Intense electroluminescence in the range 77-300 K has been observed from interface transitions in type II P-Ga0.84In0.16As0.22Sb0.78/n-In0.83Ga0.17As0.82Sb0.18 single heterojunctions grown by liquid phase epitaxy from an In-rich melt. The quaternary epitaxial layers forming the P-n heterojunction were unintentionally doped and grown lattice-matched onto a (100)-oriented n-type InAs substrate. The electroluminescence and photoluminescence emission spectra from the heterostructure were investigated in detail and are discussed below. The luminescence spectra contained two interface-induced emission bands: hnu(A) which was identified with radiative transitions between electron and hole quantum well sub-bands across the P-Ga0.84In0.16As0.22Sb0.78/n-In0.83Ga0.17As0.82Sb0.18 heterointerface, while the emission band hnu(B) originates from radiative transitions involving acceptor states in the narrow gap In0.83Ga0.17As0.82Sb0.18 near the type II heteroboundary.