Advances in (and a Brief History of) Cathodoluminescence Microscopy

Abstract

Cathodoluminescence (CL) microscopy utilizes the emission of light from a material upon interaction with an electron. Luminescence in the ranges from ultraviolet to infrared wavelengths and may be analysed spatially, spectrally and temporally to form images, spectra and spectrum-images (where each pixel in a data set contains a full spectrum). CL performed in a scanning or scanning transmission electron microscope (SEM or STEM) benefits from the fact that, in these instruments, an electron beam can be made arbitrarily small compared to the (often) nanometer scale mechanism(s) driving the optical behaviours of materials. Furthermore, direct correlation with morphology, microstructure, composition and chemistry using other analytical techniques available in the electron microscope make CL a very attractive characterization tool. Here we will review the astonishing progress made recently using the CL technique from quantification of trace impurities, revealing the local density of optical states in metallic nanoparticles far below the optical diffraction limit to the study of individual quantum emitters and look forward to the exciting research possibilities in the near future.The phenomena of cathodoluminescence was first reported in 1879 by Crooks who examined the bluegreen light emitted from synthetic calcium sulfide crystals bombarded with a cathode ray [1]. However, it wasn't until the advent of its use in petrographic studies in the 1960s and 1970s that CL found widespread application where CL imaging and spectroscopy were used for the reconstruction of processes of mineral formation and alteration by the visualization of growth textures. Since the mid-1980s, panchromatic CL imaging (collecting and detecting luminescence without recourse to dispersion or filtering) has been widely used to visualize U/Pb segregation and zonation within zircon grains for accurate isotope concentration measurements made using ion probe measurements for geochronology [2]. More recently, quantification of titanium trace element concentrations below 100 ppm in quartz has been enabled by color CL and spectrum-imaging approaches for thermobarometry purposes [3].With the growth in the optoelectronics market, spectrally resolved CL gained great popularity. The most favored and successful approach involves direct optical coupling between a specimen, a monochromator, and finally a photo-detector (photomultiplier tube or charge coupled device). CL has been used extensively to analyse point and extended defects in bulk compound semiconductors and nanostructures e.g. [4] and [5] and recently to elucidate the local density of optical states in metallic nanoparticles with analysis modalities now including angularly resolved CL [6]. The strong interest in developing light emitting diodes emitting at deep ultraviolet wavelengths (<250 nm) for water purification applications and the expansion in narrow bandgap semiconductors for mid-and long-wavelength infrared detectors (3 -10 µm) has seen the development of spectrally resolved CL systems free ...

Phase composition and genesis of pyroxenic jadeite from Guatemala: insights from cathodoluminescence

“…Cathodoluminescence (CL) is the phenomenon of light emission on the surface of a material under the bombardment of an electron beam. 14,15 The minerals belong to the materials with a very long history in CL studies. [16][17][18][19][20] In comparison with the high-purity materials, minerals and rocks are "dirty" with a lot of impurities and defects.…”