Photoluminescence Behavior Research Articles

Multi-strategy ratiometric luminescent thermometry based on Dy doped CaWO4 phosphors independent of excitation wavelength

This paper explores the detailed photoluminescence (PL) behaviors of Dy3+ doped CaWO4 (Dy:CaWO4) phosphors under multi-ultraviolet wavelength excitation. Moreover, it proposes multi-strategy ratiometric thermometry based on luminescence intensity ratio (LIR) from the transitions of thermally coupled energy levels (TCLs) of Dy3+. Under excitation of multiple ultraviolet wavelengths, the Dy:CaWO4 phosphors exhibited multi-wavelength responsive PL characteristics of Dy3+ with strong blue and yellow emissions from Dy3+ TCLs transitions. The temperature-dependent PL properties of Dy:CaWO4 phosphors were investigated over a temperature range of 300∼650 K. Multi-strategy ratiometric luminescent thermometry was examined under various excitation wavelengths by the thermal equilibrium population of Dy3+ TCLs. The proposed six LIR schemes based on the PL emissions of Dy3+ exhibited a good quantitative relationship with temperature. They showed well-luminescent thermometric behaviors with high absolute and relative sensitivities due to the largest energy gap of TCLs and a relatively larger LIR value. The thermometry properties of the multiple LIR schemes were independent of excitation wavelength, attributed to the stable site symmetry of Dy3+ and the thermal equilibrium population of TCLs under different excitation wavelengths. The multi-strategy ratiometric thermometry of Dy3+ demonstrated the merit of high sensitivity, excellent stability, and repeatability, indicating the potential luminescent thermometric application of Dy:CaWO4 phosphors.

Analysis of Structural, Photoluminescence, and Colorimetric Performance of Gd-Incorporated BNT Ceramic.

Structural, optical, photoluminescence and colorimetric analyses of Gd (1-5mol %) doped BNT ceramics synthesized by the solid-state reaction technique are reported. Structural analyses of all the samples are done by the X-ray diffraction method. It is shown that the samples have rhombohedral crystal structures with an R3C space group. The energy band gap of all the phosphors is computed from the UV-visible absorbance spectra. Photoluminescence behaviors are analyzed from the excitation along with the emission spectra of the prepared materials. The critical quenching concentration with the critical energy transfer distance is observed owing to the dipole-dipole interactions between the materials. Colorimetric analyses are carried out with the help of CIE chromaticity. Moreover, the color purity, correlated color temperature, color rendering index, and luminous efficiency of radiation values are evaluated by using the chromaticity coordinates.

Crystallization behavior and Photoluminescence of cerium doped ZAS glasses and nano glass ceramics with different Li2O content and without added nucleating agents

In this research, ZnO-Al2O3-SiO2 glass-ceramics were prepared with various contents of Li2O (1–5 mol.%). No nucleating agent was used. The prepared glasses were converted into glass-ceramics through nucleation and crystal growth processes. The physical parameters and crystallization behavior of the samples were assessed through differential thermal analysis (DTA), dilatometry, x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR). The incorporation of Li2O declined the Tg level from 820 °C to 768 °C. Gahnite and eucryptite were the dominant phases in the glass-ceramics. A rise in the Li2O content to 5 mol% led to an opaque glass-ceramic. Results showed that the addition of the lithium oxide led to the formation of a eucryptite phase alongside the primary gahnite phase. The dimension of the crystals was in the range of 20 nm through controlling the nucleation temperature and growth of the glass-ceramics. In order to induce photoluminescence (PL) property into the glasses, cerium oxide was added to all samples at 2 wt.%. The PL behavior was then investigated with the help of PL spectrum. TGC-Li3 sample exhibited up to 10 times higher PL intensities than the corresponding glass.

Effect of lanthanide doping on the optical properties of Barium Yttrium Borate

Barium Yttrium Borate Ba3Y(BO3)3 was prepared using high-temperature solid state reaction at 800°C. X-ray diffraction technique was used to confirm the crystal structure of the prepared host material Ba3Y(BO3)3. It was doped with Europium and Terbium. The doping concentration was changed as 1%, 2%, 5% and 7% mol.% in the Barium Yttrium Borate sample. FESEM analysis showed the formation of hexagonal molecular clusters of some nanometre range. The photoluminescence behaviour of all samples was studied in detail. Optimum PL intensity was recorded for 2 mol.% of Eu3+ doped in Ba3Y(BO3)3. CIE coordinates obtained for 7 mol.% doped in Ba3Y(BO3)3 showed better chromaticity near standard values as per the European Broadcasting Union (EBU). Using testing tools, such as SEM, the morphology of the prepared sample was examined. The red emission colour is due to transitions 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 , resulting in emitted wavelengths of 594 and 612 nm in Ba3Y(BO3)3:Eu3+ , respectively. The emission wavelengths of 543 nm and 551 nm are due to a transition 5 D 4 → 7 F 5 taking place in Ba3Y(BO3)3:Tb3+. This luminescent material could also be used as a downconverter material for different types of solar cells.

Low-temperature behavior of heat capacity and pho-toluminescence of a binuclear pivalate complex [Eu2(bath)2(piv)6

The low-temperature behavior of the heat capacity and photoluminescence of the previously structurally characterized binuclear pivalate complex [Eu2(bath)2(piv)6] (monoclinic, I2/a) (1), where bath = 4,7-diphenyl-1,10-phenanthroline, piv = (CH3)3CCO2-. Using the adiabatic calorimetry method, the temperature dependence of the heat capacity was measured in the temperature range 5.96–302.88 K and the thermodynamic functions Cp0(T), S0(T), Ф0(Т) and Н0(Т) - Н0(0) were calculated. The absence of low-temperature phase transformations of complex 1 was shown. It was established that in the temperature range 98-295 K, complex 1 demonstrates high temperature stability of the integral intensity of photoluminescence of the transitions of the Eu3+ ion 5D0-7Fj (j = 0.6).

Influence of PbO content on the glass forming ability, crystallization, electrical, UV–Vis. and photoluminescence spectroscopy properties of LiF.PbO system

New glass samples were synthesized from the binary system LiF. PbO with different ratiosby the traditional melt-quenching technique. The corresponding glass-ceramics were formed by heat treating the prepared glasses. Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Transmission electron microscope (TEM) were employed to study the structure of the samples; while characterization of the glass and glass-ceramics were studied using photoluminescence (PL) spectral analysis, electrical, UV–Visible absorption, optical band gap and hardness measurements. The ability to form glass was increased with increase PbO content (1LiF:≥5PbO). Tetragonal and orthorhombic PbO, orthorhombic and monoclinic Pb2O3, α-PbF2 and traces of both Li4PbO4, PbO1.37 were crystallized under specific heat-treatment circumstances as identified by XRD analysis. The crystal size decreased with increasing the PbO content; it reaches ∼15 nm in case of 10 Pb. PL revealed concentration quenching in glass with 10 Pb, a red shift and enhancement of bands intensity were observed with decrease λex, increase heat-treatment temperature and increase PbO concentration. The UV–Visible absorption elucidated that the cutoff wavelength (λ) was shifted toward lower wavelength (blue shift) by increasing PbO content and the values of optical band gap energies recorded 2.69, 2.66 and 2.72 eV for LiF·5PbO, LiF·8PbO, and LiF·10PbO, respectively. The electrical properties recorded conductivity ∼1.2 × 10−6 S m−1 and dielectric constant ∼ 46.8. These characteristics suggests that, the prepared materials exhibited semiconducting and photoluminescence behavior nominated it to be utilized in solar cell applications.

Temperature-Dependent Color-Tunable Afterglow in Zirconium-Doped CsCdCl3 Perovskite for Advanced Anti-Counterfeiting and Thermal Distribution Detection.

Persistent luminescence (PersL) materials exhibit thermal-favored optical behavior, enabling their unique applications in security night vision signage, in vivo bioimaging, and optical anti-counterfeiting. Therefore, developing efficient and color-tunable PersL materials is significantly crucial in promoting advanced practical use. In this study, hexagonal Zr4+ -doped CsCdCl3 perovskite is synthesized via a hydrothermal reaction with a tunable photoluminescent (PL) behavior through heterovalent substitution. Moreover, the incorporation of Zr4+ ions result in an extra blue emission band, originating from the enhanced excitonic recombination in D3d octahedrons. Furthermore, the afterglow performances of the samples are dramatically improved, along with the noticeable temperature-dependent PersL as well as the thermo-luminescence with tunable color output. Detailed analysis reveals that the unique temperature-dependent PersL and thermo-luminescence color change are attributed to the presence of multiple luminous centers and abundant traps. Overall, this work facilitates the development of optical intelligence platforms and novel thermal distribution probes with the as-developed halides perovskite for its superior explored PersL characteristic.

Cationic substitution engineering induced Multi-Color light emitting of bismuth in Tantalate used for WLED

Revealing and predicting the photoluminescence behavior of trivalent bismuth activated phosphors is very important for exploiting high-quality photoluminescent materials and modulating their luminescence properties, since it commonly performs multi-type electronic transitions. In this work, the chosen matrix of Gd3TaO7, which contains only one highly symmetrical cationic crystallographic site, is favorable for analyzing luminescence behavior of Bi3+ ions, and Bi3+-activated Gd3TaO7 can emit bright green light under the near-ultraviolet (NUV) light or low voltage electron beam excitation. The cationic substitution engineering of rare earths Ln (Ln = Lu, Y and La) replacing Gd3+ ions was carried out for further regulation of spectra, and multi-color light emitting was successfully realized. However, their unusual photoluminescence properties bring a novel comprehension for the photoluminescence behavior of Bi3+ ions in this system. For well rationalizing this phenomenon, the first-principles calculation was carried out for revealing their electronic structure, combined with their geometry optimization. The results indicate multi factors have contribution in modulating the luminescence behavior of Bi3+ ions, especially the interaction between 3P1 state, metal-to-metal charge transfer state and Bi-Bi dimers. The result is favorable for us to exactly adjust the luminescence properties of Bi3+ ions.

Solid superacid catalysts promote high-performance carbon dots with narrow-band fluorescence emission for luminescence solar concentrators

Facile and efficient method for constructing carbon dots (CDs) with narrow full width at half maximum (FWHM) is a major challenge in the field, and researches on regulating the FWHM of CDs are also rare and scarce. In this work, we delved into the synthesis of CDs with narrow fluorescence emission FWHM (NFEF-CDs) in the m-phenylenediamine (m-PD)/ethanol system, utilizing solid superacid resin as catalyst with solvothermal method. The resulting NFEF-CDs exhibit a photoluminescent (PL) emission peak at 521 nm with a narrow FWHM of 41 nm, an absolute PL quantum yield (QY) of 80%, and display excitation-independent PL behavior. Through comprehensive characterization, we identified the protonation of edge amino on NFEF-CDs as the key factor in achieving the narrow FWHM. Subsequently, we validated the broad applicability of solid superacid resins as catalysts for synthesizing CDs with narrow FWHM in the m-PD/ethanol system. Finally, we utilized a self-leveling method to prepare NFEF-CDs film on the surface of poly(methyl methacrylate) (PMMA) substrate and investigated the solid-state fluorescence properties of NFEF-CDs as well as their performance as luminescence solar concentrator (LSC) for photovoltaic conversion. The results revealed that the as-prepared LSC exhibit an internal quantum efficiency (ηint) of 42.39% and an optical efficiency (ηopt) of 0.68%. These findings demonstrate the promising prospects of NFEF-CDs in the field of LSCs and provide a theoretical basis for their application in photovoltaic conversion.

Unusual Thermal Quenching of Photoluminescence from an Organic–Inorganic Hybrid [MnBr4]2−‐based Halide Mediated by Crystalline–Crystalline Phase Transition

AbstractThe ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)2MnBr4 (DMML=N,N‐dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr4]2− tetrahedrons that leads to non‐radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire‐new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.

Unusual Thermal Quenching of Photoluminescence from an Organic-Inorganic Hybrid [MnBr4 ]2- -based Halide Mediated by Crystalline-Crystalline Phase Transition.

The ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)2 MnBr4 (DMML=N,N-dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr4 ]2- tetrahedrons that leads to non-radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire-new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.

Pyrazine as a More Efficient Luminophore than Benzene for Producing Red-Shifted and Enhanced Photoluminescence.

The development of organic photoluminescent (PL) materials with red-shifted and enhanced emissions is beneficial to promoting their applications. Luminescent materials based on aromatic heterocycles (e.g., pyrazine) usually have red-shifted and enhanced photoluminescence compared with phenyl-based luminescent materials. In this work, the photoluminescence behaviors of pyrazine and its derivatives (o-dichloro-, o-dicyano-, and dichlorodicyano-substituted) are compared with those of benzene and its derivatives. All compounds exhibit fluorescence emissions ranging from blue to yellow, and the fluorescence emissions of pyrazinyl compounds are more red-shifted than those of phenyl compounds. Except for the o-dicyano-substituted compound, pyrazinyl compounds exhibit stronger fluorescence emissions than corresponding phenyl compounds in both pure substances and ethanol solutions. In addition, both 5,6-dichloro-2,3-dicyanopyrazine (P4) and 4,5-dichloro-1,2-dicyanobenzene (B4) exhibit room temperature phosphorescence, and the maximum delayed emission wavelength is red-shifted from 575 nm of B4 to 637 nm of P4. The energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the monomers of pyrazinyl compounds are reduced by 0.07-1.37 eV compared with the monomers of phenyl compounds, which is the fundamental reason for the red-shifted emissions of the pyrazinyl compounds. Moreover, compared to B4, the smaller molecular spacing in the P4 crystal structure facilitates interlayer electron transfer and hence the formation of more extended through-space conjugation, resulting in the red-shifted emission of P4. This work proves that pyrazine is a more efficient luminophore than benzene for constructing PL compounds with longer emission wavelengths and higher quantum yields, which are important in guiding the design and preparation of organic PL materials.

Analysis of platinum-based anticancer injections cisplatin and carboplatin in blood serum and urine of cancer patients by photometry, fluorometry, liquid chromatography using a Schiff-base as derivatizing reagent

Photometric, fluorometric and liquid chromatographic methods were proposed to analyze Pt(II) from cis-platin and carbo-platin injections after derivatization with reagent 2-oxo-propanoic acid N-phenylhydrazonecarbothioamide. The reagent reacted with metals Au(III), Ag(I), Mn(II), Pt(II), Mo(VI), V(V/IV) to develop their characteristic colors in the pH range 3–12 and were extracted in organic solvent trichloromethane. The photoluminescent behavior of ligand and its metal complexes was investigated to correlate the emission pattern. Liquid chromatographic method was also proposed to analyze cis-platin and carbo-platin anti-cancer drugs based on the pre-column derivatizing platinum(II) with ligand. The complex of platinum was separated and eluted from HPLC column Microsorb C-18, (150 cm x 4.6 mm i.d, 5 µm) comprising eluents - tetrabutyl ammonium bromide (1 mM)-sodium acetate (1 mM)-acetonitrile-water-methanol (02:02:06:22:68 v/v/v/v/v). Metals Au(III), Ag(I), Mn(II), V(IV/V), Mo(VI) were also separated completely. The linear calibration range 0.5–2.5 µg/mL was observed following Beer’s law with detection limit of 150.00 ng/mL Pt(II). The determination of cis-platin and carbo-platin injections by photometric, fluorometric and chromatographic methods showed RSD (n = 3) 1.14–3.12, 0.98–2.84, 0.92–2.72% respectively. The developed methods were employed to analyze cis-platin in samples of serum and urine of cancer patients undergoing chemotherapy and platinum amounts were observed within 45.0—86.0, 49.0—91.0, 42.0—84.0 ng/mL and 82.0—398, 81.0—389, 74.0—391 ng/mL with relative standard deviation (RSD) (n = 4) of 2.28—3.88, 2.40—3.82, 2.52—3.82% and 2.52—3.91, 2.44—3.94, 1.98—3.24% by liquid chromatographic, fluorometric and photometric techniques respectively.

Large-scale irrigation of Cr3+ into different octahedra of zinc aluminate toward continual broadband near-infrared emission

Broadband near-infrared (NIR) phosphors, as key materials in NIR phosphor-converted light-emitting diodes (pc-LEDs) for emerging applications, have recently attracted considerable attention. Herein, by selecting a comprehensive engineering strategy of co-substituting [Al3+-Al3+] with [Mg2+-Ge4+] units and increasing Cr3+ concentration, a novel Cr3+-doped ZnAl1.16Mg0.4Ge0.4O4 (ZA(MG)0.4:2 at.%Cr3+) phosphor with continual broadband NIR emission was synthesized. The site occupation of Mg2+/Ge4+ in ZnAl2O4 is unraveled by Rietveld structure refinement and density functional theory (DFT) calculations. According to the photoluminescence behaviors, the formed defect clusters of ZnAl’-Cr3+-GeAl· and MgAl’-Cr3+-GeAl· can not only introduce shallow defects to serve as new traps to obtain long-persistent luminescence but can also enhance the emission intensity at ∼689 nm and ∼694 nm. The quantity and scale of Cr3+-Cr3+ pairs and Cr3+ in distorted sites, which can improve the thermal quenching resistance and emission intensity in the range of 700–800 nm, can be accurately regulated by varying the concentration of Cr3+. Under 387 nm excitation, the designed material exhibits intensive NIR emission from 685 to 750 nm with a wide full-width at half maximum (FWHM) of 95 nm. The electroluminescence spectrum and potential applications of the NIR pc-LED prepared using ZA(MG)0.4:2 at.%Cr3+ phosphor are also reported. The results promise a feasible strategy to develop NIR phosphors as NIR pc-LEDs lighting sources for applications in non-destructive detection and anti-counterfeiting.

Ag-Doped Free-Standing 2D TiO2 Sheets: Electronic, Optical, Magnetic, and Self-Healing Behaviour.

Beyond a critical doping level, Ag - 2D TiO2 sheets (ATO) are deemed to be a flexible transparent conductor, useful for visible-range functional photonic/optoelectronic devices/sensors, sunlight-sensitive catalysis, and light-activated resistive switching. Due to the lack of control of surface energy which often leads to the formation of structural defects and even dimensionality crossover (2D to 0D) of materials during doping reaction, it is challenging to obtain ATO with a controlled doping level. Gauging the urgency, therefore we report the surface energy-controlled synthesis of ATO employing liquid phase exfoliation of TiO2 and subsequent hydrothermal Ag-doping in the presence of Hexamethylenetetramine (HMTA). Electron microscopy and atomic force microscopy reveal ATO sheets with large lateral dimensions. 6-fold, 4-fold, and strain-mediated crystallographic phases of 2D ATO have been revealed by high-resolution electron imaging. Successful tuning of the band gap down to ~ 2 eV with Ag doping up to ~ 10% is obtained. Synthesized 2D ATO have been investigated for their electrical, optical, optoelectronic, photoluminescence, and ferromagnetic behaviour. Visible light-sensitive thermally/structurally robust semiconductor/conductor via tuneable doping will pave the way for their flexible as well as wearable device applications. Self-healing effect of AFM tip-generated mechanical stress has also been demonstrated.

Luminescence properties of ZrO2: Dy3+ phosphor for solid-state lighting applications

Herein, we report Dy3+-activated ZrO2 phosphors synthesized via the sol-gel technique. The structural, morphological, and optical properties of the synthesized powder samples annealed at 900 °C were investigated. The monoclinic phase of the synthesized phosphor was confirmed by recording the X-ray powder diffraction (XRPD) pattern. Ultraviolet–visible analysis was performed for the reflectance and bandgap measurements of the phosphors. Field emission scanning electron microscope and X-ray energy dispersive spectroscopy analyses were used to study the morphology and elemental composition of the phosphors, respectively. The distribution of ions in the undoped and Dy3+-doped samples was confirmed using time-of-flight secondary ion mass spectroscopy. The photoluminescence (PL) behavior of the synthesized phosphors was investigated by recording the excitation and emission spectra. When the synthesized phosphors were exposed to UV light at 353 nm, we observed characteristic blue and yellow Dy3+ PL emissions, corresponding to the transition 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. Additionally, we observed low-intensity red and brown-red emission peaks corresponding to 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2. These observations indicate that the non-aqueous sol-gel route, coupled with the suitable post-synthesis heat treatment, resulted in the development of a monophase (monoclinic) zirconia. This makes it a strong candidate for phosphor applications due to its high room temperature stability and efficient characteristic features of the monoclinic phase. These findings strongly suggest that Dy3+-doped ZrO2 can serve as a superior phosphor material for white light-emitting diode applications.

Temperature-dependent photoluminescent behavior of millimeter-scale Cs4PbBr6/CsPbBr3 bulk crystals and their application to white light-emitting diodes

The zero-dimensional perovskite composite Cs4PbBr6/CsPbBr3 has attracted significant attention for its remarkable photoluminescence (PL), which remains highly effective even in solid state. This work presents a detailed analysis of the steady-state and time-resolved PL (TRPL) behavior of millimeter-scale Cs4PbBr6/CsPbBr3 crystals over a temperature range of 80 to 360 K, which covers exciton binding energy, phonon energy, and PL peak energy shifting with increasing temperature. According to the results, Cs4PbBr6/CsPbBr3 exhibits high exciton binding energy and phonon energy, with calculated values of 358.7 and 94.8 meV, respectively. Specifically, when the temperature is below ∼235 K, thermal expansion dominates to influence the TRPL and peak energy, whereas electron-phonon interaction becomes the dominant factor as temperature rises from 235 to 325 K. It is found that Cs4PbBr6/CsPbBr3 has a PL behavior similar to CsPbBr3, and characterization and TRPL results demonstrate that nanometer-scale CsPbBr3 crystals embed in the Cs4PbBr6 bulk matrix. Meanwhile, a white light-emitting diode (WLED) device based on Cs4PbBr6/CsPbBr3 with luminous efficiency of 64.56 lm/W is fabricated, and its color coordinate is measured as (0.34, 0.31) under 20 mA, which is in close proximity to the standard white color coordinate. Moreover, the color gamut of the device is measured as 128.66% of the National Television Systems Committee (NTSC). The WLED electroluminescence (EL) spectra show high Correlated Color Temperature (CCT) stability for the working current varying from 5 to 100 mA, and after continuous operation for 12 h, the EL intensity decreases and stabilizes at ∼70% of the initial EL intensity. These findings suggest that Cs4PbBr6/CsPbBr3 crystals are a promising candidate for WLEDs.

Synthesis of sustainable curcumin based photo-crosslinkable benzoxazines: Thermal, hydrophobic and anti-corrosion properties

Bifunctional polybenzoxazines have been developed using sustainable bio-phenol curcumin, paraformaldehyde with varying nature of monofunctional amines through Mannich condensation. The molecular structure of synthesized benzoxazines were confirmed by ATR-FTIR, 1HNMR and 13CNMR and high-resolution mass spectroscopic (HRMS) analyses. DSC thermograms were used to ascertain the curing behaviour of curcumin-based monomers. Thermal curing of Cu-api occurs at 192 °C and that of Cu-aa undergoes dual curing at 177 °C and 209 °C due to its inherent molecular structure. The thermal stability of synthesized polybenzoxazines was studied using TGA, Cu-a exhibits higher char yield of 63% due to higher aromatic content than that of other polybenzoxazines. The occurrence of dimerization (2π+2π cycloaddition) of curcumin based benzoxazines proceeds through conjugation present in the main chain of curcumin when exposed to UV irradiation, and was monitored through UV–visible spectroscopy. All the synthesized benzoxazine monomers were excited within the wavelength of UV range with occurrence of photoluminescence behaviour in visible region ranges between 448 nm and 530 nm. The value of band gap calculated for the curcumin-based monomers ranged from 3.55 to 3.77 eV. The explicit character of curcumin based benzoxazines can be exploited in the field of optical applications. The hydrophobic behaviour of polybenzoxazines was also studied and the highest water interface angle value of 146° was observed for poly(Cu-tfma) due to the presence of fluorine groups. Furthermore, the Cu-tfma coated cotton fabric was tested for its durability and the results indicated that these materials coated cotton fabrics are better suitable for sustainable high performance hydrophobic applications. The anti-corrosion studies indicated that the poly(Cu-api) coated on mild steel exhibits greater resistance towards corrosion amongst the other polybenzoxazines which can be potentially employed as coating in marine environments.

Effect of Ce codoping on the thermoluminescence dosimetry and photoluminescence behavior of SrBPO5:Dy/Sm/Eu

Effect of Ce on the thermoluminescence and photoluminescence of Dy, Sm and Eu in SrBPO5 was investigated. Samples of Sm, Dy, Eu doped and Ce-Dy/Sm/Eu codoped SrBPO5 were prepared through the high temperature solid-state synthesis route. Prepared phosphor samples were checked for their phase purity with powder X-ray diffraction analysis. Thermoluminescence glow curves were recorded for the phosphors and explored for the dosimetric applications. TL glow curves of 20 Gy gamma irradiated SBP:Dy0.01−1/Sm0.01−1/Eu0.01−1 and SBP:Ce1-Dy0.01−1/Sm0.01-Eu0.01−1 were obtained with 2 K/s heating rate. Gamma dose response of the phosphor samples were studied from 5 mGy to 100 Gy. The SBP:Ce1-Dy0.5 and SBP:Ce1-Sm1 demonstrated excellent dose linearity to gamma dose. The thermoluminescence behavior indicated that, Ce codoping has profound effect on the amount and type of traps and the glow peak intensity of Ce codoped SBP:Dy/Sm enhanced significantly. The photoluminescence study suggested efficient exchange type energy transfer interaction between excited states of Ce3+ and Dy3+/Sm3+ in the SrBPO5 host. The results confirmed the suitability of SBP:Ce-Dy/Sm phosphors for the thermoluminescence applications. The range of dose linearity of SBP:Ce-Dy, and SBP:Ce-Sm phosphor were found to be better than the commercial CaSO4:Dy and could be promising materials for personal as well as accidental dosimetry.

Photo-Controlled Nano-Supramolecular Size and Reversible Luminescent Behaviors Based on Cucurbit[7]uril Cascaded Assembly.

Supramolecular luminescent material with switchable behavior and photo-induced aggregation with emission enhancement is a current research hot spot. Herein, a size-tunable nano-supramolecular assembly with reversible photoluminescent behavior was constructed by noncovalent polymerization of diarylethene-bridged bis(coumarin) derivative (DAE-CO), cucurbit[7]uril (CB[7]), and β-cyclodextrin-grafted hyaluronic acid (HACD). Benefiting from the macrocyclic confinement effect, the guest molecule DAE-CO was included into the cavity of CB[7] to give enhanced fluorescence emission of the resulting DAE-CO⊂CB[7]2 with longer lifetime at 432 nm to 1.43 ns, thereby further enhancing fluorescence output and lifetime (1.46 ns) when further assembled with HACD, compared with the free DAE-CO (0.95 ns). In addition, DAE-CO, DAE-CO⊂CB[7]2, and DAE-CO⊂CB[7]2&HACD all possessed characteristics of aggregation-induced emission and reversible photo-switched structural interconversion, exhibiting an obvious photophysical activation phenomenon of self-aggregation into larger nanoparticles with increase in fluorescence emission intensity, lifetime, and size after irradiation, which could be increased step by step with the alternating irradiation of 254 nm (5 min) or >600 nm (30 s) repeated 7 times. These supramolecular assemblies were successfully used in the tumor cells' targeted imaging and anti-counterfeiting because of the capability of HACD for recognizing specific receptors overexpressed on the surface of tumor cells and the excellent photo-regulated switch ability of DAE-CO, providing an approach of constructing photo-induced emission-enhanced luminescent materials.