Continuous-Flow Synthesis of Zn<sub>1–<i>x</i></sub>Mn<sub><i>x</i></sub>S Nanoparticles at\nAmbient Conditions

With\nits large direct band gap and good chemical stability, ZnS\nis suitable for many applications, including light-emitting diodes,\npanel displays, and photodetection. Here, nanoparticles of ZnS are\nsynthesized phase pure under ambient conditions by precipitation in\na simple and scalable continuous-flow reactor. Furthermore, different\ndegrees of Zn substitution with Mn have been investigated, Zn<sub>1–<i>x</i></sub>Mn<sub><i>x</i></sub>S,\nwith <i>x</i> = 0.05, 0.19, and 0.25 according to X-ray\nfluorescence measurements. The products are analyzed with multitemperature\nsynchrotron powder X-ray diffraction (PXRD) and X-ray total scattering.\nThe analysis reveals phase-pure synthesis products with the sphalerite\nstructure and crystallite sizes in the range of 3.8–4.7 nm\nin agreement with scanning transmission electron microscopy. Only\nZn<sub>0.75</sub>Mn<sub>0.25</sub>S shows traces of Mn<sub>3</sub>O<sub>4</sub>, indicating that <i>x</i> = 0.25 is above\nthe substitution limit as the impurity appears. Substitution of Zn\nwith Mn in the nanoparticles is confirmed by energy-dispersive X-ray\nspectroscopy, as well as an observed decrease in the band gap, decrease\nin the sphalerite-to-wurtzite phase transition temperature, and increase\nin the unit cell dimensions with increasing Mn content. Based on the\nmodeling of the PXRD Rietveld refined atomic displacement parameters,\nthe Debye temperature for ZnS and Zn<sub>0.95</sub>Mn<sub>0.05</sub>S is determined to be 322 ± 13 and 394 ± 22 K, respectively.