Highly crystalline, phase pure Cu₃P nanocrystals (NCs) have been successfully synthesized using ionic liquid-assisted solvothermal method at relatively low temperature (200 ^ºC). Herein, ionic liquids (ILs) are used as a structure directing/templating agent. Effect of ILs and precursor concentration on crystal phase, crystallite size, lattice strain, morphology and grain size of Cu₃P NCs is studied. In the presence of IL, crystallite size and lattice strain significantly change with changing the concentration of red phosphorus. For example, smaller crystallite size (38.5 nm) and compressive lattice strain are obtained when 10 times of red phosphorous is used. However, bigger size (41.9 nm) and tensile lattice strains are obtained for the lower concentration of phosphorous (5 times). At higher phosphorus concentration, hexagonal shaped microcrystals with prominent grain are observed. HRTEM images reveal that spherical-shaped particles on further agglomeration through Ostwald ripening process form hexagonal-shaped bigger microstructures. However, on doping the rare-earth ions (RE³⁺ = Ce³⁺/Tb³⁺) in the Cu₃P NCs show the green luminescence (at 542 nm) which is attributed to the emission of Tb³⁺ ions. To the best of our knowledge, this is the first report on rare earthdoped Cu₃P nanoparticles and shows promise on the luminescence aspect of Cu₃P nanomaterials alongwith its already existing plasmonic and semiconducting properties.