The　structural,　morphological,　and　optical　characteristics　of　GZO　ultra-thin　films　were　investigated　using　XRD　(X-ray　diffraction),　FE-SEM　(field　emission　electron　microscopy),　in　situ　EDS　(Energy　Dispersive　X-ray)　spectroscopy,　UV-VIS-IR　spectroscopy　and　photoluminescence　spectroscopy　(PL)　respectively.　Morphological　analysis　reveals　the　noodle,　seed　and　particle　like　structure　of　GZO　for　GaN,　sapphire　and　Si　substrates　respectively　with　average　grain　size　ranging　from　5　to　20　nm.　An　effective　mass　model　(EM-Model)　for　particle　in　a　cylindrical　wave　function　of　e-h　pair　was　correlated　with　experimental　results.　The　reduction　in　FWHM　value　(from　31　nm　to　13　nm)　of　NBE　(near-band-edge)　emission　peak　and　enhanced　NBE　intensity　have　been　achieved　with　small　grain　size.　Blue　shift　in　optical　band　gap　is　explained　in　term　of　grain　radius　by　EM-model.　Improved　optical　and　structural　properties　were　found　in　relation　with　quantum　confinement　effect.　The　current　study　states　that　grain　size　plays　vital　role　in　order　to　tailor　optical　properties　of　GZO　thin　films.　(C)　2017　Elsevier　B.V.　All　rights　reserved.