Progress on a method of barium tagging for the nEXO double beta decay experiment is reported. Absorption and emission spectra for deposits of barium atoms and ions in solid xenon matrices are presented. Excitation spectra for prominent emission lines, temperature dependence, and bleaching of the fluorescence reveal the existence of different matrix sites. A regular series of sharp lines observed in
Ba+ deposits is identified with some type of barium hydride molecule. Lower limits for the fluorescence quantum efficiency of the principal Ba emission transition are reported. Under current conditions, an image of fewer than or equal to
104 Ba atoms can be obtained. Prospects for imaging single Ba atoms in solid xenon are discussed.
The lifetime of the long-lived
5d2D5/2 level in
138Ba+ ions was measured in trapped single ions and small ion crystals using continuous quantum jump spectroscopy. We find ${\ensuremath{\tau}}_{{D}_{5/2}}=25.6(0.5)\phantom{\rule{0.28em}{0ex}}\text{s}$, significantly below previously reported values. We have verified our result by exploiting camera images of the stored ions, which enabled monitoring the cleanliness and sufficiently low temperature of the ion samples, and investigating common systematic effects.