Mapping of Weak Cathodoluminescence Signals

Mapping of cathodoluminescent active materials to show growth zoning, trace element variations and valence is becoming more common [1]. The desire to capture cathodoluminescence (CL) maps from samples that are weakly emitting arises for two reasons. Firstly, the chemical spatial resolution in maps is related to the accelerating voltage used, and the drive for higher resolution x-ray maps is leading to mapping being performed at lower voltages. Lowering the accelerating voltage to improve spatial resolution has the side effect of decreasing CL yield since the CL intensity from a given sample decreases as the accelerating voltage is lowered (Fig. 1a). The second reason to measure weak CL signals is in the examination of samples that are intrinsically or extrinsically weak CL emitters (Fig. 1b) and to date have been largely ignored by CL studies, for example band-gap measurements in hematite (Fig 2.) or to reveal subtle changes in CL intensity, such as radiation damage in quartz (Fig 3).