PL Properties Research Articles

Construction of metallo-complexes with 2,2′:6′,2″-terpyridine substituted triphenylamine in different modified positions and their photophysical properties

The stable coordinated metallo-complexes based on 2,2′:6′,2″-terpyridine (tpy) and its derivatives have been widely researched for various wide-ranging applications in photoelectronics, catalysis, sensor, photoluminescence, and so on. However, the most reported studies ignored the comprehensive comparison between structures modified by different positions and photoluminescence. Herein, we design a series of metallo-complexes which were assembled with tpy substituted triphenylamine (TPA) at different positions and metal ions and explored their photophysical properties. In the solution state, MLE2 based on the 5,5″-positions modification showed the highest PLQYs and PL intensity. With the increase of solvent polarity, MLB2 exhibit the largest redshift. In the solid state, from MLA2 to MLE2, the emission colours are gradually red-shifted from yellow to red. The findings in this work may pave a new way to design functional metallo-complexes, not just for PL properties.

Precise optical engineering of carbon-based photoluminescence arrays based on e-beam irradiation process

Photoluminescent carbonnanomaterials have been widely studied for their low biological toxicity, outstanding biocompatibility, unique physical–chemical properties and obvious PL properties. The reliable fabrication of high-resolution fluorescence arrays has important significance in further studies and applications. The organic resist can be in-situ transferred into specific carbon-based micro-nano structure with fluorescence properties under e-beam irradiation. In this work, polymethyl methacrylate (PMMA) thin film was adopted for preparing solid-carbon nanostructures with 23.89 nm feature size. In a dark field environment, the structure has presented broad luminescent spectrum with maximum at 600 nm. Considering the significant influence of the surface molecular state on solid-carbon arrays, ammonia solution was used to enhance the PL intensity of the sample. The results verified that PL intensity was enhanced by a factor of 17 before and after ammonia solution treatment. Then carbon-based nanostructures were also fabricated on the surface of MoS2 film for studying PL properties between 2D materials and carbon-based dot arrays. The results show that superposition state was produced based on PL intensity and peak location of the solid-carbon dot array and MoS2 film. The optical behavior study of high-resolution solid-carbon arrays will provide a powerful supplement for carbon-based photophysical study and high-performance sensing devices.

Prolonged Red Persistent Luminescence in Bi3+ Single-Doped LiGa5O8: Regulating Traps by Site Selective Occupation.

Persistent luminescence (PersL) materials with impressive superiorities in optical performance have shown tremendous potential for information encryption application. Herein, a Bi3+-doped LiGa5O8 PersL material is facilely synthesized by a simple solid-state reaction. Site selective and preferential occupation of Bi3+ ions at distinct Ga3+ and Li+ polyhedra sites in LiGa5O8 endows it with a bimodal emission at 511 and 718 nm upon UV excitation at 254 nm. After removing the light source, an intense red afterglow was observed due to the generation of more and deeper traps classified as the oxygen vacancy defect (VO••) and the impurity defect (BiLi••). It is rarely reported in inorganic phosphors to achieve the Bi3+ single doping-activated red PersL. The LiGa5O8:x% Bi3+ (with x = 0.5-5.0) samples also exhibit tunable PL and time-dependent PersL properties. Combined with the Morse Code, a multiple information encryption model based on the abnormal optical properties of LiGa5O8:x% Bi3+ (x = 0, 0.5, and 5.0) samples was designed for high-level dynamic anticounterfeiting. These achievements further validate the use of the Bi3+ single doping strategy to explore excellent PersL materials and expand their multifunctional optical applications.

Gallium Sulfide Quantum Dots with Zinc Sulfide and Alumina Shells Showing Efficient Deep Blue Emission.

Solution-processed quantum dot (QD) based blue emitters are of paramount importance in the field of optoelectronics. Despite large research efforts, examples of efficient deep blue/near UV-emitting QDs remain rare due to lack of luminescent wide band gap materials and high defect densities in the existing ones. Here, we introduce a novel type of QDs based on heavy metal free gallium sulfide (Ga2 S3 ) and their core/shell heterostructures Ga2 S3 /ZnS as well as Ga2 S3 /ZnS/Al2 O3 . The photoluminescence (PL) properties of core Ga2 S3 QDs exhibit various decay pathways due to intrinsic defects, resulting in a broad overall PL spectrum. We show that the overgrowth of the Ga2 S3 core QDs with a ZnS shell results in the suppression of the intrinsic defect-mediated states leading to efficient deep-blue emission at 400 nm. Passivation of the core/shell structure with amorphous alumina yields a further enhancement of the PL quantum yield approaching 50 % and leads to an excellent optical and colloidal stability. Finally, we develop a strategy for the aqueous phase transfer of the obtained QDs retaining 80 % of the initial fluorescence intensity.

Photoluminescence study of Sr3Al32O51:Eu3+ phosphor for Solid state lighting applications

Sr3Al32O51:Eu3+ phosphor prepared successfully by simple combustion method. Prepared matrix synthesized for different percentage of composition for rare earth Eu3+ = (0.5, 1.0, 1.5, 2.0 and 2.5). Photoluminescence property was taken for the given doped phosphor which shows the excitation peak at 395 nm and 466 nm respectively. Emission peak observed at 593 nm and 613 nm for excitation wavelength 395 nm and same emission peak observed for excitation wavelength 466 nm comparatively less intense than 395 nm. The phase of the synthesized phosphor confirmed by X-ray diffraction spectroscopy (XRD), Scanning electron microscopy (SEM), Photoluminescence (Pl) property shows that the given matrix is the one of the potential material which can be used for solid state lightening.

Mono- and Co-Doped Mn-Doped CsPbCl3 Perovskites with Enhanced Doping Efficiency and Photoluminescent Performance.

To investigate the effect of Mn and other metal dopants on the photoelectronic performance of CsPbCl3 perovskites, we conducted a series of theoretical analyses. Our findings showed that after Mn mono-doping, the CsPbCl3 lattice contracted and the bonding strength increased, resulting in a more compact structure of the metal octahedral cage. The relaxation of the metal octahedral cage, along with the Jahn-Teller effect, results in a decrease in lattice strain between the octahedra and a reduction in the energy of the entire lattice due to the deformation of the metal octahedron. These three factors work together to reduce intrinsic defects and enhance the stability and electronic properties of CsPbCl3 perovskites. The solubility of the Mn dopant is significantly increased when co-doped with Ni, Fe, and Co dopants, as it compensates for the lattice strain induced by Mn. Doping CsPbCl3 perovskites reduces the band gap due to the decreased contributions of 3d orbitals from the dopants. Our analyses have revealed that strengthening the CsPbCl3 lattice and reducing intrinsic defects can result in improved stability and PL properties. Moreover, increasing Mn solubility and decreasing the bandgap can enhance the PLQY of orange luminescence in CsPbCl3 perovskites. These findings offer valuable insights for the development of effective strategies to enhance the photoelectronic properties of these materials.

CsPbX3 (X = Cl, Br, and I) Nanocrystals in Substrates toward Stable Photoluminescence: Nanoarchitectonics, Properties, and Applications.

Cesium lead halide (CsPbX3, X = Cl, Br, and I) perovskite nanocrystals (NCs) possess great potential in light-emitting diode applications because of their high brightness, low cost, tunable luminescence, and facile synthesis nature. However, these NCs are often disadvantaged by their instability in nonsolvent environment that hinders the practical applications of the material. In order to solve these issues, cesium lead halide NCs prepared using a solvent environment can be placed on substrates to retain the high stability and expand the applicability of the material. This Review focuses on the transfer of the all-inorganic cesium lead halide NCs (synthesized in solutions) onto matrix materials and their direct synthesis on these bases, including the inert shell growth (inorganic and organic shell), embedment in matrixes (e.g., metal organic frameworks, porous SiO2, glass, ZrO2, Al2O3, and AlOOH), and direct synthesis in substrates. In particular, the strategies for stability and PL property improvement of the materials are also summarized. The purpose of this Review is to provide inspiration for the encapsulation of cesium lead halide NCs with high brightness and stability in matrixes to expand the applicability of these materials in wide color gamut backlighting (e.g., white-light-emitting devices).

Surface Modification of TiO2/g-C3N4 Electrode with N, P Codoped CQDs for Photoelectrocatalytic Degradation of 1,4-Dioxane

The aim of this study was to synthesize N, P codoped CQDs modifying TiO2/g-C3N4 nanorod array (i.e., N, P-CQD/TCN NA) photoanodes for the degradation of 1,4-dioxane (1,4-D) and to explore the possibility of the photoelectrocatalytic (PEC) process in wastewater treatment. With the characterization of N, P-CQD/TCN NA anodes, 1,4-D degradation and pesticide wastewater was tested in the PEC cell, respectively. Under a bias voltage of 1.2 V and visible light, the current density of the N, P-CQD/TCN NAs was much higher than that of the CQD/TCN NAs (0.15 vs. 0.11 mA/cm2). The removal of 1,4-D reached 97% in the PEC cell within 6 h. The high performance of the N, P-CQD/TCN NA anodes could be attributed to the efficient charge separation, narrowed energy gap, and high upconverted PL properties. The C4 and C6 positions of 1,4-D were the preferential sites for the nucleophilic attack to form intermediates. The COD removal in the pesticide wastewater was kept stable at ~80% in a five-cycle operation using the PEC cell with the N, P-CQD/TCN NA photoelectric anodes. The results from this study should provide a promising way to develop novel photoelectric catalysts and to expand PEC application in wastewater treatment.

Luminescence and energy transfer of Ce3+, Eu2+ Co-doped SrSi2O2N2 phosphors

SrSi2O2N2:Ce3+/Eu2+ phosphors have been synthesized with a high-temperature solid-state reaction method. The result shows that effective energy transfer has occurred between Ce3+ and Eu2+. The energy transfer efficiency was calculated, and the mechanism was determined as dipole-dipole interaction. The Influence of co-doping with a charge compensator M+ (M+ = Li+, Na+, K+) on the photoluminescence properties of SrSi2O2N2:Ce3+/Eu2+ was analyzed. It is clear that the PL properties of the SrSi2O2N2:Ce3+/Eu2+ phosphor are significantly improved by doping with Li+/Na+/K+, and the Li+ ions is the best charge compensator for this phosphor.

Room-Temperature Solid-State Synthesis of Cs3Cu2I5 Thin Films and Formation Mechanism for Its Unique Local Structure.

Blue-emitting Cs3Cu2I5 has attracted attention owing to its near-unity PL quantum yield and applications in DUV photodetectors and scintillators. Its PL properties originate from the unique local structure around the luminescent center, the [Cu2I5]3- polyhedron iodocuprate anion consisting of the edge-shared CuI3 triangle and the CuI4 tetrahedron dimer, which is isolated by Cs+ ions. We found that solid-state reactions between CsI and CuI occur near room temperature (RT) to form Cs3Cu2I5 and/or CsCu2I3 phases. High-quality thin films of these phases were obtained by the sequential deposition of CuI and CsI by thermal evaporation. We elucidated that the formation of interstitial Cu+ and the antisite of I- at the Cs+ site in the CsI crystal through Cu+ and I- diffusion results in the RT synthesis of Cs3Cu2I5. The unique structure formation of the luminescent center was revealed using a model based on the low packing density of the CsCl-type crystal structure, similar sizes of Cs+ and I- ions, and the high diffusivity of Cu+. The self-aligned patterning of the luminous regions on thin films was demonstrated.

Synthesis and Photoluminescence characterization of Sr3La(AlO)3(BO3)4:Eu3+,Sm3+ Phosphor for W-LED

A Red emitting with high efficiency Eu3+ doped Sr3La(AlO)3(BO3)4 and Sm3+ doped Sr3La(AlO)3(BO3)4 phosphors has been synthesized by combustion method, meanwhile, the photoluminescence properties of samples are investigated in detail. Morphology by SEM and chromaticity by CIE was studied. The results show that the excitation extends from 340 nm to 420 nm, with the highest excitation (394 nm and 406 nm) being in the violet area for Eu3+ and Sm3+ doping, indicating that the phosphor can correlate well with LED chips. Under violet light excitation of 394nm the phosphor Eu3+ doped Sr3La(AlO)3(BO3)4 and of 406 nm the phosphor Sm3+ doped Sr3La(AlO)3(BO3)4 can emit strong red light showing main emission peaks located at 617 nm and 602 nm are observed respectively. The PL properties implies the excellent stability of the phosphor. These results imply that the importance red phosphors Sr3La(AlO)3(BO3)4:Eu3+ and Sr3La(AlO)3(BO3)4:Sm3+ in W-LEDs under NUV excitation.

Exciton Localization for Highly Luminescent Two‐Dimensional Tin‐Based Hybrid Perovskites through Tin Vacancy Tuning

AbstractExciton localization is an approach for preparing highly luminescent semiconductors. However, realizing strongly localized excitonic recombination in low‐dimensional materials such as two‐dimensional (2D) perovskites remains challenging. Herein, we first propose a simple and efficient Sn2+ vacancy (VSn) tuning strategy to enhance excitonic localization in 2D (OA)2SnI4 (OA=octylammonium) perovskite nanosheets (PNSs), increasing their photoluminescence quantum yield (PLQY) to ≈64 %, which is among the highest values reported for tin iodide perovskites. Combining experimental with first‐principles calculation results, we confirm that the significantly increased PLQY of (OA)2SnI4 PNSs is primarily due to self‐trapped excitons with highly localized energy states induced by VSn. Moreover, this universal strategy can be applied for improving other 2D Sn‐based perovskites, thereby paving a new way to fabricate diverse 2D lead‐free perovskites with desirable PL properties.

Exciton Localization for Highly Luminescent Two-Dimensional Tin-Based Hybrid Perovskites through Tin Vacancy Tuning.

Exciton localization is an approach for preparing highly luminescent semiconductors. However, realizing strongly localized excitonic recombination in low-dimensional materials such as two-dimensional (2D) perovskites remains challenging. Herein, we first propose a simple and efficient Sn2+ vacancy (VSn ) tuning strategy to enhance excitonic localization in 2D (OA)2 SnI4 (OA=octylammonium) perovskite nanosheets (PNSs), increasing their photoluminescence quantum yield (PLQY) to ≈64 %, which is among the highest values reported for tin iodide perovskites. Combining experimental with first-principles calculation results, we confirm that the significantly increased PLQY of (OA)2 SnI4 PNSs is primarily due to self-trapped excitons with highly localized energy states induced by VSn . Moreover, this universal strategy can be applied for improving other 2D Sn-based perovskites, thereby paving a new way to fabricate diverse 2D lead-free perovskites with desirable PL properties.

Unveiling sub-bandgap energy-level structures on machined optical surfaces based on weak photo-luminescence.

Sub-bandgap defect energy levels (SDELs) introduced by the point defects located in surface defect areas are considered the main factors in decreasing laser-induced damage thresholds (LIDTs). The suppression of SDELs could greatly increase LIDTs. However, no available method could detect SDELs, limiting the characterization and suppression of SDELs. Herein, a self-designed photo-luminescence detection system is developed to explore the weak transient-steady photo-luminescence properties of machined surfaces. Based on the excitation laser wavelength dependence of photo-luminescence properties, a sub-bandgap energy-level structure (SELS) containing SDELs is unveiled for the first time. Based on the developed mathematical model for predicting LIDTs, the feasibility of the detection method was verified. In summary, this work provides a novel approach to characterize SDELs on machined surfaces. This work could construct electronic structures and explore the transition behaviors of electrons, which is vital to laser-induced damage. Besides, this work could predict the LIDTs of the machined surfaces based on their PL properties, which provides convenience for evaluating the LIDTs of various optical elements in industrial production. Moreover, this work provides a convenient method for raising the LIDTs of various optical elements through monitoring and suppressing the SDELs on machined surfaces.

The Effect of Different Molar Ratios of CeO2 on Photoluminescence Properties of CeO2/TiO2 Nanoparticles

The CeO2-TiO2 nanoparticles were prepared by a combination of hydrothermal and sol-gel preparation methods. the bond structures and crystal properties of the obtained materials were featured with X-ray diffraction, FTIR, Raman, and Bet analysis; surface morphologies were examined with the help of FESEM and STEM. And finally, the PL properties of the synthesized samples were also examined in this study. The excitation and emission spectra of 0.1 mol% and 0.25 mol% CeO2 doped TiO2 phosphors consist of broad bands in the UV (200–300 nm) region with maxima at 254 nm. The excitation band at 254 nm is defined as the charge transfer band (CTB). In the emission spectra, a broadband located from 400 to 700 nm is related to the 5d-4f (5d1→4f1) transition of Ce3+ in TiO2. According to the PL result, the 5d–4f transition of Ce3+ is heavily dependent on the concentration of Ce3+ in the host crystal TiO2.

Ortho-Substituted Aryldiazonium Design for the Defect Configuration-Controlled Photoluminescent Functionalization of Chiral Single-Walled Carbon Nanotubes.

Defect functionalization of single-walled carbon nanotubes (SWCNTs) by chemical modification is a promising strategy for near-infrared photoluminescence (NIR PL) generation at >1000 nm, which has advanced telecom and bio/medical applications. The covalent attachment of molecular reagents generates sp3-carbon defects in the sp2-carbon lattice of SWCNTs with bright red-shifted PL generation. Although the positional difference between proximal sp3-carbon defects, labeled as the defect binding configuration, can dominate NIR PL properties, the defect arrangement chemistry remains unexplored. Here, aryldiazonium reagents with π-conjugated ortho-substituents (phenyl and acetylene groups) were developed to introduce molecular interactions with nanotube sidewalls into the defect-formation chemical reaction. The functionalized chiral SWCNTs selectively emitted single defect PL in the wavelength range of ∼1230-1270 nm for (6,5) tubes, indicating the formation of an atypical binding configuration, different from those exhibited by typical aryl- or alkyl-functionalized chiral tubes emitting ∼1150 nm PL. Moreover, the acetylene-based substituent design enabled PL brightening and a subsequent molecular modification of the doped sites using click chemistry.

Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

We have fabricated valency-controlled Si-QDs with Ge-core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and studied the effect of phosphorus- and boron-doping on Ge-core from their PL properties. During the Ge deposition, delta doping of phosphorus or boron atoms in QDs was carried out by pulse injection using 1% PH3 or B2H6 diluted with He, respectively. No changes in dot size and density with either P- or B-doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 976-nm line from a semiconductor laser, broad PL spectra consisting of four Gaussian components originating from radiative recombination through quantized states in QDs were observed in the energy range from 0.62 to 0.85 eV without impurity doping even at room temperature. In the doped QDs, relatively-narrow components peaked at ~0.68 eV and ~0.64eV were observed with P-doping and with B-doping to Ge-core, respectively, in addition to the four components seen in undoped QDs. It is interesting noted that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in QD under weak photoexcitation.

Impact of Co2+ on the magneto-optical response of MAPbBr3: An inspective study of doping and quantum confinement effect

The current work establishes the excitonic magneto-optic (M − O) effects of magnetic circular dichroism (MCD) in Cobalt (Co2+) doped diamagnetic organic−inorganic hybrid CH3NH3PbBr3 perovskites at low magnetic field and room temperature. The solution-processed perovskites are prepared in the form of single crystal thin films and quantum dots. The structural studies confirm the successful doping of the Co2+ in the perovskite lattice. Further, the perovskites are investigated as diluted magnetic semiconductors (DMSs) related to the dopant concentration effect and the size effect on their M − O properties. Magnetic dopant Cobalt leads to the strong sp-d exchange coupling that generates higher values of Zeeman splitting (ΔEZ) than the pristine MAPbBr3 due to the excitonic 1s Pb–Br absorption quantified by analysis of MCD. The ΔEZ value increases with the Co concentration up to 10 mol % and then starts decreasing. This concentration dependency can be linked with the luminescence of the perovskites with the Co2+ doping. The rise and fall of the MO and PL properties can be defined by the formation of Co–Co pairs in heavily doped perovskites which can influence the spin conditions of the paramagnetic Co ions. Using the Kramers–Kronig relations with MCD, the calculated Verdet constant exhibits a massive increase in value with the doping of cobalt, much higher than the industry standard Faraday rotator indicating their probable usability in this industry. Further in the quantum dots, the quantum confinement effect is pronounced that increases the MCD and hence the ΔEZ multiple times higher than the bulk perovskite films. These results provide a promising pathway for the study of solution-processed hybrid perovskites as DMSs for spintronics.

Investigation on Dynamic Changes in the Morphology and Fluorescence Properties of Sulfur Quantum Dots.

Sulfur quantum dots (SQDs), an emerging metal-free quantum dot, which has received intense research interest owing to their unique optical property, good solubility, excellent biocompatibility, and facile synthetic approach. Herein, using sodium hypochlorite as the etching agent, we investigate how it functions and transforms sulfur powder to SQDs and affects the dynamics, photoluminescence, and size changes of SQDs by controlling the reaction time. Precise control of reaction time allows SQDs to be tuned between green and blue (from 515 to 420 nm) with size distribution ranging from 2.0 to 20 nm as well as the occurrence of a distinctive irregular rodlike structure. Surface functional groups and element analysis reveal that the core size and surface oxidizing sulfur species both contribute to the versatile PL properties. Morevoer, we propose a tentative formation mechanism that relies on the oxidizing sulfur surface state and quantum size effect, offering a theoretical and experimental foundation for investigation of we propose a tentative formation mechanism that relies on the oxidizing sulfur surface state and quantum size effect, offering a theoretical and experimental foundation for investigation of the formation and modulation of SQDs.

A nano-liter droplet-based microfluidic reactor serves as continuous large-scale production of inorganic perovskite nanocrystals

Lead halide perovskite nanocrystals (NCs) exhibit high photoluminescence quantum yield (PLQY), high defect tolerance, narrow half peak width, and wide luminous gamut, making them the ideal optoelectronic materials in numerous fields. Nonetheless, their production still suffers from the limited productivity at the bench level. In this work, we fabricated CsPbX3 (X = Cl, Br, I) NCs within droplet-based micro-reactors, where both the nucleation and growth processes could be precisely controlled inside 130-nL microdroplets. This provides a new paradigm for the large-scale synthesis of perovskite NCs with high PLQY. Compared with other synthetic methods, this method can increase the concentration of reactant precursors by 3–116 times, while lowering the ligand to reactant ratio to 2%–50% of the commonly used hot-injection method. By modulating the reaction temperature and residence time, the structure-function relationship between the morphology of NCs and PL properties was extensively investigated. The microfluidic-based process allows the flexible adjustment in the proportion of PbX2 precursors to achieve the fabrication of perovskite NCs whose luminescence range covers the entire visible spectrum (406–677 nm) within one reaction. Finally, perovskite NCs with different halide ions were encapsulated in polymethyl methacrylate to prepare a colored light-emitting diode strip.