  To understand the optical properties of atoms in solid state matrices, the
absorption, excitation and emission spectra of rubidium doped thin-films of
argon, krypton and xenon were investigated in detail. A two-dimensional
spectral analysis extends earlier reports on the excitation and emission
properties of rubidium in rare-gas hosts. We found that the doped crystals of
krypton and xenon exhibit a simple absorption-emission relation, whereas
rubidium in argon showed more complicated spectral structures. Our sample
preparation employed in the present work yielded different results for the Ar
crystal, but our peak positions were consistent with the prediction based on
the linear extrapolation of Xe and Kr data. We also observed a bleaching
behavior in rubidium excitation spectra, which suggests a population transfer
from one to another spectral feature due to hole-burning. The observed optical
response implies that rubidium in rare-gas thin-films is detectable with
extremely high sensitivity, possibly down to a single atom level, in low
concentration samples.
