Microwave-assisted synthesis and characterization of undoped and manganese doped zinc sulfide nanoparticles

TL;DR

This study presents the microwave-assisted synthesis of undoped and manganese-doped ZnS nanoparticles, thoroughly characterizing their structure, optical properties, and atomic-level details, revealing how Mn doping influences the crystal and electronic structure.

Contribution

It introduces a microwave-assisted solvothermal method for synthesizing Mn-doped ZnS nanoparticles and provides detailed structural and spectroscopic analysis confirming Mn substitution and its effects.

Findings

All samples have cubic zinc blende structure.

Mn doping introduces characteristic emission at 598 nm.

Manganese ions successfully substitute zinc ions in the lattice.

Abstract

Undoped and Mn-doped ZnS nanocrystals were produced by the microwave-assisted solvothermal method and characterized by X-ray diffraction, photoluminescence spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy. All samples have the cubic zinc blende structure with the lattice parameter in the range of $a$ = 5.406-5.411 \r{A}, and the average size of crystallites is in the range of 6-9 nm. These nanoparticles agglomerate and form large grains with an average size of up to 180 nm. The photoluminescence of the undoped ZnS sample shows a broad emission band located at 530 nm, attributed to the defects at the surface of nanoparticles. In all Mn-doped samples, the emission peak at 598 nm was observed assigned to the characteristic forbidden transition between excited ($^4$T$_1$) and ground ($^6$A$_1$) levels of Mn$^{2+}$. Synchrotron radiation X-ray absorption spectroscopy at the Zn and Mn K-edges combined with reverse Monte Carlo (RMC) simulations based on the evolutionary algorithm confirms that manganese ions substitute zinc ions. However, the difference in the ion sizes ($R$(Mn$^{2+}$(IV)) = 0.66 \r{A} and $R$(Zn$^{2+}$(IV)) = 0.60 \r{A}) is responsible for the larger interatomic distances Mn-S (2.40(2) \r{A}) compared to Zn-S (2.33(2) \r{A}). The static structural relaxations in ZnS:Mn nanoparticles are responsible for the large values of the mean-square displacements factors for Zn, S and Mn atoms obtained by RMC simulations.