Er–Pr doped tellurite glass nanocomposites for white light emitting diodes

In this paper, optical glass nanocomposites (nanoparticles sizes up to 100 nm) with composition TeO₂–WO₃–PbO–xEr₂O₃–yPr₆O₁₁ (x = 0.30 mol%, y = 0.70 mol%) embedded into polymer matrices was reported. The two types of polymers chosen for present study were: photopolymer oligoetheracryalte (OEA) and polymethylmethacrylate (PMMA), respectively. The incorporation of the titled nanoparticles into the polymer matrices is analyzed optically. The fluorescence spectra of the nanocomposites were compared with the fluorescence spectra of bulk glasses. Based on the comparison of Er^3 + and Pr^3 + ions' energy level schemes, possible energy transfer processes were identified. The prepared glasses are promising candidates for the white light emitting diodes applications.     

Ultraviolet spectroscopy of Pr+3 and its use in making ultraviolet filters

Sputtered deposited thin films of AlN:Pr and GaN:Pr emit in ultraviolet–visible and visible regions of the spectrum, respectively, under electron excitation in cathodoluminescence apparatus. The goal is to study the ultraviolet emission from Pr⁺³ when doped in nitride semiconductor hosts. Luminescence peaks at a wavelength of 295 nm (4.2 eV), 335 nm (3.7 eV) and 385 nm (3.24 eV) are observed as a result from ¹S₀ → ¹G₄, ¹S₀ → ¹D₂ and ¹S₀ → ¹I₆ transitions, respectively. However the ¹S₀ → ¹G₄ and ¹S₀ → ¹D₂ transitions are not observed when Pr⁺³ is doped in GaN host. The bandgap of GaN absorbs the ultraviolet radiation emitted from Pr⁺³ and hence GaN can be used as ultraviolet filter for radiation shielding and protection purposes. AlN is transparent to ultraviolet due to its wide bandgap of 6.2 eV.     

Synthesis and characterization of sulfur-containing polyacetylene derivative: Synthesis of poly(phenyl propargyl sulfide) and its electro-optical properties

Sulfur-containing conjugated polymer was synthesized by the polymerization of phenyl propargyl sulfide by transition metal catalysts such as PdCl₂, RuCl₃, (NBD)PdCl₂, WCl₆, and MoCl₅. The polymerization proceeded well in homogeneous manner to give a moderate yield of polymer. The chemical structure of poly(phenyl propargyl sulfide) was characterized by NMR (¹H–, ¹³C–), IR, and UV–visible spectroscopy, and elemental analysis to have the conjugated polymer backbone with the designed moieties. The FT-IR spectra of the polymer did not show the acetylenic CC bond stretching (2119 cm⁻¹) and acetylenic C–H bond stretching (3293 cm⁻¹) frequencies of the monomer. The thin polymer film exhibited reversible electrochemical behaviors between the doping and undoping peaks. Poly(phenyl propargyl sulfide) showed the characteristic UV–visible absorption band at 360 nm and blue PL spectrum at 460 nm, corresponding to the photon energy of 2.70 eV. The energy band gap of poly(PPS) was estimated to be 2.77 eV from the analysis of the absorption edge.     

100 MeV Si8+ ion induced luminescence and thermoluminescence of nanocrystalline Mg2SiO4:Eu3+

Nanoparticles of Mg₂SiO₄:Eu³⁺ have been prepared by the solution combustion technique and the grain size estimated by PXRD is found to be in the range 40–50 nm. Ionoluminescence (IL) studies of Mg₂SiO₄:Eu³⁺ pellets bombarded with 100 MeV Si⁸⁺ ions with fluences in the range 1.124–22.48×10¹² ions cm^?2 are carried out at IUAC, New Delhi, India. Five prominent IL bands with peaks at 580 nm, 590 nm, 612 nm, 655 nm and 705 nm are recorded. These characteristic emissions are attributed to the luminescence centers activated by Eu³⁺ cations. It is found that IL intensity decreases rapidly in the beginning. Later on, the intensity decreases slowly with further increase of ion fluence. The reduction in the ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si–O (ν₃) and Si–O (2ν₃) bonds present on the surface of the sample. The red emission with peak at 612 nm is due to characteristic emission of ⁵D₀→⁷F₂ of the Eu³⁺ cations. Thermoluminescence (TL) studies of Mg₂SiO₄:Eu³⁺ pellets bombarded with 100 MeV Si⁸⁺ cations with fluences in the range 5×10¹¹ ions cm^?2 to 5×10¹³ ions cm^?2 are made at RT. Two prominent and well resolved TL glows with peaks at ～220 °C and ～370 °C are observed. It is observed that TL intensity increases with increase of ion fluence. This might be due to creation of new traps during swift heavy ion irradiation.     

Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains

A polyphosphazene [NP(NHR)₂]_n with oligo[propylene oxide] side chains − R = –[CH(CH₃)–CH₂O]_m–CH₃ (m = 6 – 10) was synthesized by living cationic polymerisation and polymer-analogue substitution of chlorine from the intermediate precursor [NPCl₂]_n using the corresponding primary amine RNH₂. The polymer had an average molecular weight of 3.3 × 10⁵ D. Polymer electrolytes with different concentrations of dissolved lithium triflate (LiCF₃SO₃) were prepared. Mechanically stable polymer electrolyte membranes were formed using UV radiation induced crosslinking of the polymer salt mixture in the presence of benzophenone as photoinitiator. The glass transition temperature of the parent polymer was found to be − 75 °C before cross linking. It increases after crosslinking and with increasing amounts of salt to a maximum of − 55 °C for 20 wt.% LiCF₃SO₃. The ionic conductivity was determined by impedance spectroscopy in the temperature range 0–80 °C. The highest conductivity was found for a salt concentration of 20 wt.% LiCF₃SO₃: 6.5 × 10^− 6 S·cm^− 1 at 20 °C and 2.8 × 10^− 4 S cm^− 1 at 80 °C. The temperature dependence of the conductivities was well described by the MIGRATION concept.     

Effects of compositions on properties of PEO–KI–I2 salts polymer electrolytes for DSSC

The effects of compositions on properties of PEO/KI/I₂ salts polymer electrolytes were investigated to optimize the photovoltaic performance of solid state DSSCs. XRD pattern for the mole ratio 12:1 of [EO:KI] was showed the formation of complete amorphous complex. DSC results also confirmed the amorphous nature of the polymer electrolyte. The highest value of ionic conductivity is 8.36 × 10^− 5 S/cm at 303 K (ambient temperature) and 2.32 × 10^− 4 S/cm at 333 K (moderate temperature) for the mole ratio 12:1 of EO:KI complex. The effect of contribution of [I⁻] and [I₃⁻] concentration with conductivity were also evaluated. FTIR spectrum reveals that the alkali metal cations were co-ordinated to ether oxygen of PEO. The formation of polyiodide ions, such as symmetric I₃⁻ (114 cm^− 1) and I₅⁻ (145 cm^− 1) caused by the addition of iodine was confirmed by FT Raman spectroscopic measurements. The optimum composition of PEO–KI–I₂ polymer electrolyte system for higher conductivity at ambient and moderate temperatures was reported. A linear Arrhenius type behaviour was observed for all the PEO–KI polymer complexes. Transport number measurements were carried out for several polymer electrolyte compositions. Dye-sensitized solar cells were fabricated by using higher conductivity polymer electrolyte compositions and its photoelectrochemical performance was investigated. The fill factor, short-circuit current, photovoltage and energy conversion efficiency of the DSSC assembled with optimized electrolyte composition were calculated to be 0.563, 6.124 mA/cm², 593 mV and 2.044% respectively.     

Modeling and simulation of mid-IR amplifying characteristics of Tm3+-doped chalcogenide Photonic Crystal Fibers

This paper deals with the designing of a Tm³⁺-doped chalcogenide Photonic Crystal Fiber (PCF) amplifier operating in the mid-IR range. The chalcogenide glass of 72GeS₂–18Ga₂S₃–10CsI (in mol%) was fabricated with the high temperature melt-quenching method, which exhibited a strong emission peak around 3.8 μm under the excitation of a 800 nm laser. By employing the rate equations and propagation equations, the amplifying characteristics of the designed PCF amplifier were worked out. It is shown that the designed PCF amplifier exhibits a signal gain larger than 30 dB and a spectral width wider than 200 nm. The theoretical models and simulation results show that the PCF presented in this work can be used in developing high efficiency mid-IR light sources.     

Study on visible luminescence of the Tm3 +: 1D2 → 3 F4 emission state in lead borate titanate aluminumfluoride glasses

This paper reports the visible luminescence properties of ¹D₂ state of Tm^3 + -doped lead borate titanate aluminumfluoride (LBTAFTm) glasses. The absorption and luminescence was analyzed within the frame work of Judd-Ofelt model. The reliability of J-O intensity parameters obtained from the experimental oscillator strengths have satisfactorily been correlated with the calculated oscillator strengths with small r.m.s deviation of ± 0.12 × 10^-6 by the least square fit analysis. Upon 359 nm excitation, the luminescence spectra show only one emission band at 458 nm (blue) corresponding to the ¹D₂ → ³ F₄ transition in the spectral region 400–500 nm. No luminescence quenching has been observed with the increase of Tm^3 + concentration. The decay profiles of the ¹D₂ level have shown single-exponential nature for all the concentrations and the decay times were found to decrease with the increase of concentration. The stimulated emission cross-section (σ_e) for the observed emission transition has also been computed. The large quantum efficiency (η) of the ¹D₂ level suggests the utility of LBTAFTm glass as a potential host for optical device applications at 458 nm emission wavelength.     

Evaluation of rheological behavior of 10W40 lubricant containing hybrid nano-material by measuring dynamic viscosity

In the present paper, the dynamic viscosity of 10W40 lubricant containing hybrid nano-materials has been examined. Hybrid nano-materials were composed of 90% of silica (SiO₂) with 20–30 nm mean particle size and 10% of multi-walled carbon nanotubes (MWCNTs) with inner diameter of 2–6 nm and outer diameter of 5–20 nm. Nano-lubricant samples were prepared by two-step method with solid volume fractions of 0.05%, 0.1%, 0.25%, 0.5%, 0.75% and 1%. Dynamic viscosity of the samples was measured at temperatures between 5 and 55 °C and at shear rates of 666.5 s⁻¹ up to 11,997 s⁻¹. Experimental results indicated that the nano-lubricant had non-Newtonian behavior at all temperatures, while 10w40 oil was non-Newtonian only at high temperatures. With the use of the curve fitting technique of experimental data, power law and consistency indexes were obtained; furthermore, these coefficients were assessed by shear stress and viscosity diagram.     

Polymer electrolytes based on cross-linked cyclotriphosphazenes

Substituted cyclotriphosphazenes were used to prepare lithium ion conducting polymer networks. Two types of compounds were synthesized starting with the precursor hexachlorocyclotriphosphazene (HCCP): Type I (CVEEP) in which all the chlorine atoms in HCCP were replaced by vinyloxyethoxyethoxy groups (VEE = –OCH₂CH₂OCH₂CH₂OCHCH₂), and type II (CVMEEP) in which half of the chlorine was replaced by VEE and the other half by methoxyethoxyethoxy groups (MEE = –OCH₂CH₂OCH₂CH₂OCH₃). The terminal vinyl groups were used to build up a network by a thermally initiated cross-linking of lithium salt containing membranes. Polymer electrolytes with dissolved LiSO₃CF₃ and LiN(SO₂CF₃)₂ were investigated by impedance measurements. The ionic conductivity of CVMEEP with 10 wt.% LiSO₃CF₃ was 3.2 × 10^− 5 S/cm at 30 °C and 4.1 × 10^− 4 S/cm at 90 °C. Lower conductivity values in the range 10^− 8–10^− 9 S/cm were obtained at 30 °C for the highly crosslinked CVEEP. An interesting polymer electrolyte with good mechanical properties and a good conductivity of 1.3 × 10^− 5 S/cm (30 °C) was obtained from a solution of MEEP (= poly[bis(methoxy–ethoxy–ethoxy)phosphazene]) and LiSO₃CF₃ in CVEEP as an interpenetrating network.     

Infrared spectroscopic and conductivity studies of poly(N-methylpropylenimine)/lithium triflate electrolytes

Poly(propylenimine), PPI, was methylated using Eschweiler-Clark conditions to produce poly(N-methylpropylenimine), PMPI. Differences may be seen in the IR spectra of the PMPI (–CH₂CH₂CH₂NCH₃–) and its homolog poly(N-methylethylenimine), PMEI, (–CH₂CH₂NCH₃–), especially in the conformation region (~ 1100 to ~ 1400 cm^− 1). The addition of lithium trifluoromethanesulfonate, (LiCF₃SO₃), sharpens the distinctions between these systems. Comparison of IR spectra of polymer:LiCF₃SO₃ complexes at compositions ranging from pure polymer to 5:1 N:Li⁺ (molar ratio) suggests significant differences in the nature of polymer salt interactions and the complex structure present in each system. These are further evidenced by differential scanning calorimetry data in which PMPI displays less variation in glass transition temperature, T_g, with the addition of salt than seen in PMEI. These observations may be interpreted in terms of local structural changes originating in cation–anion and cation–polymer interactions, particularly at mid to high salt concentrations.     

Blue emission in Eu2+ activated MgXAl10O17 (X = Sr,Ca) phosphors

Here we reported photoluminescence properties of Eu²⁺ activated in novel and existing MgXAl₁₀O₁₇ (X = Sr, Ca) phosphor which has been prepared by combustion synthesis at 550 °C under UV and near UV excitation wavelength. The PL emission properties of MgSrAl₁₀O₁₇:Eu²⁺ were monitored at 254 nm and 354 nm respectively keeping emission wavelength at 469 nm. Whereas novel MgCaAl₁₀O₁₇:Eu²⁺ exhibit emission band at 452 nm keeping excitation at 378 nm. These blue emission corresponds to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. Further phosphor was analyzed by XRD for the confirmation of desired phase and purity.     

Photoluminescence characteristics of Pr3+ in ThO2: interplay of defects in a photo-induced charge transfer

Photo-luminescence studies of Pr³⁺ activated thorium oxide phosphor have revealed that mainly ³P→³H₄ and ¹D₂→³H₄ transitions with life-time of 30 and 600 μs are observed in this sample. An exponential reduction in the emission intensity of Pr³⁺ ions was observed on following continuous excitation with 275 nm corresponding to the f–d transition band of Pr³⁺ ions. Such a reduction in emission intensity was observed at all temperatures investigated in the range 90–330 K. The emission intensity recovered partially on dark storage only above 180 K. The recovery of emission intensity was also observed on the illumination of pre-exposed sample to light in the wavelength region 300–430 nm. Following illumination with 275 nm, Pr³⁺ activated thorium oxide phosphor has displayed a weak thermally stimulated luminescence. These results thus suggest that the optical excitation dynamically changes the state of the system under observation, and that changes are occurring in the valence state of Pr ions due to e/h transfer process on 275-nm exposure. On dark storage and also on 365-nm illumination of the pre-exposed sample, e/h traps recombine to cause emission signal recovery. The analysis of data on reduction in intensity obtained with exposure to 275 nm suggests the likelihood of the of Pr³⁺ ions existing at three different sites. The activation energies associated with the release of electrons from excited Pr³⁺ ions at different sites were determined from the temperature dependence of the photo-induced charge transfer process.     

Fourier transform measurements of SO2 absorption cross sections:: I. Temperature dependence in the 24 000–29 000 cm−1 (345–420 nm) region

Absorption cross sections of SO₂ have been obtained in the 24 000–29 000 cm^?1 spectral range (345–420 nm) with a Fourier transform spectrometer at a resolution of 2 cm^?1. Pure SO₂ samples were used and measurements were performed at room temperature (298 K) as well as at 318, 338 and 358 K. This is the first time that temperature effects in this spectral region are reported and investigated. This paper is the first of a series that will report on measurements of the absorption cross section of SO₂ in the UV/visible region at a higher than previously reported resolution and that will investigate temperature effects in support of tropospheric, stratospheric and astrophysical or planetary applications.     

Broadband 2.84 μm luminescence properties and Judd–Ofelt analysis in Dy3+ doped ZrF4–BaF2–LaF3–AlF3–YF3 glass

2.84 μm luminescence with a bandwidth of 213 nm is obtained in Dy³⁺ doped (ZrF₄–BaF₂–LaF₃–AlF₃–YF₃) ZBLAY glass. Three intensity parameters and radiative properties have been determined from the absorption spectrum based on the Judd–Ofelt theory. The 2.84 μm emission characteristics and energy transfer mechanism upon excitation of a conventional 808 nm laser diode are investigated. The prepared Dy³⁺ doped ZBLAY glass possessing high predicted spontaneous transition probability (45.92 s^?1) along with large calculated emission cross section (1.17×10^?20 cm²) has potential applications in 2.8 μm laser.     

Conductivity and optical studies of plasticized solid polymer electrolytes doped with carbon nanotube

Solid polymer electrolyte films based on Poly(ethylene oxide) (PEO) complexed with lithium hexafluorophosphate (LiPF₆), ethylene carbonate (EC) and amorphous carbon nanotube (αCNTs) were prepared by the solution cast technique. The conductivity increases from 10^?10 to 10^?5 Scm^?1 upon the addition of salt. The incorporation of EC and αCNTs to the salted polymer enhances the conductivity significantly to 10^?4 and 10^?3 Scm^?1. The complexation of doping materials with polymer were confirmed by X-ray diffraction and infrared studies. Optical properties like direct band gap and indirect band gap were investigated for pure and doped polymer films in the wavelength range 200–400 nm. It was found that the energy gaps and band edge values shifted to lower energies on doping.     

Novel UV-emitting single crystalline film phosphors grown by LPE method

This work reports the development of new types of UV-emitting phosphors based on single crystalline films (SCF) of aluminum garnet and perovskite compounds grown by the liquid phase epitaxy method. We consider peculiarities of the growth and the luminescent and scintillation properties of the following four types of UV SCF phosphors: i) Ce-doped SCF of Y–Lu–Al-perovskites with the Ce³⁺ emission in the 300-450 nm range of the decay time of 16–17 ns; ii) Pr-doped SCF of Y–Lu–Al garnets and perovskites with the Pr³⁺ emission in the 300–400 nm and 235–330 nm ranges with the decay time of 13–19 and 7–8 ns, respectively; iii) La³⁺ or Sc³⁺ doped SCF of Y–Lu–Al-garnets, emitting in the 280-400 nm range due to formation of the La_Y,Lu, Sc_Y,Lu and Sc_Al centers with decay time of the order of several hundreds of nanoseconds; iv) Bi³⁺ doped SCF of garnets with Bi³⁺ emission in 275–350 nm with decay time of about 1.9 μs.     

Conductivity and thermal studies of blend polymer electrolytes based on PVAc–PMMA

The polymer electrolytes comprising blend of poly(vinyl acetate) (PVAc) and poly(methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a dopant are prepared by solution casting technique. The amorphous nature of the polymer–salt complex has been confirmed by XRD analysis. The DSC thermograms show two T_g's for PVAc–PMMA blend. A decrease in T_g with the LiClO₄ content reveals the increase of segmental motion. Conductance spectra results are found to obey the Jonscher's power law and the maximum dc conductivity value is found to be 1.76 × 10^− 3 S cm^− 1 at 303 K for the blend polymer complex with 20 wt.% LiClO₄, which is suitable for the Li rechargeable batteries. The conductivity–temperature plots are found to follow an Arrhenius nature. The dc conductivity is found to increase with increase of salt concentration in the blend polymer complexes.     

Self and N2 collisional broadening of far-infrared methane lines measured at the SOLEIL synchrotron

Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800 hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N₂ broadening coefficients of methane pure rotation lines have been measured in the 83–261 cm^?1 spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients have also been measured in the 59–288 cm^?1 spectral range using the pure methane spectra recorded in our previous work. The measured N₂ broadening coefficients were compared to semi-classical calculations.     

Fabrication and spectroscopic properties of nanocrystalline La2Hf2O7:Pr

La₂Hf₂O₇ nanopowders doped with different Pr concentrations (0.05–10 mol.%) were synthesized by the Pechini method. XRD measurements confirmed the single crystalline phase formed already at 800 °C and the structure was cubic pyrochlore. Luminescence excitation and emission as well as radioluminescence spectra were recorded for the materials. Both optical and X-ray excitation of La₂Hf₂O₇:Pr produced a red emission resulting from the 4f–4f transitions of Pr³⁺ ions. Luminescence of materials synthesized at low temperatures was characterized by broadband glass-type emissions, while heat treatment at 1400 °C led to spectra showing the typical for crystalline hosts narrow and intense 4f–4f transitions of Pr³⁺.