Red-shift Of Emission Wavelength Research Articles

A novel coumarin based fluorescent sensor for high-sensitive detection of Cu2+ and water as well as applications in food and environmental analysis

A novel fluorescent sensor (SZ) based on coumarin was designed and synthesized for the detection of Cu2+ in DMSO/H2O solution (9/1, v/v, pH = 7.4, HEPES = 10 mM) and water in organic solvents. The sensor exhibited a low detection limit of 9.6 × 10−8 mol/L and a short response time (30 s) for Cu2+ in DMSO/H2O solution. SZ showed a red-shift in emission wavelength in more polar solvents and demonstrated high sensitivity in detecting water in various solvents including tetrahydrofuran, acetone, ethanol, methanol and acetonitrile with the lowest detection limit in ethanol as low as 0.0035 % (v/v). The mechanism for water detection by SZ was identified to be polarity dependent. Moreover, SZ was effectively employed for detecting alcohol content in Chinese Baijiu, as well as water content in sugar and salt samples. Notably, SZ has the capability to determine Cu2+ in soil and environmental water samples, showing a wide range of potential applications.

Compositions and sources of fluorescent water-soluble and water-insoluble organic aerosols

Brown carbon (BrC), the light-absorbing component of organic aerosols, plays a significant role in climate change and atmospheric photochemistry. However, the water-insoluble fractions of BrC have not been extensively studied, limiting the assessment of the overall climate effects of BrC. In this study, water-soluble and -insoluble organic carbon (i.e., WSOC and WIOC) in wintertime aerosols in Hefei were subsequently fractionated, and their fluorescence properties were comparatively investigated with the excitation–emission matrix method. WIOC contributing 57.1 % was the major component of organic carbon. WSOC with the largest contribution from humic-like regions exhibited a redshift compared to WIOC. Three humic-like substances (HULIS) with different oxidation degrees and one protein-like substances (PRLIS) were identified as the major fluorescent components by the parallel factor analysis. WSOC had more highly oxygenated HULIS, whereas low-oxygenated HULIS dominated WIOC. Nighttime WIOC contained more less-oxygenated species. The positive matrix factorization analysis suggested that biomass burning (43 %) was the largest source of both fluorescent WSOC and WIOC. Coal combustion contributed much more to fluorescent WIOC (40 %), whereas secondary formation contributed more to fluorescent WSOC (12 %). During aerosol pollution episodes, the increase in fluorescence efficiency was much greater for WIOC (25 %) than for WSOC (12 %), and WSOC and WIOC experienced a redshift and blueshift in emission wavelength, respectively. WSOC had more highly oxygenated HULIS, while WIOC had more less-oxygenated HULIS in aerosol episodes than the non-episodic periods. In addition, aerosol pollution was accompanied by the increased contributions of biomass burning and coal combustion to both fluorescent WSOC and WIOC, while the decreased relative contribution of secondary formation to fluorescent WSOC. Our findings highlighted the different fluorescence properties, compositions and sources of fluorescent WSOC and WIOC, providing a comprehensive view of BrC aerosols.

Visualization of polarity changes in endoplasmic reticulum (ER) autophagy and rheumatoid arthritis mice with near-infrared ER-targeted fluorescent probe

The crucial cellular activities for maintaining normal cell functions heavily rely on the polarity of the endoplasmic reticulum (ER). Understanding how the polarity shifts, particularly in the context of ER autophagy (ER-phagy), holds significant promise for advancing knowledge of disorders associated with ER stress. Herein, a polarity-sensitive fluorescent probe CDI was easily synthesized from the condensation reaction of coumarin and dicyanoisophorone. CDI was composed of coumarin as the electron-donating moiety (D), ethylene and phenyl ring as the π-conjugation bridge, and malononitrile as the electron-accepting moiety (A), forming a typical D-π-A molecular configuration that recognition in the near-infrared (NIR) region. The findings suggested that as the polarity increased, the fluorescence intensity of CDI decreased, and it was accompanied by a redshift of emission wavelength at the excitation wavelength of 524 nm, shifting from 641 nm to 721 nm. Significantly, CDI exhibited a notable ability to effectively target ER and enabled real-time monitoring of ER-phagy induced by starvation or drugs. Most importantly, alterations in polarity can be discerned through in vivo imaging in mice model of rheumatoid arthritis (RA). CDI has been proven effective in evaluating the therapeutic efficacy of drugs for RA. ER fluorescent probe CDI can be optically activated in lysosomes, providing a sensitive tool for studying ER-phagy in biology and diseases.

Ketocyanine-Based Fluorescent Probe Revealing the Polarity Heterogeneity of Lipid Droplets and Enabling Accurate Diagnosis of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) has gradually become a pronoun for terrifying death owing to its high mortality rate. With the progression of HCC, lipid droplets (LDs) in HCC cells exhibit specific variations such as increased LDs number and decreased polarity, which can serve as the diagnostic target. However, developing an effective method to achieve HCC diagnosis and reveal LDs polarity heterogeneity is still a crucial challenge. Herein, the first high-performance LDs-targeting probe (1) is reported based on ketocyanine strategy with ultrasensitive polarity-responding ability and near-infrared emission. Probe 1 shows excellent sensitivity to polarity parameter Δf (0.027-0.290) with 808-fold fluorescence enhancement and the emission wavelength red-shifts 91nm. In HCC cells, probe 1 shows a 2.5- to 5.9-fold fluorescence enhancement compared with normal and other cancer cells which exceeds clinical threshold of 2.0, indicating probe 1 can distinguish HCC cells. The LDs polarity heterogeneity is revealed and it displays a sequence, HCC cells < other cancer cells < normal cells, which may provide useful insight to engineer LDs-targeting probes for HCC cell discrimination. Finally, probe 1 realizes accurate HCC diagnosis on the cellular, organ, and in vivo levels, providing a satisfying tool for clinical HCC diagnosis and surgical navigation.

Theoretical study on the photophysical properties of thiophene-fused-type BODIPY series molecules in fluorescence imaging and photodynamic therapy.

As a class of photosensitizers (PSs) with dual functions of photodynamic therapy (PDT) and fluorescence imaging, the relationship between the structure and dual-function of thiophene-fused-type BODIPY dyes has not been studied in depth before. We found that the thiophene-fused-type BODIPY triplet photosensitizer is produced according to the energy level matching rule and the introduction of the thiophene ring significantly reduces the energy gap ΔEST between singlet and triplet states, as revealed by our investigation of the excited state structures and energies of thieno-fused BODIPY dyes. At the same time, a tiny ΔEST also results in a greatly enhanced intersystem crossing (ISC) rate, kISC. The kISC value of MeO-BODIPY, having the highest singlet oxygen quantum yield (ΦΔ), is the largest. Substitution with a strong electron donor N,N-dimethylaminophenyl (DMA) leads to the vertical configuration in the T1 state. The small ΔE (0.0029 eV) between the HOMO and HOMO-1 triggers the photo induced electron transfer (PET) of inhibiting ISC and fluorescence. When thieno-fused BODIPYs react with pyrrole, the increase of π-conjugation and smaller ΔEHOMO-LUMO explain the redshift in emission wavelength of thieno-pyrrole-fused BODIPY. The more planar configuration of the S1 state and the stronger oscillator intensity reflect a higher fluorescence quantum yield (ΦF). The extension of π-conjugation can cause molecules to transition to higher-level singlet excited states (Sn states, n ≥ 1) after absorbing energy and reduce the energy level of the excited state, resulting in multiple channels and favoring 1O2 production for thieno-pyrrole-fused BODIPYs with electron-withdrawing groups at the para-position of the phenyl groups. Due to ΔES0-T1 < 0.980 eV, the substitution of electron-donating groups cannot produce 1O2. In this work, we have revealed the mechanism of ISC and the fluorescence emission process in the thiophene-fused-type BODIPY dye, which has provided a theoretical foundation and guidance for the future design of BODIPY-based heavy-atom-free PSs for molecular applications in PDT.

Macrocyclization-induce emission enhancement characteristics of benzothiadiazole-based macrocycles: A theoretical study

We present a comprehensive investigation into the molecular structures in the ground state and the first singlet excited state, intramolecular and intermolecular interactions, as well as the emission properties of monomers, dimers and macrocycles using density functional theory and time-dependent density functional theory. Our study aims to unveil the macrocyclization-induce emission enhancement principle for benzothiadiazole-based macrocycles. Compared with the typical π-π stacking of monomers, macrocycles exhibit the tighter stacking arrangement due to the presence of strong intramolecular and intermolecular hydrogen bond interactions and the rigid triangular geometry of macrocycle, which is conducive to the enhancement of emissions efficiency. The calculated oscillator strength of macrocycles in the first excited state is much higher than that of dimers composed of two monomers. Meanwhile, the large transition electric dipole moment is beneficial for enhancing the emission efficiency. Additionally, our study reveals an emission wavelength red-shift for macrocycles after “CH”/N substitution in the acceptor moiety, and the transition mode from LUMO to HOMO can be mainly attributed to intramolecular charge transition characters from acceptor to donor fragments. Our theoretical study might provide valuable insights for the design of innovative luminescent macrocycles with high emission efficiency.

Theoretical study on the influence of substitution position on the luminescence properties and charge transfer characteristics of thermally activated delayed fluorescent molecules

Thermally active delayed fluorescence (TADF) molecules have potentially applications in organic light-emitting diodes (OLEDs) and biomedical sensing. Although TADF emitters have witnessed a rapid development, it remains challenging to study the relationship between molecular structures and luminescence properties as well as carrier mobility transfer properties in theory. In this work, the photophysical properties and luminescence mechanisms of isomers TPA-APQDCN-C (donors at para-position) and TPA-APQDCN-Y (donors at ortho-position) were studied based on density functional theory (DFT) and thermal vibration correlation function (TVCF) method. The results showed that both TPA-APQDCN-C with para-substituted donor and TPA-APQDCN-Y with ortho-substituted donors exhibit red emission in toluene and crystal state. Furthermore, compared to ortho-substituted donors, para-substituted donors promote a redshift in emission wavelength. In addition, the fluorescence efficiencies of TPA-APQDCN-C is obviously higher than that of TPA-APQDCN-Y due to its larger radiative rate and less non-radiative decay rate. Besides, para-substitution (TPA-APQDCN-C) leads to the smaller energy gap between S1 and T1 and the larger spin–orbit coupling (SOC) constant, which is beneficial for increasing the reverse crossing intersystem (RISC) rates. In addition, the carrier mobilities are studied based on the kinetic Monte Carlo simulations. The calculations show that TPA-APQDCN-C are more beneficial for the transfer of holes compared to TPA-APQDCN-Y. This study reveals TPA-APQDCN-C with donors at para-position has a better TADF properties and hole transfer ability, which holds guiding significance for the design of TADF devices with high luminescence efficiency and rapid hole transfer.

Tumor Stimulus-Activatable Pretheranostic Agent: One Key to Three Locks.

The uncontrollable distribution of antitumor agents remains a large obstacle for specific and efficient cancer theranostics; thus, efficient construction of tumor-specific systems is highly desirable. In this work, a general design of tumor stimulus-activatable pretheranostic agents was put forward via a series of structures-tunable triphenylamine derivatives (TPA-2T-FSQ, TPA-2T-BSZ, and TPA-2T-ML) with phenothiazine, benzothiazine, and thiomorpholine as identifying groups of hypochlorite (HClO), respectively. Notably, the sulfur atom in phenothiazine of TPA-2T-FSQ was more easily oxidized to sulfoxide groups by HClO, transforming into an electron acceptor to form an excellent push-pull electronic system, which was beneficial to a large redshift of absorbance and emission wavelengths. Based on this, TPA-2T-FSQ resorted to a key of overexpressed HClO in the tumor to open "three locks", viz, NIR fluorescence, photothermal, and photoacoustic signals for multimodal diagnostic and treatment of the tumor. This study provided an elegant design to adopt tumor stimulus-triggerable pretheranostic for improving theranostic accuracy and efficiency, which was regarded as a promising candidate for precision medicine.

Hydrogen-Bonding-Driven Nontraditional Photoluminescence of a β-Enamino Ester.

Nontraditional luminogens (NTLs) do not contain any conventional chromophores (large π-conjugated structures), but they do show intrinsic photoluminescence. To achieve photoluminescence from NTLs, it is necessary to increase the extent of through-space conjugation (TSC) and suppress nonradiative decay. Incorporating strong physical interactions such as hydrogen bonding is an effective strategy to achieve this. In this work, we carried out comparative studies on the photoluminescence behaviors of two β-enamino esters with similar chemical structures, namely methyl 3-aminocrotonate (MAC) and methyl (E)-3-(1-pyrrolidinyl)-2-butenoate (MPB). MAC crystal emits blue fluorescence under UV irradiation. The critical cluster concentration of MAC in ethanol solutions was determined by studying the relationship between the photoluminescence intensity (UV-visible absorbance) and concentration. Furthermore, MAC exhibits solvatochromism, and its emission wavelength redshifts as the solvent polarity increases. On the contrary, MPB is non-emissive in both solid state and solutions. Crystal structures and theoretical calculation prove that strong inter- and intramolecular hydrogen bonds lead to the formation of large amounts of TSC of MAC molecules in aggregated states. No hydrogen bonds and thus no effective TSC can be formed between or within MPB molecules, and this is the reason for its non-emissive nature. This work provides a deeper understanding of how hydrogen bonding contributes to the luminescence of NTLs.

Preparation of full-color carbon quantum dots with multiple emission centers

In recent years, carbon dots have attracted more and more attention due to their unique advantages, but there has been a great controversy about the study of their mechanism. A clear mechanism is of great importance for the structural design of carbon dots. To investigate the photoluminescence mechanism of carbon dots, full-color carbon dots with multiple emission centers were successfully prepared by using citric acid and water-soluble aniline blue. It is shown that the red shift of emission wavelength is attributed to the synergistic effect of N and O-related surface functional groups and quantum size. The successful preparation of cold white light diodes from mixed trichromatic carbon dots indicates that this type of carbon dot has important applications in light-emitting devices.

Syntheses, optical properties, and bioimaging application of near-infrared aza-BODIPY dyes with electronic push–pull system

It is still a challenging work of developing near-infrared (NIR) fluorescence dyes with excellent optical properties. Herein, we synthesized a series of NIR aza-BODIPY fluorescence dyes with electronic push–pull system and further investigated their photophysical properties, photostability, and application in cellular imaging. It was found that introducing electron-withdrawing groups (EWGs) on the para-position of aza-BODIPY 1,7-phenyls not only leads to the significant redshift of absorption and fluorescence emission bands of aza-BODIPY dyes but also increases their fluorescence quantum yield and photostablility. The DFT calculations and cyclic voltammetry measurements proved that introducing EWGs on para-position of 1,7-phenyls can decrease the energy level difference between HOMO and LUMO, resulting in the redshift of maximum absorption and emission wavelengths. On the basis of the feasible experiment results of cellular imaging and cytotoxicity assay, it is expected that the optimized aza-BODIPY dyes have a bright application prospect for in vivo cellular or tissue imaging.

CuInS2 Nanocrystals Embedded PMMA Composite Films: Adjustment of Polymer Molecule Weights and Application in Remote-Type White LEDs.

The commercial application of colloidal semiconductor nanocrystals has been realized owing to the development of composite film technology. Here, we demonstrated the fabrication of green and red emissive CuInS2 nanocrystals embedded polymer composite films of equal thickness by using a precise solution casting method. The impacts of polymer molecular weight on the dispersibility of CuInS2 nanocrystals were then systematically studied through evaluating the decrease in transmittance and red shift of emission wavelength. The composite films made from PMMA of small molecular weights exhibited higher transmittance. Applications of these green and red emissive composite films as color converters in remote-type light-emitting devices were further demonstrated.

The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs

Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm2. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology.

Enantioselective Recognition of L-Lysine by ICT Effect with a Novel Binaphthyl-Based Complex.

A novel triazole fluorescent sensor was efficiently synthesized using binaphthol as the starting substrate with 85% total end product yield. This chiral fluorescence sensor was proved to have high specific enantioselectivity for lysine. The fluorescence intensity of R-1 was found to increase linearly when the equivalent amount of L-lysine (0-100 eq.) was gradually increased in the system. The fluorescence intensity of L-lysine to R-1 was significantly enhanced, accompanied by the red-shift of emission wavelength (389 nm to 411 nm), which was attributed to the enhanced electron transfer within the molecular structure, resulting in an ICT effect, while the fluorescence response of D-lysine showed a decreasing trend. The enantioselective fluorescence enhancement ratio for the maximum fluorescence intensity was 31.27 [ef = |(IL - I0)/(ID - I0)|, 20 eq. Lys], thus it can be seen that this fluorescent probe can be used to identify and distinguish between different configurations of lysine.

Preparation and performance study of dye-based carbon quantum dots

The preparation of Full-color carbon dots is well established, but the explanation of its mechanism is not only highly controversial, but partly even contradictory to the project. Therefore, to investigate the red-shift mechanism of Full-color carbon dots, citric acid and Nile blue with complex composition structure were selected as raw materials, and B-,G-,Y- and R-CQDs were prepared by changing the reaction solvent with quantum yields of 49.7 %,28.2 %,72.3 %,30.3 % and average particle sizes of mainly 2.7–3.2 nm, respectively. TEM and XPS tests show that the emission wavelength redshift is mainly attributed to the reduction of the energy band gap due to the sp2 conjugate size and the increase of graphitic nitrogen content. To examine the optical properties of dye-based F-CQDs, F-CQDs/PVA polymer films and LEDs were prepared, both of which showed unique optical properties.

Toward visual chiral recognition of amino acids using a wide-range color tonality ratiometric nanoprobe

Chiral recognition has long been a challenging issue to deal with in biological systems, drug design and food authentication. Implementing nanoparticle-based probes with intrinsic or induced chirality in this field has addressed several issues concerning sensitivity, reliability, rapidness and the cost of chiral sensing platforms. Yet, research into chiral nanoprobes that can be used for visual monitoring of chiral substances is still in its infancy. As part of this study, a visual chiral recognition platform has been developed in which a combination of blue-emitting carbon dots (BCDs) and mercaptopropionic acid-capped CdTe quantum dots (MPA-QDs) with inherent chiroptical activity were employed for enantiomeric detection. The ratiometric probe displayed unique fluorescence response patterns in the presence of arginine (Arg) and histidine (His) enantiomers. Upon addition of l-amino acids, successive enhancement and quenching of emission intensity as well as a red-shift in emission wavelength of MPA-QDs were observed. The emission color of the nanoprobe changed from green to pink-red and green to brick-red red by increasing the concentration of L-Arg and L-His, respectively.In contrast, their d-amino acid equivalents have a negligible influence on the emission color and fluorescence signal of the developed nanoprobe. Due to the enantioselective vibrant color changes of the nanoprobe, RGB analysis was applied for the determination of enantiomeric excess (ee) in racemic mixture with satisfactory results, allowing smartphone-based onsite visual evaluation of ee (%). Circular dichroism, lifetime, size distribution and ζ-potential measurements were employed to study the chiroselective responses. First-principle calculations were also carried out with density functional theory (DFT) to confirm the experimental observation. Furthermore, chiroselective response patterns of the ratiometric nanoprobe were manipulated to construct a logic gate system mimicking AND, OR, and INHIBIT functions. The capability of the proposed chiral platform in visual monitoring of the fraction of enantiomers in racemic mixtures has a great potential for rapid and onsite visual discrimination of chiral compounds in the field of clinical diagnostics and drug analysis.

Effects of rice bran phenolics on the structure of rice bran protein under different degrees of rancidity

To explore the effects of rice bran endogenous phenolics on rice bran protein under rice bran rancidity-induced oxidation, the structure of non-dephenolized and dephenolized rice bran protein with different degrees of rice bran rancidity (rice bran was stored for 0, 1, 3, 5, and 10 d) were investigated. During rice bran storage, dephenolization increased the carbonyl (from 5.32-24.59 to 6.11–26.52 μmol/g) and free sulfhydryl (from 24.41-32.33 to 32.64–45.04 μmol/g) contents of rice bran protein, and decreased disulfide bonds content (from 24.26-26.61 to 21.78–25.42 μmol/g). Meanwhile, endogenous phenolics improved rice bran protein secondary structural flexibility. Moderate oxidation (rice bran was stored for 0 and 1 d) induced by rice bran rancidity unfolded rice bran protein. The increase of maximum fluorescence emission wavelength red shift and the improvement of surface hydrophobicity induced by endogenous phenolics under moderate oxidation indicated rice bran endogenous phenolics further promoted the unfolding of rice bran protein. Excessive oxidation (rice bran was stored for 3, 5, and 10 d) caused protein aggregation. This work demonstrated that endogenous phenolics significantly affected rice bran protein structure under oxidation, especially the synergistic effect of endogenous phenolics and moderate oxidation on protein unfolding state.

First-principles study of luminescence of fullerene-like clusters

Thermally activated delayed fluorescence (TADF), a unique molecular fluorescence mechanism, plays a key role in designing emitters of high efficiency. Carbon fullerenes such as C&lt;sub&gt;60&lt;/sub&gt; and C&lt;sub&gt;70&lt;/sub&gt; exhibit strong TADF with intensity even higher than that of the prompt fluorescence, owing to their long lifetimes of triplet state and modest singlet-triplet energy gaps. Thus, there arises the intriguing question whether other fullerene-like clusters can also have fluorescence and host the TADF effect. In this work, by time-dependent density functional theory (TD-DFT) calculations, we explore the excited-states of the experimentally reported boron nitride cage clusters B&lt;sub&gt;12&lt;/sub&gt;N&lt;sub&gt;12&lt;/sub&gt;, B&lt;sub&gt;24&lt;/sub&gt;N&lt;sub&gt;24&lt;/sub&gt; and B&lt;sub&gt;36&lt;/sub&gt;N&lt;sub&gt;36&lt;/sub&gt;, as well as compound clusters B&lt;sub&gt;12&lt;/sub&gt;P&lt;sub&gt;12&lt;/sub&gt;, Al&lt;sub&gt;12&lt;/sub&gt;N&lt;sub&gt;12&lt;/sub&gt; and Ga&lt;sub&gt;12&lt;/sub&gt;N&lt;sub&gt;12&lt;/sub&gt; with the same geometry as B&lt;sub&gt;12&lt;/sub&gt;N&lt;sub&gt;12&lt;/sub&gt;. Using the HSE06 hybrid functional, the predicted energy gaps of these fullerene-like clusters are obtained to range from 2.83 eV to 6.54 eV. They mainly absorb ultraviolet light, and their fluorescence spectra are all in the visible range from 405.36 nm to 706.93 nm, including red, orange, blue, and violet emission colors. For the boron nitride cages, the energy gap of excited states increases with the cluster size increasing, accompanied by a blue shift of emission wavelength. For the clusters with B&lt;sub&gt;12&lt;/sub&gt;N&lt;sub&gt;12&lt;/sub&gt; geometry and different elemental compositions, the excited energy gap decreases as the atomic radius increases, resulting in a red shift of emission wavelength. In addition, the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of these compound cage clusters are distributed separately on different elements, resulting in small overlap between HOMO and LUMO wavefunctions. Consequently, these fullerene-like clusters exhibit small singlet-triplet energy differences below 0.29 eV, which is beneficial for the intersystem crossing between the excited singlet state and triplet state, and hence promoting the TADF process. Our theoretical results unveil the fluorescence characteristics of cage clusters other than carbon fullerenes, and provide important guidance for precisely modulating their emission colors by controlling the cluster sizes and elemental compositions. These experimentally feasible fullerene-like compound clusters possess many merits as fluorophors such as outstanding stabilities, non-toxicity, large energy gap, visible-light fluorescence, and small singlet-triplet energy gap. Therefore, they are promising luminescent materials for applications in display, sensors, biological detection and labelling, therapy, and medicine.

Strain Minimization of InAs QDs Heterostructures Using Dual Quaternary-Ternary/Ternary-Quaternary Capping Materials via Digital Alloy Capping Layer Approach

The role of combinational (ternary and quaternary) capping layers to understand the strain distribution mechanism and optical properties through digital alloy capping layer (DACL) has been presented in this work. GaAsSb as ternary and InGaAsSb as quaternary capping materials have been used, and a combination of ternary-quaternary&#x002F;quaternary-ternary has been implemented. Digital alloy technique has been employed to cover the quantum dots with the combinational capping materials. The biaxial as well as hydrostatic strain is obtained using Nextnano&#x002B;&#x002B; software and compared to analyze the strain distribution inside the heterostructure. Digital alloyed structures offer a red shift in emission wavelength (&#x223C; 2 &#x00B5;m) compared to conventional structures based on the selection of capping material. However, the selection of capping materials (GaAsSb and InGaAsSb) exhibits both type-I as well as type-II band profiles which can be utilized in multiple optoelectronic applications. This detailed theoretical study of the digital and analog alloy approach of the combinational ternary&#x002F;quaternary and quaternary&#x002F;ternary capping layer would help to optimize advanced futuristic device heterostructures with reduced strain and better crystal quality.

Reduction of optical transition energy in composite GaInAsBi quantum wells

Light emitting diode structures of quaternary GaInAsBi bismide quantum wells with AlInAs barriers were grown on InP substrates by molecular-beam epitaxy. Intermediate additional layers of GaInAs were inserted between the bismide quantum wells and AlInAs barriers to reduce the electron size-quantization energy and, therefore, the energy of optical transitions. It has been demonstrated both theoretically and experimentally that the redshift of emission wavelength in the composite GaInAs1−xBix (x∼0.06) quantum wells with the additional intermediate GaInAs layers can be as large as ∼0.4μm.