Tunable visible emission of TM-doped ZnS quantum dots (TM: Mn2+, Co2+, Ag+)

3d transition-metallic ions doped ZnS quantum dots (Q-dots) were synthesized by the facile wet-chemical process. During synthesis, various ions, i.e. manganese (Mn2+), cobalt (Co2+) and silver (Ag+), were used and their photoluminescence (PL) response investigated. UV-vis absorption studies show that the various dopant ions can effectively tune energy band structure. The PL emission band is red shifted on Mn2+ doping (similar to 575 nm) as compared to pure ZnS Q-dots (similar to 420 nm) which is due to T-4(1)(G) -> (6)A(1)(S) radiative transitions. Blue/green-emission peaks at similar to 487 nm/similar to 508 nm observed, respectively, on Co2+/Ag+ doping are probably arising from the recombination between the sulfur vacancy level and the new dopant level. Luminescence emission efficiency (LEE) is found to be maximum at 5 mol% Mn2+ doping and then decreases. On doping by Ag+ the LEE is found to be maximum at 2 mol% doping and almost completely quenched at 5 mol% doping. Contrary to the above, Co2+ quenched the overall PL.