Enhancing the Ruby Phosphorescence Senior Lab: the Cr^{3+ 2}E Lifetimes and ⁴T Absorption Studies.

Many existing advanced laboratory experiences associated with the metastable ²E term of Cr³⁺ in ruby, which gives rise to the R-lines at 692.7 and 694.3 nm, focus on a room-temperature measurement of the radiative lifetime of the ²E term. In our local work developing a laboratory experience in atomic phosphorescence, we noted a lack of consistency in the literature for the lifetime of the Cr^{3+ 2}E term. These projects typically use commercially available ruby spheres for which the manufacturer(s) only state about a 2% Cr³⁺ concentration. The uncertainty in Cr concentration represents one source of systematic error for this laboratory experience. We present our measured lifetime with corrections for systematic issues that make this project a more rewarding experience for students. Our result for the room-temperature radiative-lifetime for the ²E term is 3.3 ± 0.1 ms; which, unlike some more recent reports (e.g. [1]), compares favorably with that of Nelson and Sturge [2]. In order to address the uncertainty in sample Cr concentration, our laboratory has recently begun a detailed study of the Cr^{3+ 4}T absorption using commonly available advanced-physics lab equipment. We also provide a status report on that aspect of our work to enhance this laboratory activity.