Investigations on the defect structures for Mn2+ in CdSe nanocrystals and bulk materials and the criterion of occupation for Mn2+ in CdX (X = S, Se, Te) nanocrystals

• Published in: Magnetic resonance in chemistry 2024-08, Vol.62 (8), p.610-618
• Main Authors: Li, Guo‐Liang, Wu, Shao‐Yi, Fan, Kai‐Min
• Format: Article
• Language: English
• Subjects: Cadmium selenides; CdSe; Charge transfer; Criteria; Crystal defects; defect structures; electron paramagnetic resonance (EPR); Electrons; Hyperfine structure; hyperfine structure constants (HSCs); Impurities; Mn2; Nanocrystals; Parameters; Selenium; Tellurium
• ISSN: 0749-1581; 1097-458X; 1097-458X
• DOI: 10.1002/mrc.5446

The spin Hamiltonian parameters and defect structures are theoretically studied for the substitutional Mn2+ at the core of CdSe nanocrystals and in the bulk materials from the perturbation calculations of spin Hamiltonian parameters for trigonal tetrahedral 3d5 clusters. Both the crystal‐field and charge transfer contributions are taken into account in the calculations from the cluster approach. The impurity‐ligand bond angles are found to be about 1.84° larger and 0.10° smaller in the CdSe:Mn2+ nanocrystals and bulk materials, respectively, than those (≈109.37°) of the host Cd2+ sites. The quantitative criterion of occupation (at the core or surface) for Mn2+ in CdX (X = S, Se, Te) nanocrystals is presented for the first time based on the inequations of hyperfine structure constants (HSCs). This criterion is well supported by the experimental HSCs data of Mn2+ in CdX nanocrystals. The previous assignments of signals SI as Mn2+ at the core of CdS nanocrystals are renewed as Mn2+ at the surface based on the above criterion. The present studies would be helpful to achieve convenient determination of occupation for Mn2+ impurities in CdX semiconductor nanocrystals by means of spectral (e.g., HSCs) analysis. The local angular deviations Δθ (=1.84° and −0.10°) and similar local environments were obtained for Mn2+ at the core of CdSe nanocrystals and bulks, respectively. The quantitative occupation (at the core or surface) criterion for Mn2+ in CdX nanocrystals is presented for the first time from the hyperfine structure constants. The previous assignments of signals SI as Mn2+ at the core of CdS nanocrystals are renewed as Mn2+ at the surface from this criterion.