Search

This research delves into the influence of red lead content on the red and NIR emission characteristics of Pr3+ ions within a nonconventional antimony silicate glass system. The glasses were synthesized across a composition spectrum of (40 − x) Pb3O4‒49Sb2O3‒(10 + x)SiO2:1Pr2O3, where x ranged from 0 to 35 mol%. Characterization was carried out using XRD, DSC, XPS, and IR spectroscopy. These analyses unveiled the presence of antimony ions in both Sb3+ and Sb5+ states and lead ions in Pb4+ and Pb2+ states within these glass compositions. Optical absorption and emission spectra (at λexc = 445 nm) were recorded within the wavelength range of 400‒1800 nm. Luminescence decay profiles of two pivotal transitions, namely, 3P0 → 3F2 (red emission) and 1G4 → 3H5 (1.3 µm NIR emission), were also recorded. Various radiative parameters from these spectra were extracted using the J–O theory. The findings indicated that, as the Pb3O4 content declined from 40 to 10 mol%, the covalent nature of the samples diminished, resulting in a remarkable amplification in the intensity of both the red and NIR emission bands of Pr3+ ions. The glass containing 10 mol% of Pb3O4 exhibited the most elevated radiative parameters and quantum efficiency. This augmentation was attributed to the reduction of Pb4+ and Sb5+ ions within the glass network or the augmentation of Pb2+ ions, serving as modifiers that mitigated phonon losses. Consequently, glasses with 10 mol% Pb3O4 demonstrate great potential for telecommunications applications, owing to their significant enhancement in PL emission for the 3P0 → 3F2 and 1G4 → 3H5 transitions. [ABSTRACT FROM AUTHOR]

Zinc selenium phosphate glasses added with the traces of Au2O3 were prepared and heat-treated. XRD, TEM, DSC, FT-IR and optical absorption (OA) spectroscopy methods were used for the structural assessment of these samples. Later, different dielectric parameters viz., dielectric constant (ε′), electric moduli (M), impedance (Z) and a.c. conductivity (σac) were measured over wide regions of frequency (ω) and temperature (T) as functions of Au2O3 concentration. Dielectric breakdown strength (DBS) of these samples was also measured at ambient conditions. The characterization studies indicated that multiple crystal grains were entrenched in the residual amorphous phase of the samples. The X-ray diffraction studies revealed that the bulk glasses consisted of Au2(SeO3)3 crystal phase and Au0 metallic particles (MPs). As Au2O3 content was raised, the intensity of the XRD peak related to Au3+ crystal phase indicated a growing trend, whereas that of Au0 MPs showed a decreasing trend. The results of XPS studies revealed similar inferences. The FT-IR results pointed out an improved degree of augmentation of the glass network as the content of Au2O3 was increased. Optical absorption (OA) - spectra of the glasses indicated a broad absorption band in the spectral range of 500–600 nm due to the surface plasmon resonance (SPR) of Au0 MPs. The intensity of the band was observed to decrease as Au2O3 content was increased and indicated decreasing proportion of Au0 metallic particles in the samples. The dielectric parameters exhibited a decreasing trend, whereas the dielectric breakdown strength (DBS) and electrical impedance indicated a substantial hike due to the increasing concentration of Au2O3. Overall, the presence of Au2O3 caused a significant improvement in the insulating strength of the ZnO added SeO2-P2O5 glasses and hence such glasses may be considered as insulating layers in the display panel devices. [ABSTRACT FROM AUTHOR]

This study consists of comprehensive investigations on dielectric permittivity (ε′), electric moduli (M′, M″), impedance (Z), and conductivity (σac) spectra over broad regions of frequency and temperature of lead zirconium silicate glass ceramics mixed with different concentrations of Fe2O3. The observed increase in dielectric permittivity with the content of Fe2O3 is attributed to the increasing presence of iron ions in octahedral positions. Electric moduli plots with frequency (ω) and temperature (T) exhibit dipolar effects. These effects are quantitatively analyzed by Cole–Cole plots; the analysis indicates the distribution of relaxation times. Probable dipoles for these effects are identified and discussed. AC conductivity (σac) shows a rising trend with an increase in Fe2O3 beyond 0.2 mol%, and this increase is attributed to the polaron exchange among Fe2+ and Fe3+ ions. The conduction mechanism is well explained using a polaron tunneling model in the middle‐frequency and high‐temperature regions. [ABSTRACT FROM AUTHOR]

Third-order nonlinear optical properties of tetra-phenyl porphyrin (HTPP) derivatives viz., HTPP(OH) and Zn(II)TPP doped in boric acid glass thin films were measured using single beam Z-scan and forward degenerate four-wave mixing (DFWM) techniques. Excited state lifetimes and absorption cross-sections were estimated from these experiments. Thickness of the porphyrin doped sandwich glass films were determined using DFWM technique for the first time. The values of nonlinear refractive index () obtained for these systems are are found to be sensitive to the nature of substituents in porphyrin molecule. These results are interpreted in terms of delocalized electrons contributing to the third-order optical nonlinearity. [ABSTRACT FROM AUTHOR]

Phthalocyanines (Pcs) bearing phosphonic acid groups at the periphery exhibit a potential photodynamic effect to induce phototoxicity on human bladder cancer epithelial cells (UM-UC-3). In vitro photophysical and biological studies show high intrinsic ability to inhibit the activity of urokinase plasminogen activator (uPA) and matrix metalloproteinase-9 (MMP-9). [ABSTRACT FROM AUTHOR]

Fluorescent molecular probes based on phospho-nate-functionalized porphyrin derivatives have been designed for selective detection of nitroaromatics. It is shown that molecular recognition is based on cooperative hydrogen bonding and π-π stacking interactions with electron-deficient molecules (nitro-aromatic compounds, NACs), displaying superior detection toward trinitrotoluene (TNT). The P=0 functional groups decrease the lowest unoccupied molecular orbital (l.UMO) energy level of the porphyrins and, consequently, facilitate the electron inoculation to TNT through a photoinduced electron transfer (PET) process. The hydroxyl groups of the phosphonates and pyrrole -NH protons are further engaged in donor-acceptor interactions with TNT by strong intermolecular hydrogen bonding interactions (as evidenced by single crystal X-ray, NMR, and density functional theory (DFT) showing turn off fluorescence behavior. The nonplanarity of the porphyrins induced by protonation at the central core of the porphyrin H4TPPA2+ undergoes additional interactions, furnishing an anomalous increase in the selectivity of TNT at nanomolar levels in solution (limit of detection, LOD ~ 5 nM) Porphyrin-doped hybrid PMMA [poly(methyl methacrylate)] polymer films demonstrate the reversibility of the fluorescence behavior and exhibit high photostability. The formation of discrete molecular aggregates on the surface of hybrid films and efficient diffusion of TNT vapors (10 ppb) displayed high selectivity in the solid state. The hybrid films are further used to demonstrate the detection of NACs in the aqueous medium, ultimately providing a platform for a practical strategy and implementation for the detection of toxic NACs. [ABSTRACT FROM AUTHOR]

We report a novel synthetic approach, with good yields, for the synthesis of selective dimethylamine-substituted phthalonitriles (1–3) in the presence of triethyl phosphite and dimethylformamide at 160 °C. The peripherally modified dimethylamine substituted Zn(ii)phthalocyanines (ZnPc1–3) with varied numbers and positions of dimethylamine groups were prepared for a systematic investigation of the effect of the substituents on their electronic and spectroscopic properties. Compounds show strong aggregation behaviour in methanol and this behaviour decreases with the increase of the alkyl chain length of the alcohol solvents (i.e., from methanol to octanol). The fluorescence quantum yields of ZnPc1–3 showed an excellent correlation with the extent of the molecular aggregation. The versatility of the ZnPc1–5 compounds possessing both electron donating and electron withdrawing substituents at their periphery is investigated towards the detection of nitroaromatic compounds (NACs) in solution and in the vapour phase. It was found that ZnPc1–5 exhibit high selectivity towards trinitrophenol (TNP). A good linearity of fluorescence detection using ZnPc3 as the fluorescent probe was observed in the concentration range of 50 × 10−6 to 450 × 10−6 M in chloroform, with a detection limit (LOD) of 11 ± 2 ppm. Stern–Volmer (SV) and DFT studies reveal that the fluorescence quenching behaviour occurs through photo-induced electron transfer from the excited state of ZnPcs to TNP with static quenching behaviour occurring in a predominant fashion. The formation of a porous morphology of ZnPc3 thin films promotes high selectivity and accessibility to TNP vapours (7.7 × 10−3 ppb). [ABSTRACT FROM AUTHOR]

A new class of dual fluorescent chemosensors for nitroaromatic compounds (NACs) based on phosphonated pyrene derivatives is reported, showing high selectivity towards trinitrotoluene (TNT). The strong intermolecular interactions (π- π stacking and hydrogen bonding) allow high fluorescence quenching with visual detection in short response times. [ABSTRACT FROM AUTHOR]

Diketopyrrolopyrrole (DPP) based molecular semiconductors have emerged as promising materials for high performance active layers in organic solar cells. It is imperative to comprehend the origin of such a property by investigating the fundamental structure property correlation. In this report we have investigated the role of the donor group in DPP based donor–acceptor–donor (D–A–D) structure to govern the solid state, photophysical and electrochemical properties. We have prepared three derivatives of DPP with varying strengths of the donor groups, such as phenyl (PDPP-Hex), thiophene (TDPP-Hex) and selenophene (SeDPP-Hex). The influence of the donor units on the solid state packing was studied by single crystal X-ray diffraction. The photophysical, electrochemical and density functional theory (DFT) results were combined to elucidate the structural and electronic properties of three DPP derivatives. We found that these DPP derivatives crystallized in the monoclinic space group P21/c and show herringbone packing in the crystal lattice. The derivatives exhibit weak π–π stacking interactions as two neighboring molecules slip away from each other with varied torsional angles at the donor units. The high torsional angle of 32° (PDPP-Hex) between the phenyl and lactam ring results in weak intramolecular interactions between the donor and acceptor, while TDPP-Hex and SeDPP-Hex show lower torsional angles of 9° and 12° with a strong overlap between the donor and acceptor units. The photophysical properties reveal that PDPP-Hex exhibits a high Stokes shift of 0.32 eV and SeDPP-Hex shows a high molar absorption co-efficient of 33 600 L mol−1 cm−1 with a low band gap of ∼2.2 eV. The electrochemical studies of SeDPP-Hex indicate the pronounced effect of selenium in stabilizing the LUMO energy levels and this further emphasizes the importance of chalcogens in developing new n-type organic semiconductors for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Nonlinear optical transmission of graphene oxide–(Cu, Zn, Sn, H2) porphyrin composites was investigated using the Z-scan technique at 532 nm with picosecond (ps) and 800 nm with femtosecond laser pulses. Pure porphyrins show saturable absorption (SA) in reverse saturable absorption (RSA) behaviour and graphene oxide shows complete RSA behaviour, observed in an open aperture Z-scan curve. Interestingly, composites have shown a switch-over from reverse RSA to SA and back to RSA behaviour, observed with variation of intensity towards the focus, due to strong two-photon absorption as well as excited state absorption in the ps regime. This switching behaviour was interpreted as due to long lifetimes and saturation of the excited states. This may find application in optical switching. [ABSTRACT FROM AUTHOR]

We report herein, a novel method for the formation of highly stable BF3-induced J-aggregates by interaction between meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) and BF3O(C2H5)2. The aggregates were characterized by NMR (1H, 11B and 19F), optical absorption, cyclic voltammetry, FT-IR and fluorescence spectroscopic techniques. TPPS4 readily forms a 1 : 2 adduct with BF3 which further converts into BF3-induced TPPS4 aggregates whose spectroscopic properties strongly depend on the concentration of BF3. The optical absorption spectrum shows the formation of J-type aggregates with an apparent association constant (logKapp) of 4.2 ± 0.1. The steady state emission shows formation of 1 : 2 (TPPS4–BF3) adducts at ∼685 nm and J-aggregates exhibit emission at 732 nm with a red shift of ∼17 nm in comparison to J-aggregates of TPPS4 with TFA. The fluorescence lifetime of TPPS4 : BF3 (1 : 2) adducts exhibits ∼3.68 ns and aggregates show a lifetime of 4.32 ± 0.2 ns with major abundance. NMR study reveals that proton transfer occurs from pyrrole N–H to the SO3− groups and J-aggregates were stabilized by strong intermolecular hydrogen bonding interaction between N2–BF2 and SO3H. Cyclic voltammetry shows a decrease in the reduction peak current along with a change in the peak potentials for the aggregates. The PXRD pattern of the aggregates exhibits orthorhombic structure with interplanar distance of 4.87 Å. The variations in unusual stability, photophysical, electrochemical properties and nature of the aggregates were rationalized with aggregates of TPPS4 dication. [ABSTRACT FROM AUTHOR]

Herein we report a novel fluoranthene-based fluorescent fluorophore 7,10-bis(4-bromophenyl)-8,9-bis[4-(hexyloxy)phenyl]fluoranthene ( S3) and its remarkable properties in applications of explosive detection. The sensitivity towards the detection of nitroaromatics (NACs) was evaluated through fluorescence quenching in solution, vapor, and contact mode approaches. The contact mode approach using thin-layer silica chromatograp- hic plates exhibited a femtogram (1.15 fg cm−2) detection limit for trinitrotoluene (TNT) and picric acid (PA), whereas the solution-phase quenching showed PA detection at the 2-20 ppb level. Fluorescence lifetime measurements revealed that the quenching is static in nature and the quenching process is fully reversible. Binding energies between model binding sites of the S3 and analyte compounds reveal that analyte molecules enter into the cavity created by substituted phenyl rings of fluoranthene and are stabilized by strong intermolecular interactions with alkyl chains. It is anticipated that the sensor S3 could be a promising material for the construction of portable optical devices for the detection of onsite explosive nitroaromatics. [ABSTRACT FROM AUTHOR]

Abstract: The glasses of the composition 19Na2SO4–20MO–60P2O5: 1.0Ho2O3/1.0Er2O3 (M=Mg, Ca, and Ba) have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350–2100nm were studied at ambient temperature. The spectra were characterized using Judd–Ofelt theory. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for blue (B), green (G) and red (R) emission levels of these glasses have been evaluated. The energy transfer between the two rare earth ions (Ho3+ and Er3+) in co-doped Na2SO4–MO–P2O5 glass systems in the visible and NIR regions has also been investigated. Highest intensity, the highest quantum efficiency and maximum energy transfer with low phonon losses of B, G, and R lines has been observed in BaO mixed glasses. The reasons for such higher values of these parameters have been discussed in the light of varying field strengths at the rare earths ion site due to replacement of one modifier oxide with the other. The enhanced intensity of NIR emission (at 2.0μm) has also been discussed in terms of cross relaxation of Er3+ ions from 4I13/2 level to 5I7 of Ho3+ ions. [Copyright &y& Elsevier]

Abstract: Hybrid borate glasses containing different concentrations of meso-tetrakis(p-sulfonatophenyl) porphyrin sodium salt (TPPS4) were prepared. The obtained glass samples were found to be transparent and homogeneous. Formation of TPPS4-J-aggregates in borate glass was investigated by means of optical absorption, steady state and time resolved fluorescence spectroscopy. The hybrid glasses exhibit a strong S2→S0 emission at ∼473nm and J-aggregates show emission at ∼733nm. Time resolved fluorescence show two exponential decay with lifetime of τ 1 =65±10ps (∼80%) and τ 2 =3.87±0.1ns (∼20%) respectively. Dielectric properties such as dielectric constant (ɛ′), dielectric loss (tan δ) and ac conductivity (σ ac) over a range of frequency and temperature of these glasses were studied. The ac conductivity was found to be proportional to ω s (where s <1). The observed change in dielectric parameters due to different concentrations of TPPS4 has been analyzed in light of different polarization mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid borate glasses containing different concentrations (0.5–2.0mg in 12g of boric acid) of Mesoporphyrin(IX)dimethylester, Protoporphyrin(IX)dimethylester and Hematoporphyrin(IX)dimethylester were prepared by rapid melt quench technique at 230°C. The hybrid glass samples were characterized by X-ray diffraction, optical absorption, steady state and time-resolved fluorescence emission. The optical absorption spectrum shows red-shift in Soret band along with change in Q-band pattern. The intensity of Q-band was found to increase with increase in the concentration of porphyrin in the glass. Steady state emission spectrum shows strong S2→S0 emission in the range 462–495nm and blue shift in S1→S0 emission. Time-resolved fluorescence emission and fluorescence excitation spectra showed that different structures of porphyrins were exist in the glass samples. The variation in the spectral behaviour in the glass was correlated with those in solution medium and possible structures of porphyrin in borate glass were explored. [ABSTRACT FROM AUTHOR]

PbO-As2O3 glasses mixed with different concentrations of TiO2 (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy (EDS) techniques. Studies were extended to optical absorption, IR, ESR, luminescence and magnetic susceptibility on these samples. The X-ray diffraction studies reveal the presence of Pb3O4, Ti(As2O7), Pb(As2O6), Pb3(AsO4)2 PbTi3O7 and Ti2O3 crystal phases. The optical absorption studies together with ESR and magnetic susceptibility measurements indicated that the titanium ions exist in both Ti3+ and Ti4+ states in all the samples and there is an increase in titanium ions in the trivalent state with increasing concentration of nucleating agent TiO2. The quantitative analysis of these results indicated that there is a growing degree of disorder in the glass network with increasing concentration of the crystallizing agent. The luminescence studies indicated that the samples crystallized with low concentrations of TiO2 show high luminescence efficiency in the visible region. [ABSTRACT FROM AUTHOR]

Abstract: ZnF2–As2O3–TeO2 glasses mixed with different concentrations of V2O5 (ranging from 0 to 0.6mol%) were synthesized. The amorphous nature of these glasses was checked by X-ray diffraction and scanning electron microscopy techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra and dielectric properties (constant ε′, loss tan δ, ac conductivity σ ac over a wide range of frequency and temperature) of these glasses have been explored. The optical absorption, electron spin resonance studies together indicated vanadium ions coexist in V4+ with V5+state in these samples. The IR spectra of these samples have exhibited bands due to ν s-TeO2ax and AsO3 structural groups; these results indicated the most structural disorder in the network as the concentration of V2O5 is increased. Luminescent emission spectra recorded at room temperature of these glasses excited at 640nm have exhibited a broad emission band in the spectral wavelength range of 750–850nm. The luminescence efficiency is found to be the highest for the sample doped with 0.6mol%. The dielectric parameters viz., ε′, tan δ and σ a.c are found to increase and the activation energy for ac conduction is found to decrease with the increase in the concentration of V2O5 up to 0.6mol%, reflecting an increase in the concentration of V4+ ions that take part modifying positions in the glass network. The ac conduction in these glasses could satisfactorily be explained by both classical activation energy and the tunneling phenomena. [Copyright &y& Elsevier]