The first polarized low-temperature absorption and luminescencespectra of manganese-doped crystals of BaSO
4containing essentially MnO
42- arereported. By using a flux composed of NaCl, KCl, and CsCl we wereable togrow BaSO
4:Mn
6+ crystals below 620
C.This prevents the simultaneous presence ofMnO
43- besidesMnO
42-,which was mainly responsible for the erroneous assignments of theabsorption spectrum in the literature. In t
heBaSO
4 host the MnO
42-ion occupies a site of
Cs symmetry,and the orbital degeneracies of the E and T statesare thus lifted. Above 16 000 cm
-1 theabsorption spectra consist of a series of intense ligand-to-metalchargetransfer (LMCT) excitations. Their marked polarization dependenceallows an unambiguous band assignment inthe parent
Td symmetry. Thethree origins of the
2E
2T
2ligand-field (LF) transition peak at 11 074, 11 570,and 11 790 cm
-1. The lowest-energycomponent of
2T
2 serves as the initial statefor broadband luminescence inthe near-infrared (near-IR) region with a maximum at 9300cm
-1. Below 100 K the quantum yield isunity andthe radiative lifetime is 2.75
s, and at 300 K the quantum yield isstill 20%. In both the
2E
2T
2 (d
d)absorption and luminescence spectra the vibrational structure isdominated by progressions in O-Mn-O bendingmodes whereas coupling to the totally symmetric Mn-O stretching modeis less pronounced. The luminescenceband shapes for the transitions to the two orbital components of
2E are strikingly different; the
Huang-Rhysparameters for the bending-mode progressions obtained from fits ofsimulated band shapes to the experimentalspectra are 1.3 and 3.7, respectively. This is due to weakE
e and stronger T
2eJahn-Teller (JT) effects in theground and excited LF states, respectively. The linear vibroniccoupling constants are
fE 180cm
-1 and
fT-730 cm
-1 and the corresponding JTstabilization energies
EJT(
2E)
50 cm
-1 and
EJT(
2T
2)
780cm
-1,respectively.