Near-white Light Emission Research Articles

Combustion Synthesis and Influence of Dy3+ ions on Structural and Photometric Attributes of Olivine-type LiMgPO4 Nanophosphors for Illumination Applications.

The low-cost technique of combustion synthesis was used to synthesize the trivalent Dysprosium (Dy3+) doped olivine type Lithium Magnesium Phosphate (LiMgPO4). X-ray diffraction (XRD) analysis verified the orthorhombic phase, corresponding to the space group Pnma. The crystallite size of 50.83nm was calculated using Debye-Scherre formula. FESEM technique was used to study the morphology of the sample which depicts its porous nature. High-Resolution Transmission Electron Microscopy (HRTEM) analysis provided an average particle size measurement of 65 ± 2.04nm. The phosphor's photoluminescence (PL) excitation spectrum revealed distinct peaks in the ultraviolet (UV) and near-ultraviolet (near UV) regions, aligning with the characteristics of Dy3+ ions. Four emission peaks were observed in the PL spectra at various wavelengths: 4F9/2→6H15/2 (482nm), 4F9/2→6H13/2 (578nm), 4F9/2→6H11/2 (663nm) and 4F9/2→6H9/2 (700nm). Near-white light emission was observed at the Commission International de l'Eclairage (CIE) coordinates of Dy3+ activated LiMgPO4 [LMP] phosphor, which were (x = 0.41, y = 0.42) with color purity of 49.20%. The band gap of the prepared phosphor was calculated using diffuse reflectance spectra, yielding a value of 4.47 ± 0.02eV. The results indicated that the synthesized phosphor had potential for various illumination applications when combined with other phosphors under near-UV stimulation.

Nonlinear optical properties of zinc oxide thin films

This study reports the influence of deposition temperature (573 K-773 K) on the microstructural, linear and nonlinear optical properties of zinc oxide nano thin films synthesized using the chemical spray pyrolysis method. Synthesized films are polycrystalline, exhibiting a dominant (101) orientation, for which the crystallite size is found to increase with deposition temperature up to 723 K followed by a decrease. Concurrently, the deposit prepared at 723 K showed improved electrical properties, i.e. higher charge carrier concentration and mobility. Optical studies reveal increased transmittance in the visible region and a gradual increase of optical bandgap with deposition temperature. The photoluminescence studies show a near-white light emission for all thin films, however, the density of defect states was comparatively higher for thin films deposited at lower temperatures. A saturable absorption behaviour was observed due to the presence of defects. The thin films show a negative refractive index with self-defocusing phenomena. The total nonlinear susceptibility is found to decrease with increasing deposition temperature, and the solution-processed functional thin films thus have potential implications for nonlinear optical applications such as nonlinear optical switching, optical memory management, and saturable absorbers.

Comprehensive investigation of ternary dysprosium complexes for white light emission: Synthesis, spectroscopic and colorimetric analyses

Dysprosium (Dy3+) containing four single-molecule complexes with 1,3-diketone ligand, TFPB (4,4,4-trifluoro-1-phenyl-1,3-butadionate) along with neutral co-ligands of varying denticity were synthesized and two of them were explored as potential sources of near-white light emission. The choice of ligand as well as the coordination surroundings of Dy(III) ion significantly influence the blue (B: 4F9/2 → 6H15/2) and yellow (Y: 4F9/2 → 6H13/2) emissions. The inclusion of the auxiliary ligand such as topo in D1 leads to reduction in emission intensity compared to D2-D4 due to less effective sensitization. At room temperature, the CIE color coordinates for complexes D1 and D4 approach the coordinates of perfectly balanced and idealized white light (0.333, 0.333). Furthermore, Correlated Color Temperature (CCT) values for D1 and D4 characterize them as cold-white-light emitters, while the complexes D2 and D3 are categorized as a neutral-light emitter. In addition to their visible emissions, the semi-conducting properties and suitable deactivation lifetime corresponding to these synthesized complexes (D1-D4) have also been extensively studied and found potential applications in basic research, security printing, sensors, detectors and OLEDs.

Biocidal polymer derived near white light-emitting polymeric carbon particles for antibacterial and bioimaging applications.

A growing antimicrobial crisis has increased demand for antimicrobial materials. It has become increasingly popular to convert polymeric macromolecules into polymeric carbon particles (PCP) in order to achieve highly biocompatible materials with unique properties as a result of the ability to synthesize nanomaterials of the right size and add value to existing stable polymers. This work presents the tuning of PCP for antibacterial application by combining a biocidal polymer with one-pot solvothermal synthesis. PCP displayed broad-spectrum antibacterial activity via various mechanisms, including inhibition of bacterial cell walls, ROS generation, and antibiotic resistance. Furthermore, these biocidal PCP were observed to show excitation-independent near-white light emission which on the other hand is generally possible due to mixed sizes, doping, and surface effects. As opposed to the parent biocidal polymer, PCP added ROS-mediated bactericidal activity, increased cytocompatibility, and nanofibers with anti-adhesive effects and potential of imaging bacterial cells.

The preparation of CuO film under different annealing atmospheres and investigation of the excellent electrical and undoped tunable electroluminescence characteristics of Au/i-CuO/n-GaN LED

Copper oxide (CuO) film is widely used in optoelectronic devices. The CuO films were fabricated by radio frequency (RF) magnetron sputtering and then annealed at 700 °C under different atmospheres (unannealed, O2, N2, vacuum). The physical characteristics of the films were analyzed systematically. In addition, we prepared Au/i-CuO/n-GaN metal-insulator-semiconductor (MIS) structure devices using optimized conditions. The devices had excellent rectifying characteristics at different ambient temperatures and the turn-on voltage was about 1.7 V. The working mechanism of the diode was analyzed through electroluminescence (EL) spectra and band structure. The EL spectra observed at positive and negative bias were compounded by holes and electrons on the gold electrode passing through the insulating layer into the n-GaN side. The EL spectra exhibited that a dominant ultraviolet (UV) emission peak at ∼376 nm was observed under forward bias (FB), and a strong near-white light emission peak at ∼530 nm was observed under reverse bias (RB). The device exhibited unique electroluminescent spectra tunability varying with bias conditions. The chrominance coordinate of the device under RB was (0.3067,0.3604), and the color temperature was 6585 K. This study proved the application potential of i-CuO as an insulating layer in the preparation of new reference for MIS structured GaN-based tunable light-emitting diodes.

Mechanochromism, tunable pure organic room temperature phosphorescence, single-molecule near-white emission, digital encryption, and anti-counterfeiting

The development of tunable pure organic room temperature phosphorescence and single-molecule white light emitters still faces a great challenge due to ineffective intersystem crossing and sensitive triplet excitons. Here, two phenothiazine based luminogens named PtzIP and PtzIPCN were designed and synthesized. PtzIP exhibits mechanochromic activity with hypsochromic shift of 25 nm, tunable room temperature phosphorescence from 613 nm to 530 nm and 560 nm, then to 540 nm and 585 nm by crushing and grinding, and single-molecule near-white light emission with the (CIE: Commission International de I'Eclairage) CIE coordinates of (0.33, 0.25), but PtzIPCN shows mechanochromism and room temperature phosphorescence inertness in crystalline state. By choosing polymethyl methacrylate (PMMA) and 4-fluorobenzophenone(F-BP) as host materials, as well PtzIP and PtzIPCN as guest materials, a series of host-guest doping systems were constructed and optimized by tuning doping ratio. PtzIP/PMMA and PtzIPCN/PMMA doping systems present concentration dependent fluorescence and phosphorescence emission, and RTP lifetime and afterglow of PtzIPCN/PMMA are up to 185.31 ms of 2.0 s. Furthermore, the lifetime of F-BP/PtzIPCN increases to 216.63 ms at doping ratio of 1:1000 for F-BP and PtzIPCN. Based on different luminescent properties of PtzIP and PtzIPCN in the doping systems, a series of high-level digital encryption and anti-counterfeiting patterns were successfully constructed. More importantly, the underlying mechanism behind luminescent properties were explored in detail by photophysical testing, crystal analysis, and theoretical calculations.

Near-white light emission from single crystals of cationic dinuclear gold(I) complexes with bridged diphosphine ligands.

Three cationic dinuclear Au(I) complexes containing acetonitrile (AN) as an ancillary ligand were synthesized: [μ-LMe(AuAN)2]·2BF4 (1), [μ-LEt(AuAN)2]·2BF4 (2), and [μ-LiPr(AuAN)2]·2BF4 (3) (LMe = {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, LEt = {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and LiPr = {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene}). The unique structures of complexes 1-3 with two P-Au(I)-AN rods bridged by rigid diphosphine ligands were determined through X-ray analysis. The Au(I)-Au(I) distances observed for complexes 1-3 were as short as 2.9804-3.0457 Å, indicating an aurophilic interaction between two Au(I) atoms. Unlike complexes 2 and 3, complex 1 incorporated CH2Cl2 into the crystals as crystalline solvent molecules. Luminescence studies in the crystalline state revealed that complexes 1 and 2 mainly exhibited bluish-purple phosphorescence (PH) at 293 K: the former had a PH peak wavelength at 415 nm with the photoluminescence quantum yield ΦPL = 0.12, and the latter at 430 nm with ΦPL = 0.13. Meanwhile, complex 3 displayed near-white PH, that is dual PH with two PH bands centered at 425 and 580 nm with ΦPL = 0.44. The PH spectra and lifetimes of complexes 2 and 3 were measured in the temperature range of 77-293 K. The two PH bands observed for complex 3 were suggested to originate from the two emissive excited triplet states, which were in thermal equilibrium. From theoretical calculations, the dual PH observed for complex 3 is explained to occur from the two excited triplet states, T1H and T1L: the former exhibits a high-energy PH band (bluish-purple) and the latter exhibits a low-energy PH band (orange). The T1H state is considered 3ILCT with a structure similar to that of the S0-optimized structure. Conversely, the T1L state is assumed to be a 3MLCT with a T1-optimized structure, which has a short Au(I)-Au(I) bond and two bent rods (Au-AN). The thermal equilibrium between the two excited states is discussed based on computational calculations and photophysical data in the temperature range of 77-293 K. With regard to the crystal of complex 1, we were unable to precisely measure the temperature-dependent emission spectra and lifetimes, particularly at low temperatures, because the cooled crystals became irreversibly turbid over time.

Preparation and near-white luminescence properties of Bi3+ doped and Bi3+/Eu3+ co-doped germanate phosphor powder

The Bi3+ doped and the Bi3+/Eu3+ co-doped germanate phosphor powders were synthesized by high-temperature solid-state reaction and their luminescence properties were investigated. The XRD analysis results show that the crystalline phase of all samples is the tetragonal phase of BaGeO3. The Bi3+ doped BaGeO3 phosphors exhibited an intense near-white light emission and the wavelength of the luminescence center was located at 466 nm. The Bi3+ doped BaGeO3 phosphors can be efficiently excited by the incident light of 260–430 nm. The tunability of the emission color can be achieved by changing the Bi3+ ion doping concentration and the high-temperature sintering time. The Bi3+/Eu3+ co-doped BaGeO3 phosphors exhibited an intense red emission and the wavelength of the luminescence center was located from 466 to 705 nm. The Bi3+/ Eu3+ co-doped BaGeO3 phosphors can be efficiently excited by the incident light of 312–532 nm. The emission color tunability can be obtained by changing the Eu3+ ions doping concentration and the wavelength of excitation. The visible region emission characteristics of BaGeO3:Bi3+, Bi3+/Eu3+ indicate that it can potentially be used as a new efficient near-white luminescent material.

Improvement in white light emission of Dy3+ doped CaMoO4 via Zn2+ co-doping

The research in developing a single ingredient phosphor for white-light emission is progressively increasing. It is well known that the 4F9/2 → 6H13/2 (yellow) and 4F9/2 → 6H15/2 (blue) transitions of Dy3+ ions give near-white light emission. The white light emission of Dy3+ ions can be enhanced via improving the crystallinity of the host phosphor via co-doping of transition metal ions. In this paper, we report a significant improvement in the white light emission of Dy3+ doped CaMoO4 by co-doping Zn2+ ions. The x-ray diffraction pattern confirms the tetragonal phase of pure and doped CaMoO4 phosphor. The peak broadening and a red-shift in the absorption peak are observed by UV–vis absorption analysis of Zn2+/Dy3+ doped CaMoO4. From Photoluminescence studies, we have observed that in Dy3+ doped CaMoO4, the 4% Dy3+ doped CaMoO4 exhibits maximum emission. The Zn2+ ions are co-doped to further increase the luminescence intensity of CaMoO4:4%Dy3+ and the maximum luminescence is obtained for 0.25% Zn2+ concentration. Two intense emission peaks centered at 484 nm and 574 nm related to transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 of Dy3+ ion are observed for Dy3+ doped phosphor. The 4F9/2 → 6H13/2 transition is the forced electric dipole transition which is affected by its chemical environment. After Zn2+ co-doping, the 4F9/2 → 6H13/2 transition is affected due to a change in asymmetricity around the Dy3+ ions. The 0.25% co-doping of Zn2+ gives 34% enhancement in luminescence emission of 4% Dy3+ doped CaMoO4. As a result, the CIE coordinates of chromaticity diagram and the color purity of the 0.25% Zn2+ co-doped CaMoO4:4Dy3+ show improvement in the overall white light emission. We have shown that with Zn2+ co-doping, the non-radiative relaxations are reduced which results in improved white light emission of Dy3+ions.

Salts of Lanthanide(III) Hexafluoroacetylacetonates [Ln = Sm(III), Eu(III) and Tb(III)] with Dipyridylammonium cations: Synthesis, characterization, photophysical properties and OLED fabrication

A series of tetrakis lanthanide complexes with the general formula [Ln(hfaa)4]-(DpaH)+ [Ln = (Sm-1), (Eu-1) and (Tb-1)], hfaa = hexafluroacetylacetonate and Dpa −2,2′-dipyridylamine] has been synthesized by the reaction of LnCl3, hfaa and Dpa in the presence of ammonia solution (25%). The complexes have been characterized by analytical and spectroscopic methods. The solution molecular structure of the complexes was elucidated by one- and two-dimensional NMR spectroscopy which shows that the DpaH+ cation retains a close interaction with the lanthanide anion in solution. The crystal structure of Eu-1, determined by single crystal X-ray diffraction, confirms this intermolecular interaction in the solid-state through a N–H⋯O hydrogen bond of 2.187 Å. In the [Eu(hfaa)4]- anion the EuO8 coordination polyhedron has a distorted triangular dodecahedron geometry with approximate D2d-symmetry around the metal centre. Photophysical, thermal, and electroluminescent properties of the complexes have been investigated. The Sm-1 and Eu-1 complexes displayed efficient typical red emission with a sizeable photoluminescence quantum yield (PLQY) while Tb-1 displayed near-white light emission. The complexes have been used as dopants to fabricate single- and double-emitting layer (EML) OLEDs through the thermal evaporation method. At the optimum doping concentration, double-EML Eu-1 based device displayed orange electroluminescence (EL) with a brightness (B) of 417 cd/m2 and very low Vturn-on = 3.4 V. Interestingly, the Sm-1 based single-EML device exhibited pure red emission with the Commission internationale de l'éclairage [(CIE)x,y = 0.613, 0.321], which is rare. The Sm-1 based device performance [B = 145 cd/m2, current efficiency (ηc) = 0.35 cd/A, power efficiency (ηp) = 0.15 lm/W with an external quantum efficiency (EQE) = 0.3% and Vturn-on = 7.1 V] surpassed that of the only reported Sm-based single red-OLED (R-OLED).

A Luminescent Guest@MOF Nanoconfined Composite System for Solid-State Lighting.

A series of rhodamine B (RhB) encapsulated zeolitic imidazolate framework-8 (RhB@ZIF-8) composite nanomaterials with different concentrations of guest loadings have been synthesized and characterized in order to investigate their applicability to solid-state white-light-emitting diodes (WLEDs). The nanoconfinement of the rhodamine B dye (guest) in the sodalite cages of ZIF-8 (host) is supported by fluorescence spectroscopic and photodynamic lifetime data. The quantum yield (QY) of the luminescent RhB@ZIF-8 material approaches unity when the guest loading is controlled at a low level: 1 RhB guest per ~7250 cages. We show that the hybrid (luminescent guest) LG@MOF material, obtained by mechanically mixing a suitably high-QY RhB@ZIF-8 red emitter with a green-emitting fluorescein@ZIF-8 “phosphor” with a comparably high QY, could yield a stable, intensity tunable, near-white light emission under specific test conditions described. Our results demonstrate a novel LG@MOF composite system exhibiting a good combination of photophysical properties and photostability, for potential applications in WLEDs, photoswitches, bioimaging and fluorescent sensors.

Near white light and near-infrared luminescence in perovskite Ga:LaCrO3

We report the realization of near-white light emission (near-WLE) and the selective tuning to the near-infrared (NIR) luminescence from Ga substituted lanthanum chromite perovskite with electron-beam excitation for the first time. The near-WLE in Cathodoluminescence (CL), arises from the combination of 4T1(F)→4A2(blue), 4T1(P)→4A2(green) and 4T2→4A2(red) spin allowed transitions and 2E→4A2 spin forbidden transitions from the Cr3+ ion. The spin allowed transitions from the Cr3+ ions is rare, however can be accomplished by adjusting the Cr3+/Ga3+ ion concentration in the host lattice. The NIR emission originates from the selective 2E→4A2 transition, which increases with the increasing concentration of Ga3+ions. Moreover, the Density Functional Theory (DFT) calculations point out the presence of extra electronic states in the NIR region with Ga substitution, which elucidates the observation of NIR emission in Ga substituted samples.

Fabrication, structural properties, and tunable light emission of Sm3+, Tb3+ co-doped SrSnO3 perovskite nanoparticles

• SnSrO 3 nanoparticles prepared by the sonochemical method and solid-state reactions. • Study of rare-earth doping effects on the structure and photoluminescent properties. • XRD results confirmed the orthorhombic phase of SrSnO 3 . • Near-white light emission from Sm 3+ , Tb 3+ co-doped SnSrO 3 perovskites. Sm 3+ , Tb 3+ co-doped SrSnO 3 perovskites were successfully prepared by the sonochemical method and solid-state reactions. X-ray diffraction showed well-defined peak characteristics of the SrSnO 3 orthorhombic phase, while SEM analysis revealed the formation of rod-like structures composed of particles with a mean size of 100 nm. Under the excitation of 325 nm, the photoluminescence spectra exhibited a broad emission band (380–500 nm) related to intrinsic defects and peaks attributed to characteristic electronic transitions of Tb 3+ ( 5 D 4 → 7 F 6 , 489 nm, 5 D 4 → 7 F 5 , 542 nm) and Sm 3+ ( 4 G 5/2 → 6 H 5/2 , 570 nm, 4 G 5/2 → 6 H 7/2 , 605 nm) ions. Through co-doping with these rare earths, the emission from perovskite can be tuned. The obtained chromaticity coordinates are (0.33, 0.31) and (0.34, 0.32) for 4Sm2Tb and 4Sm4Tb perovskites, respectively. It indicates the promising application potential of Sm 3+ , Tb 3+ co-doped SrSnO 3 as single-phase perovskite for UV excited white light-diodes.

Near-white light emission from samarium and dysprosium combined doped calcium zirconate spin-coated thick film

This study investigates the preparation and characterization of CaZr0.9Sm0.025Dy0.075O3-coated film system. The powder used for coating was prepared by solid-state ceramic route synthesis and spin coating technique was used to prepare the film of the CaZr0.9Sm0.025Dy0.075O3 system. Structural studies were carried out using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The XRD peaks of spin-coated system were indexed for an orthorhombic (Pnma) perovskite structure of CaZrO3. The film when excited at 350 nm yield blue-green emission at 482 and 571 nm, which corresponds to the transition from 4F9/2 to 6H15/2 and 6H13/2 levels of Dy3+ ion, respectively, and orange-red emission at 603 and 657 nm corresponds to the transition from 4G5/2 to 6H7/2 and 6H11/2 transitions of Sm3+ ions, respectively. CIE coordinates of the film show near-white light emission from the system.

Near-White Light and Near-Infrared Luminescence in Perovskite Ga:LaCrO <sub>3</sub>

We report the realization of near-white light emission (near-WLE) and the selective tuning to the near-infrared (NIR) luminescence from Ga substituted lanthanum chromite perovskite with electron-beam excitation. The Ga3+ acts as an electron donor in the LaCrO3 system and the emission intensity increases with Ga substitution. The near-WLE in CL, arises from the combination of 4T1(F)→4A2 (blue), 4T1(P)→4A2 (green) and 4T2→4A2 (red) spin allowed transitions and 2E→4A2 spin forbidden transitions from the Cr3+ ion. The spin allowed transitions from the Cr3+ ions are not common, however can be accomplished by adjusting the Cr3+/Ga3+ ion concentration in the host lattice. The NIR emission originates from the selective 2E→4A2 transition, which dominates with the increasing concentration of Ga3+ ions. The Density Functional Theory (DFT) calculations point out the presence of extra electronic states with Ga substitution, which validates the observation of NIR emission in Ga substituted samples.

Two Series of Lanthanide Coordinated Compounds and Novel Three-Component Near-White Light Emission

Two series of coordinated compounds [Ln2(TZI)2(H2O)10]n·4H2O (Ln = Er (1), Yb (2), Dy(3), (H3TZI = 5-(1H-tetrazol-5-yl)isophthalic acid) and [Ln(TZI)(H2O)4]n·3H2O (Ln = Ho (4), Eu(5) and Sm (6)) were hydrothermally synthesized by different reaction conditions. Compounds 1–3 are isostructural and show a dinuclear motif, which further develop into a 3D H-bonding supra-molecular structure, and compounds 4–6 are also isostructural and have a 1D ladder-typed chain, which further interlinked into a 3D supra-molecular architecture by H-bonding interactions. Furthermore, the fluorescent properties of compounds 3–6 exhibit intense emissions corresponding to blue-violet (3 and 4), red (5) and orange red (6), respectively. By way of the careful regulation of the relative intensity of the blue-violet (4), green (Tb) and orange red (6) emissions, a novel three-component white-light emission (Ho–Sm–Tb) has been realized.

Regioisomeric BODIPY Benzodithiophene Dyads and Triads with Tunable Red Emission as Ratiometric Temperature and Viscosity Sensors.

Regioisomeric acceptor-donor (AD) molecular rotors (p-AD, m-AD and m-ADA) were synthesized and characterized, wherein dyads p-AD and m-AD, and triad m-ADA contained 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and benzodithiophene (BDT) as electron-acceptor and electron-donor, respectively. In all the compounds, the donor and acceptor moieties are electronically decoupled by a phenyl spacer, either through a para coupling or through a meta coupling. The dyad counterparts p-AD and m-AD showed distinct photophysical characteristics in which dyad p-AD showed TICT band at ca. 654 nm characterized by a Stokes shift of ca. 150 nm and prominent solvatochromism. However, meta regioisomeric triad m-ADA showed well-defined aggregation in solution. Notably, because of the temperature-tunable and solvent-viscosity-dependent emission, efficient ratiometric temperature sensing with positive and negative temperature coefficients and viscosity sensing was observed for all compounds. Interestingly, the fluorescence of dyad m-AD (in 10/90 v/v THF/water) revealed a near-white light emission with CIE chromaticity coordinates (x, y) of (0.32, 0.29). Furthermore, the fluorescence emission of p-AD in THF at 0 °C also showed a near-white light emission with chromaticity coordinates (x, y) of (0.34, 0.27). Such multifunctional rotors with readily tunable emission in the red region and prominent temperature- and viscosity-sensing abilities are promising for sensing and bioimaging applications.

Lead–Organic Frameworks Containing Trimesic Acid: Facile Dissolution–Crystallization and Near-White Light Emission

Three new, closely similar Pb-based organic frameworks synthesized using a simple and optimized dissolution–crystallization method with benzene-1,3,5-tricarboxylic acid (H3BTC) are reported along with their structural characterizations and photoluminescent properties. Compound 1, Pb(HBTC)(1,4-dioxane)0.5, crystallizes in the C2/c space group (a = 17.239(2) A, b = 7.0225(8) A, c = 19.911(2) A, β = 104.735(10)°); compound 2, Pb2(HBTC)2(H2O)5, crystallizes in the P1 space group (a = 7.3989(4) A, b = 8.2196(4) A, c = 10.1437(5) A, α = 94.336(4)°, β = 104.943(4)°, γ = 108.270(3)°); and compound 3, Pb(HBTC)(DMF), crystallizes in the P21/n space group (a = 10.5004(3) A, b = 7.1398(3) A, c = 17.1285(5) A, β = 102.160(2)°). All three compounds are built from a slightly different one-dimensional (1D) structure interconnected into three-dimensional metal–organic frameworks by HBTC– ligands forming different pore sizes, in which the 1D moieties and pore sizes are governed by the solvent used during synthesis. Among ...

Structure characterization and photoluminescence of sol-gel synthesized Ag-Dy-codoped silica phosphor

Bulk samples of single Ag-, Dy-doped and Ag-Dy-codoped silica matrices were synthesized using the sol-gel processing. These matrices were characterized using X-ray diffractometry, ultraviolet-visible-near infrared (UV-VIS-NIR), Fourier transform infrared, photoluminescence (PL) excitation and emission spectroscopic techniques. High resolution transmission electron microscope confirmed the presence of fine spherical Ag nanoparticles (NPs), whose average size is approximately 10–15 nm, in the Ag-doped and Ag-Dy-codoped silica matrices. UV-VIS-NIR spectra revealed absorption peaks due to Dy3+ active centers in addition to the surface plasmon resonance bands of Ag NPs centered at 410 and 452 nm in these matrices, respectively. UV-excited PL of the materials was studied and compared. Near-white light emission, which was assessed by the calculated CIE chromaticity coordinates, could be observed under UV excitation at 365 nm in the Ag-Dy-codoped silica matrix. This white light was realized by appropriate combination of prominent yellow and blue emissions. Electron spin resonance spectra revealed paramagnetic spin states for Ag which can be attributed to the quantum size effect of very fine Ag NPs dispersed in the silica network. The obtained results indicate that the Ag-Dy-codoped silica phosphor could be a promising candidate for application as white light emitting phosphor for UV LED chips.

Near-White Light Emission from Lead(II) Metal-Organic Frameworks.

Reaction of bpy (bpy = 4,4'-bipyridine) with Pb(OAc)2·3H2O in DMF (DMF = dimethylformamide) afforded a metal-organic framework (MOF), [Pb2(μ-bpy)(μ-O2CCH3)2(μ-O2CCH3)2]·H2O (1). Reaction of bpy with Pb(O2CCF3)2 in a methanol and chloroform mixture furnished another MOF, [Pb(μ-bpy)(μ-O2CCF3)2]·1/2CHCl3 (2). However, the reaction of bpy with Pb(OAc)2·3H2O in the presence of trifluoroacetic acid in a similar reaction condition yielded a hydrogen-bonded zwitter-ionic complex of Pb(II), [Pb(bpy-H)2(O2CCF3)4] (3). All compounds have been characterized by single crystal X-ray crystallography, FT-IR, and 1H NMR spectroscopies. Compound 1 forms four heptacoordinated Pb(II) joined by (OCCH3)-O- linkages, resulting in a 3D noninterpenetrated MOF net with a four-connected uninodal sra (SrAl2) topology. However, in 2, tetra-connected Pb4(O2CCF3)8 cluster units are linked further through eight bpy ligands to furnish a doubly interpenetrated MOF with a new topology but having the very similar connectivity of 1, whereas 3 forms a zigzag hydrogen-bonded chain structure. The variation of carboxylate anions, pH of the reaction medium, and the ratio of the reactants profoundly affected the final topological structure of the compounds synthesized. The solid-state photoluminescence of 1-3 was investigated at room temperature. Interestingly 1, 2, and 3 achieved close to white light emission when excited at 329, 376, and 330 nm, respectively. The systematic understanding of the photophysical properties of analogous Pb-based compounds may open new perspectives for developing single-phase white-light-emitting materials using Pb(II) based MOFs.