LAUSR

Abstract Novel environment friendly inorganic nano green pigments, Ni1−xCuxAl2O4 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) were successfully synthesised by simple, cost effective sol–gel method using citric acid as a gelling agent. Synthesised nano pigments were characterised by powder XRD, FT-IR, UV-DRS, SEM–EDX and TEM. Distribution of elements such as Ni, Cu, Al and O for the pigment Ni0.98Cu0.02Al2O4 was authenticated by elemental mapping analysis. The colour parameters were studied using CIE-LAB parameters. It is evident from the DRS measurement that the band gap energy of NiAl2O4 (3.11 eV) has been massively diminished to 2.63 eV when x = 0.02, unexpectedly changed the colour of the pigment from cyan to green. Whilst x = 0.1 the pigment colour has turned into grey and the corresponding band gap condensed into 2.17 eV. Effect of mineralisers like NaF, CaF2, NH4H2PO4 and Li2CO3 on the colour of Ni0.98Cu0.02Al2O4 was investigated.