Amorphous non-doped and Se-, Cu-, and Zn-doped Sb2S3 nanoparticles prepared by a hot-injection method: bandgap tuning and possible observation of the quantum size effect

Abstract The modified hot-injection method was applied for the synthesis of amorphous non-doped and copper (Cu) and selenium (Se) doped antimony (III) sulfide (Sb2S3) nanoparticles with reduced sizes. Moreover, zinc (Zn) doped Sb2S3 nanoparticles were synthesized for the first time by the same approach. High-resolution transmission electron microscopy (HRTEM) and TEM of amorphous undoped and doped samples revealed small spherical nanoparticles of a few (1-4) nanometers aggregated into larger spherical clusters, while introducing different dopant ions into the Sb2S3 structure did neither influence the spherical morphology nor the sizes of samples. The presence of the basic elements (S and Sb) and dopants (Cu, Se, or Zn) was confirmed by EDX analysis and mapping. Additionally, field emission scanning electron microscopy (FE-SEM) was performed on the Zn-doped Sb2S3 sample, confirming spherical morphology as well as quantitative incorporation of Zn in the Sb2S3 lattice. X-ray powder diffraction (XRPD) results of the non-doped and doped samples revealed an amorphous structure. The crystalline Zn-doped Sb2S3 samples obtained by heating the amorphous ones revealed well-defined peaks from only the Sb2S3 phase, confirming a successful doping process. Diffuse reflectance spectroscopy (DRS) revealed high optical bandgap energies (2.03–2.12 eV) in comparison to the values (1.6–1.7 eV) obtained for large spherical non-doped and doped particles. It was demonstrated that there is not only a significant reduction in particle size compared to previously synthesized non-doped and doped amorphous nanoparticles of the same composition, but that there is also a significant increase in the bandgap values of 0.4-0.5 eV, which could be attributed to a quantum size effect. X-ray photoelectron spectroscopy (XPS) measurements revealed pure phase composition without any impurities for the undoped sample, and characteristic peaks for copper 2p, selenium, and zinc Auger peaks for the doped samples, respectively. The XPS valence band measurements were performed due to the weak Zn Auger peak, confirming a shift towards lower binding energy compared to the non-doped sample, demonstrating the doping of the observed sample. Photoluminescence (PL) measurements show that embedding Zn into the Sb2S3 host lattice suppresses the wide luminescence band with peaks at 1.7 eV, 2.0 eV, 2.2 eV, and 2.4 eV, which is related to intrinsic defects. Furthermore, the energy dependence of the light emission on the size of the synthesized nanoparticles suggests that the quantum confinement effect causes the light emission.