Synthesis and luminescence properties of Ca8NaGd(PO4)6F2: Eu2+, Mn2+ for white LEDs

A series of luminescent emission-tunable phosphors Ca₈NaGd(PO₄)₆F₂: Eu²⁺, Mn²⁺ have been prepared by a combustion-assisted synthesis method. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca₈NaGd(PO₄)₆F₂. The photoluminescence (PL) properties of Eu²⁺ and Mn²⁺-codoped Ca₈NaGd(PO₄)₆F₂ phosphors were also investigated. The phosphors can be efficiently excited by ultraviolet (UV) light and show a blue emission band at about 450 nm and a yellow emission band at about 574 nm, which originated from the Eu²⁺ ions and the Mn²⁺ ions, respectively. The efficient energy transfer from the Eu²⁺ ions to the Mn²⁺ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. A color-tunable emission in Ca₈NaGd(PO₄)₆F₂ phosphors can be realized by Eu²⁺ → Mn²⁺ energy transfer. Our results indicate that the developed phosphor may be used as a potential white emitting phosphor for UV based white LEDs.     

Enhancement of red emission intensity of Ca9Y(VO4)7:Eu phosphor via Bi co-doping for the application to white LEDs

The present investigation aims at the luminescence properties of Ca₉Y(VO₄)₇:Eu³⁺, Bi³⁺ red phosphor materials. The red emission at 613 nm originating from ⁵D₀–⁷F₂ transition of Eu³⁺ in Ca₉Y(VO₄)₇ is enhanced strongly with Bi³⁺–V⁵⁺ couple as the sensitizer, under excitation either into the ⁵L₆ state or the ⁵D₂ state. The energy transfer from Bi³⁺–V⁵⁺ to Eu³⁺ is discussed. For a fixed Eu³⁺ concentration, there is an optimal Bi³⁺ concentration with 15 mol%, at which the maximum luminescence intensity of Eu³⁺ is achieved. The red emission of Ca₉Y(VO₄)₇:0.8Eu³⁺, 0.15Bi³⁺ (under 395 nm and 465 nm excitations) is stronger than that of commercial Y₂O₃:Eu³⁺ phosphor (under 395 nm and 467 nm excitations). Based on the ratios of the red emission at 613 nm to orange one at 592 nm, it is considered that the symmetry of Eu³⁺ site decreases with doping of Bi³⁺, leading to more opposite parity components. Lifetime and diffuse reflection spectra measurements indicate that the red emission enhancement is due to the enhanced transition probabilities from the ground state to ⁵L₆ and ⁵D₂ states of Eu³⁺ in the distorted crystal field. Therefore the present material is a promising red-emitting phosphor for white-light diodes with near-ultraviolet/blue GaN-based chips.     

Optoelectronic properties of a perylene substituted (cholesteryl)benzoateethynylene co-polymer

A perylene cholesteryl-benzoateethynylene co-polymer was synthesized by Sonogashira reaction and characterized by NMR, UV–Vis, static and dynamic fluorescence spectroscopy and cyclic voltammetry. The optical and electrochemical properties in solution are consistent with photoinduced energy transfer from the electron donor conjugated backbone to the electron acceptor perylene substituent. Photovoltaic properties are indeed found, even if the performance of the solar cells is quite low due to the formation of aggregates. The incorporation of (6,6)-phenyl C61–butyric acid methyl ester (PCBM), however, increases by an order of magnitude the efficiency of the prototype (from 10⁻⁴ to 10⁻³%) due to both better phase mixing and improved electrical continuity as supported by Atomic Force Microscopy (AFM) and Electrical Force Microscopy (EFM) studies.     

A new red-emitting Ce, Mn-doped barium lithium silicate phosphor for NUV LED application

A series of new red-emitting Ce³⁺, Mn²⁺-doped barium lithium silicate phosphors, with general formula Ba₂Li₂Si₂O₇: Ce³⁺, Mn²⁺, were synthesized by solid-state reactions. The Mn²⁺ in this system can be effectively excited in a wide UV region especially in the NUV range, and has broad red emission after NUV excitation through Ce³⁺-Mn²⁺ energy transfer, as well as excellent thermal stability. The blue-shift behavior of Mn²⁺ emission with increasing temperature can be described in terms of the phonon-electron interaction. The promising luminescence properties make it a red candidate for application in NUV chip pumped LED.     

Structure, thermal properties and mechanical properties of sPS-based nanocomposites with and without styrenic elastomer inclusions

Syndiotactic polystyrene (sPS)-based nanocomposites with and without toughener inclusions were successfully prepared. One organo-montmorillonite (20A) and two styrenic elastomers (SBS and SEBS) served as the reinforcing filler and as tougheners, respectively. XRD and TEM results confirmed the achievement of intercalated and partially exfoliated sPS/20A nanocomposites. The presence of SBS or SEBS slightly depressed the dispersibility of 20A. DSC results indicated that 20A inhibited the crystallization of sPS. The presence of SBS or SEBS further retarded the crystallization of sPS; this effect was more apparent with SEBS. The presences of 20A and SBS/SEBS facilitated the formation of α-form sPS crystals. The thermal stability enhancement of sPS/20A nanocomposites was confirmed, and was further improved with the inclusion of SBS or SEBS. The stiffness of sPS increased with the sole addition of 20A. The addition of SBS or SEBS greatly increased the impact strength of the composites, especially with the addition of SEBS. The achievement of toughened sPS-based nanocomposites was confirmed.     

Luminescence properties and energy transfer of a novel bluish-green tunable NaBa4(BO3)3:Ce3+, Tb3+ phosphor

A series of single-phased emission tunable NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors were synthesized by solid-state reaction. The crystal structure, photoluminescence properties, concentration quenching and energy transfer of NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ were systematically investigated. The wavelength-tunable bluish-green light can be realized by coupling the emission bands centered at 425 and 543 nm ascribed to the contribution from Ce³⁺ and Tb³⁺, respectively. The energy transfer from Ce³⁺ to Tb³⁺ in NaBa₄(BO₃)₃ host was studied and demonstrated to be a resonant type via a dipole–dipole interaction mechanism. The energy transfer efficiency (Ce³⁺ → Tb³⁺) obtained by decay curves was consistent with the result calculated by the emission intensity, which gradually increased from 0% to 84.5% by increasing the Tb³⁺ doping content from 0 to 0.45. The results indicate that the NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang.     

New fluorinated poly(ether sulfone imide)s with high thermal stability and low dielectric constant

A new aromatic diamine monomer with four pendant trifluoromethyl groups, 2,2′-bis{3-[3,5-di(trifluoromethyl)phenyl]-4-[4-amino-phenoxy]phenyl}sulfone (3), was successfully synthesized through free-radical substitution, Suzuki coupling and nucleophilic substitution reactions using bis(4-fluorophenyl)sulfone and N-bromosuccinimide as starting materials. Then it was employed to prepare a series of fluorinated poly(ether sulfone imide)s (PESIs 5a–c) with various commercial aromatic dianhydrides via a one-step high-temperature polycondensation. These polymers could be easily dissolved in some strong polar organic solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, chloroform, dichloromethane and tetrahydrofuran at room temperature. Flexible and transparent films can be obtained easily by solution casting. They had high thermal stability and didn't show significant weight loss up to temperature of approximately 530 °C in nitrogen and air atmospheres. They also revealed low dielectric constants with the values in the range of 2.74–2.90 at 1 MHz measured for their capacitance.     

Novel blue-emitting Sr3Ga2O5Cl2:Eu phosphor for UV-pumped white LEDs

A novel blue-emitting Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor has been synthesized by a two-step solid-state reaction. The luminescence properties have been investigated by photoluminescence (PL) spectra, and temperature-dependent PL spectra. It shows an efficient broad absorption band around 400 nm, which matches well with the commercial near-ultraviolet light-emitting chips, and an efficient blue emission. It shows a higher thermal quenching temperature than that of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor. Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor is a promising blue-emitting component for UV chip excited white light-emitting-diodes.     

Synthesis and calcination temperature dependent photoluminescence properties of novel bromosilicate phosphors

Novel Eu²⁺-doped bromosilicate phosphors, (CaO-CaBr₂-SiO₂):0.03Eu²⁺, were prepared by the traditional solid-state method under a different calcination temperature. The as-prepared (CaO-CaBr₂-SiO₂):0.03Eu²⁺ phosphors obtained under various reaction temperatures all indicated a broad excitation in the near ultraviolet region (350-450 nm). The phosphor system exhibits bluish-green light with a peak wavelength at 498 nm when the calcination temperature is below 800 °C, while it shows a strong blue emission light with a peak wavelength at 474 nm as the calcination temperature is above 800 °C, and it also gives an interesting greenish-yellow long-lasting phosphorescence with a peak wavelength at 540 nm in the dark.     

New class of 2,5-di(2-thienyl)pyrrole compounds and novel optical properties of its conducting polymer

New type 2,5-di(2-thienyl)pyrrole derivative namely 4-amino-N-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzamide (HKCN) have been synthesized via reaction of 1,4-di(2-thienyl)-1,4-butanedione and p-aminobenzoyl hydrazide. Using hydrazide instead of amine not only increases product yield but also improves properties of the corresponding polymer. Spectroelectrochemical investigations revealed that P(HKCN) is more stable and it has lowest band gap and better long-term stability compared with other SNS derivatives. Chronoamperometry experiment showed that P(HKCN) polymer film has excellent redox stability, moderate switching time and high optical contrast. Electrochemical copolymerization of HKCN with EDOT was performed in DCM/TBP₆ solution for different feed ratios of monomers. We describe a proposal to determination copolymer composition by means of the optical properties of conducting copolymers.     

Preparation and optical properties of silica gels doped with a new Eu(III) complex

The preparation and incorporation in silica gels of a novel europium complex, [Eu(ntac)₃][pphendcn] containing 4,4,4-trifluoro-1-(naphthalene-2-yl) butan-1,3-dione (Hntac) and pyrazino[2,3-f][1,10-phenathroline-2,3-dicarbonitrile (pphendcn) is demonstrated. An effective energy transfer from the organic ligands to the Eu(III) ions leads to a strong f-f luminescence even at low activator concentrations, n_Eu/n_Si ≈ 1 × 10⁻⁵. The new amorphous materials are characterized by UV/Vis reflectance and transmission spectroscopy, luminescence/excitation spectroscopy, X-ray diffraction, elemental analysis, IR spectroscopy, DTA/TG and NMR. The optical properties of gels with a different Eu(III) doping are discussed. The stability of the europium complex in the silica matrix during time (up to 4 months) and after heating is discussed. The Eu(III) spectra-structure correlation is used to characterize the site symmetry of the activator.     

Visible quantum cutting via downconversion in a novel green-emitting K2Gd(WO4)(PO4):Tb phosphor

A novel phosphor K₂Gd(WO₄)(PO₄):Tb was prepared via a solid-state reaction. The crystal structure of K₂Gd(WO₄)(PO₄) as a new host matrix for luminescence was defined to be the orthorhombic system with space group Ibca (73). Visible quantum cutting under Tb³⁺ 4f⁸–4f⁷5d¹ excitation and host excitation in K₂Gd(WO₄)(PO₄):Tb³⁺ via a downconversion was identified. In order to rationalize the quantum cutting effect, the proper mechanism was proposed. According to calculations, the quantum efficiency was up to 183.2% and 176.4% under excitation at 235 nm and 150 nm, respectively. When compared with Zn₂SiO₄:Mn²⁺ (P1-G1S), KGWP:0.5Tb³⁺ is slightly less bright over 450–650 nm but has a shorter decay time.     

Synthesis and characterization of a novel photocrosslinkable fluorinated poly(arylene ether) for optical waveguide

To improve its chemical resistance and mechanical stability, a novel fluorinated poly(arylene ether) bearing a photocrosslinkable chalcone group in the main chain was successfully synthesized by means of polycondensation between 4,4′-dihydroxychalcone and decafluorobiphenyl in N,N-dimethylacetamide in the presence of the excess anhydrous potassium carbonate. The structure of polymer was characterized by ¹H NMR and ¹⁹F NMR spectroscopies. The resulting polymer shows excellent solubility in common organic solvents, high glass transition temperature and good thermal stability. Crosslinking of the resulted polymer has been demonstrated by UV irradiation. Near-IR spectra of polymer film before and after UV irradiation show no absorption at the telecommunication wavelengths of 1310 and 1550 nm, demonstrating that the resulting polymer is good candidate material for optical waveguide application.     

Intense red-emitting phosphors for LED solid-state lighting

The phosphors Gd_2−xEu_x(MoO₄)₃ (x = 0.20, 0.40, 0.60, 0.80, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0), Gd_0.8−xY_xEu_1.2(MoO₄)₃ (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8) and Gd_0.2Y_0.6−xEu_1.2Sm_x(MoO₄)₃ (x = 0.02, 0.024, 0.028, 0.032, 0.036, 0.04) were prepared by solid-state reaction technique at 950 °C. The presence of the Y³⁺ and Sm³⁺ ions strengthen and broaden the absorption of the phosphors at ∼400 nm. The intense red-emitting phosphor Gd_0.2Y_0.572Eu_1.2Sm_0.028(MoO₄)₃ with orthorhombic structure was obtained. Both Eu³⁺ and Sm³⁺ f-f transition absorptions are observed in the excitation spectra, the main emission line is at 616 nm (⁵D₀ → ⁷F₂ transition of Eu³⁺) and the chromaticity coordinates (x = 0.66, y = 0.33) is very close to the NTSC standard values (x = 0.67, y = 0.33). It is considered to be an efficient red-emitting phosphor for GaN-based light emitting diode (LED).     

Optical and thermal properties of a cyanine dye medium for next-generation DVD-Rs

Abstract

A dye material for the next generation of digital versatile disk-recordables (high-definition DVD-Rs) is required to absorb at a shorter wavelength compared with conventional dye media. For this purpose, l,3,3,l’,3’,3’-hexamethyl-2,2’-indocyanine perchlorate (D-l), whose maximum absorption band exists at 434.5 nm, was selected. Reflection and transmission spectra of D-l thin films were studied. Oscillation of the reflectance and transmittance around 480 nm with film thickness can be seen. The calculated complex refractive index is 2.15 + i0.085. Its decomposition temperature was measured to be around 282°C and no melting point was observed in its differential scanning calorimeter (DSC) curve. The optical and thermal properties of D-l and longer wavelength-absorbing indocyanine dyes were also compared.     

A potential Eu-activated Ca10K(PO4)7 red phosphor for white light-emitting diodes

New red Ca₁₀K(PO₄)₇:Eu³⁺, K⁺ phosphors were synthesized by solid state reaction and their photoluminescence properties as well as those by co-doping Mo⁶⁺ under near ultraviolet excitation were investigated. From the excitation spectra monitored at 611 nm, it can be seen that the strongest excitation peak is situated at 393 nm, well matching with the emission wavelength of near-ultraviolet chips for white LEDs. Upon 393 nm excitation, the brightness of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ with the optimal Eu³⁺-doping concentration is about 2.3 times stronger than that of the commercial red Y₂O₃:Eu³⁺ phosphor. The introducing of Mo⁶⁺, which results in a possible variety for the excited energy level of the host, can enhance the brightness of Eu³⁺ to be maximized by about 15%. The CIE chromaticity coordinates of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ are calculated to (0.654, 0.345), which are close to the (0.67, 0.33) standard of the National Television System Committee. All the above results indicate Eu³⁺-activated Ca₁₀K(PO₄)₇ is a potential candidate for white LEDs.     

Influence of hydrothermally-synthesized LaPO4:Tb nanorods on the physical and physico-chemical properties of photo-structured acrylate material

This paper presents some encouraging features on Tb³⁺-doped LaPO₄, used for the first time as nanoparticles (NPs) for photo-structured composite material. First, LaPO₄:Tb³⁺ nanorods are hydrothermally synthesized. TEM analysis point out that their size distribution and their morphology are well defined. Then, a small amount of NPs (2 or 3.9 wt%) is dispersed in acrylate monomers mixture and the photo-patterning is performed by using holography, a technique among the others. It is interesting to note that even if the loading of the NPs is weak, these last ones significantly influence the physical properties of the gratings. Indeed, the observed increase in the refractive index modulation depth is ascribed to both phenomena: the sequestration of LaPO₄:Tb³⁺ nanorods within the periodic structure and the change in the kinetics of photopolymerization. The localization of NPs in the non-illuminated zones, evidenced by fluorescence microscopy, is favoured by the decrease in the rate of polymerization, revealed by infrared spectroscopy.     

Generation of white light from oxy-fluoride nano-glass doped with Ho, Tm and Yb

Thermal treatment at 480 °C for 40 h resulted in the precipitation of β-PbF₂ nano-crystals inside the oxy-fluoride glasses co-doped with Ho³⁺, Tm³⁺ and Yb³⁺. Generation of white light was achieved through the simultaneous blue, green and red up-converted emissions by pumping at 900 nm. Simulation of sunlight was most successfully achieved with pump power of ∼ 150 mW.     

Indium(III) and Gallium(III) phthalocyanines-based nanohybrid materials for optical limiting

Linear and nonlinear optical properties of a phthalocyanine (Pc)-based nanohybrid material PCIGS [Cu₂(tBu₄PcGa)(tBu₄PcIn)S₂TPP₂] are described. The overall aggregation of phthalocyanines in poly(methylmethacrylate) (PMMA) films was evident, which is indicated by the broadening of linear spectra in the Q-band region and the shift of wavelength. Upon excitation with nanosecond laser pulse at 355 nm, the transient absorption band appeared at about 500 nm is attributed to the triplet–triplet absorption of the Pcs. For PCIGS and its starting materials tBu₄PcGaCl and tBu₄PcInCl, all Z-scans exhibit a decrease in transmittance about the focus typical of an induced positive nonlinear absorption of incident light. The absorption mechanism is due to population of excited states through a multi-step nonlinear absorption. When these Pc compounds were embedded into a commercially available polymer PMMA, all the Pc/PMMA composites display much larger nonlinear absorption coefficient and lower saturable fluence for optical limiting when compared to the same Pc molecules in solution. However, in contrast to tBu₄PcGaCl and tBu₄PcInCl, PCIGS displayed decreased optical limiting response, possibly due to competing electron accepting processes in the In and Ga metals, and the highly ordered structure of the PCIGS complex itself.     

Synthesis and efficient blue-emitting of Eu2+-activated borate fluoride BaAlBO3F2

Eu²⁺-doped borate fluoride BaAlBO₃F₂ was synthesized by the conventional high temperature solid state reaction. The crystal phase formations were confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence (PL) excitation and emission spectra, and the decay curves were investigated. Eu²⁺-doped BaAlBO₃F₂ phosphor can be efficiently excited by near-UV light and presents narrow blue luminescence band centered at 450 nm. The maximum absolute quantum efficiency (QE) of BaAlBO₃F₂:0.05Eu²⁺ phosphor was measured to be 76% excited at 398 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability with high thermal activation-energy on temperature quenching effects because of the rigid crystal lattices.