Correlation between thermoluminescence and mechanoluminescence of γ-ray-irradiated Dy-doped BaB<Subscript>4</Subscript>O<Subscript>7</Subscript> phosphors

Undoped and dysprosium (Dy)-doped BaB₄O₇ phosphors have been synthesised by solid-state diffusion technique and its thermoluminescence (TL) and mechanoluminescence (ML) has been studied. A single peak at 162 °C along with two shoulders around 242 and 294 °C was observed in TL glow curve of undoped BaB₄O₇ phosphors. TL intensity increased with increasing dopant concentration and broad band was observed for the sample having 0.5 mol% of dopant concentrations. For higher concentration of dopant, concentration quenching occurred. ML has been excited impulsively by dropping a piston of mass 0.6 kg on the phosphors with various impact velocities. As the piston was dropped on to the sample, ML intensity initially increased with time attained an optimum value for a particular time then decreased and finally disappeared. ML intensity varied with dopant concentration and it has been obtained optimum for the sample having 0.5 mol% of dopant. TL and ML intensity increased with gamma doses given to the sample. ML intensity increased almost linearly with the impact velocity of the piston dropped on to the sample, however, time corresponding to ML peak shifted towards shorter time value with increasing impact velocity of the piston dropped on to it. ML emission spectrum showed characteristic emission of Dy³⁺ ions. In order to study the influence of deformation on TL, TL was recorded after deforming the sample by dropping the load on to it. When the TL was recorded after deforming the sample, it is found that TL yield decreased markedly and it further decreased with increasing the height of the piston from which it was dropped. Results suggest that though the mode of excitation is different in these two phenomena but similar states are responsible for TL and ML.     

Study of electron vibrational interaction parameters in chlorophosphate activated with Eu ion

We present the results of theoretical study of photoluminescence of Eu²⁺ ions activated chlorophosphate M_5.17(PO₄)₃Cl₅:Eu²⁺ with M = Ca, Sr and Ba estimating electron-vibrational interaction (EVI) parameters such as Huang–Rhys factor, effective phonon energy, Stokes shift and zero phonon line position. Validity of the calculated result was established by modeling the emission line which was found to be in good agreement with the measured photoluminescence spectrum of Eu²⁺ doped chorophosphates.     

Precipitation based synthesis and luminescence of Ln (Eu,Ce, Dy,Sm, Tb) activated BaCa2Si3O9-Walstromite cyclosilicate phosphors

A series of new phosphors of BaCa₂Si₃O₉:Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) were synthesized by precipitation based method. Good crystallinity was achieved after annealing the sample at 750 °C for 1 h in air. X-ray powder diffraction (XRD) result confirmed the formation of desired BaCa₂Si₃O₉ host. The photoluminescent excitation and emission properties of Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) activated BaCa₂Si₃O₉ were investigated in detail. The photoluminescence (PL) analysis of individual Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) activated BaCa₂Si₃O₉ phosphors exhibits interesting characteristic emission properties in their respective regions. From the measured emission spectra, Judd–Ofelt (J–O) intensity parameters (Ω₂, Ω₄, Ω₆) have been calculated and using these J–O parameters various radiative parameters such as radiative transition probabilities (A_rad), radiative lifetimes (τ_R), branching ratios (β_R) and relative quantum yield have been calculated for the studied ions.     

Controlled synthesis of low‐molecular‐weight polyethylene waxes by titanium–biphenolate–ethylaluminum sesquichloride based catalyst systems

Soluble complexes of titanium(IV) bearing sterically hindered biphenols, such as biphenol, 1,1′‐methylene di‐2‐naphthol, 2,2′‐methylene bis(4‐chlorophenol), 2,2′‐methylene bis(6‐tert‐butyl‐4‐ethyl phenol), and 2,2′ ethylidene bis(4,6‐di‐tert‐butyl phenol), were prepared and characterized. These catalyst precursors, formulated as [Ti(O∧O)X₂], were active in the polymerization of ethylene at high temperatures in combination with ethylaluminum sesquichloride as a cocatalyst. The ultra‐low‐molecular‐weight polyethylenes (PEs) were linear and crystalline and displayed narrow polydispersities. The catalytic polymerization leading to PE waxes in this reaction exhibited unique properties that have potential applications in surface coatings and adhesive formulations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1531–1539, 2007     

Luminescent studies of impurity doped SrS phosphors

SrS phosphors activated with Ce and Dy ions were prepared by solid-state diffusion method. Photoluminescent study was carried out on SrS : Ce, SrS : Dy and SrS : Dy, Ce. Thermoluminescence and electron spin resonance studies were also carried out on SrS : Dy phosphor. The thermoluminescence glow curve shows a peak at around 142° C. Irradiated SrS : Dy exhibits an ESR line due to a defect centre. Thermal annealing behaviour indicates that this centre correlates with the TL peak at 142°C. The centre is characterized by an isotropicg-value of 2.0039 and is assigned to aF ⁺centre.     

Mechanical properties of PP-LDPE blends with novel morphologies produced with a continuous chaotic advection blender

When immiscible polymer melts are combined by chaotic advection, melt domains are recursively stretched and folded. A multi-layer blend morphology results that has a hierarchical structure and intrinsic mechanical interlocking. Novel derivative morphologies can be obtained via the formation and interactive growth of holes among melt layers. In this study, a unique continuous chaotic advection blender (CCAB) was used to investigate influences of these morphologies on tensile and impact toughness properties of polypropylene (PP)-low density polyethylene (LDPE) blends. Although prior related work has focused on batch processing, this study also demonstrated the viability of chaotic advection in continuous flow modes suited for extruding blends with target morphologies. Extrusions were producible with morphologies giving an overall combination of improved properties relative to properties associated with droplet morphologies typically obtained with conventional compounding equipment. Applicability to injection molding is also discussed. Novel processing control features of the CCAB-type devices are briefly described.     

Synthesis and photoluminescence properties of La1−xAlO3:xTb green phosphors for white LEDs

Tb³⁺-doped La_1−xAlO₃ phosphor powders are successfully synthesized by the solution combustion method, using citric acid as the combustion fuel. The crystal structure and photoluminescence properties of La_1−xAlO₃:xTb³⁺ phosphors are studied, depending on Tb³⁺ content. The strongest emission peak is found at 543 nm, which originates from the ⁵D₄→⁷F₅ transition of Tb³⁺ ions, indicating green emission. Among the fabricated phosphors, the La_0.9AlO₃:0.1Tb³⁺ phosphor emits the strongest green light. The excellent luminescent properties make it a possible candidate for white light-emitting diodes and various photonic applications.     

Electron–vibrational interaction in 5d state of Ce ion in (LiMg/Li2Na/Li3)BF6 phosphors

The electron–vibrational interaction (EVI) parameters such as Huang–Rhys factor, effective phonon energy and zero phonon line position were estimated using data from our recent reported work, on photoluminescence in rare earth doped complex hexafluorides phosphors LiMgBF₆, Li₂NaBF₆ and Li₃BF₆ Validity of results were established by modeling the emission line which was found to be in good agreement with experimental photoluminescence spectra.