Becquerel summary

Summary Radioactivity, the spontaneous decay of an unstable isotope to a more stable one, was first discovered by Henri Becquerel in 1896. Marie Curie and her husband expanded on his work and developed most of the concepts that are used today. 

The spectroscopic properties of ruby have been studied for over one hundred years starting with the work by Becquerel (1867), who excited ruby with sunlight. He claimed that the properties of this crystal were intrinsic, but later it was shown that the color as well as the luminescence of ruby are due to the Cr ion that plays the role of an optical center in the nonabsorbing AI2O3 host. Only much later these properties could be explained by considering the influence of the surroundings of the Cr center on its energy levels (crystal-field theory). For a summary of ruby history the reader is referred to ref. 1. 

Gaudin s memoir, dated 30 October 1831, was sent in lithographed form (8 pp. la. 4°) on 7 November to the Academy of Sciences, without result. A long summary (with diagrams) was given by A. C. Becquerel in a widely-read book. 2 It was unfavourably noticed by Berzelius. ... 

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