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Graphical abstract Highlights • Preparation of highly fluorescent carbon quantum dots (CQDs). • Cu2+ strongly quenched the fluorescent intensity as compared with the other metal ions. • Density functional theory revealed preferential binding between the carboxyl functionalized CQDs and Cu2+ ion. • CQDs have been applied in sensing of Cu2+ with a low detection limit (LOD) of 10 nM. • Sensing of Cu2+ in real tap and river water samples with excellent selectivity and high sensitivity. Abstract A facile, rapid and frugal approach was developed for the preparation of highly fluorescent carbon quantum dots (CQDs) by pyrolysis of Finger millet ragi (Eleusine coracana) as a carbon source. The optical properties of as-synthesized CQDs were analyzed by using UV-Visible and fluorescence spectroscopies. Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed the formation of CQDs that predominantly consists of carbonyl and hydroxyl groups which can provide more adsorption sites. The X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy indicated that the synthesized CQDs made of amorphous graphitic carbon like structure. The size distribution was in the range of 3–8 nm with a high abundance of 6 nm particles. The CQDs exhibited bright blue fluorescence emission (wavelength ∼425 nm) under UV-light with an excitation wavelength of 340 nm. Our study indicated that Cu2+ strongly quenched the fluorescent intensity of CQDs compared to other metal ions (Al3+, Ca2+, Mg2+, Ni2+, Pb2+, Mn2+, Cr3+ and Hg2+). There was a linear correlation between the quenching efficiency vs. concentration of Cu2+ ions in the range from 0 to 100 μM (R2 = 0.9918). Furthermore, CQDs have been applied in sensing of Cu2+ in real water samples with a detection limit (LOD) of 10 nM. In addition, density functional theory (DFT) calculations revealed that there was a strong interaction between CQDs with divalent metal ions whereas trivalent metal ions adsorbed weakly. Particularly, Ni2+ and Cu2+ formed a very strong bonding with CQDs compared to other divalent ions. The metal-CQDs complex structure was reported with optimized highest occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) energy gap. The nature of interaction and optical properties of the COOH-CQD's have been studied with metal ion adsorbed on the surface. Charge analysis corroborated that there was a significant charge transfer between CQDs with Ni2+ and Cu2+. Our study revealed that Cu2+ preferentially get adsorbed on aromatic C C (π-bond) of CQDs whereas other divalent metals form σ-bond(s) with the CQDs. This observation further confirmed by the HOMO-LUMO band gap (E g) and Frontier molecular orbital analysis. [ABSTRACT FROM AUTHOR]

Abstract: A new organic nonlinear optical single crystal, l-phenylalanine-4-nitrophenol (LPAPN) belonging to the amino acid group has been successfully grown by slow evaporation technique. The lattice parameters of the grown crystal have been determined by X-ray diffraction studies. FT-IR spectrum was recorded to identify the presence of functional group and molecular structure was confirmed by NMR spectrum. Thermal strength of the grown crystal has been studied using TG–DTA analyses. The grown crystals were found to be transparent in the entire visible region. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064nm. [Copyright &y& Elsevier]

Abstract: Single crystals of l-phenylalanine-benzoic acid (LPBA) were successfully grown from aqueous solution by solvent evaporation technique. Purity of the crystals was increased by the method of recrystallization. The XRD analysis confirms that the crystal belongs to the monoclinic system with noncentrosymmetric space group P21. The chemical structure of compound was established by FT-NMR technique. The presence of functional groups was estimated qualitatively by Fourier transform infrared analysis (FT-IR). Ultraviolet–visible spectral analyses showed that the crystal has low UV cut-off at 254nm combined with very good transparency of 90% in a wide range. The optical band gap was estimated to be 6.91eV. Thermal behavior has been studied with TGA/DTA analyses. The existence of second harmonic generation (SHG) efficiency was found to be 0.56 times the value of KDP. The dielectric behavior of the sample was also studied for the first time. [Copyright &y& Elsevier]

Abstract: Good transparent single crystals of l-phenylalanine l-phenylalaninium malonate (LPPMA) have been grown successfully by slow evaporation technique from aqueous solution. Single crystal X-ray diffractometer was utilized to measure unit cell parameter and to confirm the crystal structure. The chemical structure of compound was established by FT-NMR technique. The vibrational modes of the molecules of elucidated from FTIR spectra. Its optical behaviour has been examined by UV–vis spectral analysis, which shows the absence of absorbance in the visible region. Thermal properties of the LPPMA crystal were carried out by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) techniques, which indicate that the material does not decompose before melting. The melting point of grown crystal was observed as 180°C by melting point apparatus. The NLO property was confirmed by the powder technique of Kurtz and Perry. The dielectric behaviour of the sample was also studied for the first time. [Copyright &y& Elsevier]

Abstract: Tris(l-phenylalanine)l-phenylalaninium nitrate, C9H12NO2 +·NO3 −·3C9H11NO2 (TPLPN), a new organic nonlinear optical material was grown from aqueous solution by slow evaporation solution growth at room temperature. The grown crystals were subjected to powder X-ray diffraction and single crystal X-ray diffraction studies to confirm the crystalline nature and crystal structure. The modes of vibration of different molecular groups present in TPLPN have been identified by FTIR spectral analysis. The presence of hydrogen and carbon in the grown crystal were confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. The optical transmission spectral study establishes good transmitting ability of the crystal in the entire visible region. The thermogravimetric (TG) and differential thermal analyses (DTA) were carried out to understand the thermal stability of the sample. The nonlinear optical property of the compound observed using Kurtz powder second harmonic generation test assets the suitability of the grown material for the frequency conversion of laser radiation of Nd:YAG. [Copyright &y& Elsevier]

Abstract: Bulk single crystals of l-alanine alaninium nitrate [abbreviated as LAAN], an intriguing material for frequency conversion has been grown from its aqueous solution by both slow solvent evaporation and by slow cooling techniques. The optimized pH value to grow good quality LAAN single crystal was found to be 2.5. The grown crystals were subjected to single crystal X-ray diffraction studies to determine the unit cell dimensions and morphology. Vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopic technique were investigated. Also, the presence of hydrogen and carbon atoms in the grown sample was confirmed using proton and carbon NMR analyses. The dielectric constant and dielectric loss measurements of the as grown crystal at different temperatures and frequencies of the applied field are measured and reported. LAAN has good optical transmission in the entire visible region with cutoff wavelength within the UV region confirms its suitability for device fabrications. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064nm. Its Laser Damage Threshold (LDT) was measured and also tested by using a Q-switched Nd:YAG laser and the value of LDT of LAAN is 17.76GW/cm2 respectively, is found to be better than certain organic and semiorganic materials. [Copyright &y& Elsevier]

Abstract: Amino acid based crystals exhibit excellent nonlinear and electro-optical properties. A new nonlinear optical single crystal l-phenylalaninium trichloroacetate (LPTCA) belonging to the amino acid group was grown by the slow evaporation solution growth method. The grown crystals have been subjected to powder X-ray diffraction studies to identify the crystalline nature. Single crystal X-ray diffraction study showed that LPTCA belongs to monoclinic crystal system. Fourier transform infrared study is used to confirm the presence of various functional groups in the grown crystal. Optical transparency of the grown crystals was investigated by UV–vis–NIR spectrum. The lower optical cutoff wavelength for this crystal is observed at 254nm and energy band gap is 4.89eV. Thermal properties of the LPTCA crystal were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques, which indicate that the material does not decompose before melting. The melting point of grown crystal was observed to be 136°C in a melting point apparatus. The existence of nonlinear optical (NLO) property of LPTCA was confirmed by second harmonic generation test using Nd:YAG laser fundamental wavelength of 1064nm. [Copyright &y& Elsevier]

Abstract: Langmuir films of long chain Schiff base compounds: N-(4-fluorobenzylidene)hexadecanamine (compound 1), N-(4-fluorobenzylidene)octadecanamine (compound 2) and 4-{[(4-fluorobenzylidene)amino]methyl}-N-hexadecylaniline (compound 3) have been studied at air/water interface using the characteristic surface pressure-molecular area (π–A) and surface potential-molecular area (ΔV–A) isotherms. Photoelastic modulated Fourier transform infrared spectroscopy has been used to analyze the films of the three compounds at air/water interface. The Langmuir–Blodgett films of these compounds have been characterized using X-ray diffraction that shows layered structures, with interlayer distances of up to 4.4nm for compound 3. The results show that the layer-to-layer distance can be easily and rationally designed by choosing alkyl chains of different lengths and spacer. Compound 3 packs in an interdigitated bilayer structure with longer lamellar spacing whereas compounds 1 and 2 show a noninterdigitated monolayer structure. Atomistic model calculations have been carried out on the three compounds and the dipole moment values obtained agreed well with the experimental results of surface potential in Langmuir films. Among the three compounds, compound 3 forms stable vesicles spontaneously at room temperature. [Copyright &y& Elsevier]

Abstract: TiAlN films were deposited on silicon (111) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N2 plasma. Films were prepared at various nitrogen flow rates and TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900kg/mm2, whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000kg/mm2, respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (TA) of 500–900°C for 30min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800°C and got oxidized substantially at 900°C. On the other hand, the TiAlN films were stable up to 700°C and got completely oxidized at 800°C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200kg/mm2 at TA=700°C and TiAlN/CrN multilayers retained hardness as high as 2600kg/mm2 upon annealing at 800°C. [Copyright &y& Elsevier]

Optically active single crystals of L -phenylalanine D -methionine (LPDM) were grown by slow evaporation technique by co-crystallization of amino acids L -phenylalanine and D -methionine in water. The unit cell dimensions have been identified from single crystal X-ray diffraction technique. The existences of various hydrocarbyls were examined by FTIR and FT-Raman spectroscopy. The carbon and hydrogen environment of the grown crystals were analyzed by FT NMR spectrum. The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 259 nm and there by optical band gap energy E g is calculated to be 5.35 eV. The Urbach energy, extinction coefficient, reflectance were calculated from UV-absorption data. Further, the thermal stability and accurate melting point has been investigated by TG/DSC techniques. The Kurtz powder SHG was confirmed using Nd:YAG laser with fundamental wavelength of 1064 nm. The dielectric behavior of the specimen has been determined for various temperatures (313 K, 333 K, 353 K, 373 K) at different frequencies. Fluorescence study and the time resolved decay calculation was also performed for the LPDM crystal. Optical nonlinear susceptibility was measured in LPDM and the real and imaginary part of χ 3 was evaluated by Z-scan technique using open and closed apertures. [ABSTRACT FROM AUTHOR]

An organic conjugated chromophore dl -mandelic acid (DLMA) single crystal was synthesized and grown-up by means of slow evaporation technique. Single crystal X-ray diffraction study proclaimed that the DLMA crystal crystallized in monoclinic system with centrosymmetric space group P 2 1 / c . The various characteristic fundamental vibration frequencies were identified by FTIR spectroscopic studies. UV–visible spectral analysis concluded that the lower cut-off wavelength and calculated direct optical band gap of DLMA as 257 nm and 5.40 eV respectively. Thermal property of dl -mandelic acid was established through thermogravimetric and differential scanning calorimetric technique. The electric field response of DLMA crystal was investigated from the dielectric studies at a few selected temperatures and frequencies. The quantum chemical assessments such as HOMO-LUMO, molecular electrostatic potential and NLO activity were calculated and presented. In order to determine mechanical strength of DLMA crystal for various loads using Vickers microhardness tester. The real and imaginary parts of the third-order susceptibility (χ 3 ) were evaluated with the Z-scan technique using closed and open signatures respectively and was found to be Re (χ 3 ) = 4.15 × 10 −6 esu and Im (χ 3 ) = 0.47 × 10 −6 esu. [ABSTRACT FROM AUTHOR]

Structural characterizations usingXRD and 13C NMR spectroscopyof two rodlike mesogens consisting of (i) three phenyl ring core witha polar cyano terminal and (ii) four phenyl ring core with flexibledodecyl terminal chain are presented. The three-ring-core mesogenwith cyano terminal exhibits enantiotropic smectic A phase while thefour-ring mesogen reveals polymesomorphism and shows enantiotropicnematic, smectic C, and tilted hexatic phases. The molecular organizationin the three-ring mesogen is found to be partial bilayer smectic Adtype, and the interdigitation of the molecules in the neighboringlayers is attributed to the presence of the polar terminal group.For the four-ring mesogen, the XRD results confirm the existence ofthe smectic C and the tilted hexatic mesophases. A thermal variationof the layer spacing across the smectic C phase followed by a discretejump at the transition to the tilted hexatic phase is also observed.The tilt angles have been estimated to be about 45° in the smecticC phase and about 40° in tilted hexatic phase. 13CNMR results indicate that in the mesophase the molecules are alignedparallel to the magnetic field. From the 13C–1H dipolar couplings determined from the 2D experiments, theoverall order parameter for the three-ring mesogen in its smecticA phase has been estimated to be 0.72 while values ranging from 0.88to 0.44 have been obtained for the four-ring mesogen as it passesfrom the tilted hexatic to the nematic phase. The orientations ofthe different rings of the core unit with respect to each other andalso with respect to the long axis of the molecule have also beenobtained. [ABSTRACT FROM AUTHOR]