gems, corundum, color.4, luminescence

Describes the principles and gemological applications of microspectrofluorescence, with particular emphasis on corundum and ruby. The authors discuss chromium-induced luminescence in ruby and describe a prototype microspectrofluorimeter capable of recording high-resolution emission spectra from areas as small as approximately 0.5 μm. Spectra obtained from a series of Verneuil synthetic rubies are examined in detail, including emission lines associated with isolated Cr³⁺ ions, pairs of Cr³⁺ ions, and phonon interactions. The relative intensities of these features vary with crystallographic orientation and chromium concentration. The technique demonstrates the potential of highly localized fluorescence spectroscopy for detecting and characterizing trace elements and growth-related variations in gemstones.