Luminescence properties of strontium(x)calcium(1-x)sulfur:copper thin film phosphors for flat panel displays.

摘要

The luminescence properties of MBE grown CaS:Cu and SrxCa 1-xS:Cu thin-film phosphors were investigated using photoluminescence (PL) emission, excitation and decay time studies and the results were interpreted in the frame work of the configuration coordinate and crystal field theories. These are important tools in understanding the optical transitions and local symmetries of luminescent ions. The main issues in this thesis were to (i) investigate the luminescence and thermal quenching properties of CaS:Cu, (ii) understand the observed change in the spectroscopic properties of the Cu+ emission in SrxCa1-xS:Cu alloy as a function of Sr composition and to identify physical mechanisms responsible for these changes, (iii) quantitatively examine the excitation properties of SrxCa 1-xS:Cu.; From the analysis of the excitation power dependence of the photoluminescence spectra and from photoluminescence excitation spectra, the luminescence mechanism in CaS:Cu was confirmed to be a localized transition within the Cu ion. The semi-classical Mott's activation energy and the quantum mechanical Struck and Fonger model were applied to interpret the temperature evolution of the PL emission for Cu+ in CaS. Based on the spectroscopic properties and the similarity of the ionic radii of Cu+ and Ca 2+, it was concluded that Cu+ is on-center in the sulfur octahedron. By varying the bandgap of SrxCa1-xS:Cu chromaticity changes between bluish-purple with CIE coordinates (x = 0.1628, y = 0.0241) and blue/green (x = 0.1733, y = 0.2978) were achieved. The spectroscopic properties of Cu in SrxCa1-xS:Cu showed distinct patterns centered at x = 0.35 and x = 0.65 as the Sr composition was increased. These patterns were interpreted by invoking type I and type II stress fields that occurred as a result of the ionic radii mismatch of the cations. The results obtained from the decay time and site selection spectroscopy for Sr 0.82Ca0.18S:Cu strongly suggested the existence of two Cu sites.