We report optical properties and bonding behavior of nitrogen in InSbN alloys grown by metal-organic chemical vapor deposition (MOCVD) on InSb substrates in different conditions. Energy bandgap reduction is demonstrated in the alloys and the reduced value varies with growth temperature and N/(N+Sb) flux ratio. In addition to In-N bonds which are the main factor for bandgap narrowing, In-N-Sb, N-N and Sb-N bonds also exist in the alloys and they create localized states in the conduction band tail which cause non-Varshni like behavior and lattice mismatch to the InSb substrate. The Sb-N bonds are found to be more abundant than other forms of bonding in the MOCVD grown alloys due likely to the low growth temperature and high Sb/In flux ratio. (C) 2015 Elsevier B.V. All rights reserved.