Structural Evolution Controls Photoluminescence of Post-Synthetically Modified Doped Semiconductor Nanoparticles

Abstract

This work discusses the photoluminescence properties of doped semiconductor nanoparticles by adding cadmium(II) nitrates post-synthetically to the terbium cation incorporated zinc sulfide [Zn(Tb)S] nanoparticles at room temperature to generate the Zn(Tb)S/Cd nanoparticles. The evolution of nanoparticle's emission is monitored as a function of amount of Cd 2+ , with [Zn(Tb)S]/[Cd 2+ ] = 1:10 −4 to 1:10, providing an opportunity to access materials of different chemical compositions. Structural features, as evaluated by X-ray diffraction and energy-dispersive X-ray spectroscopy, indicate a partial cation exchange of zinc by cadmium. No apparent replacement of terbium is noticed throughout the post-synthetic modification of the Zn(Tb)S nanoparticles until the relative reactant ratio reaches 1:10, and this only becomes noticeable with [Zn(Tb)S]/[Cd 2+ ] = 1:50. Remarkable differences in both broad and sharp emissions of nanoparticles and Tb 3+ , respectively, have been observed in the post-synthetic modification. The reaction initiates with a blue shift of nanoparticle's broad emission, and a further increase in Cd 2+ content results in a red shift. Tb 3+ emission, despite its insensitivity in the spectral band position due to the intra-configurational 4f transitions, shows a decrease in emission efficiency following post-synthetic modification. Formation of alloyed particles, however, significantly improved excitation contribution approaching the visible spectral region. Lifetime measurements of nanoparticles and Tb 3+ emission support the exchange of cations and the role of competitive nonradiative deactivation pathways, respectively. Collectively, nanoparticles with [Zn(Tb)S]/[Cd 2+ ] = 1:10 −4 to 1:10 −3 , 1:10 −2 , 1:10 −2 to 1:10, and 1:50 are argued to form Cd 2+ -induced surface trap-passivated Zn(Cd)(Tb)S, onset of Zn 1−x Cd x (Tb)S alloy formation, Zn 1−x Cd x (Tb)S alloys of varying compositions, and Zn 1−x Cd x S nanoparticles, respectively. Finally, this work provides a foundation to tune the properties of any emissive doped semiconductor nanoparticles in a lesser synthetically demanding fashion and has important implications in developing such materials.

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.…”

“…The displacement of Zn 2+ by Cd 2+ tunes the band gap of the NPs in the UV–visible spectral region, resulting in a trend of broad host centered and sharp Tb 3+ emissions as a function of relative reactant ratio . In the range of [Zn­(Tb)­S]: [Cd 2+ ] = 1:10 –2 – 1:10, Zn 1– x Cd x (Tb)S alloys of varying compositions form, and at higher reactant ratios of 1:50, Tb 3+ replacement from NPs becomes noticeable (see Figures and S5).…”

“…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 .…”

Postsynthetic‐Modified PANI/MOF Composites with Tunable Thermoelectric and Photoelectric Properties

“…Intentional insertion of impurity atoms into nanocrystals by cation exchange has been used to modify semiconductor properties [34–36] . Similarly, we think that the synthesis of doped crystalline MOF by heterovalent cation substitution reaction deserves to be explored.…”

“…Intentional insertion of impurity atoms into nanocrystals by cation exchange has been used to modify semiconductor properties. [34][35][36] Similarly,w et hink that the synthesis of doped crystalline MOF by heterovalent cation substitution reaction deservest ob ee xplored. Univalent silver ions are gaining increasinga ttention due to their excellent photosensitivity and conductivity.H ence, we attempted to introduces ilver ions into Co-MOF by SC-SC conversion for adjusting the opticala nd electricalproperties.…”