We propose inversion domains (IDs) to be the origin of the 3.42 eV photoluminescence (PL) band in GaN epilayers and nanocolumns. A shift of the band relatively to the near-edge PL band is induced presumably by different strain in the IDs. Micro-PL studies of nanocolumns enriched by IDs reveal anti-correlated intensity variation as well as a similarity between temperature and power dependences of both bands. A change of dominant polarization takes place across the spectra, being likely related to variation of exciton level ordering at tensile strain. Discrete narrow lines observed in the spectra are considered as manifestation of strain-induced one-dimensional carrier confinement in the IDs.
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