Influence of Mn2+ concentration on Mn2+-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties

Abstract

The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn(2+) (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn(2+)-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn(2+) and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions.

L-cysteine capped ZnS:Mn quantum dots for room-temperature detection of dopamine with high sensitivity and selectivity

“…In particular, Mn-doped ZnS (ZnS: Mn) QDs with intrinsic solubility in water have appeared as a potential fluorescent probe since they exhibit high resistance to photobleaching, broad absorption with relatively-narrow and symmetric emission, high quantum yield, and strong resistance to degradation. Their main features are not only analogous to those observed in Cd (Se, Te) QDs (most used as standards), but also ZnS:Mn QDs are nontoxic in a wide range of concentrations (Diaz-Diestra et al, 2015;Li et al, 2011b;Sotelo-Gonzalez et al, 2013;Zhang et al, 2011). In addition, the Mn-doping into the ZnS host further advances multiplicity of decay times, flexible bioconjugation approaches, enhanced surface passivation, large-effective Stokes shifts, intermittency under continuous excitation, and optical tunability (DiazDiestra et al, 2015;Liu et al, 2008a;Quan et al, 2009).…”

An Interactive Quantum Dot and Carbon Dot Conjugate for pH‐Sensitive and Ratiometric Cu2+ Sensing

“…The decrease in the lifetime of the shorter component ( τ 1 ) was more drastic than the longer lifetime component ( τ 2 ). The shorter component is attributed to surface‐exposed Mn 2+ ions, whereas the longer component has been ascribed to the 4 T 1 – 6 A 1 transition of lattice‐bound Mn 2+ ions present in the doped ZnS host . The gaps between the conduction band ( E CB ) and valence band ( E VB ) of Qdots and Cdots were determined by using cyclic voltammetry and from the Tauc plot (Figure S8).…”

“…The shorter component is at-tributedt os urface-exposed Mn 2 + ions, whereas the longer component has been ascribed to the 4 T 1 -6 A 1 transition of lattice-bound Mn 2 + ions present in the doped ZnS host. [34] The gaps between the conductionb and (E CB )a nd valenceb and (E VB )o fQ dots and Cdots were determined by using cyclic voltammetry and from the Ta uc plot ( Figure S8). The results indicated that the E CB value of Cdots is situated below the E CB value of Qdots, which provides favorable conditions for electron transfer from Qdots to Cdots.U pon electron transfer to Cdots, the population of the faster lifetime component (t 1 )i ncreaseda sc ompared with the slower lifetimec omponent (t 2 ) because both componentsa re mutually dependento ne ach other.T he surface-exposed Mn 2 + ions are affected more than the lattice-bound Mn 2 + ions because the Qdots and Cdots interact throught he electrostaticm ode, as described below, which is supported by faster decay (t 1 )a nd an almost1 00 % contribution from the faster component (a 1 ).…”

Effect of Mn doping on structural, optical and photocatalytic behaviors of hydrothermal Zn1−xMnxS nanocrystals

“…The sharp fall in intensity of the Mn 2+ emission for the 5 at.% Mndoped ZnS sample can be attributed to the concentration quenching effect and to the fact that the isolated Mn ions may stay at the surface or interstitial positions of the crystallites and these do not favor radiative transitions [51]. The initial increase in the intensity of the peak with Mn 2+ concentration (up to 3%) was due to the formation of more and more Mn 2+ luminescent centers, whereas the quenching of the orange luminescence at higher doping level was due to the interaction of the neighboring Mn 2+ ions.…”