Maximum Photoluminescence Quantum Yield Research Articles

Highly luminescent and stable CH3NH3PbBr3 quantum dots with 91.7% photoluminescence quantum yield: Role of guanidinium bromide dopants

Abstract Although perovskite quantum dots (PQDs) have received considerable attention, defects in PQDs can significantly degrade the properties and device performance. In this study, we report on an effective strategy for synthesizing highly luminescent CH3NH3PbBr3 quantum dots (QDs) by a simple doping. To remove such defects, guanidinium bromide (GuBr) was doped into the CH3NH3PbBr3 QDs synthesized by the ligand-assisted reprecipitation technique. From XRD and TEM studies, the doping of GuBr into the QD lattices was verified. In addition, the surfaces of PQDs with and without GuBr dopants were analyzed by XPS to trace the metallic Pb acting as a major recombination center. The GuBr doping resulted in the size uniformity of QDs and effectively eliminated defects and metallic Pb, which enhanced the photoluminescence quantum yield (PLQY) through the inhibition of the non-radiative recombination pathway. Furthermore, the recombination dynamics in the QDs were examined by using time-resolved photoluminescence and fluorescence lifetime imaging to verify the role of GuBr dopants. By optimizing the amount of GuBr doping, the CH3NH3PbBr3 QDs with strong green emission achieved a maximum PLQY of 91.7%.

Structure-Function Correlation: Engineering High Quantum Yields in Down-Shifting Nanophosphors.

Lanthanides are routinely incorporated into quantum dots to act as down-shifting and up-converting phosphors in display and lighting applications due to their high photoluminescence quantum yields (PLQY). Recent efforts in the field have demonstrated that trivalent lanthanide, Ln(III), incorporated into ZnAl2O4 spinel nanocrystals can achieve PLQYs of 50% for down-shifting nanophosphors using earth abundant materials. The high PLQY is surprising as the Al(III) site in a spinel is centrosymmetric, which should lead to poor performance for these nanophosphors. However, spinels are prone to formation of an admixture of inverse and normal spinel lattices when the cation size ratio is not optimal. Such behavior can produce local cation disorder that can influence the phosphor performance. Herein, we describe the use of Tb(III) as an optical probe to evaluate the fractional population of the inverse and normal spinel structures within TbxZnAl2-xO4. The experimental data exhibits a Tb(III) concentration dependent change in the fractional population that results in a maximum PLQY of 37% with 3.56% Tb(III) incorporation. A decrease in the degree of inversion (cation disorder) leads to larger amounts of the cubic Fd3m phase resulting in the observed photoluminescence behavior. The correlation of NMR, pXRD, and optical methods provides direct insight into the high PLQY behavior for this class of nanophosphor.

Cold bluish white and blue emissions in Cu+-doped zinc phosphate glasses

Reducing agent-free zinc phosphate glasses doped with cooper ions (Cu+) were synthesized by melt-quenching technique. The physical properties of these glasses such as density, molar volume and refractive index were studied. The X-ray diffraction (XRD) patterns for all prepared glasses, confirm their amorphous structure. Raman spectroscopy suggest that the phosphate network is composed by tetrahedral PO4 units, since the vibrations of P–O–P, PO2 and PO, observed in the spectra, belong to the PO4 units. All glasses display absorptions bands in the ultraviolet and near infrared regions, associated with the absorption edge and contribution of the Cu+:1Ag → 1T2g + 3T2g (280 nm) and Cu2+: 2Eg → 2Tg (890 nm) transitions, respectively. The optical band gap values determined from the absorption spectra assuming indirect optical band gap, are reduced from 4.83 to 2.95 eV for Cu+ content in the range of 0–0.3 mol%. For Cu+ concentration higher than 0.3 mol%, band gap values increase up to 3.17 eV. Such last behaviour was attributed to the reduction of the amount of Cu+ species and/or Moss-Burstein effect. The emission spectra of the Cu+-doped zinc phosphate glasses upon 272 and 290 nm excitation, displayed overall bluish white light and blue emission, depending the excitation wavelength and Cu+ contents. A maximum photoluminescence quantum yield value of 12.5% with an inherent uncertainty up to 3.75%, was reached under 290 nm excitation. The emission decay time profiles were well fitted to a bi-exponential function from which the average lifetimes values resulted to be in the interval of 26.8–16.7 μs, which are shortened for Cu+ contents higher than 0.3 mol%. The structural and photoluminescence characteristic makes of the reducing agent-free Cu+-doped zinc phosphate glasses potentially attractive for blue phosphors and WLEDs applications.

Subnanomolar FRET-Based DNA Assay Using Thermally Stable Phosphorothioated DNA-Functionalized Quantum Dots.

Quantum dots (QDs) can serve as an attractive Förster resonance energy transfer (FRET) donor for DNA assay due to their excellent optical properties. However, the specificity and sensitivity of QD-based FRET analysis are prominently reduced by nonspecific DNA adsorption and poor colloidal stability during DNA hybridization, which hinders the practical applications of QDs as a biosensing platform. Here, we report subnanomolar FRET assay of DNA through the stabilization of DNA/QD interface using DNA-functionalized QDs with phosphorothioated single-stranded DNA (pt-ssDNA) as a multivalent ligand in an aqueous solution. In situ DNA functionalization was achieved during the aqueous synthesis of CdTe/CdS QDs, resulting in the maximum photoluminescence quantum yields of 76.9% at an emission wavelength of 732 nm. Conventional monothiolated ssDNA-capped QDs exhibited particle aggregation and photoluminescence (PL) quenching during DNA hybridization at 70 °C due to the dissociation of surface ligands. Such colloidal instability induced the nonspecific adsorption of DNA, resulting in false-positive signal and decreased sensitivity with the limit of detection (LOD) of 16.1 nM. In contrast, the pt-ssDNA-functionalized QDs maintained their colloidal stability and PL properties at elevated temperatures. The LOD of the pt-ssDNA-functionalized QDs was >30 times lower (0.47 nM) while maintaining the high specificity to a target sequence because the strong multivalent binding of pt-ssDNA to the surface of QDs prevents the detachment of pt-ssDNA and nonspecific adsorption of DNA. The study suggests that the ligand design to stabilize the surface of QDs in an aqueous milieu is critically important for the high performance of QDs for specific DNA assay.

Highly luminescent and stable green-emitting In(Zn,Ga)P/ZnSeS/ZnS small-core/thick-multishell quantum dots

Fluorescent InP-based quantum dots (QDs) have attracted much attention as materials for display applications. Over the past few years, persistent effort has focused on improving photoluminescence (PL) quantum yields and narrowing PL bandwidths through synthesis; as a consequence, the PL properties of InP-based QDs are now comparable to of those of CdSe QDs. Unfortunately, the lack of PL stability in degradable environments has hindered investigations into the applications of these materials. Herein, we report the synthesis of green-emitting In(Zn,Ga)P/ZnSeS/ZnS small-core/thick-multishell QDs that exhibit 78% of the maximum PL quantum yield. Zn and Ga impurities in the InP-QD cores reduce the lattice constant of the InP QDs, which facilitates the growth of thick ZnSeS/ZnS shells. Due to protection of the QD exciton, which is spread away from the surface of the In(Zn,Ga)P/ZnSeS (core/shell) structure by the perfect passivating properties of the thick ZnS shell, the green-emitting In(Zn,Ga)P/ZnSeS/ZnS (core/multishell) QDs are significantly more photostable than In(Zn,Ga)P/ZnSeS QDs. A close-packed QD film displayed bright green (532 nm) emission with suppressed concentration quenching, which is useful for environmentally friendly QD-based displays.

VUV/Vis Photoluminescence, Site Occupancy, and Thermal‐Resistance Properties of K4SrSi3O9:Ce3+

A series of Ce3+ -activated K4 SrSi3 O9 materials emitting bright blue light under near-UV excitation was obtained by a facile solid-state reaction. The luminescence of Ce3+ -doped K4 SrSi3 O9 shows excellent thermal stability in a large temperature range. The detailed temperature/concentration-dependent luminescent properties of Ce3+ confirm that there are two different Ce3+ sites in K4 SrSi3 O9 :Ce3+ , and energy transfer from the high-energy Ce(1)3+ sites to the low-energy Ce(2)3+ sites was demonstrated to occur by electric dipole-dipole interaction. The maximum photoluminescence quantum yield of Ce3+ -doped K4 SrSi3 O9 can reach 56 %, and a UV-excited white LED device with low correlated color temperature (CCT=4617 K) and high color-rendering index (Ra =80) was fabricated with K4 SrSi3 O9 :Ce3+ .

Phosphine-Free, Highly Emissive, Water-Soluble Mn:ZnSe/ZnS Core–Shell Nanorods: Synthesis, Characterization, and in Vitro Bioimaging of HEK293 and HeLa Cells

Phosphine-free, highly luminescent one-dimensional Mn2+ ion-doped ZnSe(core)/ZnS(shell) nanorods (NRs) were synthesized by heating-up method (core) followed by hot injection route (shell). Effect of Mn2+ doping and shell thickness on structural and optical properties is reported. The NRs were formed with wurtzite-structured Mn:ZnSe core (diameter 2.52 nm) encapsulated epitaxially by a wurtzite-structured ZnS shell (thickness of 3.51 nm) with 3.1% lattice mismatch that alters the band alignment of the overall core–shell structure. A redshift was observed in optical absorption and photoluminescence (PL) emission due to an overall size increase with increasing shell thickness. Because of the reduction of defects/traps by surface passivation, the maximum photoluminescence quantum yield (QY) was obtained to be 49.35%. The exciton radiative lifetime for the core–shell NRs (1.678 ms) was more prolonged than that of the core (0.573 ms). A clear dependence of QY and lifetime was established on the Mn2+ content and...

Synthesis and Optical Properties of CdTe<SUB><I>x</I></SUB>Se<SUB>1-<I>x</I></SUB>-Based Red to Near-Infrared Emitting Quantum Dots

A series of red to near-infrared (NIR) emitting quantum dots (QDs) with spherical morphologies and tunable photoluminescence (PL) properties have been synthesized by a facile organic route using octadecene (ODE) as solvent and oleic acid (OA) as single capping agent. CdSe cores with the average size of 4.5 nm display the typical optical behaviors with the PL emission peak around 610 nm. The coating CdZnS shells are introduced on the surface of CdSe cores for improving the photostability and PL efficiency of the initial QDs. As the thickness of CdZnS shells increasing, the gradual red-shift of emission wavelength varying from 617 to 634 nm of the resulting QDs can be observed, along with the remarkable increase of PL quantum yield (QY). The composition-dependent CdTe(x)Se(1-x) (CdTeSe) cores with the emission in NIR region are easily carried out by adjusting the molar ratio of Se/Te. The abnormal variation of optical bowling effect is mainly ascribed to the composition effect of alloyed QDs. Compared with CdTe0.1Se0.9/CdZnS core/shell QDs, the introducing of CdZnS shells on CdTe0.05Se0.95 cores can exhibit better passivation effect on surface status, consequently leading to the red-shifted emission peaks in the range of 739-752 nm with the maximum PL QY reaching up to 45.09%. The unique PL properties of CdTeSe-based QDs in the red to NIR range make these core/shell QDs attractive for future biological sensing and labeling applications.

High-efficiency CdTe/CdS core/shell nanocrystals in water enabled by photo-induced colloidal hetero-epitaxy of CdS shelling at room temperature

We report high-efficiency CdTe/CdS core/shell nanocrystals synthesized in water by epitaxially growing CdS shells on aqueous CdTe cores at room temperature, enabled by the controlled release of S species under low-intensity ultraviolet (UV) light illumination. The resulting photo-induced dissociation of S2O 3 2− ions conveniently triggers the formation of critical two-dimensional CdS epitaxy on the CdTe surface at room temperature, as opposed to initiating the growth of individual CdS core-only nanocrystals. This controlled colloidal hetero-epitaxy leads to a substantial increase in the photoluminescence (PL) quantum yield (QY) of the shelled nanocrystals in water (reaching 64%). With a systematic set of studies, the maximum PL QY is found to be almost independent of the illuminating UV intensity, while the shell formation kinetics required for reaching the maximum QY linearly depends on the illuminating UV intensity. A stability study of the QD films in air at various temperatures shows highly improved thermal stability of the shelled QDs (up to 120 °C in ambient air). These results indicate that the proposed aqueous CdTe/CdS core/shell nanocrystals hold great promise for applications requiring efficiency and stability.

Scaling up the Aqueous Synthesis of Visible Light Emitting Multinary AgInS2/ZnS Core/Shell Quantum Dots

Approximately 3 g of water-soluble AgInS2/ZnS core/shell quantum dots (AIS/ZnS QDs) with a maximum photoluminescence quantum yield of up to 39.1% was synthesized in an aqueous solution of gelatin and thioglycolic acid (TGA). The composition of the AIS QDs could be readily adjusted by controlling the molar ratio of the starting Ag/In precursors in the reaction solution, which leads to a tunable emission ranging from 535 to 607 nm. The as-prepared core/shell QDs exhibit excellent photostability and water/buffer stability. More importantly, these cadmium-free hydrophilic AIS/ZnS core/shell QDs are biocompatible and can be directly utilized in cancer cell imaging.

Synthesis, Structure, and Photophysical Properties of Blue‐Emitting Zinc(II) Complexes with 3‐Aryl‐Substituted 1‐Pyridylimidazo[1,5‐a]pyridine Ligands

AbstractSix zinc(II) complexes of the general formula [Zn(LR)X2] (1: R = Me, X = Cl; 2: R = Me, X = Br; 3: R = Me, X = I; 4: R = OH, X = Cl; 5: R = OH, X = Br; 6: R = OH, X = I), in which LR is 1‐(pyridin‐2‐yl)‐3‐o‐tolylimidazo[1,5‐a]pyridine (LMe) or 2‐[1‐(pyridin‐2‐yl)imidazo[1,5‐a]pyridin‐3‐yl]phenol (LOH), have been prepared and characterized. The X‐ray structural analysis performed on complexes 1, 3, and 4 showed that both LMe and LOH act as N,N‐bidentate ligands and coordinate to the ZnII metal center through the pyridine ring (Npy) and the pyridine‐like nitrogen atom of the imidazo[1,5‐a]pyridine group (Nim). The photophysical properties of these compounds have been investigated, both in solution and in the solid state. The complexes showed intense blue luminescence when excited with UV light (λexc = 366–410 nm) with λmax of emission between 440–460 nm in the solid state. Complexes 1–3 showed moderate‐to‐good absolute photoluminescence quantum yields (PLQYs) in the solid state with a maximum PLQY of 0.40 for 1. These values were slightly lower than the PLQY of free LMe (0.60). On the other hand, the PLQY of LOH increased after coordination to ZnCl2, and a PLQY of 0.29 was recorded for 4. A possible interpretation of this behavior is reported.

Near-infrared broadly emissive AgInSe2/ZnS quantum dots for biomedical optical imaging

Highly luminescent AgInSe2/ZnS core/shell quantum dots (AISe/ZnS QDs) have been synthesized via a facile low-temperature solution chemistry route. The as-prepared core/shell QDs have a narrow size distribution, and exhibit composition-tunable photoluminescence (PL) emission in the near-infrared (NIR) range from 700 to 820 nm with a maximum PL quantum yield (QY) of 40%. By using the poly(acrylic acid)–octylamine (PAA-based) amphiphilic polymer, these oil-soluble AISe/ZnS core/shell QDs could be effectively solubilized in water, while retaining their initial morphology, crystal structure and PL properties. Importantly, the results from animal and cell experiments confirm that these highly luminescent, broadly emissive AISe/ZnS QDs are new promising fluorescent probes for biomedical optical imaging (namely, in vivo animal and in vitro cell imaging), as an alternative for Cd-, Hg- and Pb-based QDs and organic dyes.

Ultrasonic-assisted synthesis of aqueous CdTe/CdS QDs in salt water bath heating

A novel simple method for fast and efficient synthesis of aqueous CdTe/CdS quantum dots (QDs) with core–shell structure was developed by using salt water bath heating with the ultrasonic-assisted technique in this paper. The formation of crystal nucleus was promoted by ultrasonic and CdTe/CdS QDs with blue fluorescence were synthesized only in 0.5h. The heat source was bath heating in salt water solution at 60% NaCl and the heating temperature could reach 105°C. The heating method solved the biggest drawback of low photoluminescence quantum yield (PLQY) of ordinal bath heating in water. The preparation was cheap, simple and had less pollution to the environment. The properties of the CdTe/CdS QDs were thoroughly investigated by ultraviolet–visible (UV–vis), photoluminescence (PL), transmission electron microscope (TEM), laser size analysis, fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Different CdTe/CdS QDs with core shell structure were efficiently synthesized and the maximum PLQY could reach 97.13% when refluxing at 105°C for 2h. These QDs exhibited uniform dispersity, high fluorescence intensity, good optical property and long life of fluorescent. The synthesis mechanism of the core shell structure of the QDs was inferred that the Cd2+ might coordinate with sulfur (S) as well as thiol propionate (–SCH2CH2COO−1) to constitute two relatively thick compound layers on the QDs surface as passive shells.

Luminescent properties of CdTe quantum dots synthesized using 3-mercaptopropionic acid reduction of tellurium dioxide directly

A facile one-step synthesis of CdTe quantum dots (QDs) in aqueous solution by atmospheric microwave reactor has been developed using 3-mercaptopropionic acid reduction of TeO2 directly. The obtained CdTe QDs were characterized by ultraviolet–visible spectroscopy, fluorescent spectroscopy, X-ray powder diffraction, multifunctional imaging electron spectrometer (XPS), and high-resolution transmission electron microscopy. Green- to red-emitting CdTe QDs with a maximum photoluminescence quantum yield of 56.68% were obtained.

One-pot synthesis of CdTe quantum dots using tellurium dioxide as a tellurium source in aqueous solution

A novel route has been developed for the synthesis of l-cysteine (Cys)-capped CdTe quantum dots (QDs) in an aqueous medium. Compared with previous reports, this synthesis was carried out in air atmosphere with one pot by using TeO2 to replace Te or Al2Te3 as tellurium source. The mechanism for the formation of CdTe QDs is elucidated. The influences of various experimental variables on the luminescent properties of the obtained CdTe QDs have been systematically investigated, including refluxing time, pH value, Cd/Cys and Cd/Te molar ratios. Furthermore, the obtained QDs were characterized by Fourier transform infrared spectra, X-ray powder diffraction, and transmission electron microscopy, respectively. The results demonstrate that the obtained QDs have zincblende crystal structure with a sphere-like shape. Under the optimized experimental conditions, green- to yellow-emitting CdTe QDs with a maximum photoluminescence quantum yield of 14.6 % can be obtained.

Synthesis of CdTe Quantum Dots with Tunable Photoluminescence Using Tellurium Dioxide as Tellurium Source

AbstractA simple and convenient method has been developed for synthesis of water‐soluble CdTe quantum dots (QDs) under ambient atmospheric conditions. In contrast to the traditional aqueous synthesis, green to red emitting CdTe QDs were prepared by using TeO2 to replace Te or Al2Te3 as tellurium source in this method. The influences of experimental variables, including pH value, 3‐mercaptopropionic acid (MPA)/Cd and Te/Cd molar ratios, on the emission peak and photoluminescence (PL) quantum yield (QY) of the obtained CdTe QDs have been systematically investigated. Experimental results indicate that green to red emitting CdTe QDs with a maximum photoluminescence quantum yield of 35.4% can be prepared at pH 11.3 and n(Cd):n(Te):n(MPA)=1:0.1:1.7.

High-Quality CuInS2/ZnS Quantum Dots for In vitro and In vivo Bioimaging

The exploration of biocompatible quantum dots (QDs) for biomedical imaging is currently one of the fastest growing fields of nanotechnology. This strategy overcomes the intrinsic toxicity of well-developed II–VI and other semiconductor QDs (Cd, Hg, Pb, Se, Te, As, etc.) that remains a major obstacle to their clinical use. In this report, we synthesized high-quality CuInS2/ZnS (CIS/ZnS) QDs without using conventional toxic heavy metals. These QDs exhibited improved photoluminescence (PL) properties, with tunable emission peaks ranging from 550 to 800 nm and a maximum PL quantum yield (QY) up to 80%. Next, we explored the effective loading of the prepared oil-soluble CIS/ZnS QDs using biodegradable folate-modified N-succinyl-N′-octyl chitosan (FA-SOC) micelles. Targeting efficacy of the resulting QDs-loaded micelles to tumors using in vitro and in vivo optical imaging techniques was also investigated. The results show that the micelle platform allowed successful formulation of these oil-soluble QDs in water, while retaining the morphology, crystal structure, and PL of the initial CIS/ZnS QDs. This study demonstrates the versatility of using the biocompatible CIS/ZnS QDs across different spatial scales (in vitro cell imaging and in vivo small animal imaging) for multicolor biological imaging applications.

Tunable photoluminescence from the visible to near-infrared wavelength region of non-stoichiometric AgInS2 nanoparticles

Non-stoichiometric AgInS2 (AIS) semiconductor particles were synthesized by the thermal decomposition of single-source precursors in solutions of two kinds of primary amines (oleylamine and octylamine). The Ag content in the resulting nanoparticles was controlled by adjusting the chemical composition of the precursor used, in which the mole ratio of Ag+ to total metal ions was varied from 0.1 to 0.7, resulting in the production of non-stoichiometric AIS particles with varying amounts of Ag vacancies. The average size of AIS particles was slightly decreased from 4.3 to 3.8 nm on changing the solvent from oleylamine to octylamine in the preparation, while the particle size seemed to be constant regardless of the content of Ag. On the other hand, the optical properties of AIS particles were considerably modified depending on the Ag content in the particles. The absorption onset was blue-shifted from 750 to 580 nm with a decrease in the Ag content, due to the enlargement of the energy gap of particles. Intense photoluminescence originating from the donor–acceptor pair recombination was observed for each kind of AIS particle and then the photoluminescence peak wavelength was also blue-shifted from 830 to 650 nm, being similar to the behavior of the absorption onset. The maximum photoluminescence quantum yield was ca. 70% for octylamine-modified AIS nanoparticles having a ratio of Ag+ to total metal ions of 0.37, which probably contained the optimum amount of Ag vacancies acting as the sites of donor–acceptor pair recombination with few surface defect sites for non-radiative recombination.

Synthesis of stable near-infrared emitting HgTe/CdS core/shell nanocrystals using dihydrolipoic acid as stabilizer

HgTe/CdS core/shell nanocrystals (NCs) with highly-stable near-infrared (NIR) emissions were synthesized by employing dihydrolipoic acid (DHLA) as a stabilizer. This synthetic route was performed using Te powder as the tellurium source to prepare HgTe NCs, and H2S generated by the reaction of Na2S–H2SO4 as the sulfur source for synthesizing HgTe/CdS core/shell NCs at room temperature. The fluorescence emission peaks of DHLA-capped HgTe/CdS NCs could be facilely tuned from 910 nm to 1200 nm by varying the reflux time at 100 °C, with a maximum photoluminescence quantum yield of 52%. The obtained HgTe/CdS NCs exhibited an NIR stable emission when heated at 75 °C. Correspondingly, these HgTe/CdS core/shell NCs displayed excellent colloidal dispersion stability and long exciton lifetimes that reached up to 47.6 ns in an aqueous medium. The resultant HgTe/CdSe NCs have been successfully used to fabricate NIR emitting thin films on the surface of polymers and to perform fluorescence imaging in a live animal.

Facile, air-insensitive solvothermal synthesis of emission-tunable CuInS2/ZnS quantum dots with high quantum yields

Yellow-to-red emitting CuInS2/ZnS (CIS/ZnS) core/shell quantum dots (QDs) with a maximum photoluminescence quantum yield (QY) of ∼65% were facilely synthesized via a stepwise, consecutive solvothermal approach. The size-sorting experiments on CIS/ZnS QDs indicated that the ZnS shell was formed with a relatively uniform thickness even though the size of pre-existing CIS core QDs was not monodisperse. CIS core QDs solvothermally grown for different reaction times of 5–6 h exhibited poor QYs of <8.8% with deep red emissions as a result of donor–acceptor pair (DAP) recombination. Upon shell overcoating, the band gap energies of CIS/ZnS QDs increased by 0.14–0.23 eV, depending on the CIS core growth time. Such increased band gaps were attributed presumably to the reduction of actual CIS core size, originating from the formation of the alloyed interfacial layer at CIS/ZnS during a long shell growth. Compared to CIS core QDs, the emission of CIS/ZnS QDs was markedly blue-shifted by 0.10–0.18 eV. This blue-shift was discussed based on the shift of QD band gap-dependent donor/acceptor energy levels and the donor–acceptor distance-dependent DAP recombination process.