans, University of the Free State, South Africa H.C. Swart, University of the Free State, South Africa |
| Correspondent: | Click to Email |
Phosphors have many uses today, such as information display, medical imaging, and theft prevention. The phosphors are often used as powders, even though thin films offer higher resolution and better chemical stability. We have investigated the cathodoluminescent (CL) and photoluminescent (PL) properties of thin films of several phosphors (e.g. SrAl2O4:Eu2+,Dy3+; SiO2:PbS; Gd2O2S:Tb3+; SiO2:Ce3+,Tb3+ and Y2SiO5:Ce3+) that were ablation deposited onto Si (100) substrates using either conventional pulsed laser deposition (PLD) or pulsed reactive crossed beam laser ablation (PRCLA). Several deposition parameters were varied, including vacuum versus partial pressure of gas (O2 or Ar), type of laser pulse, and substrate temperature using either a 307 nm XeCl or 248 nm KrF excimer laser. The CL spectrum and intensity were measured in vacuum from films irradiated with 2 keV electrons for a prolonged period of time, while PL data were collected in air under excitation by either a 325 nm HeCd laser or a monochromatized xenon lamp. Both the CL and PL intensities were strongly dependent on the deposition conditions and post-deposition annealing. Data from scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the major influence of the deposition conditions on the CL/PL intensity was through changes in the morphology and topography of the films, which affects light scattering and out-coupling. Finally, the CL intensity from the films decreased significantly during prolonged electron beam irradiation. The degraded CL intensity resulted from the formation of non-luminescent oxide layers on the film surfaces. The chemical composition and electronic states of the ‘dead’ layers were analyzed using x-ray photoelectron spectroscopy (XPS). The influence of the various deposition conditions on the luminescent intensities will be discussed. The mechanism leading to lower CL intensities will be concluded to be electron stimulated surface chemical reactions.