Halide exchange mediated cation exchange facilitates room temperature co-doping of d-and f-block elements in cesium lead halide perovskite nanoparticles.

This study presents a halide exchange mediated cation exchange reaction to co-dope d- and f-block elements in CsPbX3 NPs at room temperature. Addition of MnCl2 and YbCl3 to CsPbBr3 NPs induces ion exchange reactions generating the corresponding CsPbBr3/MnCl2YbCl3 NPs. In addition to the perovskite emission, the NPs display sensitized Mn2+ and Yb3+ emissions in concert spanning the UV, visible, and NIR spectral region. Structural and spectroscopic characterizations indicate a substitutional displacement of Pb2+ by the Mn2+ and Yb3+. The identity of the host halide in modulating the ion exchange reactions was also tested. An effective perovskite host NP is presented that can be used to incorporate d-f or f-f dopant combinations to realize a gamut of dopant emission lines. A charge trapping based photophysical model is developed that focuses on rational energy alignments to predict dopant emissions semi-empirically and aids the design of optimal perovskite host-multi-dopant combinations.

Size-dependent chiro-optical properties of CsPbBr3 nanoparticles.

Chiral metal halide perovskites have garnered substantial interest because of their promising properties for application in optoelectronics and spintronics. Understanding the mechanism of chiral imprinting is paramount for optimizing their utility. To elucidate the nature of the underlying chiral imprinting mechanism, we investigated how the circular dichroism (CD) intensity varies with nanoparticle size for quantum confined sizes of colloidal CsPbBr3 perovskite nanoparticles (NPs) capped by chiral ß-methylphenethylammonium bromide ligands. We find that the CD intensity decreases strongly with increasing NP size, which, along with the shape of the CD spectra, points to electronic interactions between ligand and NP as the dominant mechanism of chiral imprinting in smaller NPs. We observe that as the NP size increases and crosses the quantum confinement threshold, the dominant mechanism of chirality transfer switches and is dominated by surfaces effects, e.g., structural distortions. These findings provide a benchmark for quantitative models of chiral imprinting.

Room temperature doping of Ln3+ in perovskite nanoparticles: a halide exchange mediated cation exchange approach.

This study presents a halide exchange mediated cation exchange strategy for a room temperature doping of trivalent lanthanide cations (Ln3+) in cesium lead halide (CsPbX3) nanoparticles (NPs). Post-synthetic addition of LnCl3 [Ln = Nd, Sm, Eu, Tb, Dy, and Yb] to a solution of CsPbBr3 NPs generates the corresponding lanthanide doped NPs which display host sensitized Ln3+ emission. Structural and spectroscopic characterizations indicate a successful halide exchange and substitutional displacement of Pb2+ by Ln3+. The effect of halide identity in controlling the Ln3+ sensitization was also evaluated. A photophysical framework is presented that can be used to predict the Ln3+ sensitization in perovskite NPs semiempirically, thereby removing the constraints of trial and error in designing a perovskite NP-Ln3+ host-guest combination.

Using post-synthetic ligand modification to imprint chirality onto the electronic states of cesium lead bromide (CsPbBr3) perovskite nanoparticles.

This study presents a post-synthetic ligand modification strategy for the generation of chiroptically active, blue emitting CsPbBr3 nanoparticles (NPs) - an expansion to the library of 3D chiral perovskite nanomaterials. Addition of [R- and S-] 1-phenylethylamine, 1-(1-naphthyl)ethylamine, or 2-aminooctane to the synthesized CsPbBr3 NPs is shown to induce Cotton effects in the NP first exciton transition, suggestive of a successful electronic coupling between the chiral ligands and the NPs. The availability of these chiral CsPbBr3 NPs thrusts them into the forefront of perovskite nanomaterials for examining the implications of the chiral induced spin selectivity (CISS) effect and other applications in spintronics.

Delivery of thymoquinone through hyaluronic acid-decorated mixed Pluronic® nanoparticles to attenuate angiogenesis and metastasis of triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic subtype of breast cancer showing non-responsiveness to most available therapeutic options. Therefore, smart therapeutic approaches to selectively transport and target TNBCs are required. Herein, we developed thymoquinone (TQ)-loaded, hyaluronic acid (HA)-conjugated Pluronic® P123 and F127 copolymer nanoparticles (HA-TQ-Nps) as a selective drug-carrying vehicle to deliver anticancer phytochemical TQ to TNBC cells. The mean size of nanoparticles was around 19.3 ± 3.2 nm. and they were stable at room temperature up to 4 months. HA-TQ-Nps were immensely cytotoxic towards TNBC cells but did not show the toxic effect on normal cells. Detailed investigations also demonstrated its pro-apoptotic, anti-metastatic and anti-angiogenic activity. In-depth mechanistic studies highlighted that HA-TQ-Nps retarded cell migration of TNBC cells through up-regulation of microRNA-361 which in turn down-regulated Rac1 and RhoA mediated cell migration and also perturbed the cancer cell migration under the influence of the autocrine effect of VEGF-A. Moreover, HA-TQ-Np-treatment also perturbed tumor-induced vascularization by reducing the secretion of VEGF-A. The anti-metastatic and anti-angiogenic activity of HA-TQ-Nps was found to be evident in both MDA-MB-231 xenograft chick embryos and 4T1-mammary solid tumor model in syngeneic mice. Thus, an innovative targeted nano-therapeutic approach is being established to reduce the tumor burden and inhibit metastasis and angiogenesis simultaneously for better management of TNBC.

Host sensitized lanthanide photoluminescence from post-synthetically modified semiconductor nanoparticles depends on reactant identity.

This work investigates the photoluminescence characteristics where cadmium selenide (CdSe) and zinc sulfide (ZnS) nanoparticles are treated post-synthetically by the trivalent lanthanide cations (Ln3+) [Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb] separately to form either CdSe/Ln or ZnS/Ln nanoparticles. Host sensitized Ln3+ emission was found to be present only in CdSe/Eu, CdSe/Tb, ZnS/Eu, ZnS/Tb and ZnS/Yb nanoparticles. In all the cases tuning of emission of the nanoparticles has been observed, irrespective of the presence or absence of host sensitization. The elemental compositions of CdSe and ZnS nanoparticles upon post-synthetic treatment show a remarkable difference. Incorporation of lanthanides in the nanoparticles is evident with significant alteration in the anionic content, and complete cation exchange of either Cd2+ or Zn2+ by Ln3+ has not been detected; as evaluated from energy dispersive X-ray spectroscopy. Further evaluation on this comes from considering thermodynamic parameters of inter cation interaction. In cases where the host sensitized Ln3+ emission have been observed, luminescence lifetime measurements reveal significant protection of Ln3+ in the nanoparticles. Noticeable difference in photophysical properties for a given Ln3+ has been realized in the two hosts. The photophysical observations have been rationalized using (i) charge trapping mediated host sensitized dopant emission, (ii) autoionization of excited electrons, and (iii) environment induced photoluminescence quenching. The post-synthetic modification discussed in the present work provides an easy and less synthetically demanding room temperature based protocol to avail lanthanide incorporated (doped) semiconductor nanoparticles that can potentially use the unique emission properties of the lanthanide cations.

What Is Beyond Charge Trapping in Semiconductor Nanoparticle Sensitized Dopant Photoluminescence?

A systematic comparison of the Ln3+ [Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb] photoluminescence in doped tin dioxide [Sn(Ln)O2] and doped titanium dioxide [Ti(Ln)O2] nanoparticles shows that the emission efficiency of trivalent lanthanide cations (Ln3+) in an oxide matrix can be improved by change of the cation site symmetry. An analysis of Ln3+ emission quantum yield and asymmetry ratio is used to identify the importance of symmetry breaking around the dopant site for enhancing the Ln3+ emission intensity. These findings identify an important criterion for engineering the luminescence intensity of dopant ions in semiconductor nanoparticle-based luminophores, which goes beyond the primary criterion of engineering the relative positions of the dopant energy levels with respect to the band edges of the host nanoparticle matrix.

Role of reactant concentration and identity of added cation in controlling emission from post-synthetically modified terbium incorporated zinc sulfide nanoparticles: an avenue for the detection of lead(ii) cations.

This work reports the photophysical properties of 1-thioglycerol capped hydrophilic terbium cation incorporated (doped) zinc sulfide [Zn(Tb)S] nanoparticles, which have been post-synthetically modified using Pb2+ [Zn(Tb)S/Pb] under ambient conditions with [Zn(Tb)S] : [Pb2+] = 1 : 10-5-1 : 10, essentially providing a scenario with low to heavy co-doping and ultimately the possibility of forming a material of different chemical identity. The effects of selected concentrations of [Zn(Tb)S] : [M n+] = 1 : 1 and 1 : 10-2 have also been evaluated for the post-synthetic addition of Hg2+, Cd2+, Ca2+, Mg2+, Na+ and K+. The broad zinc sulfide nanoparticle and sharp Tb3+ emission have different dependence on the relative reactant concentration, with cation identity playing a significant role. The underlying photophysical processes have been rationalized based on the interplay among the (i) cation exchange, (ii) modification of the structural properties of the nanoparticles without necessarily exchanging the cations and (iii) emission enhancement of terbium dopants. In cases where Tb3+ emission is apparent, all the nanoparticles studied demonstrate an optical antenna effect, thus accessing a lower Tb3+ concentration regime compared to in bulk environments. The results presented provide an avenue for the detection of heavy metal ions in general and Pb2+ in particular, with a limit of detection that is at least in the range of sub-ppm, using either the broad ZnS or sharp Tb3+ emission, respectively. This strategy provides an avenue to combine (i) the extremely sensitive and easily accessible analytical technique of photoluminescence spectroscopy, (ii) post-synthetic modification reactions in semiconductor nanoparticles that can be performed with less experimental demand, (iii) time-gated measurement related to the longer luminescence lifetime of terbium cations and (iv) the simultaneous use of broad ZnS nanoparticle and sharp Tb3+ emission from the same assembly, helping eliminate false positive results.

How Important is the Host (Semiconductor Nanoparticles) Identity and Absolute Band Gap in Host-Sensitized Dopant Photoluminescence?

This work reports the host (semiconductor nanoparticles) sensitized dopant (lanthanides, Ln) photoluminescence in near band gap matched Sn(Ln)O2 and Zn(Ln)S [Ln = Sm, Tb] nanoparticles to address the importance of the nanoparticle identity and absolute band gap in the underlying process. While the sensitization was evident in the Sn(Sm)O2 and Zn(Tb)S nanoparticles, the same was not observed in the Sn(Tb)O2 and Zn(Sm)S nanoparticles. This observation stresses the importance of nanoparticle identity as the determining factor in realizing the host-sensitized dopant photoluminescence and provides important insight into developing novel doped inorganic nanoparticle-based optical materials.