Update on the Ruby Phosphorescence Senior Lab: Cr$^{\, 3+\, \, 2}$E Lifetime and $^{4}$T Absorption Studies.

Our lab previously reported that many existing advanced laboratory experiences associated with the metastable $^{2}$E term of Cr$^{\, 3+}$ 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 $^{2}$E term. We have since published [1] techniques for students to make a consistent Cr$^{\, 3+\, \, 2}$E lifetime measurement without systematic errors associated with the Cr concentration of the ruby samples. Our result for the room-temperature radiative-lifetime for the $^{2}$E term is 3.3 \textpm 0.1 ms [1]. This type of senior lab exercise typically uses commercially available ruby spheres for which the manufacturer(s) only state an approximately 2{\%} Cr concentration. The uncertainty in Cr concentrations in commercially available ruby spheres has motivated our lab to begin a detailed study of the Cr$^{\, 3+\, \, 4}$T absorption bands near 410nm and 544nm, respectively, using commonly available advanced-physics lab equipment. We provide a status report on this aspect of our work to enhance this senior-level laboratory activity. [1] Z. Jones, J. Hinds, S. Woznichak, {\&} A. Calamai, J. of Undergrad. Rept. in Phys. \textbf{30}, 100004 (2020), \textit{and references therein}