Time resolved microscopic cathodoluminescence spectroscopy for phosphor research

In impurity doped inorganic luminescent materials, there is often a close relation between the structural and optical properties. When a phosphor shows a distribution of structural properties (such as local variations in composition, dopant concentration, crystalline phase or particle size), the luminescence properties can show a similar distribution. When evaluating the synthesized phosphors at the macroscopic scale only, these properties are averaged out, which can lead to a broadened emission spectrum or a luminescence decay curve consisting of several exponentials. This paper discusses cathodoluminescence detection inside a scanning electron microscope (SEM-CL) for the study of local emission characteristics in phosphors. In this type of instrument, imaging, local element identification as well as cathodoluminescent spectral mapping can be performed. It is shown that with the aid of a beam blanker, local decay time analysis and spectrally resolved decay time mapping can be performed. By correlating simultaneously obtained structural, compositional and luminescence properties, a profound understanding of a phosphor's behavior can be obtained. This is illustrated on Ca2SiS4:Eu, a red-emitting phosphor material of current interest for white light emitting diode (LED) wavelength conversion.