Two series of cationic heteroleptic osmium(II) complexes with a coordinated CO molecule, a chloride Cl⁻ or hydride H⁻ anion, two monodentate triphenylphosphine (tpp) ligands and one bidentate α-dimine (N^∧N) ligand were prepared from an OsCl₂(CO)₂(tpp)₂ precursor. The investigated complexes, available in the form of PF₆⁻ salts, have been identified by means of FT-IR, ¹H and ³¹P NMR spectroscopy and X-ray diffraction studies. Their photophysical properties have been investigated in dichloromethane solutions at room temperature and 1 : 1 ethanol–methanol matrices at 77 K. The investigated complexes exhibit metal to ligand charge-transfer (MLCT) phosphorescence with the emission characteristics distinctly affected by the nature of coordinated α-diimine N^∧N and Cl⁻ or H⁻ ligands. Franck–Condon emission spectral band shape analyses and DFT/TD-DFT calculations have been applied to obtain more detailed insight into the nature of emissive ³*[Os(H)(CO)(N^∧N)(tpp)₂]⁺ and ³*[Os(Cl)(CO)(N^∧N)(tpp)₂]⁺ species.