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

Department of Physics, Malek-Astar University of Technology, PO Box 83145/115, Isfahan, Shahin Shahr, Iran

^a e-mail: smt.otaqsara@gmail.com

Received: 19 April 2012
Revised: 19 June 2012
Accepted: 20 June 2012
Published online: 3 August 2012

Abstract

3 d 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 (~575 nm) as compared to pure ZnS Q-dots (~420 nm) which is due to ⁴T₁(G) → ⁶A₁(S) radiative transitions. Blue/green-emission peaks at ~487 nm/~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.