Photoluminescence Emission Intensity Research Articles

Intensive and broad bound exciton emission at cryogenic temperature in suspended monolayer transition metal dichalcogenides

Two-dimensional (2D) transition metal chalcogenides (TMDCs) are expected to play an important role in next-generation optoelectronic devices. However, the properties of 2D TMDCs can be largely affected by defects, and thus, many efforts have been made to characterize and eliminate the defects. Here, we investigate defect-related trap states, particularly in large-area suspended ${\mathrm{WS}}_{2}$ monolayers at cryogenic temperatures, using steady-state and time-resolved photoluminescence (TRPL) spectroscopy. We observed an intensive and broad (full width half maximum $\ensuremath{\sim}170\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$) photoluminescence (PL) emission centered at 1.83 eV, 0.3 eV lower than the free exciton transition energy. From temperature-dependent PL spectra, the thermal activation energy of excitons escaping from trap states is determined to be 30 meV. The TRPL spectrum shows an ultralong lifetime at 13 K. The long-lived emission with the broad PL linewidth is attributed to excitons bound to defects of possibly chalcogenide-site substitution and sulfur vacancies. Compared with the supported monolayer, the defect-related trap states are found to be deeper in the suspended layer and can trap excitons more efficiently due to less dielectric screening. In this letter, we provide further understanding of trap states and decay channels in monolayer TMDCs and show that suspended 2D TMDCs can provide a pure platform for studying defect-related properties.

Effect of U on the photoluminescence of Pr and structural properties of U/Pr doped and co-doped Li2O–ZnO–SrO borophosphate glass

U/Pr doped and co-doped Li2O–ZnO–SrO borophosphate glasses were prepared using the melt quenching method. XRD, SEM-EDX, and FTIR investigations were carried out to ascertain the structural properties, morphological features and homogeneity of elemental distribution in the synthesised glass phosphors. Differential thermal analysis was used to examine the thermo-physical properties. It was observed that uranium doping improved the thermal stability and rigidity of the synthesised glass host. Intense photoluminescence (PL) emissions were observed both from uranium and praseodymium in the U/Pr doped glass. Uranium showed a broad emission spectrum with peak a maximum at 526 nm and resembles the typical emission pattern of hexavalent uranyl species (UO22+) in the amorphous environment. UO22+ emission increased linearly until the onset of concentration quenching at 1.0 mol%. Similarly, praseodymium doped glasses exhibited intense red emission from overlapped 3P0→ 3H6 and 1D2 →3H4 transitions, and centred at around 609 nm. At 0.2 mol%, the Pr emission intensity was highest, concentration quenching was prevalent beyond it. The emission decay of both uranium and praseodymium followed the bi-exponential decay model and the lifetime values decreased with increasing the dopant concentration in singly doped as well as co-doped samples. The Inokuti-Hirayama model was employed for the fitting of decay profiles to explicate the nature of non-radiative interaction of excited states. The donor-acceptor coupling parameters (Cda) were determined for U–U, Pr–Pr, and U–Pr interaction. Appreciable U–Pr energy transfer via dipole-dipole interaction was observed with Cda = 4.79 × 10−40 cm6s−1. Emission of both Pr and U get suppressed in the co-doped glass samples possibly due to the concomitant U–Pr redox interactions. The CIE color coordinates and color purity suggested that U/Pr doped Li2O–ZnO–SrO borophosphate glass can be used for solid-state lighting applications.

Enhancing Photoluminescence Intensity and Spectral Bandwidth of Hybrid Nanofiber/Thin-Film Multilayer Tm3+-Doped SiO2-HfO2.

Multilayering of optical thin films is widely used for a range of purposes in photonic technology, but the development of nanofiber structures that can outperform thin films and nanoparticles in optical applications cannot simply be disregarded. Hybrid structures composed of Tm3+-doped SiO2-HfO2 in the form of nanofibers (NFs) and thin films (TFs) are deposited on a single substrate using the electrospinning and dip-coating methods, respectively. Ultrafine nanofiber strands with a diameter of 10-60 nm were fabricated in both single and multilayer samples. Enhanced photoluminescence emission intensity of about 10 times was attained at wavelengths of around 457, 512 and 634 nm under an excitation of 350 nm for NF-TF-NF* hybrid structures when compared with single-layered NF and TF structures. The arrangement of nanofibers and thin films in a multilayer structure influenced the luminescence intensity and spectral bandwidth. High transparency in the range of 75-95% transparency across the wavelength of 200-2000 nm was achieved, making it ideal for photonic application. Theoretical findings obtained through IMD software were compared with experimental results, and they were found to be in good agreement.

Anti-counterfeiting, latent fingerprint detection and optical thermometry using a multi-stimulus down-converting La2CaZnO5:Er3+ phosphor

The development of new inorganic phosphors for the use of latent fingerprint detection and anticounterfeiting applications has aroused attention. In this report, a series of Er (0.5–4 mol %) doped La2CaZnO5:Er3+ phosphors are prepared by a simple solution combustion process. The photoluminescence emission (PLE) intensity is found to be dependent on the Er3+ ions concentration and its maximum value is achieved when the doping concentration is 1 mol %. From theoretical analysis, one knows that the concentration quenching mechanism is dominated by the electric dipole-dipole interaction with a critical distance of 14.84 Å. The temperature sensing capabilities of the resulting compounds are investigated on the basis of the temperature-dependent PLE from the 2H11/2 and 4S3/2. The sensor sensitivity of the examined samples increased up to 11.45% K−1 at 300 K. The sensor sensitivity of the obtained phosphor affected hardly varied by the doping concentration. The optimized phosphor powder is utilized for LFP and anticounterfeiting applications. The results clearly found that powder dusting method exhibited high contrast, high sensitivity, high selectivity, and extensive applicability in fingerprint development. We have established a straightforward dip pen, screen printing, and inkjet printing techniques for designing various patterns from the fabricated anti-counterfeiting security ink.

Synthesis of CsPbX3 lead halide perovskite nanocrystals in flower-like TiO2 matrices with enhanced stability

The instability of the cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) upon exposure to humidity or heat strongly hinders their applications in optoelectronic devices. In this work, an in situ adsorption strategy is adopted to directly grow uniform CsPbX3 nanocrystals (NCs) on flower-like TiO2 microspheres to achieve a hybrid structure. Benefiting from the isolation effect of flower-like structure, the as-synthesized TiO2–CsPbBr3 composites exhibit excellent water stability when soaked in water for 35 days and retain 62.7% of the initial photoluminescence (PL) emission intensity. CsPbBr3 NCs also present enhanced thermal stability under the protection of TiO2 matrix. It is intriguing that the TiO2-CsPbX3 composites with blue, green and red emissions are fabricated successfully by this method with excellent moisture and thermal stability, which provides a feasible solution for the effective application of CsPbX3 NCs in light emitting diode (LED) devices.

(INVITED)Judd-Ofelt analysis, visible to NIR photoluminescence emission under 450 nm and 976 nm excitations and energy transfer of barium fluorotellurite glasses doping with Ho3+, Yb3+, Ho3+:Yb3+

Barium fluorotellurite glasses doping with Ho3+, Yb3+, and Ho3+:Yb3 were fabricated using the conventional melt and quenching method, and their optical properties were studied using different optical spectroscopic techniques. The FITR absorption band at 3000 cm−1 was used to investigate OH- concentrations of the prepared glasses, which increased with Yb3+ content. However, it decreased by substituting a portion of BaF2 content with Ba2CO3 concentration. The electric dipole line strengths and Judd-Ofelt parameters were estimated using UV–visible near-infrared (NIR) optical absorption spectra to gain information on the rare earth ions doped glasses for laser applications. The various radiative parameters such as line strengths, optical intensity, and radiative rates from the higher energy levels, including 5F4+5S2, 5F5, 5I4,5I5,5I6 and 5I7, to the ground state, 5I8 have been reported and discussed. The influence of the Yb3+ and Ba2CO3 concentrations on the upconversion and downconversion photoluminescence emission intensities of the glasses prepared have been investigated by pumping with 450 nm and 976 nm excitation sources. Under 450 nm and 976 nm, the NIR photoluminescence emissions reveal a band ranging from 980 nm to 1220 nm attributing to an overlap between Yb3+ and Ho3+ transitions. The influence of Yb3+ concentration on photoluminescence lifetime at the 2F5/2→2F7/2, 5F4+5S2 →5I8 and 5I6 →5I8 transitions under 976 nm laser excitation has been studied and reported. The results indicate that lifetime decreases with increasing Yb3+ concentration attributing to an efficient energy transfer from Yb3+ to Ho3+ ions. The energy transfer efficiency from Yb3+ → Ho3+ has been examined, which rises from 30% to 47% upon increasing Yb3+ content. Nevertheless, it decreases with the mixing of BaF2 and Ba2CO3 lattice modifier contents. The results demonstrated that the 1200 nm (5I6 →5I8 transition) has remarkable potential for developing fiber lasers.

Micro-strain governed photoluminescence emission intensity of sol-gel spin coated Eu doped ZnO thin films

The objective of the present study is to analyze the role of surface free energy and microstrain on optical properties of Eu- (1, 2, 3, 5 and 6 at.%) doped sol-gel spin coated ZnO film on glass substrates. X-ray diffraction results revealed the presence of (100) plane indicating highly oriented monocrystalline film. The crystallite size was in the range of 43 to 86 nm, and the microstrain in ZnO thin films decreased from 0.00079 to 0.00040 with Eu doping. UV–vis transmission indicated transparency of 80 to 95 percent with a dip at 377 nm for undoped ZnO, which was slightly displaced to 380 nm on doping with Eu. The reduction in band gap values calculated using Tauc's plot was in the range of 3.33 to 3.17 eV. The photoluminescence (PL) emission spectra demonstrated unaltered UV emission peak on doping with Eu, however, the reduction in PL intensity was governed by microstrain induced in ZnO thin film by Eu doping. PL intensity and microstrain both decreased with Eu doping up to 3 at.%, then increased for Eu 5 at.% and eventually decreased again for Eu 6 at.%. Field emission scanning electron microscopy results exhibited a variety of irregular multi-dimensional morphological characteristics. Rectangular, square, and spherical structures were observed in 1, 2, 5, and 6 at.% Eu doped ZnO thin film. In contrast, 3 at.% Eu doping revealed long chain linkage structures that stuck together. The water contact angle measurements established the hydrophilic nature of all the doped-films. The reduced surface free energy was implied by decreased contact angle for Eu doped ZnO thin films (1, 2, and 3 at.%). This result suggested that surface free energy can be tuned with the Eu-content in ZnO. Such synergistic optical and mechanical features in ZnO based materials can give opening to diverse applications ranging from brain inspired neural network to reduction of power consumption.

Enhanced Photoluminescence of 1.3 μm InAs Quantum Dots Grown on Ultrathin GaAs Buffer/Si Templates by Suppressing Interfacial Defect Emission.

We report on the photoluminescence enhancement of 1.3 μm InAs quantum dots (QDs) epitaxially grown on an ultrathin 250 nm GaAs buffer on a Si substrate. Decreasing the GaAs buffer thickness from 1000 to 250 nm was found to not only increase the coalesced QD density from 6.5 × 108 to 1.9 × 109 cm-2 but also decrease the QD photoluminescence emission intensity dramatically. Inserting an Al0.4Ga0.6As potential barrier layer maintained strong photoluminescence from the QDs by effectively suppressing carrier leakage to the GaAs/Si interfacial region even when the GaAs buffer was thinned to 250 nm. We then fabricated a light-emitting diode using the ultrathin 250 nm GaAs buffer on Si and confirmed strong electroluminescence peaking at 1.28 μm without interfacial defect emission at room temperature. We believe that this work is promising for monolithically integrated evanescent Si lasers using InAs/GaAs QDs.

Photoluminescence properties of Eu3+-doped Na2CaSiO4 phosphor prepared by wet-chemical synthesis route

The present investigation focuses on the development of Eu3+ activated phosphors for near ultraviolet (NUV) excited light emitting diode (LED) applications. In this investigation, we have synthesized a series of Na2CaSiO4:Eu3+phosphors via wet-chemical method and characteristic of synthesized phosphors have been analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Thermo gravimetric analysis– Differential thermal analysis (TGA–DTA) and photoluminescence (PL) techniques. The recorded excitation band indicates a broad excitation band centered at 262 nm due to charge transfer (CT) band and sharp peaks at 395 nm and 466 nm due to 7F0→5L6 and 7F0→5D2 transition of Eu3+ ions. The highest excitation intensity was observed at 396 nm wavelength. Therefore under 396 nm excitation, the emission spectrum showed characteristics peaks located at 595 nm and 615 nm, which are attributed due to the 5D0→7F1 and 5D0→7F2 transition of Eu3+ ions. Emission spectra shows dominant emission peak at orange region around 595 nm due to the magnetic dipole transition of5D0→7F1. In addition, the effects of the Eu3+ ions on the emission intensity were investigated, it was found that the emission intensity increases as the concentration of Eu3+ ions increases up to 0.5 mol%. Thereafter, PL emission intensity was decreased due to concentration quenching. The CIE Chromaticity coordinate of the prepared phosphor was located in the orange region around (0.584, 0.421) with high color purity. As per the investigation of prepared Na2CaSiO4:Eu3+phosphors, it was concluded that it is a promising candidate for lighting and display applications.

Highly Luminescent and Photostable Core/Shell/Shell ZnSeS/Cu:ZnS/ZnS Quantum Dots Prepared via a Mild Aqueous Route.

An aqueous-phase synthesis of 3-mercaptopropionic acid (3-MPA)-capped core/shell/shell ZnSeS/Cu:ZnS/ZnS QDs was developed. The influence of the Cu-dopant location on the photoluminescence (PL) emission intensity was investigated, and the results show that the introduction of the Cu dopant in the first ZnS shell leads to QDs exhibiting the highest PL quantum yield (25%). The influence of the Cu-loading in the dots on the PL emission was also studied, and a shift from blue–green to green was observed with the increase of the Cu doping from 1.25 to 7.5%. ZnSeS/Cu:ZnS/ZnS QDs exhibit an average diameter of 2.1 ± 0.3 nm and are stable for weeks in aqueous solution. Moreover, the dots were found to be photostable under the continuous illumination of an Hg–Xe lamp and in the presence of oxygen, indicating their high potential for applications such as sensing or bio-imaging.

Efficient luminescence of doped bismuth oxychloride nanophosphors and its surfaces prompted applications

The materials which cater to excellent sensitivity, superior contrast, inexpensive and eco-friendly are in urgent need for law enforcement applications. To overcome these barriers, red-emitting BiOCl:Eu3+ (1–9 ​mol %) nanophosphors were prepared by the self-ignited combustion method. The powdered x-ray diffraction profiles were well indexed to a tetragonal phase of BiOCl without any traces of impurities. The 2-dimensional agglomerated irregular flake-like structures without any clear boundaries were clearly revealed. The photoluminescence emission spectra consist of distinct sharp peaks at ∼ 536, 555, 594, 621, 652 and 698 ​nm, which were owing to 5D1→7F1, 5D1→7F2, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transitions of Eu3+ ions, respectively. A noticeable increment in the photoluminescence emission intensity with an increase of activator Eu3+ concentration up to 5 ​mol % and later it diminished. The dipole-dipole interaction was mainly responsible for observed concentration quenching. The estimated commission international de l'eclairage coordinates are found in orange-red as well as a red region in the diagram, indicating that the emission color can be tuned by varying activator Eu3+ ions concentration. The fingerprints developed using optimized nanophosphor showed distinctive papillary ridge particulars and hence specifies the higher sensitivity without any background hindrance. The aged fingerprints developed on the glass surface retained their ridge characteristics up to level 2 even after being stored for 180 days. The developed anti-counterfeiting labels can only be decoded under ultra-violet 365 ​nm light with clear intense red color. The obtained results clearly demonstrated the effectiveness of the fluorescence nanophosphor for latent fingerprint visualization and data encryption applications.

Regulating polymerization degree of heptazines in carbon nitride with fumaric acid to enhance photocatalytic activity

Carbon nitride (CN) has a wide range of applications in photocatalytic treatment of environmental pollution. One of key challenges in the field is to conveniently prepare CN with tunable band gap towards efficient pollution degradation, which can be overcome by regulating the polymerization degree of its heptazines. Herein, a facile and green strategy to construct CN through co-firing urea, melamine and fumaric acid was reported. By simply inducing appropriate amount of fumaric acid during amidation reaction between fumaric acid and amino groups, the distance between heptazines of CN could be modified to obtain optimized polymerization degree and morphology. Among the considered CN systems, the modulated CN sample with the doped ratio of 2.50: 0.50: 0.03 m urea/m melamine/m fumaric acid (CNF30) displayed remarkable photocatalytic ability due to the largest specific surface area, the lowest photoluminescence emission intensity, and narrowest band gap, which led to the highest 98.0% methyl orange degradation within 60 min under a 10 W lamp and room temperature with the harmless and valuable carboxylic acids products. This study provides a new sight for the design of photocatalysts with tunable band structure towards green and efficient photocatalytic degradation of environmental pollution.

Gated Photodetector with a Bipolar Response from Single-Crystal Halide Perovskite Using a Polymeric Electrolyte as the Gate Dielectric

In this report, we show that a gated optical detector working in the visible wavelength region can be made on single-crystal halide perovskite methylammonium lead bromide (CH3NH3PbBr3 or MAPB). A polymeric electrolyte (PEO/LiClO4) is used as the gate dielectric, which forms an electric double layer (EDL) at the electrolyte/MAPB interface, leading to high specific gate capacitance and enabling enhanced carrier induction at a low gate bias. The photoresponse of the detector can be enhanced significantly by a large factor (e.g., by a factor of 35) by a bias Vg of 10 V. The core gate operation is due to the field effect, and the detector shows the characteristics of a field effect transistor (FET) with bipolar nature, thereby operating with both polarities of the gate bias. This is enabled by the special feature of halide perovskites, that is, they have appreciable mobility for both types of carriers. It is established that the enhancement of the detector current response occurs due to the synergy of carriers created by illumination as well as the gate when they are present simultaneously, which modifies the near-band-edge trap states close to valence band maxima (VBM) and conduction band minima (CBM) and enhances the carrier mobility. The proposed synergy mechanism is validated by the gate-induced enhancement of the photoluminescence (PL) emission intensity and narrowing of the emission line.

Influence of Cr substitution on structural, optical, and magnetic properties of La2SrFe2O7: Their application as a photocatalyst for the degradation of Rhodamine B dye

A new n = 2 Ruddlesden-Popper (RP) series La2SrFe2-xCrxO7 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been prepared via Sol-gel Pechini method, and their structural, optical, and the magnetic characterization was done. Furthermore, we are for the first-time reporting on the photo-catalytic degradation of a dye by a complete n = 2, La2SrFe2-xCrxO7 RP series. Rietveld refinement analysis confirms the formation of single-phase compounds with tetragonal crystal symmetry and I4/mmm space group. The results indicate a steady decrease in unit cell parameters and cell volume with Cr3+ doping. Dominant anti-ferromagnetic (AFM) interactions were observed in all the phases and the appearance of weak ferromagnetic (FM) interactions takes place owing to the Fe3+―O―Cr3+ FM interaction with Cr3+ doping. The χM−FC curve for x = 0.8 phase shows the magnetization reversal (MR) phenomenon and becomes zero at Tcomp ∼127 K and the value becomes negative on further decreasing the temperature. The MR phenomenon is discussed in terms of the competing Fe3+―O―Fe3+, Fe3+―O―Cr3+, and Cr3+―O―Cr3+ super-exchange interactions. Enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) dye was obtained for x = 0.2 substituted phase, displaying a ∼99% degradation of dye in 30 min followed by ∼83%, ∼75%, ∼64% and ∼61% by x = 0.4, 0.0, 0.8 and 0.6 phases respectively in the same time interval. The results are explained in terms of crystallite size, the narrowing of band gap with Cr3+ substitution, and based on of recombination of charge carriers which, are in good agreement with the results of Photoluminescence (PL) emission intensity spectra.

The study of polychromatic luminescence mechanism of ZnO and ZnO/NiS@NiO heterojunction under different alkali source concentrations

ZnO and ZnO/NiS@NiO (ZNN) composites with different precursor concentration ratios (Zn(CH3COO)2•2H2O: NaOH = 1:1, 1:5 and 1:10) were prepared using a hydrothermal method. The study found that as the concentration of NaOH decreased, the crystallinity of ZnO gradually decreased, the internal defects increase significantly, and the visible light emission intensity in the photoluminescence (PL) spectra also increased. Meanwhile, pure ZnO prepared under the condition of the ratio of 1:1 exhibited completely different defect types of PL characteristics from the products prepared at the ratio of 1:5 and 1:10. The PL emission intensity of ZNN composites prepared by combining various pure ZnO and NiS@NiO has been significantly enhanced, and all ZNN composites exhibited the same type of luminescence characteristics. It is concluded that with the addition of NiS@NiO, the green emission of ZnO is significantly enhanced, and the emission of some defects is shielded. Based on the discussion and analysis, a possible mechanism for the PL process of ZnO and its ZNN composites prepared with different alkali source concentrations was presented.

Intense and stable room-temperature photoluminescence from nanoporous vanadium oxide formed by in-ambient degradation of VI3 crystals

Vanadium oxides have attracted research interest because their optoelectronic properties make them optically active with room-temperature photoluminescence (PL) emission, which, however, is not sufficiently intense for real applications. For this reason, many nanostructured vanadium oxides are currently fabricated through several precursors and different treatments to improve the PL efficiency and enhance the PL intensity. Herein, we propose an alternative and facile route to the fabrication of nanoporous vanadium oxide flakes through the spontaneous in-ambient degradation of layered van der Waals VI3 crystal, which is composed of a mixture of V2O5 and V3O7 phases. The as-grown VI3 crystals and the formed nanostructured vanadium oxide have been thoroughly studied using X-ray diffraction (XRD) and Raman spectroscopy to access the structural properties, X-ray photoemission spectroscopy (XPS) and synchrotron-based XPS to analyze the electronic core levels and valence bands, scanning electron microscopy (SEM) to access the morphology, and PL spectroscopy to grasp the optoelectronic properties. The nanoporous vanadium oxide system reveals an intense room-temperature PL emission in the red light visible range between 1.7 and 2.0 eV (620 and 730 nm), which is consistent with the V2O5 PL response. Remarkably, the PL emission reaches high intensity compared with those of different V2O5 nanostructures and is stable for months without intensity quenching and energy shifting. This discovery easies the integration of nanostructured vanadium oxides in optoelectronic nanodevices. Besides, the facile methodology proposed here promises to be applied to realize other nanostructured transition metal oxides.

Optimum chemical states and localized electronic states of SnO2 integrated PTh– SnO2 nanocomposites as excelling emissive layer (EML)

Luminescent PTh–SnO2 nanocomposite was synthesized via chemical oxidative polymerization technique in presence of thiophene monomer with varying concentrations of SnO2 nanoparticles. The physico-chemical and morphological studies revealed the integration of SnO2 nanoparticles in the polythiophene matrix of PTh–SnO2 nanocomposites. Particle size of the derived nanocomposite laid in the 16–31 nm range and it was examined using HR-TEM. The optimized binary nanocomposite (15% PTh–SnO2) showed inflated thermal stability than pure PTh due to integration of SnO2 nanoparticles in PTh matrix. Further, it exhibited reduced optical band gap of 2.07 eV that was attributed to the inserted SnO2 nanoparticles which formed the localized electronic states in the optical band gap of PTh. Highest photoluminescence emission intensity was recorded for yellow-green band (∼562 nm) of 15% PTh–SnO2 and three emission bands (∼451 nm, ∼468 nm and ∼620 nm) of notable intensities were also observed. Photometric analysis of 15% PTh–SnO2 sample finally gives the emission color in blue-green region (near to white light) which enabled it to be used as successful emissive layer for its application in organic light emitting diodes (OLEDs).

Enhancement of intrinsic green emission in phase pure ZnO

The Phase pure wurtzite structured ZnO phosphor was prepared by sintering three different precursors viz. zinc acetate, zinc nitrate, and ZnO at 800 °C, 900 °C, and 1000 °C in a reducing atmosphere for 1 h. The prepared ZnO phosphor samples were characterized by powder X-ray diffraction and the Rietveld refinement analysis in order to study their structural information that confirms their wurtzite hexagonal phase. Scanning electron microscopy (SEM) pictures exhibited irregular spherical morphology with an average particle size between 1 and 3 μm. The corresponding EDAX spectrum confirmed the presence of Zn and O species. Dependence of sintering temperature on the photoluminescence (PL) properties of ZnO samples and their enhancement on deep-level emission were studied. Deep level green emission around 505 nm was observed for the ZnO samples sintered in the reducing atmosphere without adding any impurities. Among three samples, the maximum PL emission intensity and better CIE colour coordinates under 380 nm excitation were obtained for the ZnO sintered at 900 °C and 1000 °C. Maximum Entropy Method (MEM) were used to determine the electron distributions in the unit cell which supports the PL investigation.

Strategy to improve the performance of solution-processed phosphorescent organic light-emitting diodes using heteroleptic green Ir(III) complexes bearing multi-functional units

For solution-processed phosphorescence organic light-emitting diodes (PHOLEDs), two multi-functional units functionalized green triplet emitters Ir(ET)-Pic and Ir(HT)-Pic were designed and synthesized. They were synthesized by employing a 2-ethylhexyl substituted amide-bridged phenylpyridine moiety applied as main ligand and picolinate (Pic) as an ancillary ligand. In addition, the 1,3-bis(N-carbazolyl)benzene (mCP) and 1,3,4-oxadiazole (OXD) groups were introduced into 3-position of main ligand via non-conjugated benzyl ether linkage. Ir(ET)-Pic and Ir(HT)-Pic exhibited an intensive green photoluminescence (PL) emission at 502 nm, narrowed full-width at half maximum (FWHM), high PL quantum yields (PLQYs) and good solubility in organic solvents. Hence, the hole injection layer optimized device using Ir(ET)-Pic and Ir(HT)-Pic as dopants showed excellent performances with a maximum external quantum efficiency (EQEmax) of 21.5 and 19.6%, and the maximum current efficiency (CEmax) of 79.4 and 69.2 cd A−1 with Commission International L'Eclairage (CIE x,y) color coordinates of (0.36, 0.60) and (0.31,0.62), respectively. In addition, we found that the presence of bulky mCP unit in the Ir(III) complex affect the hole transport characteristics in the emissive layer. The result findings, the construction of multi-functional Ir(III) complexes are an attractive design strategy for fabrication of highly efficient green solution-processed PHOLEDs.

Study of Fe-doped and glucose-capped CeO2 nanoparticles synthesized by co-precipitation method

CeO2, Fe-doped CeO2 (Fe-CeO2), and glucose-capped CeO2 (G-CeO2) nanoparticles (NPs) with crystallite sizes between 31.1 and 45.03 nm were prepared by co-precipitation method. XRD, FT-IR spectroscopy, UV–Vis spectroscopy, Photoluminescence, and bacterial analysis studies were conducted. The XRD patterns revealed a single-phase cubic structure formation of all samples. The formation of absorption bands in all samples was identified by FT-IR analysis between 400 and 4000 cm−1. All samples were optically activated in the ultraviolet light region. The band gap values were found as 3.21, 3.33, and 3.39 eV for CeO2, Fe-CeO2, and G-CeO2 NPs, respectively. Fe-CeO2, and G-CeO2 NPs delivered lower photoluminescence emission intensity. Enhancement of antibacterial activity was observed because of Fe-doping and glucose-capping in CeO2 NPs. Among all samples, G-CeO2 NPs exhibited excellent antibacterial activity against E. coli bacteria.