Cathodoluminescence study of apatite crystals

Cathodoluminescence (CL) spectrometry represents a promising technique for the analysis of trace-element concentrations and distributions in minerals. However, a higher precision and a standardization of the recording conditi ons are required to use CL spectral data quantitatively. A significant step towards a more quantitative treatment of CL spectra is presented in this s tudy. A procedure to correct the spectra for the various efficiencies as a functi on of the wavelength of the CL detector is proposed using low-pressure merc ury-vapor and quartz-iodine lamps. CL spectra presented in this study are t hus corrected for the system response. Apatite CL spectra, which are common ly composed of two broad bands centered at 3.5 and 2.2 eV, are deconvoluted to isolate component bands and determine their areas. The crystallographic control by prismatic or basal sections of apatite on spectral intensities is significant and only prismatic sections should be used. Signal decrease associated with electron bombardment (electron beam aging) is exponential a nd appears drastic in the first hundred seconds but continues even after 15 minutes of beam bombardment. All observed CL bands could be correlated with a specific activator [rare e arth elements (REE) or manganese]. The 3.5 eV band is composed of three ban ds at 3.59 eV, 3.29 eV, and 2.87 eV. Ion microprobe results and comparison between CL and photoluminescence data support Ce3+ activation for the origi n of these bands. The relationship between CL band intensity and REE concentration measured b y ion microprobe analysis demonstrates that CL also can provide semi-quanti tative data for Gd3+, Ce3+, Dy3+, and Sm3+ when recording conditions are st rictly controlled.