Boron atoms have been produced by laser ablation and trapped in solid Ar, Kr, and Xe matrices. In addition to stable doublet absorptions at 210-230 nm, broad temperature dependent bands less in blue have been recorded. With the aid of laser induced fluorescence measurements, ab initio pair potential calculations, and diatomics-in-molecules simulations these novel broad lines at 241 nm in Ar, 247 nm in Kr, and 254 nm in Xe were assigned to boron 3s(S-2)<-- 2p(P-2) transitions. The thermal behavior of the broad absorption bands is similar to what was reported for boron atoms detected by electron paramagnetic resonance [J. Chem. Phys. 114, 7144 (2001)]. The revised interpretation based on the new spectroscopic observations is in good agreement with theoretical predictions.