Orange-red Luminescence Research Articles

Structure and luminescent properties of Sm3+ doped SrO-MgO-SiO2 glass ceramics

A new type of samarium ion activated luminescent glass ceramics with main crystal phase of melilite was prepared. The effect of heat-treatment temperature on the structure of glass ceramics was investigated by X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and fluorescence spectrometer. In the Sm3+ doped SrO-MgO-SiO2 glass ceramic, its excitation spectra are in the wavelength range of 350–500 nm, and its excitation peaks are at 360 nm, 374 nm, 404 nm, 417 nm, and 475 nm with the host excitation peak of 404 nm, showing a strong orange-red luminescence when using 404 nm violet to excite it, and its emission peaks are at 564 nm, 600 nm and 648 nm with the host emission peak at 600 nm. The increase in the heat-treatment temperature has no influence on the position of the fluorescent spectra. However, with the increase of heat-treatment temperature, the intensity of fluorescence spectrum shows an increasing tendency. The increase in the concentration of Sm3+ also improves the intensity of the fluorescent spectra. In the experimental concentration range (0.05mol%–0.30mol%), a special concentration quenching phenomenon happens.

Luminescent rhenium(I)–chromone bioconjugate: Synthesis, photophysical properties, and confocal luminescence microscopy investigation

Luminescent Re(I) complexes represent important materials for bioimaging applications. Herewith a new Re-complex Re(CO)3(phen)L1, where phen = 1,10-phenanthroline and L1 = 3-CCCH2NHCOCH2CH2-6-bromo-chromone, is reported. The new conjugate displays moderately intense orange-red luminescence stemming from a 3MLCT excited state associated with the organometallic Re(CO)3(phen) fragment. At ambient temperature, the emission quantum yield amounts to 0.2–0.9 % in aerated organic solvents and 7% in poly(methyl methacrylate). The emission decay times are in the order of several tens of nanoseconds to a few microseconds depending on the polarity and viscosity of the medium. Re(CO)3(phen)L1 penetrates into the mouse C2C12 cancer cells where it accumulates in cytoplasm, mitochondria, and endoplasmic reticulum, as it was determined by means of confocal fluorescence microscopy. Furthermore, the complex shows high photostability in live cells. No photobleaching was observed under prolonged intense irradiation (λ = 405 nm, I = 0.8 W/cm2, t = 30 min), whereas at similar conditions significant photobleaching of commonly used fluorescent stains, e.g. DAPI, occurs.

BaGa4O7, a new A3BC10O20 crystalline phase: synthesis, structural determination and luminescence properties

A new compound, BaGa4O7, is found by cooling from the melt. Part of the A3BC10O20 family, it exhibits strong orange-red luminescence emission when doped with Eu3+.

Reddish-orange Ca3−xAl2O6:xEu3+ nanophosphors: Fast synthesis and photophysical properties

This paper focuses on the synthesis and the photoluminescent properties of Ca3−xAl2O6:xEu3+ (0≤x≤0.1) nanophosphors prepared by microwave-assisted combustion method without any further heat treatment. X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy were used to characterize the produced samples. Nanosized particles smaller than 120nm were obtained as confirmed by SEM. When exposed to UV light radiation at 254nm, the europium-doped nanoparticles showed strong reddish-orange luminescence due to the characteristic transitions 5D0→7F1 (orange) and 5D0→7F2, (red). The maximum emission intensity of the visible emission was obtained for x=0.05. It was also found that higher doping concentrations led to the luminescence quenching by a cross-relaxation mechanism between Eu3+ ions in the lattice.

Structural and luminescence behavior of Sm3+ ions doped lead boro-telluro-phosphate glasses

The Sm3+ ions doped lead boro-telluro-phosphate glasses with the chemical composition 30H3O3+(20–x)PbO+15TeO2+10P2O5+10ZnO+15BaCO3+xSm2O3 (x=0.05, 0.1, 0.25, 0.5, 1.0 and 2.0 in wt%) have been prepared by a melt quenching technique and their structural and optical behavior were studied and reported. The physical properties like, refractive index, density and dielectric constant etc., have been estimated. FTIR and Raman spectral studies have been made to explore the presence of functional groups and various structural units in the prepared glasses. The formation of bridging and non-bridging oxygens of BO4, BO3, TeO3, TeO6 and PbO4 structural units have been investigated. From the absorption spectra, the direct (n=1/2), indirect (n=2) band gap, band tailing parameter (B) and Urbach energy (ΔE) values were estimated. The ionic nature of the metal–ligand bond in the title glasses has been discussed. The Judd–Ofelt intensity parameters (Ωλ,λ=2, 4, and 6), oscillator strength of ƒ−ƒ electric dipole transitions and transition probability (A) have been evaluated. The predicted radiative lifetime (τrad) and branching ratio (βR) values of the 4G5/2 excited level of the Sm3+ ions to the lower energy levels were determined and compared with the experimentally measured values. From the recorded fluorescence spectra, the strong transitions of Sm3+ ions 4G5/2→6H5/2 (565nm), 4G5/2→6H7/2 (602nm), 4G5/2→6H9/2 (648nm) and a weak transition, 4G5/2→6H11/2 (709nm) have been observed. The significant laser parameters like, gain bandwidth (σpE×λeff), optical gain (σpE×τrad) and stimulated emission cross-section (σpE) values were estimated for the 4G5/2→6HJ (J=5/2, 7/2, 9/2 and 11/2) emission transitions. The decay profile of the present glasses reveal the single exponential nature at small concentrations (≤0.25%) and non-exponential at higher concentrations (≥0.5%) due to cross-relaxation and non-radiative energy transfer processes and the same has been discussed using I–H model. The 0.5wt% of the Sm3+ ions doped lead boro-telluro-phosphate glasses exhibit reddish orange luminescence indicating its usefulness for the development of optical, display and LED devices.

Inorganic–organic hybrid with one-dimensional face-sharing iodoplumbate chain showing novel dielectric anomaly and semiconductor emission

An inorganic–organic hybrid [tetrabutylammonium][PbI3] crystallizes in tetragonal space group I-42d, which inorganic components form one-dimensional (1D) face-sharing iodoplumbate chain. This hybrid shows a novel dielectric anomaly around 125°C. The variable-temperature single crystal and powder X-ray diffraction (PXRD) measurements revealed that the dielectric anomaly arises from the disorder–order transformation of tetrabutylammonium. The hybrid emits orange-red luminescence, ascribed to the semiconductor emission of 1D [PbI3]∞ chain.

New Luminescing Oxyfluoride Glass with Europium and Ytterbium Ions

New oxyfluoride glasses containing Eu3+ and Yb3+have been synthesized in the system SiO2–PbO–PbF2–CdF2 and their physical-chemical properties and the optical absorption and up-conversion of luminescence have been studied. Intense orange-red luminescence (color coordinates x = 0.64, y = 0.36) peaking near 612 nm was obtained by excitation in the IR range by a commercially available laser diode. This glass is promising for obtaining nano-phase luminescing glass-ceramics for use in up-conversion luminophores and solid-state lasers.

Is Bi2+ Responsible for the Red-Orange Emission of Bismuth-Doped SrB4O7?

Red-orange luminescence from bismuth-doped SrB4O7 has previously been reported and assigned to 6p-6p transitions of divalent Bi. To provide support for this assignment and for the stability of this unusual valence state of Bi, we report here results from low-temperature luminescence spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and wave function based ab initio calculations. Low-temperature luminescence spectra reveal zero-phonon lines (ZPLs) in excitation and emission spectra, allowing an accurate determination of the energies for the electronic transitions. The influence of the Bi concentration on the emission intensity is shown to be small, and only a small increase of the red-orange emission is observed upon raising the nominal Bi concentration from 0.02% (200 ppm) to 2%. This result indicates that only a very low concentration of Bi2+ can be incorporated in SrB4O7. This observation is supported by EPR experiments, which do not show a signal that can be assigned to Bi2+, and by XANES experiments showing that most Bi is in the trivalent state. An upper limit of the Bi2+ concentration is estimated to be 20 ppm. Ab initio calculations on the (BiO9)16– cluster embedded in SrB4O7 give energies for excited states that are close to the experimentally observed energies. Also, the luminescence lifetime for the red-orange emission (∼12 μs) is consistent with the lifetime for 6p-6p emission calculated for the Bi2+ emission (3.5 μs). Equivalent ab initio calculations for Bi2+ luminescence are very far from the experimental results, providing independent evidence and additional support for the interpretation of stable Bi2+ species being responsible for the red-orange luminescence. The calculations provide a new interpretation of the third excitation band, which is not due to a 2S1/2 state of the 6s27s configuration of Bi2+, as previously assumed, but is due to a state with important characters of 6s6p2–4P (63%) and doublets of the 6s6p2, 6s26d, and 6s26p configurations; its higher intensity is due to its character of parity-allowed 6s → 6p and 6p → 6d excitations.

Eu3+-site occupations and peculiar reddish orange luminescence in aluminates Sr3RAl2O7.5:Eu3+ (R=Y, Lu)

A novel reddish orange-emitting phosphor of Eu3+-doped aluminate Sr3RAl2O7.5 (R=Lu, Y) was successfully synthesized by wet-chemistry sol–gel method. The samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The luminescence properties such as photoluminescence excitation and emission spectra, decay curves, CIE color coordinates and luminescence quantum efficiency were investigated. This phosphor can be efficiently excited by UV and near-UV light and exhibits a bright reddish orange luminescence with the abnormally strongest 5D0→7F0 transition. Two distinct Eu3+ sites can be observed on the emission spectra under the excitation of UV light (excitation at charge transfer band of Eu3+ ions) or dye laser in the 5D0→7F0 wavelength region (selective excitation into each site). The site-selective luminescence decay curves have been investigated in the 5D0→7F0 region of each Eu3+ site by using a pulsed, tunable, and narrowband dye laser. Each Eu3+ site presents the distinct luminescence lifetime with different rise time. The Stark energy levels of two Eu3+ sites were assigned from the site-selective emission spectra. The energy transfer can happen between the closely neighbored Eu3+ sites in Sr3RAl2O7.5 (R=Lu, Y). The luminescence mechanism responsible for the abnormally strong 5D0→7F0 transition was discussed.

Synthesis, structural and optical properties of SrZrO3:Eu3+ phosphor

Eu3+ activated Sr1−xEuxZrO3 (x=0.01−0.04) phosphor with perovskite structure was successfully synthesized by using combustion method. The structure, morphology and optical properties of the material were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometry. The XRD results indicated that crystals of SrZrO3:Eu3+ belongs to tetragonal perovskite system. The phosphor could be effectively excited by UV light and the emission spectra results indicated that reddish-orange luminescence of SrZrO3:Eu3+ due to magnetic dipole transition 5D0→7F1 at 593 nm was dominant. Thus, the prepared phosphor showed remarkable luminescent properties which find applications in field emission display (FED) and plasma display panel (PDP) devices.

Na2Y3Cl3[TeO3]4: Synthesis, Crystal Structure and Spectroscopic Properties of the Bulk Material and its Luminescent Eu3+-doped Samples

Colorless, platelet-shaped single crystals of Na2Y3Cl3[TeO3]4 were synthesized by a reaction of Y2O3 and TeO2 (molar ratio 3 : 8) in evacuated silica ampoules within five days at 775 °C with an excess of NaCl added as flux and reagent. The new quintenary compound crystallizes in the monoclinic space group C2/c with the lattice parameters a = 2380:69(14), b = 552:76(3), c = 1662:48(9) pm, β = 134:045(3)° and Z = 4. The crystal structure presents one of the rare oxotellurates(IV) containing isolated [TeO3]2− units, which could be verified by Raman spectroscopy. Doping with Eu3+ (3 mass-%) at the Y3+ sites in eightfold oxygen coordination leads to a strong orange-red luminescence of Na2Y3Cl3[TeO3]4:Eu3+ under UV excitation with a wavelength of λ = 254 nm. Beyond the electronic Eu3+ transitions of the 4 f 6 state, the fluorescence excitation spectrum shows an intense broad charge-transfer band resulting from both O2−→Eu3+ ligand-to-metal charge-transfer (LMCT) as well as electronic Eu3+ d→f and Te4+s→p transitions. The emission spectrum features the prominent f→f transitions of Eu3+-doped oxidic compounds. The optical band gaps of the undoped and doped samples were determined by diffuse reflectance spectroscopy revealing just minimal doping effects on the crystal structure. The optical band gaps could be assigned in the excitation spectrum in the charge-transfer broad-band region supporting the assumption of an inorganic antenna effect of the Te4+ cations.

Hydrothermal synthesis and luminescence properties of Eu3+ and Sm3+ codoped BiPO4

Eu3+/Sm3+ codoped BiPO4 phosphors were synthesized via a facile hydrothermal method with surfactant-free environment. The X-ray diffraction analysis demonstrated that the samples possessed the standard BiPO4 monoclinic structure. Scanning electron microscopy images showed that all samples composed of well-dispersed, micrometer-sized crystals with shuttle-like shape. Energy transfer from Sm3+ to Eu3+ was confirmed by the luminescence spectra and the decay processes of Sm3+ 4G5/2→6H5/2 emission. Orange-red luminescence could be obtained in Eu3+/Sm3+ codoped BiPO4 phosphors. The average lifetime of Sm3+ 4G5/2→6H5/2 emission decreased from 2.70 ms in BiPO4:0.03Sm3+ to 2.37 ms in BiPO4:0.03Sm3+,0.05Eu3+. The strong and wide absorption band around 395 nm, originating from both 7F0→5L6 transition of Eu3+ and 6H5/2→4K11/2 transition of Sm3+, endowed BiPO4:Eu3+,Sm3+ phosphors with the potential application in the fields of near UV-excited white-light-emitting diodes.

Optical characterization of Sm3+-doped calcium-orthosilicate phosphors prepared using the solid-state reaction method

Trivalent samarium-doped calcium-orthosilicate (Ca2SiO4:Sm3+) powder is synthesized by varying Sm2O3 amounts and the solid-state reaction method. X-ray diffraction patterns show that the obtained powders formed as orthorhombic-structured Ca2SiO4. Scanning electron microscope images show that the powders have uniform structures of a few micrometers in size. Photophysical features are analyzed by taking absorption, excitation, and emission spectra. Emission spectra exhibit a red-orange luminescence from the 4G5/2 → 6H7/2 transition of Sm3+ in all synthesized phosphors. Both the physical and the optical properties show that Ca2SiO4:Sm3+ is an encouraging red-orange emitting phosphor applicable to photonics operating with near ultra-violet excitation.

Optical spectroscopy and optical waveguide fabrication in Eu3+ and Eu3+/Tb3+ doped zinc–sodium–aluminosilicate glasses

Optical and spectroscopic properties of 2.0% Eu(PO3)3 singly doped and 5.0% Tb(PO3)3–2.0% Eu(PO3)3 codoped zinc–sodium–aluminosilicate glasses were investigated. Reddish-orange light emission, with x=0.64 and y=0.36 CIE1931 chromaticity coordinates, is obtained in the europium singly doped glass excited at 393nm. Such chromaticity coordinates are close to those (0.67,0.33) standard of the National Television System Committee for the red phosphor. When the sodium–zinc–aluminosilicate glass is co-doped with Tb3+ and Eu3+, reddish-orange light emission, with (0.61,0.37) CIE1931 chromaticity coordinates, is obtained upon Tb3+ excitation at 344nm. This reddish-orange luminescence is generated mainly by 5D0→7F1 and 5D0 →7F2 emissions of Eu3+, europium being sensitized by terbium through a non-radiative energy transfer. From an analysis of the Tb3+ emission decay curves it is inferred that the Tb3+→Eu3+ energy transfer might take place between Tb3+ and Eu3+ clusters through a short-range interaction mechanism, so that an electric dipole–quadrupole interaction appears to be the most probable transfer mechanism. The efficiency of this energy transfer is about 62% upon excitation at 344nm. In the singly doped and codoped glasses multimode optical waveguides were successfully produced by Ag+–Na+ ion exchange, and they could be characterized at various wavelengths.

Crystal Structure and Luminescent Properties of Eu3+-Doped A-La2Si2O7 Tetragonal Phase Stabilized by Spray Pyrolysis Synthesis

Pure A-La2Si2O7 powder has been synthesized through a spray pyrolysis method followed by calcination at 1100 °C for 15 h. The crystallographic structure, refined from the synchrotron powder diffraction pattern of the sample, showed tetragonal symmetry with space group P41, a = 6.83565(1) Å, and c = 24.84133(1) Å. The 29Si and 139La NMR spectra have been described here for the first time in the literature and could be simulated with four Si and four La resonances, respectively, in good agreement with the presence of four Si and four La crystallographic sites in the unit cell. The same synthesis method was successful for the synthesis of Eu3+-doped A-La2Si2O7 (%Eu = 3– 40). The analysis of the unit cell volumes indicated that Eu3+ replaces La3+ in the unit cell for all Eu3+ substitution levels investigated. However, anomalous diffraction data indicated that the La/Eu substitution mechanism was not homogeneous, but Eu much prefers to occupy the RE3 sites. The Eu-doped A-La2Si2O7 phosphors thus synthesized exhibited a strong orange-red luminescence after excitation at 393 nm. Lifetime measurements indicated that the optimum phosphor was that with an Eu3+ content of 20%, which showed a lifetime of 2.3 ms. The quantum yield of the latter was found to be 12% at 393 nm excitation. These experimental observations together with the high purity of the phase obtained by the proposed spray pyrolysis method make this material an excellent phosphor for optoelectronic applications.

Facile synthesis of reduced graphene oxide/selenium nanocomposites with orange red luminescence by in situ redox

Selenium nanospheres assembled by a large amount of nanocrystals (NCs) were facilely synthesized through in-situ reduction of graphene oxide (GO) using NaHSe as reducing agent as well as Se source. The structural and optical characterizations of these as-prepared products have been carried out at room temperature. The reduction of graphene oxide was accompanied by the deposition of Se nanospheres uniformly on the surface of reduced graphene oxide (RGO) sheets. Moreover, the product was found to exhibits orange red color luminescence under ultraviolet (UV) lamp for the first time with higher quantum yield (QY) of 8.11%, which is six times higher than that of GO aqueous solution (1.32%).

Bright-yellow to orange-red thermochromic luminescence of an AgI6–ZnII2 heterometallic aggregate

A novel octanuclear Ag(I)(6)-Zn(II)(2) heterometallic aggregate, (NH(4))(2){[Zn(2)(phen)(2)(H(2)O)(4)][Ag(6)(mna)(6)]}·2H(2)O·2CH(3)CH(2)OH (1, H(2)mna = 2-mercaptonicotinic acid, phen = 1,10-phenanthroline), was stepwisely obtained based on a hexanuclear silver(i) metalloligand using a liquid-liquid diffusion method. It is an exceedingly rare example that exhibits interesting temperature dependent photoluminescence behaviors, including gradual changes in energy and intensity upon cooling.

Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

AbstractSilicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO2 side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ∼2.4 µm under solar irradiation of 100 mW/cm2 (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co2+ successfully incorporated into the Zn2+ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.

Hydrothermal syntheses, crystal structures and properties of lanthanide complexes with 4-Hydroxy-6-methylnicotinic acid

Four isomorphous lanthanide complexes, [Ln2(L)6(H2O)2]·2H2O [Ln=Ce (1), Ln=Nd (2), Ln=Sm (3), Ln=Pr (4)] (HL=4-Hydroxy-6-methylnicotinic acid) were synthesized by the reaction of nitrate salts of LnIII and HL by hydrothermal method, which were characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectra, UV–vis spectra, TG analyses and X-ray powder diffraction (XRPD). The crystal structures of 1–4 consist of homodinuclear species, which bridged by two oxygen atoms from two L ligands. The photoluminescence properties of compounds 3 and 4 in the solid state at room temperature were investigated. The complex 3 is demonstrated orange–red luminescence, while the luminescence spectrum of complex 4 is typical for the praseodymium complexes.