Photoluminescence Wavelength Research Articles

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

A parallel investigation of un-doped and manganese ion-doped zinc selenide quantum dots at cryogenic temperature and application as an optical temperature sensor

In this work, un-doped and manganese ion (Mn2+)-doped zinc selenide (ZnSe) quantum dots (QDs) were investigated by measuring photoluminescence (PL) and photoluminescence excitation (PLE) spectra in the temperature range from 300 to 77 K. Intense blue and orange PL were observed for ZnSe and Mn@ZnSe QDs, respectively. The intensity of PL spectra is found to be exceedingly dependent on temperature. The highest PL intensity is obtained at 77 K and then reduced with rising temperature up to 300 K. To understood the temperature-dependent PL origin and mechanism, the PL spectra with different excitation and PLE spectra at different PL wavelengths were investigated at decreasing temperature (300 - 77 K) and vis-a-vis. The calculated activation energy values come out to be 42.2 and 66.4 meV for ZnSe and Mn@ZnSe QDs, respectively. Furthermore, the lifetimes of Mn@ZnSe QDs were discussed at different temperatures. The absolute sensitivity (S) for the temperature sensor is calculated, and the maximum S values come out to be 0.58% K−1 at 225 K and 0.44% K−1 at 250 K for ZnSe and Mn@ZnSe QDs, respectively. The wide range linearity in temperature-dependent PL and moderate activation energy values suggest that the prepared QDs can be cast for a PL-intensity-based optical temperature sensor.

Effects of substrate temperature on the uniformity of InGaAs epilayers using a dual-zone manipulator

Three-inch InGaAs epilayers are grown by solid source molecular beam epitaxy using the manipulator equipped with dual-zone heaters. The effects of the substrate temperature on the uniformity of material surface morphology, indium composition, photoluminescence, electronic mobility, and background doping are investigated. As the temperature of the outer heater in the range of 625 °C to 655 °C, no dim area is observed on the edge of the material surface. At the same time, the indium composition fluctuation of the high-resolution X-ray diffraction and the photoluminescence wavelength fluctuation are less than ±0.1% for the epilayers grown at the optimum substrate temperatures.

Ligand Assisted Control of Photoluminescence in Organometal Perovskite Nanocrystals

Organometal perovskite nanocrystals have shown remarkable properties not only in photovoltaics, but also in light-emitting devices. In this work colloidal nanocrystals of organometal perovskite CH3NH3PbBr3 (MAPBr) with effective visible photoluminescence were synthesized by the ligand assisted reprecipitation method. The studies were carried out by photoluminescence spectroscopy and optical transmission spectroscopy. Analysis of the photoluminescence and transmission spectra showed that by changing the concentration of the ligands oleylamine and octylamine, it is possible to control the size of nanocrystals and the photoluminescence wavelength due to the quantum confinement effect. It was shown that the increase in ligands concentration in MAPBr perovskite nanocrystals (NCs) solutions decreases the width of the peak which indicates a better quality of the obtained nanocrystals. An increase in the band gap indicates a decrease in the size of the nanocrystals. Replacing the ligands in the colloidal perovskite NCs solutions leads to shift of the photoluminescence peak from 456 to 535 nm.

Luminescence Fine Structures in Single Lead Halide Perovskite Nanocrystals: Size Dependence of the Exciton–Phonon Coupling

Lead halide perovskite nanocrystals (NCs) have superior photoluminescence (PL) properties, such as high PL quantum yields and wide PL wavelength tunability, for optoelectronic applications. Here, we report the PL spectra of single formamidinium lead halide perovskite FAPbX3 (X = Br, I) NCs examined by single-dot spectroscopy at low temperature. We found four PL peaks in the low-energy region below the strong exciton PL peak that originate from two longitudinal-optical (LO) phonon replicas of the exciton PL, biexcitons, and charged excitons (trions). The binding energies of the biexcitons and trions become larger as the NCs decrease in size. The LO phonon energies show no size dependence, but the Huang-Rhys factors, which reflect the strength of the exciton-phonon coupling, become larger for smaller NCs. Our findings provide important insights into the exciton properties of perovskite NCs.

Synthesis and Optical Properties of In2S3-Hosted Colloidal Zn-Cu-In-S Nanoplatelets.

High-efficiency photoluminescence quaternary hexagon Zn–Cu–In–S (ZCIS) nanoplatelets (NPls) have been synthesized by a two-step cation exchange method, which starts with the In2S3 NPls followed by the addition of Cu and Zn. It is the first time that In2S3 NPls are used as templates to synthesize ZCIS NPls. In this paper, the reaction temperature of In2S3 is essential for the formation of NPls. The photoluminescence wavelength of NPls can be tuned by adjusting the temperature of Cu addition. To enhance the stability of the resulting NPls and to improve their optical properties, we introduced Zn2+ and obtained ZCIS NPls by cation exchange on the surface. It is worth noting that the obtained ZCIS NPls show a shorter fluorescence lifetime than other ternary copper sulfide-based NPls. This work provides a new way to synthesize high-efficiency, nontoxic, and no byproduct ZCIS NPls.

Synergistic enhancement of photoluminesent intensity in monolayer molybdenum disulfide embedded with plasmonic nanostructures for catalytic sensing

Enhancing photoluminescence (PL) of semiconducting 2D materials is proven essential for many applications related to optoelectronics and sensing. Here, we demonstrate synergistic PL enhancement in 2D materials by incorporating silver plasmonic nanodiscs in defect-induced monolayer molybdenum disulfide (MoS2) for luminescent quench sensing of dopamine with high accuracy and selectivity. We develop a hole-array perforated 2D MoS2 embedded with plasmonic silver dimers to harmonize the surface plasmon resonance with the PL wavelength of monolayer MoS2, which enhance it by 56-fold. We implemented the optimized perforated MoS2/dimers platform as a catalytic assay for on-chip PL quenching detection of dopamine, achieving a low limit of detection of 9.3 nM. This approach opens avenues of high-performance molecular sensing applications by improving the PL emission of 2D materials.

(Invited) Molecular Structure-Based Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes Using Bis-Aryl Functionalization

Single-walled carbon nanotubes (SWCNTs) show photoluminescence (PL) in the near infrared (NIR) region, which is applicable to bioimaging and telecommunication devices. Recently, local chemical functionalization of SWCNTs has been developed to enhance their NIR PL properties, in which defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the functionalization.[1-3] Actually, E 11* PL of the locally functionalized SWCNTs (lf-SWCNTs) is observed with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. It is due to formation of new emissive sites with narrower band gaps and exciton trapping features in the tube structures.In the local chemical functionalization, doped site structures of the lf-SWCNTs can be changed depending on modifier molecules, which results in effective modulation of the NIR PL wavelengths of the lf-SWCNTs beyond 1000 nm-region. Previously, we have developed bis-aryldiazonium salts (bAs) that have two reactive aryldiazonium groups connected with a methylene linker and observed E 11 2* PL over 1200 nm regions from the lf-SWCNTs with (6,5) chirality based on its proximal aryl functionalization.[4]Here, we synthesize new modifier molecules with the bis-aryldiazonium motif and modify the geometry of the proximal aryl-functionalized sites of the lf-SWCNTs. As a result, for example, methylene linker positions on the aryldiazonium groups of bAs clearly changed the trend of methylene length-dependent wavelength shifts of E 11 2* PL. [5] Moreover, bAs having rigid linker structures changed peak positions of E 11 2* PL, indicating that the control of the proximal defect configuration would be an effective way for the PL property modulation of lf-SWCNTs. As another aspect of the proximal aryl functionalization, we found that E 11 2* PL showed unique wavelength shift behaviors by microenvironment changes using various organic solvents. The observed trend was different from those of E 11 PL and E 11* PL[6], in which proximal defect distances could be an important factor for their microenvironment responsiveness.Therefore, molecularly designed bis-aryldiazonium modifiers become promising tools to create structurally controlled bis-aryl functionalized sites of lf-SWCNTs and precisely modulate their NIR PL wavelengths (> 1000 nm).[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki et al. Sci. Rep., 6, 28393 (2016). [5] T. Shiraki et al. Chem. Lett., 48, 791 (2019). [6] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). Figure 1

Ion Exchange Lithography: Localized Ion Exchange Reactions for Spatial Patterning of Perovskite Semiconductors and Insulators.

Patterning materials with different properties in a single film is a fundamental challenge and essential for the development of next-generation (opto)electronic functional components. This work introduces the concept of ion exchange lithography and demonstrates spatially controlled patterning of electrically insulating films and semiconductors with tunable optoelectronic properties. In ion exchange lithography, a reactive nanoparticle "canvas" is locally converted by printing ion exchange "inks." To demonstrate the proof of principle, a canvas of insulating nanoporous lead carbonate is spatioselectively converted into semiconducting lead halide perovskites by contact printing an ion exchange precursor ink of methylammonium and formamidinium halides. By selecting the composition of the ink, the photoluminescence wavelength of the perovskite semiconductors is tunable over the entire visible spectrum. A broad palette of conversion inks can be applied on the reactive film by printing with customizable stamp designs, spray-painting with stencils, and painting with a brush to inscribe well-defined patterns with tunable optoelectronic properties in the same canvas. Moreover, the optoelectronic properties of the converted canvas are exploited to fabricate a green light-emitting diode (LED), demonstrating the functionality potential of ion exchange lithography.

Rapid synthesis of highly stable all-inorganic perovskite nanocrystals exhibiting strong blue luminescence

With the development of blue-emitting all-inorganic Pb-based perovskite nanocrystals (NCs), the perovskite family (e.g., CsPbCl3−xBrx NCs) has drawn researchers’ attention. Although the hot injection method has been widely used to fabricate blue-emitting perovskite NCs, this synthesis method generally needs an inert gas atmosphere, high temperature, and localized injection operation, leading to high cost and limiting the applications of perovskite NCs. Herein, we synthesized mixed-halide blue-emitting CsPbCl3−xBrx (x = 0.0–2.5) perovskite NCs rapidly at room temperature. The as-prepared perovskite NCs exhibited excellent stability and high photoluminescence quantum yields up to 89% because of their low non-radiative recombination rate. The photoluminescence wavelength of the NCs was precisely regulated across the whole visible region (406–488 nm). Importantly, this facile method to synthesize perovskite NCs not only requires mild experimental conditions, dramatically lowering the cost of synthesis, but also provides a feasible route for the industrial production of efficient blue-emitting devices.

A co-delivery platform for synergistic promotion of angiogenesis based on biodegradable, therapeutic and self-reporting luminescent porous silicon microparticles

Insufficient angiogenesis happened in body defects such as ulceration, coronary heart disease, and chronic wounds constitutes a major challenge in tissue regeneration engineering. Owing to the poor bioactivity and maintenance of pro-angiogenic cells and factors during transplantation, new bioactive materials to tackle the barrier are highly desirable. Herein, we demonstrate a co-delivery platform for synergistic promotion of angiogenesis based on biodegradable, therapeutic, and self-reporting luminescent porous silicon (PSi) microparticles. The biodegradable and biocompatible PSi microparticles could quickly release therapeutic Si ions, which is bioactive to promote cell migration, tube formation, and angiogenic gene expression in vitro. To construct a highly efficient angiogenesis treatment platform, vascular endothelial growth factor (VEGF) was electrostatically adsorbed by PSi microparticles for effective drug loading and delivery. The dual therapeutic components (Si ions and VEGF) could release with the dissolution of Si skeleton, accompanying by the decay of photoluminescence (PL) intensity and blue shift of the maximum PL wavelength. Therefore, real-time drug release could be self-reported and assessed with the two-dimensional PL signal. The co-delivery of Si ions and VEGF displayed synergistic effect and highly efficient angiogenesis, which was evidenced by the enhancement of endothelial cell migration and tube formation in vitro with approximately 1.5–5 times higher than control. The blood vessel formation in vivo was also significantly improved as shown by the chick chorioallantoic membrane (CAM) model, in which the total length, size and junctions exhibited 2.1 ± 0.4, 4 ± 0.4, and 3.9 ± 0.3 times in comparison to control, respectively. The PSi and VEGF co-delivery system display great potential in tissue engineering as a biodegradable and self-reporting theranostic platform to promote angiogenesis.

Low temperature photoluminescence and solvatochromic studies of organic hybrid 4-methoxybenzylammonium chloride (4-MBACl)

We report temperature dependent photoluminescence (PL) and solvatochromic studies of 4-methoxybenzylammonium chloride (4-MBACl). The single crystals of 4-MBACl has been grown using slow solvent evaporation method under ambient conditions and have been confirmed using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic studies. Thermal stability of the material has been analyzed by thermogravimetric (TG) and differential thermal analyzes (DTA). 4-MBACl crystal is photoluminescent with emission wavelength maximum at 300 nm. Exciton-phonon coupling in 4-MBACl is realized from temperature dependent PL studies. Changes in full width at half maximum (FWHM) of PL emission peak, intensity maximum (Imax) and wavelength maximum (λmax) have been analyzed systematically between temperatures 290–10 K in order to understand the photophysical phenomenon behind the emission. Optical band gap (Eg) of 4-MBACl has been varied using solvent polarity, proticity and solution concentration. Interactions like OH---O, OH---π and π-π stacking are explained to reason the notable shifts.

Group-IV-semiconductor quantum-dots in thermal SiO2 layer fabricated by hot-ion implantation technique: different wavelength photon emissions

We experimentally studied three types of group-IV-semiconductor quantum-dots (IV-QDs) of Si-, SiC-, and C-QDs in a thermal SiO2 layer that were fabricated using a very simple hot-ion implantation technique for Si+, double Si+/C+, and C+ into the SiO2 layer, respectively, to realize a different wavelength photoluminescence (PL) emission from near-IR to near-UV ranges. TEM analyses newly confirmed both Si- and C-QDs with a diameter of approximately 2–4 nm in addition to SiC-QDs in SiO2. We successfully demonstrated very strong PL emission from three IV-QDs, and the peak photon energies (E PH) (peak PL-wavelength) of Si-, and SiC-, and C-QDs were approximately 1.56 eV (800 nm), 2.5 eV (500 nm), and 3.3 eV (380 nm), respectively. IV-QDs showed that the PL properties strongly depend on the hot-ion doses of Si and C atoms and the post N2 annealing processes. Consequently, it is easy to design peak PL wavelengths by controlling the ion doses of Si+ and C+ implanted into the SiO2 layer.

Bias-dependent time-resolved photoluminescence spectroscopy on 265 nm AlGaN-based LEDs on AlN substrates

Time-resolved photoluminescence spectroscopy under an external bias is performed on 265 nm AlGaN-based LEDs on AlN substrates. The bias dependences of the photoluminescence wavelength, intensity, and decay time are observed. Our experimental results indicate that the built-in electric field has the opposite sign as the polarization-induced electric field in the quantum-well layers. These results agree with the first-principles calculations but are contrary to a previous experimental study. Additionally, thermionic and tunneling escape processes from the quantum-well layers play a minor role in the non-unity current injection efficiency at room temperature under a low injection (non-droop) regime.

Synthesis of brightly luminescent colloidal formamidinium lead bromide perovskite FAPbBr3 nanoplatelets with tunable emission

Hybrid halide perovskites are semicondoctor materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology. They have size-tunable emissions due to quantum size effects. In this work, the Formamidinium Lead Bromide perovskite CH(NH2)2PbBr3 nanoplatelets (NPLs) were successfully synthesized by ligand-assisted reprecipitation method under room condition, in which the emission color-tunability was realized via quantum size effect without anion–halide mixing, by varying the oleylamine to oleic acid volume ratio as surfactants, while the total amount of oleic acid remained unchanged. We are able to adjust the optical proprieties of FAPbBr3 NPLs and, consequently, their structural properties. The obtained colloidal solutions of FAPbBr3 nanoplatelets with uniform size exhibited different photoluminescence wavelengths covering the spectral region from 440 to 525 nm. The maximum absolute PL quantum yield (PLQY) of the green emission was measured to be as high as 80% at room temperature. The size of FAPbBr3 NPLs could be effectively tuned from 15.5 to 38.1 nm with an increase in the oleylamine and oleic acid ligands ratio.

Optimization of (In)GaN Heterostructures for Sensing Applications

Herein, the optimization of (In)GaN heterostructures for chemical sensing is presented. The metalorganic vapor phase epitaxy (MOVPE)‐grown sensor consists of an InxGa1−xN quantum well (QW) placed close to the surface of a GaN substrate with a thin GaN cap layer on top. The photoluminescence (PL) wavelength of this QW is sensitive to surface potential changes and thus its optical signal is used as sensor response. Simulations are performed with nextnano to improve its sensitivity. Sensor parameters such as the cap layer thickness d, QW thickness Lz, background buffer layer doping concentration N, and indium concentration x of the QW are varied. It is found that a thin cap layer, together with high background doping and medium QW thickness, is ideal. The indium content does not show a strong influence on sensitivity. The trends found in the simulations are mostly confirmed in real‐world experiments performed in a chemical sensing setup, yet quantitative deviations exist.

Excitons competition regulation via organic cation-site and halogen-site co-halogenation of (X-p-PEA)2Pb(Cl/Br)4 perovskites

In this work, we report a family of co-halogenated two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead halogen ((PEA)2Pb(Cl/Br)4) in which the organic cation-site (PEA) is substituted with halogen at the para-site, namely the formation of 4-halophenethylamine (X-p-PEA) (X = Cl, Br; p: para-site). The organic cations are regulated by introducing halogen ions at the para-site of the benzene ring to promote the structural distortion of the lead halide octahedral inorganic layer. Furthermore, (X-p-PEA) causes a shift in the energy band distribution of 2DHPs. In this case, the photoluminescence competition of free excitons (FEs) and self-trapped excitons (STEs) changes the microscopic relaxation process of excitons. In addition, we found that (Br-p-PEA) can increase the photoluminescence quantum yield (PLQY). At the same time, we regulate the halogen-site of perovskites from lead-chloride perovskites (LCPs) to lead bromine perovskites (LBPs), achieving emission from white light to blue light. Therefore, the co-halogenation regulation strategy of organic cation-site and halogen-site can effectively regulate the photoluminescence wavelength and improve the PLQY. This is of great significance for the development of perovskite materials with specific optoelectronic applications.

Mass production of highly fluorescent full color carbon dots from the petroleum coke

Heavy oil is treated as an undesirable raw material in traditional refining markets because of its low yield. However, its rich natural aromatic structure and heteroatomic compounds make it possible to be a precursor to large-scale production of carbon materials. Using heavy oil and three SDA products as precursors, we synthesized highly fluorescent multi-color carbon dots (CDs) by hydrothermal method, which can precisely control the photoluminescence wavelength in the range of 350−650nm. The synthesized carbon dots have the advantages of good long-term stability and stability under extreme pH conditions and low price. Importantly, the carbon dots synthesized with asphalt as the precursor have the highest fluorescence quantum yield. X-ray photoelectron spectroscopy (XPS) is used to elucidate the effects of different precursor on emission color change and photoluminescence quantum yield (PLQY), thus providing a controlled tuning of the system for the functionalization of CDs. And we further used the CDs in macrophage labeling. This pathway gives a reliable and repeatable industry possibility and may boost the applications of CDs into reality.

Impact of Mesoporous Silicon Template Pore Dimension and Surface Chemistry on Methylammonium Lead Trihalide Perovskite Photophysics

AbstractIn influencing fundamental properties—and ultimately device performance—of lead halide perovskites, interfacial interactions play a major role, notably with regard to carrier diffusion and recombination. Here anodized porous Si (pSi) as well as porous silica particles are employed as templates for formation of methylammonium lead trihalide nanostructures. This allows synthesis of relatively small perovskite domains and comparison of associated interfacial chemistry between as‐prepared hydrophobic hydrideterminated functionalities and hydrophilic oxide‐terminated surfaces. While physical confinement of MAPbBr3 has a uniform effect on carrier lifetime, pore size (7–18 nm) of the silicon‐containing template has a sensitive influence on perovskite photoluminescence (PL) wavelength maximum. Furthermore, identity of the surface functionality of the template significantly alters the PL quantum efficiency, with lowest PL intensity associated with the H‐terminated pSi and the most intense PL affiliated with the oxideterminated pSi surface. These effects are explored for green‐emitting MAPbBr3 as well as infrared‐emitting MAPbI3. In addition, the role of silicon surface chemistry on the time‐dependent stability of these perovskites packaged within a given mesoporous template is also evaluated, specifically, a lack of miscibility between MAPbI3 and the H‐terminated pSi template results in a diffusion of this specific perovskite composition eluting from this porous matrix over time.

Effect of oxygen and polymer matrix on photo-induced changes in CdSe quantum dots

When quantum dots (QDs) are irradiated with light, they are subject to photoinduced phenomena, such as photooxidation, photoluminescence (PL) blue-shift, photodarkening (PD) and photobrightening (PB). Some applications of QDs require their dispersion in a polymer matrix. In the present work, the type of polymeric matrix and surrounding gas were investigated as interdependent factors that induce blue shift, PD, and PB of CdSe QDs. CdSe QDs were dispersed in films of polystyrene (PS) and poly (methylmethacrylate) (PMMA). The films were purged with Ar and O2 gases for 8 h and then continuously irradiated with a 0.115 W visible laser while collecting PL spectra at time intervals. PD was obvious in PS, while in PMMA, significant PB was observed with no sign of PD. Irradiation under O2 led to a pronounced blue shift, but this was not observed under Ar. In summary, these polymers either protected against or contributed to photochemical alteration of the QDs in very different ways. PS/O2 is a suitable combination for illumination-based applications/studies that require conservation of PL intensity, but not wavelength. On the other hand, PMMA/Ar is suitable for those that require high PL intensity and conservation of PL wavelength. The changes are explained on the basis of the tendencies of molecular oxygen and the PMMA ester group to oxidize or passivate the QDs, while PS and Ar act as spectators.