Blue Shift Research Articles

One-dimensional photonic crystals based on porous anodic alumina: Optical and morphology changes under thermal and chemical treatments

One-dimensional photonic crystals (1D PCs) based on porous anodic aluminium oxide (AAO) are promising for light manipulation and sensing. As-prepared AAO, being amorphous material, suffers degradation in acidic and alkaline media. It is commonly known that the chemical stability of AAO increases drastically after thermal treatment. Here, the effect of annealing up to 1200 °C on the morphology and the optical properties of AAO PCs is studied. The two-step crystallization of as-prepared AAO at 860 and 1190 °C leads to a two-step blue shift of the central wavelength of photonic band gap (PBG) and the decrease in PBG depth, whereas the Q-factor of the PBG enhances. The observed changes in optical transmittance spectra of PCs are mainly attributed to the increase in pore diameter, the formation of crystalline particles of alumina polymorphs, and the removal of impurities. Annealed AAO PCs demonstrate much higher stability of optical parameters during exposure in acidic media compared to the as-prepared ones. Thermal treatment at 600 °C results in 30% decrease in the rate of the PBG shift during chemical etching. Furthermore, AAO crystallization into a mixture of low-temperature alumina polymorphs at 860 °C leads in a negligible change in transmittance spectra even after chemical etching in 1 M HCl for 75 h. The excellent stability achieved for the annealed AAO PCs in aggressive media proves the perspectives of their application as the optical sensors with long-term stability.

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample.

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6M and 1.733 × 107M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

Observations on “Mg” incorporated oxides of tungsten for superconducting applications

The present work involves in the synthesis and characterization of pristine and "Mg" associated WO3.H2O nano powders by a high yield irradiation technique using microwaves. The diffraction patterns present phased orthorhombic phase and retained even after annealing process. Clear evidence noticed for pure and doped samples in morphological behavior of the samples. The change in optical properties in terms of energy values revealed the contribution of dopants with the evident at 360 nm wavelength blue shift. The obtained magnetic behavior on the annealed samples revealed the transition offer magnetic state to diamagnetic state may be investigated for super conducting applications.

A Ratiometric Green Fluorescent Carbazole-bis(hydrazinobenzothiazole) Probe for the Selective Detection of Toxic Hg2+ Ions in Real Water Samples.

A dyad Carbazolyl-bis(hydrazinobenzothiazole) was designed to form a symmetrical structure that containing two-arm active binding sites facilitates coordination with Hg2+ ion. This sensor has imparted a colorimetric and fluorometric changes in presence of Hg2+ ions. The ligand showed a selective blue shift in presence of Hg2+even in co-existence with heavy metal ions with luminescence change from colorless to blue and colorless to green under day light. Enhanced Intramolecular charge transfer process is responsible for fluorescence transformation when ligand interacts with Hg2+ ion. The emission spectra showed a ratiometric response to increasing addition of Hg2+ ions. The sensor is capable of detecting above the lower concentration of 6.8025 × 10-8 M. The fluorescence efficiency of CBT-2 with Hg2+ ion is quite stable under different co-metal ions and wide range of pH 6 to 9. The sensor CBT-2 forms a 1:1 stoichiometric complex with Hg2+ ions and the binding nature is confirmed from the 1H-NMR, FTIR, and mass spectroscopic studies. The sensor CBT-2 and its Hg2+ complex possess good binding nature to protein in Bovine Serum Albumin which could be good in biological applications. Additionally, wedevelop a practical application in real water sample analysis and electrochemical detection viaoxidation potential discrimination.

Catalyst-regulated conversion of p-phenylenediamine-based carbon dots from red to deep-blue emission

Deep-blue emission (＜450 nm) is significant in high-density information storage, solid-state lighting, and vivid displays. However, the carbon dots (CDs) obtained from p-phenylenediamine (pPD) have only red fluorescence, which greatly limits the application and development of pPD-based CDs. As we all know, a catalyst is a substance that can change the rate and pathway of a chemical reaction. Herein, we designed to add a catalyst to realize the conversion of pPD-based CDs from red to deep-blue fluorescence. The emission peak of obtained deep-blue CDs was 440 nm, and the full-width at half-maximum (FWHM) was only 58 nm, with a high color purity. In addition, through in-depth analysis of microstructure and photoluminescence (PL) properties, it is found that the decrease of the sp2-conjugated domain and the graphite N content and the increase in pyridinic N content were the main reasons for the blue shift of the spectra. Based on this, the formation process and mechanism of red and deep-blue CDs were further elucidated. This work not only efficiently realized the design of the deep-blue CDs but also provided a new idea for the luminescence regulation of CDs without changing the raw materials and reaction conditions.

Disentangling Acid-Base Chemistry through Blue Shifting Hydrogen Bond Contributions.

The blue shifting of vibrational frequencies in hydrogen bonded molecules, as observed in aqueous environments, has been attributed to local partial charge transfer from solvation. Here, we extrapolate the blue shift model to the stronger ionic interactions between hydrogen bond acceptors associated with protonation through augmented pH levels and competitive interactions with counter ion pairing. The chemical model we utilize in this work is the aqueous pyridine-pyridinium equilibrium to characterize the blue shifts observed in the pyridinium chloride ionic system. The observed agreement between observed experimental and calculated spectral shifts shows that the blue shifting model can be extrapolated to stronger interactions and accurately describe the nature of the hydrogen bond.

Molecular Hydrogen Acts as a Hydrogen Bond Proton Acceptor: From Protonated Betaine Tagging to the Weakest Hydrogen Bond.

In an attempt to gain further insights into the intermolecular interactions implied by Rizzo's group's cautionary tale related to molecular tagging in infrared multiple photon dissociation (IRMPD) spectroscopy with molecular messengers [Masson, A. . J. Chem. Phys. 2015, 143, 104313], in the present study, we provide an in-depth analysis of the noncovalent interaction between the molecular hydrogen and protonated betaine molecule in the gas phase. We aim to shed some new light on the fundamental issues concerning the wide diapason of hydrogen-bonding-type intermolecular interactions, with a wide variety of proton acceptors. We demonstrate that in the course of tagging the protonated betaine with molecular hydrogen from the OH group side, it is the σ bond of molecular hydrogen that plays the role of hydrogen-bonding proton acceptor. The tagging thus induces a small yet significant red shift of the protonated betaine O-H stretching mode. We investigate the performance of a wide range of density functional theory (DFT) functionals for the calculation of anharmonic vibrational frequency shifts of the studied system, which are essential for the correct interpretation of the experimental IRMPD data. For an accurate prediction of the OH stretching frequency shifts, specifically designed functionals such as Handy's group HCTH/407 should be applied. The empirical dispersion correction enhances the systematic overestimation of the anharmonic frequency shift, characteristic of the most widely used DFT functionals. Combining the full-wave function approach with the charge field perturbation and natural bond orbital (NBO) deletion analyses, we demonstrate that the frequency shift in the OH-tagged structure is governed by the σHH → σ*OH intermolecular charge transfer. This interaction stabilizes the OH-tagged dimer as well, in contrast to the dipole-quadrupole electrostatic interaction energy term. Topological analysis of the electron density reveals the presence of an intermolecular bond critical point with a positive value of the density Laplacian very close to the lower limit for hydrogen bonds. NCI analyses demonstrate that the OH···H2 interaction is weaker than the intramolecular CH···O one within the protonated betaine molecule, with the through of reduced density gradient appearing at less negative sign(λ2)·ρ values. Analyzing the O-H stretching vibrational potential with the second-generation absolutely localized molecular orbitals energy decomposition analysis (ALMO-EDA 2) revealed that in the case of betaineH(+) tagged from the OH group side, the permanent electrostatics (ΔEelec), polarization (ΔEpol), and charge-transfer (ΔEct) contributions to the total intermolecular interaction energy contribute favorably to the weak hydrogen bond formation and to the red shift of the fundamental O-H stretching frequency, the ΔEct contribution being the most significant in the last context. The Pauli repulsion term, on the other hand, favors an O-H stretching frequency blue shift as a consequence of the vibrational confinement effects.

Synthesis and thermally-induced gelation of interpenetrating nanogels

Thermally-induced in-situ gelation of polymers and nanogels is of significant importance for injectable non-invasive tissue engineering and delivery systems of drug delivery system. In this study, we for the first time demonstrated that the interpenetrating (IPN) nanogel with two networks of poly (N-isopropylacrylamide) (PNIPAM) and poly (N-Acryloyl-l-phenylalanine) (PAphe) underwent a reversible temperature-triggered sol-gel transition and formed a structural color gel above the phase transition temperature (Tp). Dynamic light scattering (DLS) studies confirmed that the Tp of IPN nanogels are the same as that of PNIPAM, independent of Aphe content of the IPN nanogels at pH of 6.5 ∼ 7.4. The rheological and optical properties of IPN nanogels during sol-gel transition were studied by rheometer and optical fiber spectroscopy. The results showed that the gelation time of the hydrogel photonic crystals assembled by IPN nanogel was affected by temperature, PAphe composition, concentration, and sequence of interpenetration. As the temperature rose above the Tp, the Bragg reflection peak of IPN nanogels exhibited blue shift due to the shrinkage of IPN nanogels. In addition, these colored IPN nanogels demonstrated good injectability and had no obvious cytotoxicity. These IPN nanogels will open an avenue to the preparation and thermally-induced in-situ gelation of novel NIPAM-based nanogel system.

THE DEPENDENCE OF ACID-BASE EQUILBRIA AND ACIDITY CONSTANTS OF CONGO RED IN BUFFER SOLUTIONS ON THE IONIC STRENGTH

In this study, the spectrophotometric studies of aqueous ethanol solution of Congo red in various buffers solutions at room temperature 25oC and at different ionic strength of 0.05, 0.1, 0.3, and 0.5 KCl mol L-1 were investigated. The acidity constants of Congo red were estimated by three different methods. The two protonation stages were observed in pH range 2 - 4 and 4 - 6 as result as protonation of amino group and azo groups. The dependence of absorption spectra of Congo red on the ionic strength of solutions which exhibited blue shift with increases ionic strength in addition the shape and intensity were varied. Therefore, the acid-base equilibria shifted toward the higher pHs with the rise in ionic strength. Also, the acidity constants were affected by the ionic strength which the acidity constants decrease with increasing ionic strength of solution because the electrostatic interaction force increased.

DFT-D3 and TD-DFT Studies of the Adsorption and Sensing Behavior of Mn-Phthalocyanine toward NH3, PH3, and AsH3 Molecules

This study employs density functional theory (DFT) calculations at the B3LYP/6-311+g(d,p) level to investigate the interaction of XH3 gases (X = N, P, As) with the Mn-phthalocyanine molecule (MnPc). Grimme’s D3 dispersion correction is applied to consider long-range interactions. The adsorption behavior is explored under the influence of an external static electric field (EF) ranging from −0.514 to 0.514 V/Å. Chemical adsorption of XH3 molecules onto the MnPc molecule is confirmed. The adsorption results in a significant decrease in the energy gap (Eg) of MnPc, indicating the potential alteration of its optical properties. Quantum theory of atoms in molecules (QTAIM) analysis reveals partially covalent bonds between XH3 and MnPc, and the charge density differenc (Δρ) calculations suggest a charge donation-back donation mechanism. The UV-vis spectrum of MnPc experiences a blue shift upon XH3 adsorption, highlighting MnPc’s potential as a naked-eye sensor for XH3 molecules. Thermodynamic calculations indicate exothermic interactions, with NH3/MnPc being the most stable complex. The stability of NH3/MnPc decreases with increasing temperature. The direction and magnitude of the applied electric field (EF) play a crucial role in determining the adsorption energy (Eads) for XH3/MnPc complexes. The Eg values decrease with an increasing negative EF, which suggests that the electrical conductivity (σ) and the electrical sensitivity (ΔEg) of the XH3/MnPc complexes are influenced by the magnitude and direction of the applied EF. Overall, this study provides valuable insights into the suggested promising prospects for the utilization of MnPc in sensing applications of XH3 gases.

Structure Engineering of Acridine Donor to Optimize Color Purity of Blue Thermally Activated Delayed Fluorescence Emitters.

9,9-Dimethyl-9,10-dihydroacridine (DMAC) is one of the most widely used electron donor for constructing high-performance thermally activated delayed fluorescence (TADF) emitters. However, DMAC-based emitters often suffer from the imperfect color purity, particularly in blue emitters, due to its strong electron-donating capability. To modulate donor strength, 2,7-F-Ph-DMAC and 2,7-CF3-Ph-DMAC were designed by introducing the electron-withdrawing 2-fluorophenyl and 2-(trifluoromethyl)phenyl at the 2,7-positions of DMAC. These donors were used, in combination with 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor, to develop novel TADF emitters 2,7-F-Ph-DMAC-TRZ and 2,7-CF3-Ph-DMAC-TRZ. Compared to the F- or CF3-free reference emitter, both two emitters showed hypsochromic effect in fluorescence and comparable photoluminescence quantum yields without sacrificing the reverse intersystem crossing rate constants. In particular, 2,7-CF3-Ph-DMAC-TRZ based OLED exhibited a blue shift by up to 39 nm and significantly improved Commission International de l'Éclairage (CIE) coordinates from (0.36, 0.55) to (0.22, 0.41), while the external quantum efficiency kept stable at about 22.5%. This donor engineering strategy should be valid for improving the color purity of large amount of acridine based TADF emitters. It can be predicted that pure blue TADF emitters should be feasible if these F- or CF3-modifed acridine donors are combined with other weaker electron acceptors.

Polymer Passivated All Inorganic Micro‐Structured CsPbIxBry Perovskite Toward Highly Efficient Photodetectors

AbstractSolution‐processed inorganic perovskites cause chemical and structural defects unfavorable for photodetector application. Using a binary solvent, defects in CsPbIxBry (CPIB) perovskite are passivated with poly 4‐vinylpyridine (PVP) and Poly methyl methacrylate (PMMA) polymers. X‐ray photoelectron spectroscopy and FTIR spectra reveal a Lewis base‐acid interaction between Pb2+ and polymer, confirming the passivation of CPIB perovskite. Scanning electron microscopy analysis shows a dual‐surface morphology with microribbons and microcrystals in perovskites. After PMMA treatment, CPIB perovskite exhibits a blue shift in the bandgap (1.8 to 1.95 eV), while the PVP induced a redshift, reducing the bandgap to 1.7 eV. Blue shift in PL analysis indicates modification of grain boundaries. A higher lifetime obtained for CPIB/PVP confirms the restraint of non‐radiative recombinations. Photodetectors are fabricated with pristine CPIB, CPIB/PVP, and CPIB/PMMA perovskites. The passivated CPIB/PVP‐based photodetector exhibits a quick rise time of ≈23 ms and a decay time of ≈17 ms. It also demonstrates a remarkable photoresponsivity of 23 mA W−1, an internal quantum efficiency of 4.9%, and a detectivity of 15.0 × 1010 Jones at 10 mW cm−2 light intensity. This approach shows the potential for environmentally stable polymers to passivate inorganic perovskites for high photodetection performance.

Investigation of electrochemical and photoluminescence properties of Dy[formula omitted] doped SrO/BaO/Al2O3 nanocomposite for supercapacitor and display applications

The current study investigates the synthesis and characterization of dysprosium-doped strontium barium aluminum nanocomposites (SBAD NCs), aiming to enhance their suitability for display and supercapacitor applications. SBAD NCs are synthesized by Solution combustion synthesis using aloevera extract as a reducing agent. Multi-phase formation of NCs due to SrO, BaO, and γ-Al2O3 phases was confirmed by PXRD analysis, and crystallite size is found to be in the range of 26 nm to 36 nm. SEM analysis confirmed the surface morphology and the elemental composition was affirmed by the EDAX spectrum which confirmed the purity of the synthesis. The blue shift in the UV-visible absorption peak with increasing dopant concentration suggests a rise in the direct energy band gap from 4.07 eV to 4.11 eV. FTIR analysis confirmed functional groups and fingerprint region affirmed the presence of Sr-O, Ba-O, and Al-O bonds. Photoluminescence analysis performed under excitation wavelength 276 nm revealed a prominent emission peak at 565 nm, and the CIE values fall in the yellow-green region of visible spectra. The CCT value was found to be 4490 K–4542 K which might find an application as a nanophosphor in cool light-emitting diodes. The tailored nanocomposites exhibit exceptional electrochemical performance characterized by superior specific capacitance, and improved charge–discharge kinetics, as evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The specific capacitance is found to be in the range of 103.26 F/g to 173.24 F/g at a scan rate of 10 mV/s with increasing Dy3+ dopant concentration from 1 mol% to 9 mol% respectively. The dysprosium-doped SBAD NCs emerge as promising candidates for high-performance energy storage systems and vibrant display technologies, offering a synergistic integration of efficient energy storage and vivid display functionalities.

Impact of blue-shifted effective joint density of electronic states on the photoluminescence of nanostructured silicon

Light emission from nanostructured silicon has triggered tremendous research interest for three decades. Yet, the exact mechanism of photoluminescence from silicon-based nano-systems is still not completely understood. It is generally believed that quantum confinement and surface chemistry play a combined role in determining the luminescence characteristics on nano silicon. In this work, we show that the evolution of electron-hole effective joint density of states, resulting from the relaxation of k-selection rule, can account for the much-observed temperature dependent shift of the luminescence spectra of nanostructured silicon. Deconvolution of the emission characteristics reveals three distinct radiative recombination channels that can be attributed to band-to-band, band-to-trap and trap-to-trap transitions. At temperatures below ∼200 K, the peak due to band-to-band transition exhibit a nearly linear blue shift with increasing temperature while at higher temperatures this trend is reversed. The rate of variation of emission peak energy with temperature is also found to be dependent on average crystallite size. These results are explained in terms of shift in the effective joint density of state function of photogenerated electron-hole pairs. The shift provides experimental evidence of the pseudo-direct transitions in the quantum-confined nanostructure of silicon.

Multiple Dyes Applications for Fluorescent Convertible Polymer Capsules as Macrophages Tracking Labels

Tracing individual cell pathways among the whole population is crucial for understanding their behavior, cell communication, migration dynamics, and fate. Optical labeling is one approach for tracing individual cells, but it typically requires genetic modification to induce the generation of photoconvertible proteins. Nevertheless, this approach has limitations and is not applicable to certain cell types. For instance, genetic modification often leads to the death of macrophages. This study aims to develop an alternative method for labeling macrophages by utilizing photoconvertible micron-sized capsules capable of easy internalization and prolonged retention within cells. Thermal treatment in a polyvinyl alcohol gel medium is employed for the scalable synthesis of capsules with a wide range of fluorescent dyes, including rhodamine 6G, pyronin B, fluorescein, acridine yellow, acridine orange, thiazine red, and previously reported rhodamine B. The fluorescence brightness, photostability, and photoconversion ability of the capsules are evaluated using confocal laser scanning microscopy. Viability, uptake, mobility, and photoconversion studies are conducted on RAW 264.7 and bone marrow-derived macrophages, serving as model cell lines. The production yield of the capsules is increased due to the use of polyvinyl alcohol gel, eliminating the need for conventional filtration steps. Capsules entrapping rhodamine B and rhodamine 6G meet all requirements for intracellular use in individual cell tracking. Mass spectrometry analysis reveals a sequence of deethylation steps that result in blue shifts in the dye spectra upon irradiation. Cellular studies on macrophages demonstrate robust uptake of the capsules. The capsules exhibit minimal cytotoxicity and have a negligible impact on cell motility. The successful photoconversion of RhB-containing capsules within cells highlights their potential as alternatives to photoconvertible proteins for individual cell labeling, with promising applications in personalized medicine.

Investigating a batch-flow photocatalytic LED system for diclofenac removal in wastewater treatment plants: Assessing the influence of reaction conditions on photocatalytic efficiency

This work introduces an innovative batch-flow photocatalytic LED system aimed at efficiently removing diclofenac from wastewater. The study highlights the novelty of fabricating TiO2-loaded carbon fiber photocatalysts through a hydrothermal process, exhibiting a blue shift in their absorption spectrum and enhancing their photon absorption capability. A crucial design feature is the spectral matching between the LED light source and the photocatalyst, which is critical for achieving high photodegradation efficiency. A significant innovation of our study is the testing of the system under real conditions at an operational sewage treatment plant. Here, the designed system demonstrated high efficacy in degrading diclofenac across various treatment stages, highlighting its robustness and adaptability to changing environmental conditions. The highest degradation efficiency was achieved with sewage from the secondary settling tank, where nearly 90 % efficiency was observed after 6 h of irradiation. Moreover, the use of renewable energy sources emphasizes the system's sustainability, presenting a greener alternative to traditional wastewater treatment methods. The investigation not only showcases the system's effectiveness in diclofenac degradation but also its adaptability and stability under real-world conditions, marking a significant advancement in sustainable wastewater treatment technologies.

Influence of FRET, charge separation, and density of defect states on the improvement of UV light-driven photocatalytic activity of PMMA capped ZnO nanomaterials

This study employs oxidative polymerization, co-precipitation, and ex-situ surface capping techniques to fabricate pristine PMMA, ZnO, and PMMA-capped ZnO specimens with varying PMMA concentrations. X-ray diffraction reveals reduced directional growth of ZnO, while Fourier transform infrared spectroscopy confirms PMMA chain bonding with ZnO in PMMA-capped specimens. Scanning electron microscopy illustrates decreased average length and thickness of ZnO nanoplates post-surface modification, indicating a robust interaction between PMMA and ZnO. X-ray photoelectron spectroscopy identifies suppressed defects, including zinc interstitials and oxygen vacancies, affirming ZnO surface capping by PMMA. Absorption spectra display a blue shift in band-edge or increased bandgap, attributed to the combined effects of band alignment offset and reduced oxygen vacancy states. Luminescence spectra show gradual quenching linked to PMMA content increase, with defect-related emission suppression attributed to ZnO surface capping. UV emission suppression is ascribed to donor concentration-dependent Förster resonance energy transfer (FRET) from PMMA to ZnO. Photocatalytic tests reveal enhanced efficiency in PMMA-capped ZnO catalysts attributed to synergies involving charge separation, bulk recombination centers, oxygen vacancy states, and FRET. Efficiency improves with higher PMMA content, aligning with changes in emission intensity. The study demonstrates emission intensities' tunability through surface capping and donor concentration-dependent FRET, ultimately influencing degradation efficiency.

Characterisation of the interplay between microstructure and opto-electronic properties of Cu(In,Ga)S2 solar cells by using correlative CL-EBSD measurements

Cathodoluminescence and electron backscatter diffraction have been applied to exactly the same grain boundaries (GBs) in a Cu(In,Ga)S2 solar absorber in order to investigate the influence of microstructure on the radiative recombination behaviour at the GBs. Two different types of GB with different microstructure were analysed in detail: random high angle grain boundaries (RHAGBs) and Σ3 GBs. We found that the radiative recombination at all RHAGBs was inhibited to some extent, whereas at Σ3 GBs three different observations were made: unchanged, hindered, or promoted radiative recombination. These distinct behaviours may be linked to atomic-scale grain boundary structural differences. The majority of GBs also exhibited a small spectral shift of about ±10 meV relative to the local grain interior (GI) and a few of them showed spectral shifts of up to ±40 meV. Red and blue shifts were observed with roughly equal frequency.

Preparation, structure and luminescence properties of Ce3+: Y3(Al,Ga)5O12 translucent glass ceramics for AC-LEDs

Translucent glass ceramics containing Ce3+:Y3(Al,Ga)5O12 microcrystals were prepared by spontaneous crystallization in the SiO2–B2O3–Al2O3–Ga2O3–Y2O3–PbO–CeF3 glass system. The sample exhibits around 45 % transmittance in the range of 500–800 nm. X-ray diffraction patterns confirm the garnet phases. Scanning electron microscope and laser scanning confocal microscopy images suggest that about 5 μm grains are dispersed uniformly in the glass matrix. With increasing Ga/Al ratio in the components, both excitation and emission peaks blue shift. The emission intensity reaches to the maximum at Ga/Al ratio of 8/22, and the optimized Ce3+ content is 0.4 mol%. The sample exhibits yellowish-green persistent luminescence with lifetime of 47.3 ms. The glass ceramic-based device exhibits near standard white light emission with luminous efficiency of 64.7 lm/W, correlated color temperature of 6979 K, color rendering index of 65.4 and flicker index of 76.9 %. It indicates that the Ce3+:Y3(Al,Ga)5O12 glass ceramics are promising in the alternating current directly driven white light-emitting diodes (AC-LEDs).

Crystallographic phase stability of nanocrystalline polymorphs TiO2 by tailoring hydrolysis pH

Nanocrystal TiO2 of high crystallinity (88.72 %) polymorphs have been synthesized by a unique simple route. At a low temperature under a measurable condition with differentiated hydrolysis pH of the reaction. Here titanium isopropoxide (TTIP) is used as a precursor, isopropyl alcohol (IP) is a peptizing agent and hydrolysis medium with variable pH (2.0, 2.5, 3.5, 4.5, 5.5, 7.0, 8.5, 9.5) acts as a promoter or catalyst of the reaction. We observed in the whole powder pattern fitting (WPPF) method, TiO2 consisting of 65.0 % anatase, 68.0 % brookite and 45.0 % rutile phase in weight fraction by tailoring different hydrolysis conditions with predominant crystal plane (101), (111), (110) for the individual polymorph anatase, brookite and rutile. The crystal lattice parameters, crystal structure, volume of the crystal lattice, crystal strain, asymmetry, d-spacing and average crystallite size were also studied for the polymorph. The percent of crystallinity dominating around 54.0 to 89.0 % of the titanium and oxygen atoms are arranged regularly and periodically observed for change in the molar ratio (r) tailoring the polymorph phase stability. TiO2 polymorph followed the blue shift at 319.00 to 336.00 nm and had good stability for the decreasing particle size (11.03 nm). This phenomenon has been revealed by transmission electron microscopy (TEM) into the polymorphs. Selected area electron diffraction (SAED) and nanobeam diffraction (NBD) showed the nanocrystal anatase with the prominent miller indices (101) and interplanar distance of 0.35 nm that was revealed by HR-TEM at the lowest pH. Nano anatase is ultrafine which was confirmed by EDS.