Photoluminescent Research Articles

Luminescence enhancement of high temperature hexagonal phase of Ba0.99MgAl10O17: Eu0.01 nanophosphor synthesized at moderately low temperature

Photoluminescent (PL) properties of Eu2+-doped BaMgAl10O17 (BAM:Eu2+) phosphors are significantly influenced by its crystallanity, phase and regular morphology. To obtain a high brightness blue-emitting BAM:Eu2+ nanophosphor, a pH-controlled polymeric gel deflagration method was performed at ~ 600 °C followed by post calcination at 1300 °C for 3 h under mild reducing atmosphere. It is one of the very few reports that depicts the formation of hexagonal phase of BAM:Eu2+ nanophosphor at relatively lower (~600 °C) temperatures, which is otherwise possible at very high (>1500 °C) sintering temperatures. A drastic improvement in crystallanity, phase, morphology and PL intensities has been achieved in BAM:Eu2+ nanophosphors with the addition of ammonium fluoride (NH4F) during post-calcination treatment. The presence of NH4F benefitted the thermal stability of BAM:Eu2+ nanophosphors as well. X-ray diffraction studies confirmed the phase purity while the scanning electron microscopy revealed regular morphology with non-aggregated nanoparticles. The improvement in crystallanity of BAM:Eu2+ nanophosphors led to almost four times increase in PL intensity in comparison to its bulk counterpart synthesized by solid-state reaction method. Intentional gamma irradiation of the samples for the creation of F+ centres is another unique feature studied in the current work. The obtained results clearly indicate that BAM:Eu2+ nanophosphor prepared in the study would be an ideal candidate for enhancing the properties of many active displays.

Heterogeneous optoelectronic characteristics of Si micropillar arrays fabricated by metal-assisted chemical etching

Recent progress achieved in metal-assisted chemical etching (MACE) has enabled the production of high-quality micropillar arrays for various optoelectronic applications. Si micropillars produced by MACE often show a porous Si/SiOx shell on crystalline pillar cores introduced by local electrochemical reactions. In this paper, we report the distinct optoelectronic characteristics of the porous Si/SiOx shell correlated to their chemical compositions. Local photoluminescent (PL) images obtained with an immersion oil objective lens in confocal microscopy show a red emission peak (≈ 650 nm) along the perimeter of the pillars that is threefold stronger compared to their center. On the basis of our analysis, we find an unexpected PL increase (≈ 540 nm) at the oil/shell interface. We suggest that both PL enhancements are mainly attributed to the porous structures, a similar behavior observed in previous MACE studies. Surface potential maps simultaneously recorded with topography reveal a significantly high surface potential on the sidewalls of MACE-synthesized pillars (+ 0.5 V), which is restored to the level of planar Si control (− 0.5 V) after removing SiOx in hydrofluoric acid. These distinct optoelectronic characteristics of the Si/SiOx shell can be beneficial for various sensor architectures.

Bright silicon vacancy centers in diamond/SiC composite films synthesized by a MPCVD method

SiC is always produced forming diamond/SiC composite films owing to the oversaturated doping of Si atoms during the preparation of high emission SiV centers. As a higher refractive index material (n = 2.72), the presence of SiC could possibly lead to inefficient photo-luminescent (PL) collection of SiV centers with total internal reflection. In order to understand such effect, different diamond/SiC films were deposited in a 915 MHz microwave plasma CVD (MPCVD) using the reactive gas of tetramethylsilane (TMS). The microstructure and photoluminescence of SiV centers were systematically investigated. It is found that the addition of TMS gas leads to the formation of cubic β-SiC and the refinement of diamond crystals. At the TMS gas flow of 5 sccm, the concentration of β-SiC is about 10% and the average diamond size is about 98 nm. The film exhibits the optimized PL emission of SiV centers, with the ratio of SiV PL to diamond Raman peak being 21.4. Increasing TMS gas flow leads to the increase of the concentration of β-SiC and the deterioration of PL emission of SiV centers. These results reveal that the introduction of TMS gas at a low flow advances the formation of diamond/SiC film containing high-brightness SiV centers.

The synthesis and modification of highly fluorescent carbon quantum dots for reversible detection of water-soluble phosphonate-1-hydroxyethane-1,1-diphosphonic acid by fluorescence spectroscopy.

Photoluminescent (PL) carbon quantum dots (CQDs) were prepared successfully using a facile and green procedure. They exhibited striking blue fluorescence and excellent optical properties, with a quantum yield as high as 61.44%. Due to the fluorescence quenching effect and the stronger complexing ability of the phosphoric acid group of 1-hydroxyethane-1,1-diphosphonic acid (HEDP) to Fe3+ , CQDs doped with Fe3+ were adequately constructed as an efficient and sensitive fluorescent probe for HEDP-specific sensing. The proposed fluorescent probe had a sensitive and rapid response in the range 5-70 μM. Furthermore, quantitative molecular surface (QMS) analysis based on the Multiwfn program was applied to explore the complexation mode of HEDP and metal ions. The distribution of electrostatic potential (ESP), average local ionization energy (ALIE), the minimum value points and the position of the lone pair electrons on the surface of molecular van der Waals were further determined. More strikingly, this experiment achieved the quantitative detection of water-soluble phosphonate-HEDP, for the first time using fluorescence spectrometry. It has been proved to be an effective and intuitive sensing method for the detection of HEDP in real samples.

Characterization of substitutional and interstitial Eu+3-positions in CdS lattice

Cd1-xEuxS thin films, with x in the 0 ≤ x ≤ 5 at% range, were prepared by chemical bath at 80 °C on glass substrates. X ray diffraction (XRD) patterns reveal that the samples crystallize in cubic zinc blende phase, with high preferred orientation along the (111) direction. From XRD data the (111) interplanar spacing (IS) and average crystal size (CS) were calculated. IS(111) decreases from 0.3350 nm for x = 0.0–0.3346 nm for x = 1.2 at%, then increases from here to the initial value for x = 3.0 at%, after decreases slightly until x = 5.0 at%. CS follows approximately an inverse behavior of that of IS(111) vs x taking values in the 29.0–31.5 nm range. The vibrational mode 1LO hardens when x decreases and softens when x increases following the opposite behavior of IS(111), as is expected, however, 1TO follows an opposite behavior to that of 1LO. The direct optical band gap Eg reduces when x decreases and the contrary when x rises, which is the opposite to commonly observed. Besides, the photoluminescent (PL) energy-emissions exhibit a contrary dependence on x as that followed by Eg, this behavior is associated with the distortion of the host CdS lattice due to the Eu doping. PL signals from m1Dn1 → m2Fn2 transitions of E2+,3+ ions are also affected by the behavior of IS(111). All the experimental results are discussed based on the relation among the different observations, and those results reported in the literature.

Photoluminescent hydrophilic cyclodextrin-stabilized cysteine-protected copper nanoclusters for detecting lysozyme.

Lysozyme (LYZ) sensors have attracted increased attention because rapid and sensitive detection of LYZ is highly desirable for various diseases associated with humans. In this research, we designed L-cysteine-protected ultra small photoluminescent (PL) copper nanoclusters (CuNCs) conjugated with β-cyclodextrin (β-CD) for rapid detection of LYZ in human serum samples at room temperature. The proposed β-CD-CuNCs exhibited excellent water solubility, ultrafine size, good dispersion, bright photoluminescence, and good photostability. The β-CD-CuNCs exhibit an excitation and emission maximum at 370nm and 492nm, respectively, with an absolute quantum yield (QY) of 54.6%. β-CD-CuNCs showed a fluorescence lifetime of 12.7ns. The addition of LYZ would result in PL quenching from β-CD-CuNCs. The lowest detectable LYZ concentration was 50nM for the naked eye and the limit of detection (LOD) and limit of quantification (LOQ) were 0.36nM and 1.21nM, respectively, by emission measurement observed in the LYZ concentration range from 30 to 100nM. It is important to note that the PL β-CD-CuNC strategy possessed great selectivity toward LYZ relative to other biomolecules. The proposed nanosensor was efficiently applied to determine the LYZ level in human serum sample average recoveries from 96.15 to 104.05% and relative standard deviation (RSD) values lower than 3.0%. Moreover, the proposed sensing system showed many advantages, including high speed, high sensitivity, high selectivity, low cost, and simple preparation.

Full-Color Spectrum Coverage by High-Color-Purity Perovskite Nanocrystal Light-Emitting Diodes

Summary Although many synthetic methods such as hot injection and anionic exchange can produce full-color perovskite nanocrystals (PNCs), their emission spectra are broadened by compositional non-uniformity. Here, we propose the synthetic method, hydrogen halide (HX; X = Cl, Br, and I)-mediated uniform halide anion exchange at mild temperatures, for high color-purity PNCs emitters across the full-color spectrum. The HX-mediated exchange reaction produces high-purity PNCs without metallic Pb impurities due to the use of volatile HX as the X source. The blue, green, and red PNCs show narrow emission spectra, with 16, 18, and 18.5 nm of full width at half-maximum, respectively. The red PNC emitter synthesized by the HX-mediated method has a single photoluminescent (PL) peak, with a narrow emission spectrum at low temperature due to compositional uniformity, whereas the PNCs produced by other methods have multiple PL peaks. Accordingly, the red/green/blue electroluminescent devices also have narrow emission spectra.

Thin film electroluminescent device based on magnetron sputtered Tb doped ZnGa2O4 layers

Photoluminescent (PL) layers and electroluminescent (EL) systems prepared by different methods have been systematically studied for the fabrication of flat panel displays, monitoring screens, and lighting systems. In this work we report about a new procedure of preparing Tb doped ZnGa2O4 green luminescent thin films at low temperature that consists of the simultaneous reactive magnetron sputtering (R-MS) deposition of a Zn–Ga mixed oxide acting as a matrix and the plasma decomposition (PD) of evaporated terbium acetylacetonate. The resulting films were transparent and presented a high PL efficiency making them good candidates for EL applications. Layers of this phosphor film with thickness in the order of hundreds nanometers were sandwiched between two dielectric layers of Y2O3 and AlSiNxOy that were also prepared by R-MS. The response of the resulting EL device was characterized as a function of the applied voltage and the type of AC excitation signal. The high luminance and long-term stability of these thin film electroluminescent devices (TFELDs) proves the reliability and efficiency of this kind of transparent R-MS multilayer system (with a total thickness in order of 650 nm) for display and lighting applications.

Surface-Modified Ultrathin InSe Nanosheets with Enhanced Stability and Photoluminescence for High-Performance Optoelectronics.

Indium selenide (InSe) has become a research hotspot because of its favorable carrier mobility and thickness-tunable band gap, showing great application potential in high-performance optoelectronic devices. The trend of miniaturization in optoelectronics has forced the feature sizes of the electronic components to shrink accordingly. Therefore, atomically thin InSe crystals may play an important role in future optoelectronics. Given the instability and ultralow photoluminescent (PL) emission of mechanically exfoliated ultrathin InSe, synthesis of highly stable mono- and few-layer InSe nanosheets with high PL efficiency has become crucial. Herein, ultrathin InSe nanosheets were prepared via thermal annealing of electrochemically intercalated products from bulk InSe. The size and yield of the as-prepared nanosheets were up to ∼160 μm and ∼70%, respectively, and ∼80% of the nanosheets were less than five layer. Impressively, the as-prepared nanosheets showed greatly enhanced stability and PL emission because of surface modification by carbon species. Efficient photoresponsivity of 2 A/W was achieved in the as-prepared nanosheet-based devices. These nanosheets were further assembled into large-area thin films with photoresponsivity of 16 A/W and an average Hall mobility of about 5 cm2 V-1 s-1. Finally, one-dimensional (1D) InSe nanoscrolls with a length up to 90 μm were constructed by solvent-assisted self-assembly of the exfoliated nanosheets.

Tunable photoluminescence of CaCu3Ti4O12 based ceramics modified with tungsten

CaCu3Ti4O12 (CCTO): x% W (x = 0.00, 0.02, 0.05, 0.10, 2.50, and 5.00) powders were prepared via solid-state reaction. The effect of W addition in the (micro)structure and optical properties was analyzed using computing simulations and experimental techniques. The widespread application of perovskite-light-emitting diodes (PeLEDs), photovoltaic devices, and photocatalysis is limited by the intrinsic instability of the perovskite materials (e.g., metal halides), compromising operational efficiency, and pushing for the development of novel perovskite materials. The Rietveld analysis and XPS results confirm the presence of W5+, Ti3+, and Cu+ ions in all samples of the CaCu3Ti4O12: x% W system, leading to structural changes that strongly influence the PL response of the material. Based on a correlation approach, a practical model explaining the relationship between electronic defects and photoluminescent (PL) emissions in the CCTO system is proposed. On samples x = 0.00, 0.10, and 5.00, red PL emissions are due to the presence of metal vacancies, and deep-level defects, while blue PL emissions on samples x = 0.02, 0.05, and 2.50 are associated with shallow defects. Thus, our research shows evidence that CaCu3Ti4O12 (CCTO): W ceramic systems may be promising to photonics applications.

Synthsis and characterization of Tb3+/Eu3+ complexes based on 2,4,6-tris-(4-carboxyphenyl)-1,3,5-triazine ligand for ratiometric luminescence temperature sensing.

By choosing C3 symmetric 2,4,6-tris-(4-carboxyphenyl)-1,3,5-triazine (TCTZ) as the ligand, a series of lanthanide metal-origanic complexes Tb1-xEux-TCTZ(DMF)·2H2O(x=0, 0.01, 1) have been successfully synthesized via solvothermal reaction. The complexes present intense emission although with coordinationofwater molecules. The temperature-dependent photoluminescent (PL) properties of Tb-TCTZ is investigated both in terms of emission intensity and lifetime in order to establish their potentials as luminescent themometers. It shows excellent responseto temperature from 303 to 403K and exhibits the maximum relative sensitivity(Sr) as high as 5.36% K-1 at 403K. Tb0.99Eu0.01-TCTZ is evaluated for application as ratiometric luminescence thermometers, which exhibits high sensitivity to temperature in range of 303-403K, with the maximum absolute sensitivity (Sa) and Sr as 5.16% and 3.22% K-1 respectively. The obtained maximum sensitivities in this study is superior to many materials reported. Moreover, the emission color changes from green at 303K to red at 403K, so that it is also suitable to act as colorimetric luminescent probes.

Structural Characterization and Photoluminescent Behavior of CO3 Intercalated Zn-Fe Layered Double Hydroxide (LDH) and its Colloids

Carbonate intercalated Zn-Fe layered double hydroxide (LDH) with Zn2+/Fe3+ molar ratios 2, 3 and 4 were synthesized by coprecipitation in order to study the photoluminescent (PL) properties of their colloids with various wt.% of LDH in formamide. These synthesized LDHs were characterized by various techniques including x-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron mMicroscopy (FE-SEM), energy-dispersive x-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), and photoluminescence spectroscopy (PL). The rhombohedral phase and crystallite size of Zn-Fe LDH were confirmed by XRD. Crystallite size plays an important role in the PL mechanism. HR-TEM showed hexagonal nanosheets with 5–6 nm average particle size. To investigate the PL mechanism of pristine LDH and their colloids, these prepared Zn-Fe LDHs were exfoliated in formamide by varying their Zn2+/Fe3+ molar ratios (2,3, 4) and LDH concentration (0.2 wt.%, 0.4 wt.%, 0.6 wt.%, 0.8 wt.% of LDH). Results revealed that surface charge density and surface defects are the main reasons for PL generation in LDH colloids.

Fabrication, characterization and optical properties of transparent PP/Yttria-stabilized zirconia (YSZ) based nanocomposites

In this study have been prepared optically transparent polymeric nanocomposites based on PP/YSZ by combination of ex-situ and hot pressing methods. The structure of the synthesized nanocomposites was studied by XRD analysis, UV spectroscopy, scanning electron microscopy. The optical and photoluminescent (PL) properties of polymer nanocomposites were investigated. It was found that with an increase in the concentration of YSZ nanoparticles in the PP matrix to 3% of the content of nanoparticles, the PL intensity increases, with a further increase in the nanoparticles content, the PL intensity decreases. This is explained by the fact that with an increase in the concentration of YSZ nanoparticles, their size increases and their specific surface decreases, and this leads to a decrease in the contacting region between the polymer and the nanoparticle. A decrease in the interphase boundary leads to a decrease in interphase interactions, and this in turn leads to a change in the PL intensity. It was also shown that the PL intensity for nanocomposites at all wavelengths increases with increasing annealing temperature to 120°C, and then decreases. Possible reasons for a significant increase in the PL intensity after thermal annealing are the redistribution of charge carriers between levels in the band gap or the recharging of recombination centers and the removal of organic compounds adsorbed on the surface of nanocomposites.

Facile pH-sensitive optical detection of pathogenic bacteria and cell imaging using multi-emissive nitrogen-doped carbon dots

Rapid detection of lethal pathogens is critical to abate the mortality rate of patients suffering from infectious diseases. Herein, we report a pH-sensitive detection of the pathogenic bacteria using multicolor emissive Nitrogen-doped Carbon Dots (NtCD) synthesized by a one-step hydrothermal method. The unique pH-sensitive interaction of NtCD with bacteria was best studied at pH 2. NtCD was competent to detect several pathogenic bacteria such as; Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Proteus vulgaris (P. vulgaris). The fluorescence spectral investigations of NtCD revealed the excitation dependent emission property with a red-shift. It shows an intense photoluminescent (PL) emission at λex/λem = 340/435 nm. The calculated quantum yield of NtCD was 27.2%. It also possesses multicolor emission at different excitation wavelengths. TEM analysis displayed the uniform spherical morphology of NtCD particles with an average hydrodynamic diameter of 3.11 ± 0.75 nm. The zeta potential of NtCD was measured as −8.4 mV at pH 2. The interaction between NtCD and bacteria was explained on the basis of their zeta potential values. The PL emission response of NtCD tagged bacteria was investigated at λex = 340 nm. It was potentially tagging to both E. coli and S. aureus but with a better response towards E. coli cells. The human squamous epithelial cells (SEC) were deployed as a fitting substitute for achieving NtCD-mammalian cell imaging. Both NtCD tagged bacterial cells and SEC exhibited multicolor emission as well. Mechanistic implications of pH-dependent PL emission property of NtCD and its bacterial interaction were discussed extensively.

Luminescent Solar Power-PV/Thermal Hybrid Electricity Generation for Cost-Effective Dispatchable Solar Energy.

The challenge in solar energy today is not the cost of photovoltaic (PV) electricity generation, already competing with fossil fuel prices, but rather utility-scale energy storage and flexibility in supply. Low-cost thermal energy storage (TES) exists but relies on expensive heat engines. Here, we introduce the concept of luminescent solar power (LSP), where sunlight is absorbed in a photoluminescent (PL) absorber, followed by red-shifted PL emission matched to an adjacent PV cell’s band edge. This way the PV cell operates nearly as efficiently as under direct illumination but with minimal excessive heat. The PL absorber temperature rises because of thermalization, allowing it to store the excessive heat, which can later be converted into electricity. Tailored luminescent materials that support an additional 1.5 kW h PV electricity for every 1 kW h of (virtual) heat engine electricity with a dynamic shift between the two sources are experimentally demonstrated. Such an ideal hybrid system may lead to a potential reduction in the cost of electricity for a base-load solution.

Site occupation and energy transfer of Ce3+-Activated oxynitride Lu4SiAlO8N with broad-cyan-light-emitting property used for WLEDs

The systems of Si-Al-O-N originated from the outstanding nitrogen ceramic of Si3N4 have received considerable attention due to their significant luminescence properties. In this work, to explore its potential in the full-spectrum lighting applications, a novel oxynitride based phosphor Lu4SiAlO8N: Ce3+ was investigated in detail by using the Rietveld refinement, DFT calculations, photoluminescent (PL) and time-resolved PL (TRPL) spectra. The results indicate that Lu4SiAlO8N performs a tight host lattice formed by the edge-sharing LuO6 polyhedrons and (Si, Al) (O, N)4 tetrahedrons; the multiple crystallographic Lu3+ sites in the host lattice contribute to the broad emission band. Under the near ultraviolet (NUV) light excitation, Lu4SiAlO8N: Ce3+ emits a bright cyan light peaked at 470 nm, and its full width at half maximum (FWHM) can reach 120 nm, which well replenishes the “cyan cavity”. Moreover, the energy transfer between the multiple luminescent centers was verified through the TRPL spectra. The temperature-dependent spectra of Lu4SiAlO8N: Ce3+ was measured to prove its acceptably thermal stability. All the results indicate the Lu4SiAlO8N: Ce3+ to be a promising candidate for the application in WLEDs.

CuO nanoparticles: preparation, characterization, optical properties, and antibacterial activities

Firstly, new copper precursor was prepared from the mixture of Cu(CH3COO)2∙H2O and salicylic acid (1:1 weight ratio) ground for 5 min, and secondly, copper oxide nanoparticles were prepared by calcination of copper precursor at 500 oC and 600 oC for 1.5 h. The products were characterized by Fourier Transform infrared (FT-IR), UV–Vis and photoluminescent (PL) spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). The FT-IR, UV–Vis, PL, and XRD analysis confirmed the formation of CuO nanoparticles of high purity with a monoclinic structure. TEM images showed that the nanoparticles in both samples had almost similar shape with high agglomeration. The optical band gap value was estimated to be 4.5 and 4.8 eV, respectively, for the as-prepared CuO at 500 and 600 oC, using Tauc’s plot. In addition, antibacterial activity against two gram-positive and two gram-negative stains were studied and the inhibition effect of the as-prepared CuO at 500 and 600 oC on gram-negative bacteria is higher than that on gram-positive bacteria

ZnSeTe Quantum Dots as an Alternative to InP and Their High-Efficiency Electroluminescence

Last decade witnessed great advancement in the photoluminescent (PL) quality of visible III–V InP quantum dots (QDs) toward bright, sharp emissivity. Now, InP QDs hold an unrivaled position in the ...

Optical Properties of Composites Based on Graphene Oxide and Polystyrene.

In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm−1. The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm−1. These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets’ concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.

The influence of Eu3+ doping on the studies of luminescent properties and quantum efficiency of ZnWO4 phosphor

ZnWO4:Eu3+ red nanophosphors have been synthesized by a simple environmentally friendly and low-cost molten salt method. The phase structure, morphology, SAED, photo-luminescent (PL), lifetime, color rendering, quantum efficiency and stability properties of the phosphor were investigated in detail. The XRD results indicated that all Eu3+ ions doping ZnWO4 samples crystallize in a single crystal wolframite structure and exhibit superior crystallinity. Under the excitation of 394 and 465 nm, ZnWO4:Eu3+ phosphors can be exhibited red light emission. The photoluminescence excitation spectra of ZnWO4:Eu3+ phosphors show several emission peaks, on account of the f–f transitions of Eu3+ ions. The quantum efficiency of ZnWO4:0.07Eu3+ phosphors were calculated to be 40.5%, the CIE chromaticity coordinate of ZnWO4:0.07Eu3+ phosphors were (0.631, 0.364) closed to the red phosphors standard value (0.670, 0.330), based on the Judd–Ofelt analysis, Judd–Ofelt intensity parameters (Ω2/Ω4) includes symmetry of Eu3+ ions crystal field environment, it was suggested that ZnWO4:0.07Eu3+ phosphors were a potential phosphor in LEDs. This research sheds new light on improving the quantum efficiency, stability properties and CIE chromaticity coordinate.