What Role Can Surface Capping Ligand Play To Control Dopant Emission in Semiconductor Nanoparticles?

Abstract

The role of surface capping ligands in controlling dopant photoluminescence in semiconductor nanoparticles is examined by monitoring emission in terbium cation incorporated zinc sulfide [Zn­(Tb)­S] nanoparticles, as a function of [H+] that is varied postsynthetically. Increases in Tb3+ emission of ∼6 and ∼1.3 times are observed on changing the pH from 4 to 7 and from 7 to 11, respectively. An increased contribution of host sensitization over direct excitation is observed under basic conditions. Subtle structural modification of the capping ligand is argued to be solely responsible for the dopant emission in the acidic–neutral range. The neutral–basic range in addition to this effect has a minor contribution from alteration in band alignment as well. A major outcome from this work relates to identifying the role of the terminally placed functional group in the capping ligand to control emissions from both the host (zinc sulfide nanoparticles) and guest (Tb3+), with a pronounced effect on dopant Tb3+ emission in the 1-thioglycerol capped Zn­(Tb)S nanoparticles. These results identify surface engineering as an important modulator, in addition to the primary criteria of (a) band gap engineering and (b) breaking (or optimizing) dopant local site symmetry in maximizing (or guiding) dopant emission in doped semiconductor nanoparticles.

Optimizing the Key Variables to Generate Host Sensitized Lanthanide Doped Semiconductor Nanoparticle Luminophores

“…For postsynthetically modified II–VI NPs energy dispersive X-ray spectroscopy (EDS) showed (a) incorporation of Ln in the NPs, (b) significant changes in anion content of the NPs, and (c) an absence of complete cation exchange which is consistent with thermodynamic expectations . While Ln 3+ emission is appreciable in semiconductor NPs with a concentration in the range of tens of micromolar, the same can only be realized with a millimolar concentration for their free salts. ,, Dramatically altered excitation profiles upon monitoring Ln 3+ emissions in NPs, which overlap with NPs electronic absorption spectra, ,,− ,,− demonstrate the sensitization of the Ln 3+ emission by the NP. The significant lengthening of Ln 3+ emission lifetime in the NPs, as opposed to their corresponding free Ln 3+ salts in bulk solvent, , and the spectral changes of the NP capping ligand’s IR absorption spectrum by Ln 3+ ,, further substantiate the incorporation of the Ln 3+ in the NP lattice.…”

“…This difference has been explained as arising from a more effective emission quenching of Tb 3+ by the OH oscillators in the 1-thioglycerol. Corroboration of this interpretation comes from pH studies which show a strong increase in Tb 3+ emission with increasing pH, see Figures c and S8, that is reversible. The NP size and the asymmetry ratio of Tb 3+ emission bands do not change significantly with pH, from 4 to 10, indicating that energy band alignments and the Tb 3+ co-ordination environment are not changing.…”

“…The Ln 3+ incorporation (in both synthetic and postsynthetic cases) has been demonstrated through observation of energy dispersive X-ray spectroscopic signatures for Ln 3+ in purified NPs, − and the increase in Ln 3+ photoluminescence in the NPs as compared to that found for free salts in bulk solvent. For postsynthetically modified II–VI NPs energy dispersive X-ray spectroscopy (EDS) showed (a) incorporation of Ln in the NPs, (b) significant changes in anion content of the NPs, and (c) an absence of complete cation exchange which is consistent with thermodynamic expectations .…”

Regulating the Fluorescence Emission of CdSe Quantum Dots Based on the Surface Ligand Exchange with MAA

“…Figure 4(A) showed the schematic diagram of the formation of heterojunction on the interface between the QDs ligands and AAO substrate, and Figure 4(B) corresponded to the physical mechanism of the electron transfer. Due to the oxygen vacancy on the surface of Al 2 O 3 nanofilm, there appeared a series of surface defects in the forbidden band, providing a large number of composite centers for photon generated carriers 45‐47 . Generally, the fluorescence lifetime of the fluorescent radiation compound is about 10 μs, which could provide enough time to complete the electron transfer process 48,49 .…”

Влияние Ионов Неодима (III) На Фотолюминесценцию Сульфидов Кадмия И Цинка В Полиакрилатной Матрице

“…Востребованными оптическими активаторами являются ионы лантанидов. Они применяются в сочетании с неорганическими полупроводниками [25][26][27][28][29][30][31]. Исследованы преимущественно КТ, легированные ионами Eu 3+ и Tb 3+ .…”