Luminescent Nanocrystals Research Articles

Thiophene Derivatives as Ligands for Highly Luminescent and Stable Manganese-Doped CsPbCl3 Nanocrystals.

Ligands on the surface of perovskite nanocrystals are important to stabilize the nanocrystal structure. However, the research of ligands on Mn2+ ion-doped CsPbCl3 nanocrystals (Mn: CsPbCl3 NCs), a promising candidate family for the lightning community, is relatively rare. Here, we demonstrate a new ligand modification strategy for preparing high-quality Mn: CsPbCl3 NCs by a simple hot-injection method. Thiophene derivative, for the first time, is applied as ligands for perovskite nanocrystals. The new ligands of thiophene derivatives passivate defects on the surface of NCs and enhance optical properties, originating from the sulfur in thiophene additives binding to the uncoordinated lead ions. The photoluminescence quantum yield of the modified Mn: CsPbCl3 NCs is 93% in comparison with 46% of the pristine counterparts, whose value is the highest to date for ligand-modified Mn: CsPbCl3 NCs. Meanwhile, the thermal, storage, and purification stability are also significantly improved. The performance of related LEDs is also investigated.

Understanding the Shell Passivation in Ln3+‐Doped Luminescent Nanocrystals

Shell Passivation Effect The effectiveness of shell passivation in alleviating the surface quenching in Ln3+-doped luminescent nanocrystals has long been approved, yet the understanding of passivation mechanisms remains elusive. In article number 2100194, Rui Shi, Carlos D. S. Brites, and Luís D. Carlos review the context of debates on this topic and emphasize the impacts brought by chemical disorders, which provides new perspectives for understanding the shell passivation in general cases.

Spatial and Temporal Resolution of Luminescence Quenching in Small Upconversion Nanocrystals.

Luminescent upconversion nanocrystals (UCNCs) have become one of the most promising nanomaterials for biosensing, imaging, and theranostics. However, their ultimate translation into robust luminescent probes for daily use in biological and medical laboratories requires comprehension and control of the many possible deactivation pathways that cause upconversion luminescence (UCL) quenching. Here, we demonstrate that thorough modeling of UCL rise and decay kinetics using a freely accessible software can identify the UCL quenching mechanisms in small (<40 nm) UCNCs with spatial and temporal resolution. Applied to the most relevant β-NaYF4:Yb3+,Er3+ UCNCs, our model showed that only a few distinct nonradiative low-energy transitions were deactivated via specific solvent and ligand vibrations with a strong downstream effect on the population and depopulation dynamics of the emitting states. UCL quenching could penetrate ca. 4 nm inside the UCNC, which resulted in significant size-dependent changes of UCL intensities and spectra. Despite the large surface-to-volume ratios and UCL quenching via the UCNC surface, we found strong contributions of the outer layers to the overall UCL, which will be highly important for the design of UCNPs to investigate biomolecular interactions via distance-dependent energy transfer methods. Our advanced kinetic model is easily scalable to different UCNC architectures, environments, and energy transfer interactions such that relatively simple modeling of UCL kinetics can be used for efficiently optimizing UCNCs for their final application as practical luminescent probes.

Bright CsPbBr3 Perovskite Nanocrystals with Improved Stability by In-Situ Zn-Doping.

In this study, facile synthesis, characterization, and stability tests of highly luminescent Zn-doped CsPbBr3 perovskite nanocrystals (NCs) were demonstrated. The doping procedure was performed via partial replacement of PbBr2 with ZnBr2 in the precursor solution. Via Zn-doping, the photoluminescence quantum yield (PLQY) of the NCs was increased from 41.3% to 82.9%, with a blue-shifted peak at 503.7 nm and narrower spectral width of 18.7 nm which was consistent with the highly uniform size distribution of NCs observed from the TEM image. In the water-resistance stability test, the doped NCs exhibited an extended period-over four days until complete decomposition, under the harsh circumstances of hexane-ethanol-water mixing solution. The Zn-doped NC film maintained its 94% photoluminescence (PL) intensity after undergoing a heating/cooling cycle, surpassing the un-doped NC film with only 67% PL remaining. Based on our demonstrations, the in-situ Zn-doping procedure for the synthesis of CsPbBr3 NCs could be a promising strategy toward robust and PL-efficient nanomaterial to pave the way for realizing practical optoelectronic devices.

Insights into the Oxidation State of Cu Dopants in II-VI Semiconductor Nanocrystals.

Luminescent Cu-doped semiconductor nanocrystals have played a pivotal role in the emergence of lighting and display applications for a long time. However, consensus regarding the Cu oxidation state and hence their emission mechanism has not been attained. Distinction between seemingly simple optically and magnetically active Cu2+ and inactive Cu1+ has surprisingly been the subject matter of debate in the literature for more than a decade. In this Perspective, we first discuss the fundamental quantum mechanical phenomenon explaining the optical properties of the monovalent and divalent Cu dopants. We then focus down on various techniques used to differentiate between these two fundamental mechanisms, their benefits, and their pitfalls arising in large part because of the lack of spatial separation. Hence, to obtain a cohesive story consistent with all the observations, we discuss recent results from single-molecule spectroscopy to understand the optical properties and hence the oxidation state of internally doped Cu in doped nanocrystals.

Observation of waveguide Fabry-Perot lasing in highly efficient Si nanocrystals

A luminescent Si nanocrystal (SiNC) thin film with photoluminescence quantum yield (PLQY) > 70% was made by using hydrogen silsesquioxane (HSQ), followed by long-time high-pressure hydrogenation. A net optical gain of 524 ± 21 cm−1 was obtained by means of variable stripe length-shifting excitation spot (VSL-SES). A rectangularly shaped SiO2 Fabry-Perot (F-P) cavity with size of 1.5 μm (width) × 0.7 μm (height) × 2000 μm (length) was made on top of the SiNC thin film. The waveguide F-P device was pumped with a 400 nm femtosecond pulsed laser. A threshold behavior of the light emission intensity as a function of the pumping power was observed. Other lasing characteristics including spectral narrowing, polarization of the emission, and small emission angle were also observed beyond the threshold pumping power.

Structural and Optical Characterization of Silica Nanospheres Embedded with Monodisperse CeO2-Eu3+ Nanocrystals

Luminescent nanocrystals embedded into silica microspheres were shown to be useful for silica labeling for biological applications, ensuring mechanical and chemical stability, nontoxicity, biocompatibility and optical properties. We used sol–gel technology to prepare silica nanospheres embedded with fluorescent and magnetic Eu3+(1 mol%)-doped CeO2 nanocrystals. The X-ray diffraction pattern analysis and transmission electron microscopy investigations showed CeO2:Eu3+(1 mol%) nanocrystals of about 9 nm size and Ce3+ ions substitution by the Eu3+ ions; the nanocrystals dispersed inside the nanosized silica spheres of about 400 nm diameters. The photoluminescence spectra recorded under UV-light excitation showed Eu3+ ions luminescence peaks (5D0-7FJ, J = 0–4) accompanied by a weaker 425 nm luminescence due to the silica matrix; the quantum yield was 0.14. The weak hysteresis loop and magnetization curves recorded up to 20,000 Oe showed dominantly paramagnetic behavior associated with the silica matrix; a slight opening of the hysteresis loop to a very small magnetic field (about 0.005 Oe) was due to the presence of the two rare earth ions. The photonic crystal properties of SiO2-CeO2:Eu3+(1 mol%) silica nanospheres deposited as films on quartz plates were revealed by the two weak attenuation peaks at 420 and 500 nm and were associated with the reflection from different planes. The SiO2-CeO2:Eu3+(1 mol%) nanospheres are attractive potential candidates for photonics-related applications or for multifunctional bio-labels by combining the luminescence and magnetic properties of the nanocrystals.

Continuous-flow synthesis of ultrahigh luminescent perovskite nanocrystals using forced thin film reactor and application for light-emitting diodes

Owing to their excellent optical properties, organolead halide perovskite nanocrystals (PeNCs) have gained significant attention. Considering their industrial contribution, exploring practical production of high-quality PeNCs is of major importance. In this work, we demonstrate continuous-flow synthesis of ultrahigh luminescent PeNCs with high color purity using a forced thin film reactor. We successfully demonstrate the effectiveness of this reactor as a crystal growth environment. The photoluminescence quantum yields were improved to 94% as a result of the unique mixing process. After film formation, this reactor enabled the application for perovskite light-emitting diodes.

Cost-effective synthesis of 2D molybdenum disulfide (MoS2) nanocrystals: An exploration of the influence on cellular uptake, cytotoxicity, and bio-imaging.

Ultrasmall MoS2 nanocrystals have unique optoelectronic and catalytic properties that have acquired significant attraction in many areas. We propose here a simple and economical method for synthesizing the luminescent nanocrystals MoS2 using the hydrothermal technique. In addition, the synthesized MoS2 nanocrystals display photoluminescence that is tunable according to size. MoS2 nanocrystals have many advantages, such as stable dispersion, low toxicity and luminescent characteristics, offering their encouraging applicability in biomedical disciplines. In this study, human lung cancer epithelial cells (A549) are used to assess fluorescence imaging of MoS2 nanocrystals. MTT assay, trypan blue assay, flow cytometry and fluorescence imaging results have shown that MoS2 nanocrystals can selectively target and destroy lung cancer cells, especially drug-resistant cells (A549).

Eu3+, Tb3+ Doping Induced Tunable Luminescence of Cs2agincl6 Double Perovskite Nanocrystals and its Mechanism

Eu3+, Tb3+ Doping Induced Tunable Luminescence of Cs2agincl6 Double Perovskite Nanocrystals and its Mechanism

Modulation of upconversion luminescence spectrum of single rare-earth-doped upconversion nanocrystal based on plasmonic nanocavity

Plasmonic nanocavities can effectively modulate the upconversion luminescence properties of lanthanide doped upconversion nanocrystals (UCNCs), which not only enhances the luminescence intensity, but also modifies the luminescence spectrum. However, currently reported studies of upconversion luminescence spectrum modulation by using nanocavities are mainly based on ensemble experiments. Compared with ensemble experiments, single-particle experiments facilitate the comparative studies for the same upconversion nanocrystal and therefore the influence of inhomogeneity in ensemble samples can be avoided. Here in this work, we couple a single particle of Yb&lt;sup&gt;3+&lt;/sup&gt;/Tm&lt;sup&gt;3+&lt;/sup&gt; co-doped nanocrystal with a plasmonic nanocavity composed of a single gold nanorod by using the in-situ nano-manipulation technique based on an atomic force microscope. Experimentally, we compare the upconversion luminescence spectra, upconversion luminescence lifetimes and excitation-power dependent upconversion luminescence intensities of the same single nanocrystal before and after coupling with the single gold nanorod. The experimental measurements are consistent with the theoretical calculations from rate equations combined with electromagnetic simulations. The results indicate that the plasmaonic nanocavity modulated nanocrystal upconversion luminescence spectrum is the combined result of three effects: the excitation field enhancement effect, the Purcell effect and the change of radiation efficiency.

Water-Soluble Luminescent Silicon Nanocrystals by Plasma-Induced Acrylic Acid Grafting and PEGylation.

Luminescent silicon nanocrystals are promising nanomaterials for biomedical applications due to their unique optical properties and biocompatibility. Here, we demonstrate a two-step surface modification approach coupling gas-phase and liquid-phase methods to synthesize PEGylated acrylic acid grafted silicon nanocrystals with near-infrared emission in water and biological media. First, acrylic acid grafted silicon nanocrystals are synthesized by an all-gas-phase approach on a millisecond time scale, omitting high temperature and postpurification processes. Subsequently, room-temperature PEGylation is carried out with these acrylic acid grafted silicon nanocrystals, yielding stable colloidal dispersions in both water and high ionic strength Tyrode's buffer with 20-30 nm hydrodynamic diameters. The PEGylated silicon nanocrystals exhibit photoluminescence in the 650-900 nm near-IR window with quantum yields of ∼30% and ∼13% in deionized water and Tyrode's buffer, respectively, after a 7-day oxidation in water. The surface-functionalized Si NCs exhibit relatively small toxicity to MDA-MB-231 cells at concentrations relevant to bioimaging applications.

Luminescent Anisotropic Wurtzite InP Nanocrystals.

Indium phosphide (InP) nanocrystals are emerging as an alternative to heavy metal containing nanocrystals for optoelectronic applications but lag behind in terms of synthetic control. Herein, luminescent wurtzite InP nanocrystals with narrow size distribution were synthesized via a cation exchange reaction from hexagonal Cu3P nanocrystals. A comprehensive surface treatment with NOBF4 was performed, which removes excess copper while generating stoichiometric In/P nanocrystals with fluoride surface passivation. The attained InP nanocrystals manifest a highly resolved absorption spectrum with a narrow emission line of 80 meV, and photoluminescence quantum yield of up to 40%. Optical anisotropy measurements on ensemble and single particle bases show the occurrence of polarized transitions directly mirroring the anisotropic wurtzite lattice, as also manifested from modeling of the quantum confined electronic levels. This shows a green synthesis path for achieving wurtzite InP nanocrystals with desired optoelectronic properties including color purity and light polarization with potential for diverse optoelectronic applications.

Optical Properties of Transparent Rare-Earth Doped Sol-Gel Derived Nano-Glass Ceramics.

Rare-earth doped oxyfluoride glass ceramics represent a new generation of tailorable optical materials with high potential for optical-related applications such as optical amplifiers, optical waveguides, and white LEDs. Their key features are related to the high transparency and remarkable luminescence properties, while keeping the thermal and chemical advantages of oxide glasses. Sol-gel chemistry offers a flexible synthesis approach with several advantages, such as lower processing temperature, the ability to control the purity and homogeneity of the final materials on a molecular level, and the large compositional flexibility. The review will be focused on optical properties of sol-gel derived nano-glass ceramics related to the RE-doped luminescent nanocrystals (fluorides, chlorides, oxychlorides, etc.) such as photoluminescence, up-conversion luminescence, thermoluminescence and how these properties are influenced by their specific processing, mostly focusing on the findings from our group and similar ones in the literature, along with a discussion of perspectives, potential challenges, and future development directions.

Investigation of spectral properties of potassium-aluminum-borate glass with CuCl - CuBr nanocrystals

Heat treatment conditions effect on the characteristics of exciton absorption and luminescence of CuCl and CuBr nanocrystals in potassium-aluminaborate glass is studied. The size effect of the band edge absorption and luminescence energy is confirmed. The simultaneous presence of copper halide nanocrystals and free monovalent copper ions in the glass matrix is shown. Possible conditions for the formation of mixed CuCl-CuBr crystals are considered.

A novel one-step synthesis of bright luminescent silicon nanocrystals capped with hydrophobic surface

Visible photoluminescent silicon nanocrystals (Si NCs) capped with hydrophobic surface are synthesized via a novel and one-step bottom-up strategy by utilizing trialkoxysilane as silicon source. Ascorbate sodium as reducing agent facilitates the hydrothermal-assisted hydrolysis and condensation of trialkoxysilane molecule to generate a SiSi rich core and promotes the formation of Si NCs. The synthesized hydrophobic Si NCs give an average size of 3.4 nm and exhibit visible photoluminescence with a maximum emission wavelength around 450 nm accompanying a high absolute quantum yield of 17% which could be attributed to the enhanced radiative recombination by present efficient hydrophobic surface capping on Si NCs.

Cd+2-sensing property of highly luminescent CdTe nanocrystals in the presence of Na2S2O3

Cd+2-sensing property of highly luminescent CdTe nanocrystals in the presence of Na2S2O3

Super-Resolution Imaging With Lanthanide Luminescent Nanocrystals: Progress and Prospect.

Stimulated emission depletion (STED) nanoscopy has overcome a serious diffraction barrier on the optical resolution and facilitated new discoveries on detailed nanostructures in cell biology. Traditional fluorescence probes employed in the super-resolution imaging approach include organic dyes and fluorescent proteins. However, some limitations of these probes, such as photobleaching, short emission wavelengths, and high saturation intensity, still hamper the promotion of optical resolution and bio-applications. Recently, lanthanide luminescent probes with unique optical properties of non-photobleaching and sharp emissions have been applied in super-resolution imaging. In this mini-review, we will introduce several different mechanisms for lanthanide ions to achieve super-resolution imaging based on an STED-like setup. Then, several lanthanide ions used in super-resolution imaging will be described in detail and discussed. Last but not least, we will emphasize the future challenges and outlooks in hope of advancing the next-generation lanthanide fluorescent probes for super-resolution optical imaging.

Highly luminescent ZnCdTeS nanocrystals with wide spectral tunability for efficient color-conversion white-light-emitting-diodes

CdTe-based semiconductor nanocrystals (NCs) with size and composition-dependent efficient bandgap properties are historically mature nanomaterials for colloidal optoelectronic applications. In this work, we present the highly luminescent quaternary ZnCdTeS NCs with tunable emission across a wide visible spectrum from green to red spectral range. Prepared via a direct aqueous-based approach, a second capping agent of trisodium citrate (TSC) was used to enhance the photoluminescence (PL) emission efficiency, the chemical stability, and to spectrally widen the coverage of the emission spectra of ZnCdTeS NCs. Adding TCS created a remarkable blue shift from 572 nm in the absence of TSC, to 548 nm. On the other hand, upon optimization of experimental parameters, superior ZnCdTeS NCs with a narrow PL profile typically less than 50 nm, the high quantum efficiency of 76%, and tunable emission from 515-to-645 nm were synthesized in an aqueous solvent. The keynotes were the superior and reproducible luminescent properties for the core only NCs, without shell and using relatively low reaction temperatures. It was shown that in the suggested synthesis method, the high efficiency emitted color of ZnCdTeS NCs can be easily controlled from 515-to-650 nm with excellent stability against harsh conditions. The biexponential decay profiles of samples prepared at different reaction temperatures demonstrated that the average recombination lifetime is below 40 ns and increases with the growth of the ZnCdTeS NCs. Results reveal that the excitonic energy levels have the main role in the recombination process. Finally, to demonstrate the functional advantages of the prepared NCs in optoelectronics, the NCs were used to fabricate color-conversion white light-emitting diodes. The color coordinate of the device is recorded as (0.4951, 0.3647) with CRI of 91, CCT of 1954 K, and LER of 251 lm W−1 by employing only two distinct emitters for color conversion.

Resolving the Triexciton Recombination Pathway in CdSe/CdS Nanocrystals through State-Specific Correlation Measurements.

As luminescence applications of colloidal semiconductor nanocrystals push toward higher excitation flux conditions, there is an increased need to both understand and potentially control emission from multiexciton states. We develop a spectrally resolved correlation method to study the triply excited state that enables direct measurements of the recombination pathway for the triexciton, rather than relying on indirect extraction of rates. We demonstrate that, for core-shell CdSe-CdS nanocrystals, triexciton emission arises exclusively from the band-edge S-like state. Time-dependent density functional theory and extended particle-in-a-sphere calculations demonstrate that reduced carrier overlap induced by the core-shell heterostructure can account for the lack of emission observed from the P-like state. These results provide a potential avenue for the control of nanocrystal luminescence, where core-shell heterostructures can be leveraged to control carrier separation and therefore maintain emission color purity over a broader range of excitation fluxes.