Davy Wauters

Photoluminescent and structural properties of CaS:Pb electron beam deposited thin films

The structural and optical properties of electron beam deposited CaS:Pb thin films were investigated as a function of annealing temperature and lead concentration. X-ray diffraction measurements show weak crystallinity for such layers. Although this improves with higher annealing temperatures, no difference in the grain size could be seen by means of atomic force microscopy. This can be explained by columnar growth or relaxation of strain. At high annealing temperatures (1000 °C for 2 min) and sufficiently high lead concentrations (0.74 at%), a bright blue photoluminescence could be observed. Excitation spectra were acquired showing different excitation bands.

Influence of sintering on photoluminiscent emission of SrS:Cu,Ag powders and e-beam evaporated phosphor layers

Abstract Recently, SrS:Cu,Ag has been studied by several research groups as a blue emitter for thin film electroluminescent (EL) devices. However, both EL and PL (photoluminescent) spectra of these thin film phosphors suffer from severe non-reproducibility. In order to solve this problem, the effect of sintering the deposition source material (in N 2 and H 2 S) on the PL characteristics of both this source material and the deposited thin films is studied. It will be shown that sintering SrS:Cu,Ag in H 2 S enhances blue Ag emission in thin films, which is normally partly quenched at room temperature. Sintering also drastically increases the reproducibility of the emission spectra. In order to understand the underlying physical changes, optical and structural/morphological characterizations were performed.

Intrinsic optical and structural properties of SrS thin films

Abstract SrS thin films were deposited by electron beam evaporation on heated silica substrates. The optical properties of the layers – complex refractive index and optical band gap –were derived from optical transmission spectra, measured by means of UV-VIS-NIR spectrophotometry. The influence of post-deposition annealing by rapid thermal processing (RTP) was studied. X-ray powder diffraction (XRD) was used to study the film crystal structure and preferential orientation.

Photoluminescent, electroluminescent and structural properties of CaS:Cu and CaS:Cu, Ag thin films

Photoluminescent, electroluminescent and structural properties of CaS thin films doped with Cu and Ag have been investigated. The emission spectrum and the crystallinity are discussed for different Cu concentrations and different annealing conditions. Codoping with Ag has been evaluated, leading to a more elaborate study of CaS:Cu, Ag layers. The morphology of these layers is investigated with AFM and SEM. Measurements of the PL intensity as a function of working temperature revealed the good quenching behaviour of the layers. For the first time, blue electroluminescent emission could be obtained from a CaS:Cu, Ag thin film system.

Microoptical characterization of electroluminescent SrS:Cu,Ag thin films by photo- and cathodoluminescence observations

For SrS:Cu,Ag thin film phosphors, a postdeposition annealing step is imperative in order to obtain bright photo- or electroluminescence. However, it is not clear to date what is the most important effect of this treatment, a recrystallization of the host lattice or a redistribution of the activators. The present article discusses the microscopic emission characteristics of annealed photoluminescent layers SrS:Cu,Ag. Using cathodoluminescence measurements, it is shown that emission, originating from the grain boundaries, is very weak compared to the emission from the bulk of the grains.