Relaxation Dynamics of Excited States in Mn 2+ -Doped ZnCdS (Core)/ZnS (Shell) Quantum Dots Ions in Propylene Carbonate
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Relaxation Dynamics of Excited States in Mn2+-Doped ZnCdS (Core)/ZnS (Shell) Quantum Dots Ions in Propylene Carbonate A. N. Kostrova, F. E. Gosteva, I. V. Shelaeva, A. V. Aybusha, Yu. A. Kabachiyb, S. Yu. Kochievb, O. Yu. Antonovab, P. M. Valetskyb, and V. A. Nadtochenkoa, * a
Semenov Federal Scientific Center of Chemical Physics, Russian Academy of Sciences, Moscow, 119991 Russia b Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, 119334 Russia *e-mail: [email protected] Received July 7, 2020; revised July 7, 2020; accepted July 8, 2020
Abstract—It has been shown that luminescence in [email protected]/ZnS quantum dots (QDs) in propylene carbonate is due to a single Mn2+(4T1 → 6A1) band and has a quantum yield of ~24%. The Mn2+(4T1) level is excited through the light absorption in the exciton absorption bands of Zn0.49Cd0.51S/ZnS. The femtosecond dynamics of the difference spectra of [email protected]/ZnS QDs show fast relaxation of the exciton on the subpicosecond–picosecond timescale. At delay times in picosecond range, the band of stimulated luminescence has been detected in difference absorption spectra in the Mn2+(4T1 → 6A1) transition region. A qualitative hypothetical mechanism of nonradiative energy transfer from the exciton to Mn2+(4T1) involving the Auger transition in the trap states has been proposed. The assumption solves the problems of the energy excess of 0.98 eV in the energy transfer to the 3d5 level of Mn and of the conservation of the total spin of the system. Keywords: quantum dots, femtosecond spectroscopy, energy transfer DOI: 10.1134/S0018143920060090
Semiconductive nanocrystals or quantum dots (QDs) derived from zinc and cadmium chalcogenides and doped with transition metal ions, such as Mn2+, attract significant attention for application in photonics and optoelectronics and as biomedical sensors [1– 3]. Alloyed of ZnxCd1 – xS QDs are promising materials for application in light-emitting devices and as an active medium for lasers in the short-wavelength visible range [4, 5]. It was shown earlier by the example of QDs from Zn and Cd chalcogenides that Mn2+ imbedded in the QD crystal lattice could quench exciton luminescence and be the main emitting state in QDs [6]. The alloyed ZnxCd1 – xS QDs are easier to dope with Mn2+ ions than the QDs from a single metal. The aim of this study is to investigate the photophysical properties of Mn@ZnCdS/ZnS colloid QDs in propylene carbonate, an aprotic polar solvent. In this work, we studied excitonic states in Mn@ZnCdS/ZnS QDs, determined the luminescence quantum yields, and considered possible mechanisms of energy transfer between electronic states of the core and the 3d5 levels of Mn2+ in Mn@ZnCdS/ZnS QDs.
EXPERIMENTAL Materials Zinc acetate dihydrate (Zn(OAc)2 ⋅ 2H2O, 98%), cyclohexane (99 + %, for spectroscopy), 1-octadecene (ODE, 90%, technical grade), tetramethylammonium hydroxide (TMAH, 25 wt % in methanol), manganese(II) chloride (MnCl2, anhydrous, 99%), CdO (99.5%), oleic acid (HОl, 90%, technical
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