High Luminescence Intensity Research Articles

Structure and Optical Properties of (CdS–ZnS): Cu and Ag Films Obtained by Aerosol Pyrolysis

The results of the study of CdS–ZnS films obtained by aerosol pyrolysis of solutions of thiourea coordination compounds [Cd(N2H4CS)2Br2] and [Zn(N2H4CS)2Br2] at a temperature of 400°C and impurities doped with copper and silver at a concentration of 10–7 to 10–2 at % are presented. The crystal structure, phase composition, and surface morphology of the synthesized films are studied by X-ray phase analysis, scanning electron microscopy, and atomic force microscopy. It is found that, under these conditions, Cd1 — xZnxS solid solutions of a wurtzite structure are formed. In the range of activator concentrations 10–7–10–5 at %, the Cd1 — xZnxS:Cu layers luminesce more intensely. For films doped with copper ions, the highest luminescence intensity is observed at a concentration of 10–6 at %, and with the introduction of an impurity of silver ions of 10–4 at %.

Roles of (NH4)2HPO4 and NH4H2PO4 in the phase transition and luminescence enhancement of YPO4:Eu

Investigating crystal phase transition helps in understanding new crystal structures and obtaining novel performance. The conventional approaches to realizing phase transition usually require extreme conditions such as high temperature, high pressure, or heavy ion doping. In this work, we achieve phase transition from hexagonal to tetragonal YPO4:Eu crystals just by increasing the concentration ratio of (NH4)2HPO4 to NH4H2PO4 in the precursor. When increasing the ratio, the underlying transition mechanism modifies the free energy of the crystalline system and in turn selects the tetragonal phase with higher formation energy. The difference in preferred growth direction endows tetragonal and hexagonal microcrystals with sphere- and prism-like morphology, respectively. The luminescence intensity is stronger in the tetragonal than the hexagonal phase, due to stronger non-radiative energy transfer induced by high-frequency vibrations in the hexagonal lattice. The efficient method provided here allows convenient production of tetragonal samples with high luminescence intensity on a large scale, and could be well applied to other phosphate systems for phase selection.

Luminescence sensitization of Ln3+ impurity ions in BaGdF5 host matrix: Structural investigation, color tunable luminescence and energy transfer

A series of Sm3+ and/or Eu3+ doped luminescent BaGdF5 nanophosphors were synthesized hydrothermally at 180 °C for 24 h using EDTA as chelating ligand. The structure of synthesized nanophosphors was confirmed by XRD pattern, SEM and TEM studies. The Sm3+ and/or Eu3+ doped BaGdF5 nanophosphors showed irregular sphere like morphology. The minimum average particle size was about 105 nm. The multicolor luminescence was obtained upon excitation at 272 nm depending on the dopant lanthanide ions. The luminescence decay profile of BaGdF5:Sm3+,Eu3+ nanophosphors with different concentrations of Eu3+ ions were obtained by monitoring emission due to magnetic dipole transition at 589 nm for Sm3+ ions. The highest luminescence intensity was obtained for BaGdF5:0.03Sm3+,0.04Eu3+ nanophosphor as a result of efficient energy transfer from Gd3+ to Sm3+ ions and Sm3+ to Eu3+ ions. The color coordinates for all the synthesized nanophosphors were calculated and represented in the form of CIE chromaticity diagram. The energy transfer mechanism for nanophosphors was also explained.

Triboluminescence of trans-stilbene, p-terphenyl and polycyclic aromatic hydrocarbons

Abstract The luminescence of trans-stilbene, p-terphenyl and polycyclic aromatic hydrocarbons (PAHs) during the mechanical grinding of microcrystals in a working cell is studied. The triboluminescence of trans-stilbene, p-terphenyl, naphthalene, anthracene, pyrene, and coronene was detected. No triboluminescence spectrum of tetracene was recorded because of low intensity. No gas component of a triboluminescence spectrum (the lines of N2 molecules and atoms of inert gases) was recorded for all polyaromatic hydrocarbons in air and inert gases (Ne, Ar, and Kr). The bands coinciding with fluorescence spectra of trans-stilbene, p-terphenyl, naphthalene, and anthracene are observed in their triboluminescence spectra during the mechanical grinding of their crystals. High-intensity luminescence of excimers is observed in the triboluminescence spectrum of pyrene and coronene, and there is no luminescence of their monomers. Stable triboluminescence of a pyrene monomer, however, is observed during the grinding of a 200:1 naphthalene/pyrene microcrystal mixture, and it appeared due to the transfer of excitation energy from a naphthalene molecule to pyrene one. The triboluminescence of tetracene was also detected in an anthracene/tetracene mixture. A mechanism of triboluminescence of trans-stilbene, p-terphenyl and PAHs is proposed as electroluminescence arising due to recombination of charge carriers in the electric field of a crystalline layer electrified during the grinding.

The synthesis and luminescence properties of Lu2O3:Eu3+ rods and its comparative analysis with Lu2O2S:Eu3+ rods

Abstract Rod-like Lu2O3:Eu3+ nanoparticles were successfully prepared by solvothermal method and subsequent calcination. Thermogravimetric (TG), X-ray diffraction (XRD) Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM) and photoluminescence (PL) spectrum were utilized to characterize the samples. According to the results of XRD and SEM, 600 °C is the optimum calcination temperature. PL spectra show that concentration quenching occurs when the concentration of Eu3+ in Lu2O3 reaches 4%. The symmetry of the local environment of Eu3+ activators in Lu2O3 has been described in the frame of Judd-Ofelt (J-O) theory. Then the luminescence properties of Lu2O3:Eu3+ and Lu2O2S:Eu3+ phosphors were compared. By comparison, it was found that the synthesized Lu2O3:Eu3+ phosphors had higher luminescence intensity and longer fluorescence time than Lu2O2S:Eu3+ phosphors at their respective optimal Eu3+ doping concentrations. The reasons for the luminescence differences were attributed to the lower band-gap energy of the matrix and the lower symmetry around Eu3+.

СИНТЕЗ, СТРОЕНИЕ И СВОЙСТВА КОМПЛЕКСНЫХ СОЕДИНЕНИЙ АНТАНОИДОВ С 4-[(3,4-ДИМЕТОКСИБЕНЗИЛ) АМИНО] БЕНЗОЙНОЙ КИСЛОТОЙ

The synthesis of complex compounds of 4 - [(3,4-dimethoxybenzyl) amino] benzoic acid (HL) with ions of samarium (III), europium (III), terbium (III), gadolinium (III) and dysprosium (III). According to the data of elemental analysis and thermogravimetry, the obtained complexes are hydrates of the composition LnL3 · nH2O, where n = 0-2. The area of their thermal stability is in the range from 100 ° С to 150 ° С. Electronic and infrared absorption spectra of the ligand and complexes with rare-earth metal ions have been measured. According to the IR spectra, the coordination of the ligand with the metal ion occurs at the carboxyl group. The carboxyl group is bidentate coordinated. To excite luminescence, a line of a mercury lamp with a wavelength of 248 nm was used. The highest luminescence intensity is observed for the coordination compounds Eu3 +, Tb3 +, Sm3 +, and Dy3 +.

Enhancing sensitivity of carbon dots as Fe ion sensor using time-resolved photoluminescence technique

Carbon dots are carbon-based nano materials that have been widely used as heavy metal ion detectors to replace quantum dot semiconductors such as CdS, CdSe, and CdTe which are dangerous to the environment. Cdots are known to be used as nanoparticle probe for the detection of heavy metal ions. Since the advantages of Cdots are sensitive and non toxic. Cdots also have some special properties such as biocompatible, high water solubility, and have high luminescence intensity. However, the detection of heavy metal ions using Cdots still have many limitations such as requiring doping materials Several techniques have been used to measure heavy metal by using CDots; however, their sensitivity needs to improve. We propose time-resolved photoluminescence (TRPL) measurement method to detect Fe3+ ions using CDots made of citric acid and urea. We conducted several other detection methods and compare the results to TRPL method. We found that TRPL method provides direct and high sensitivity compared with other methods. Concentration of Fe3+ ions as low as 0.23 nM can be easily detected using TRPL. Our TRPL measurement is also better than inductively coupled plasma optical emission spectrometry (ICP-OES) measurement system.

Experimental and theoretical study of dense YBO3 and the influence of non-hydrostaticity

YBO3 is used in photonics applications as a host for red phosphors due to its desirable chemical stability, high quantum efficiency and luminescence intensity. Despite its fundamental thermodynamic nature, the isothermal bulk modulus of YBO3 has remained a contentious issue due to a lack of comprehensive experimental and theoretical data and its vibrational modes are far from being understood. Here, we present an experimental-theoretical structural and vibrational study of YBO3. From structural data obtained from synchrotron X-ray diffraction data and ab initio calculations, we have determined the YBO3 bulk modulus, isothermal compressibility tensor and pressure-volume (P-V) equation of state (EoS). The isothermal compressibility tensor reveals that the compressibility of YBO3 is highly anisotropic, with the principal compression axis lying perpendicular to the ab-plane being approximately twice as stiff as the two axes perpendicular to it. From the vibrational data obtained from Raman scattering measurements and ab initio calculations, the experimental and calculated pressure response of the YBO3 Raman modes is also determined with the corresponding Grüneisen parameters and the symmetry of the experimental modes has been tentatively assigned and discussed. No evidence for a pressure-induced phase transition in YBO3 is observed up to 27 GPa, however we note that an apparent discontinuity in the compressibility at 8 GPa, likely due to the onset of non-hydrostaticity, could lead to the misinterpretation of an atypically high bulk modulus.

Longer and Stronger: Improving Persistent Luminescence in Size-Tuned Zinc Gallate Nanoparticles by Alcohol-Mediated Chromium Doping.

Benefiting from near-infrared persistent luminescence, chromium-doped zinc gallate nanoparticles have become appealing for background-free biomedical imaging applications, where autofluorescence from adjacent tissues no longer poses a problem. Nevertheless, the synthesis of persistent luminescent nanoparticles with controllable and biologically appropriate size, high luminescence intensity, and long persistent duration remains very challenging. Herein, we report a solvothermal synthetic route for preparing differently sized ZnGa2O4:Cr nanoparticles with a particle size tunable from 4 to 31 nm and afterglow duration longer than 20 h. The route involves lower reaction temperatures and involves no reworking of the particles postsynthesis, providing materials that have far fewer unwanted defects and much higher luminescence yields (up to 51%). It was found that methanol played a paramount role in obtaining the Cr3+-doped ZnGa2O4 nanoparticles. The effects of methanol were discussed in combination with NMR spectroscopy studies and theoretical calculations, and the underlying alcohol-mediated growth and doping mechanisms were elucidated, which will be beneficial for developing highly persistent luminescent nanoparticles.

Influence of annealing process on the stable luminous CsPbCl3 perovskite films by thermal evaporation

Inorganic perovskites (CsPbX3, X = Cl, Br and I) have aroused great interest due to their extraordinary optoelectronic properties. Despite their rapid progress, device performances are hindered by the instabilities of perovskites. Herein, we employed a thermal co-evaporation method to prepare stable and compact CsPbCl3 films. These films could maintain stability in ambient air for 12 months. The effect of annealing temperature and annealing time on the CsPbCl3 films were researched. Films had high crystallinity and luminescent intensity with 3 μm large grains at optimal annealing condition. This result provides an insightful understanding of annealing process on CsPbCl3 films, as well as to offer a valuable approach for the future of optoelectronic devices based on perovskite materials.

Core/shell type, Ce3+ and Tb3+ doped GdBO3 system: Synthesis and Celecoxib drug delivery application

Abstract In this study, luminescent and magnetic core/shell Gd1-x-yCexTbyBO3@SiO2 nanoparticles were synthesized and used to design a drug delivery system for Celecoxib (CLX). CLX was chosen as the model drug because it is a nonsteroidal anti-inflammatory drug that is highly hydrophobic with relatively low bioavailability. The core was synthesized by Pechini sol-gel method and silica coating was carried out by a Modified Stober method. Drug loading was carried out in ethanol with high efficiency and an improved drug dissolution was obtained in phosphate-buffered saline (PBS) at pH 7.4. Dissolution rate of CLX adsorbed onto the drug carrier at different pH conditions were examined and compared. The obtained core particles had a diameter of about 240 nm and core/shell particles had a diameter of about 300 nm. The core/shell particles possessed high luminescence intensity and soft magnetic properties. Drug loading was carried out in ethanol with 12.7% loading efficiency and a substantial decrease of about 8% in photoluminescence intensity was observed in drug loaded samples, which made the quantification of the released drug possible by comparing the photoluminescence intensities. The solubility of the drug was enhanced when compared to crystalline CLX, a sustained release profile was achieved and increasing luminescence intensity was observed during drug release. 55% of the loaded drug was released after 72 h in PBS at pH 7.4 while 20% drug release was observed in a pH 5.5 solution. Drug release at pH 5.5 followed a first order release kinetic model while the release at pH 7.4 followed a Higuchi's kinetic model with Fickian diffusion mechanism. An in vitro loss in cell viability with CLX loaded carrier was observed for the colon cancer cell line HCT-116. These results suggest that the designed drug carrier has promising applications for poorly soluble drugs with improved bioavailability, in addition to its application as a bioimaging agent in fluorescence microscopy and magnetic resonance imaging.

Power density dependent upconversion properties of NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 nanoparticles and their application in white-light emission LED

White light sources play a vital role in our daily lives, which were usually generated by optimizing the proportions of individual emitters with different colors. Benefiting from the abundant energy levels of rare earth ions (Re3+), Re3+ doped upconversion nanoparticles (UCNPs) with multicolor luminescence output in one fixed structure have attracted broad attention. Here, we constructed a NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 core-shell-shell structure with Er3+ and Tm3+ in different layers to avoid the cross-relaxation. In the structure, red and green emissions were originated from Er3+, and blue emission was generated by Tm3+ through the upconversion process. The simultaneous red, green and blue emissions in the designed structure made it possible to realize white light emission. More importantly, the NaYbF4 host leads to three photons upconversion pathway and result in tunable color output under moderate varying power density. The results showed that warm white color was achieved at the excitation power of 20.9 W/cm2, meanwhile, tunable output colors were also realized by changing the external excited power density. Finally, the high luminescence intensity of NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 makes it possible to be excited by a near infrared-light emitting diode (NIR-LED), and a white emission LED was prepared by encapsulating the prepared UCNPs on a NIR chip.

Experimental and theoretical investigations of the [Ln(β-dik)(NO3)2(phen)2]⋅H2O luminescent complexes

In this work, the coordination compounds presenting the formulas [Eu(acac)(NO3)2 (phen)2]⋅H2O (Eu1) and [Eu(bzac)(NO3)2(phen)2]⋅H2O (Eu2), acac: acetylacetonate, bzac: benzoylacetonate and, phen: 1,10-phenantroline, were successfully synthesized and some spectroscopic properties were investigated by theoretical and experimental methods. These compounds were characterized via elemental analysis, FTIR spectroscopy and thermogravimetric analysis (TGA). The X-ray diffraction data revealed that the compound Eu1 crystallizes in the monoclinic space group P2/n. Spectroscopic data showed that ligand-to-metal charge transfer states (LMCT) in the [Eu(β-dik)(NO3)2(phen)2]⋅H2O complexes (β-dik: acac or bzac) are redshift as compared with [Eu(β-dik)3(phen)] complexes. These data showed that LMCT states play the most important role on the luminescence quenching in the complexes Eu1 and Eu2, which only exhibit high luminescence intensities at low temperatures. Furthermore, the role of changes in the chemical environment on the intensity parameters Ωλ (λ = 2 and 4) have been investigated from the theoretical point of view for the complexes Eu1 to Eu2, and from these to tris β–dik complexes. Interestingly, the theoretical intensity parameters ratio Ω2/Ω4 calculated are in a good agreement with those experimental ones.

СИНТЕЗ, СТРОЕНИЕ И СВОЙСТВАКОМПЛЕКСНЫХСОЕДИНЕНИЙЛАНТАНОИДОВС2-(МЕТИЛАМИНО) БЕНЗОЙНОЙ КИСЛОТОЙ

Synthesis of complex compounds of 2-(methylamino) benzoic acid (L) with ions of samarium (III), europium (III), terbium (III), gadolinium (III) and dysprosium (III). According to elemental analysis and thermogravimetry, the complexes obtained are hydrates of the composition LnL3 • nH2O, where n = 1-5. The area of their thermal stability ranges from 100 ° C to 240 ° C. Electronic and infrared absorptionspectra of the ligand and complexeswith rare-earth metal ions were measured. According to the IR spectra, coordination of the ligand with the metal ion is carried out on the carboxyl group. The carboxyl group is coordinated bidentately. A mercury lampwith a wavelength of 248 nm was used to excite the luminescence. The highest luminescence intensity is observed for the coordination compounds Eu3 +, Tb3 +, and Dy3 +

Luminescent properties of titania doped with nanoparticles of gadolinium oxide and europium

In this work we synthetized seven samples of titania doped with nanoparticles of gadolinium oxide which, previously, were doped with europium at 2 mol%. The doped samples of titania were synthetized using the sol gel method and the nanoparticles of gadolinium oxide were synthetized by the precipitation reaction of precursors of gadolinium nitrate hexahydrate and europium nitrate pentahydrate. All the titania samples were submitted to a thermal treatment at 750 °C. Optical properties, such as the absorption, emission, and emission decay times, besides the X-ray diffraction patterns and the Raman spectra were recorded and analysed. The band gap was calculated from the extrapolation of the linear fit in the absorption edge range in the Tauc plot, the electronic transitions of the europium were identified. Finally, due to the high luminescent intensity of the nanoparticles of gadolinium oxide doped with europium, the possible incorporation of these into the matrix of titania, the possibility for exciting these using lower energy (375 nm) and consequently the shift in the band gap; made it possible to propose the material be used for photocatalytic and photonic applications.

Structural and photoluminescence properties of Eu3+ activated ZnAl2O4 orange-red phosphor

Europium doped zinc aluminum oxide (Zn0.93Al2O4:Eu0.07) was successfully prepared by a combustion method at 550 °C, in which urea, glycine, urea–glycine, citric acid, carbohydrazide, tartaric acid, carbohydrazide–glycine, oxalic acid–glycine, and tetraformaltrisazine were used as a fuel (complexing reagents). The structural and morphological properties were measured and elemental analysis carried out using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and energy-dispersive X-ray (EDX), respectively. The photoluminescence (PL) spectra were monitored by excitation spectra (λex. = 378 nm) and emission spectra (λem. = 614 nm), to assess various complexing reagents in which urea was found to be the most efficient for synthesizing ZnAl2O4:Eu3+orange-red phosphor. The discussed zinc aluminate (U-1) phosphor has a higher luminescence intensity at 614 nm. It is concluded, therefore, that the ZnAl2O4:Eu phosphor can be used widely in various solid-state lighting as an orange-red phosphor.

Direct Growth of Nanopatterned Graphene on Sapphire and Its Application in Light Emitting Diodes

AbstractDirect growth of graphene films on functional substrates is immensely beneficial for the large‐scale applications of graphene by avoiding the transfer‐induced issues. Notably, the selective growth of patterned graphene will further boost the development of graphene‐based devices. Here, the direct growth of patterned graphene on the c‐plane of nanopatterned sapphire substrate (NPSS) is realized and the superiority of the patterned graphene for high‐performance ultraviolet light‐emitting diodes (UV‐LED) is demonstrated. As confirmed by density functional theory calculations and analog simulations, compared to the concave r‐plane the flat c‐plane of NPSS is characterized by a lower active barrier for methane decomposition and carbon species diffusion, as well as a greater supply of carbon precursor for graphene growth. The synthesized patterned graphene on the c‐plane of NPSS is verified to be monolayer and high quality. The patterned graphene enables the selective and well‐aligned nucleation of aluminium nitride (AlN) to promote rapid epitaxial lateral overgrowth of single‐crystal AlN films with low dislocation density. Consequently, the fabricated UV‐LED demonstrates high luminescence intensity and stability. The method is suitable for obtaining various patterned graphene by substrate design, which will allow for greater progress in the cutting‐edge applications of graphene.

Chitosan coating of BaTiO3@ZnO:Yb heterostructures: synthesis and properties

In this study, BT@ZnO:Yb heterostructures prepared using the combined sol-gel-hydrothermal methods were coated with chitosan (Qo) to obtain a hybrid heterostructure [BT@ZnO:Yb]-Qo. The structure, particle morphology, luminescence properties, and cytotoxicity of the hybrid heterostructure are discussed. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infra-red (FT-IR) as well as Raman and photoluminescence spectra, were used for characterisation and monitoring of the heterostructure formation process. The results reveal the formation of the BT@ZnO:Yb heterostructure, and are consistent with the relative intensities and positions of peaks in the XRD spectra of BT and ZnO:Yb, with the average particle size of ~75 nm. Effective Qo coating was achieved and a narrow, well-defined, and high-intensity luminescence signal was detected at ~610 nm for all the analysed samples. In vitro studies suggested that treatment with 1 µg/ml BT@ZnO:Yb 3 mol% induced very low cytotoxicity on HeLa cells.

Spectral-Luminescent Properties of Mixed-Ligand Europium(III) Complexes with O-Methoxybenzoic Acid and Phosphorus-Containing Neutral Ligands

The spectral-luminescent properties of europium(III) complexes with o-methoxybenzoic acid and phosphorus-containing neutral ligands with an island structure and the compositions Eu(MOBA)3 · 3H2O and Eu(MOBA)3 · L, where MOBA is o-methoxybenzoic acid and L is hmpa (hexamethylphosphortriamide, tppo (triphenylphosphinoxide), and Et6pa (hexaethylphosphortriamide), are studied. It is found that the excitation energy transfer to the europium ion occurs from the levels of both o-methoxybenzoic acid and phosphorus-containing neutral ligands. The electronic absorption and luminescence excitation spectra, as well as the Stark structure of the 5D0−7Fj ( j = 0–2) electronic transitions in the luminescence spectra of mixed-ligand complexes of europium(III) o-methoxybenzoates, are analyzed. The highest luminescence intensity is demonstrated by europium(III) methoxybenzoate with triphenylphosphinoxide.

The effects of divalent and trivalent dopants on the luminescence properties of ZnO fine particle with oxygen vacancies

The engineering, various factors, and mechanism responsible for emission and high intensity of ZnO luminescence are well developed. Only a few researchers investigate the role of oxygen vacancy on the luminescence properties of doped ZnO. The objective of this research is to synthesize the ZnO fine particle with tailored oxygen vacancy by doping with 5 at.% of divalent and trivalent dopants, i.e., magnesium (ZnO:Mg2+), calcium (ZnO:Ca2+), gadolinium (ZnO:Gd3+), and lanthanum (ZnO:La3+) using spray pyrolysis method. The samples prepared at 700 °C with 5 l/min carrier gas flow characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The oxygen vacancy was successfully tuned by introducing various doping into ZnO fine particles. It is found that the oxygen vacancy responsible for the increase of DLE intensity (IDLE) on the deconvoluted of PL spectra. When the ZnO fine particle doped with trivalent ions (Gd3+, La3+), the contribution of NBE intensity (INBE) is higher than IDLE. Important phenomena also observed when the excitation wavelength was tuned. The contribution of IDLE and INBE changes, lead to control the luminescence properties.