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A novel and unique understanding pertaining to the synthesis of Cu(1.8)S and CuS in bulk was achieved from the analysis of the products of the Cu-Tu precursors, with Cl(-), NO(3)(-), and SO(4)(2-) as the counteranions, in ethylene glycol. Cu(4)(tu)(9)(NO(3))(4)·4H(2)O always yielded CuS whether the dissociation was carried out in ethylene glycol in the presence of air or argon or under solvothermal conditions. Cu(1.8)S was the only product when Cu(tu)(3)Cl was dissociated in air as well as in flowing argon in ethylene glycol. A mixture of Cu(1.8)S and CuS was formed from the chloride ion containing precursor when dissociated solvothermally. Cu(2)(tu)(6)SO(4)·H(2)O yielded a mixture of CuS and Cu(1.8)S on dissociation in the presence of air and argon, as well as under solvothermal conditions. The oxidizing power of the anions Cl(-), SO(4)(2-), and NO(3)(-), present in the precursor, greatly determined the extent of formation of Cu(1.8)S and CuS. While Cu(1.8)S showed hexagonal plate like morphology, flower like morphology was observed for CuS in the SEM images. In the mixed phase, Cu(1.8)S + CuS, both these morphologies were present. Cu(1.8)S and CuS showed scattering resonances at 470 cm(-1) and 474 cm(-1), respectively, in the Raman spectrum. Magnetization measurements at room temperature revealed diamagnetic behavior for Cu(1.8)S indicating the presence of +1 oxidation state for copper. Weak paramagnetic behavior was observed for CuS with χ(M) value of 1.198 × 10(-3) emu/mol at 300 K. Both Cu(1.8)S and CuS showed similar emission behavior in the photoluminescence spectrum with band positions centered at around 387, 390, 401, 423, and 440 nm. The origin of photoluminescence in these two copper sulfides remains elusive.
Kumar et al. (Thu,) studied this question.