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Corresponding to each group Γ, a mixed graph G = (Γ,E,E′) called C-graph is assigned, such that the vertex set of G is the group itself. Two types of adjacency relations, that is, one way and two way communication is defined for vertices, to get a clear idea of the underlying group structure. An effort to answer the question, ‘Is there any relation between the order of an element in the group and degrees of the corresponding vertex in the C-graph’, by proposing a mathematical formula connecting them is made. Established an upper bound for the total number of edges in a C-graph G. For a vertex z in G, the concept Connector Edge CEz is defined, which convey some structural properties of the group Γ. The Connector Edge Set is defined for both a vertex z and the whole C-graph G, and is denoted as C E z and C E G respectively. Proposed the result, C E G = E if and only if |Γ| = 2n, n ∈ N. Finally, the properties of G, which the Connector Edge Set C E G carry out are discussed.

In the present study, total suspended particulate matter (TSP) samples were collected at 47 different sites (47 grids of 5 × 5 km2 area) of Delhi during winter (January–February 2019) in campaign mode. To understand the spatial variation of sources, TSP samples were analyzed for chemical compositions including carbonaceous species [organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC)], water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), polycyclic aromatic hydrocarbons (16 PAHs), water-soluble inorganic species (WSIS) (F−, Cl−, SO42−, NO2−, NO3−, PO43−, NH4+, Ca2+, Mg2+, Na+, and K+), and major and minor trace elements (B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Fe, Zn, Cr, Mn, Cu, As, Pd, F, and Ag). During the campaign, the maximum concentration of several components of TSP (996 μg/m3) was recorded at the Rana Pratap Bagh area, representing a pollution hotspot of Delhi. The maximum concentrations of PAHs were recorded at Udhyog Nagar, a region close to heavily loaded diesel vehicles, small rubber factories, and waste burning areas. Higher content of Cl− and Cl−/Na+ ratio (>1.7) suggests the presence of nonmarine anthropogenic sources of Cl− over Delhi. Minimum concentrations of OC, EC, WSOC, PAHs, and WSIS in TSP were observed at Kalkaji, representing the least polluted area in Delhi. Enrichment factor

Trivalent samarium activated β-Wollastonite (β-CaSiO3:Sm3+) nanostructured phosphor powders have been synthesized by modified sol-gel method at various concentrations (0.0, 0.2, 0.4, 0.6, 0.8 and 1 mol %) employing rice husk ash (RHA) and eggshell (ES) as the precursors for SiO2 and CaO respectively. The powder x-ray diffraction peaks disclose structure of sintered samples as monoclinic structure with space group P1 21/c1. The average crystallite sizes were determined by Debye scherrer's formula in the range of 26–34 nm. The average particle size was 84.5 nm found from TEM images. The photoluminescence excitation (PLE) spectra recorded high intensity peak at 400 nm was owing to 6H5/2 → 4K11/2 transition. The emission (PL) spectra of prepared samples exhibit intense orange–red color emission peak at 602 nm due to 4G5/2 → 6H7/2 transition. All the prepared samples emission tuned towards white region of the CIE diagram with the increment of Sm3+ content. This new nanostructured phosphor material could be a probable candidate for white light display and solid-state lighting (SSL) applications.

Optically transparent single crystals of ethyl p-hydroxybenzoate (EPHB) were successfully grown by the vertical Bridgman technique. The crystalline phase and unit-cell dimensions were obtained from powder X-ray diffraction using Rietveld analysis. The presence of defects and grain boundaries was investigated by high-resolution X-ray diffraction. The optical quality of the grown single crystal was assessed by UV–Vis and photoluminescent spectroscopies. A blue emission, with a bi-exponential decay time, was obtained from time-resolved photoluminescence upon laser excitation at 266 nm. The mechanical strength of the EPHB single crystal was studied by Vickers hardness testing. A decrease in the laser-damage threshold was observed with a nanosecond Nd:YAG laser source for increased pulse repetition rates. The third-order nonlinearity, nonlinear absorption coefficient and nonlinear refractive index were measured using the Z-scan technique with a femtosecond Ti:sapphire laser. The third-order nonlinear coefficient values for the grown crystal were compared with those of a potassium dihydrogen phosphate single crystal.

Organic nonlinear-optical single-crystal methyl p-hydroxybenzoate (MPHB) is one of the potential candidates for use in terahertz applications. The focus of this work is to study the response of MPHB single crystal in the terahertz region of the electromagnetic spectrum using time-domain terahertz spectroscopy (THz-TDS). Single-crystal MPHB was grown by the conventional slow evaporation solution growth technique (SEST). The structural confirmation of the title compound was assessed by powder x-ray diffraction (PXRD) analysis. The optical bandgap of ingot crystal was calculated using Tauc’s equation based on ultraviolet–visible (UV–Vis) spectroscopy. The photoluminescence emission spectrum revealed a major emission in the blue region corresponding to 457 nm. The dominant color emission for the title compound was assessed by converting the major emission peak to a Commission Internationale de l’Eclairage (CIE) chromaticity diagram, which further confirmed the emission of blue light from the crystal. The dynamics of the photon emission and its decay time for the title compound were studied by time-resolved photoluminescence (TRPL). THz-TDS was performed in the range from 0.2 THz to 3.0 THz on the title single crystal to observe its optical absorption behavior in the THz energy range. The variation of the absorption coefficient at terahertz frequencies is also presented herein.

The study represents the seasonal characteristics (carbonaceous aerosols and elements) and the contribution of prominent sources of PM2.5 and PM10 in the high altitude of the eastern Himalaya (Darjeeling) during August 2018–July 2019. Carbonaceous aerosols [organic carbon (OC), elemental carbon (EC), and water soluble organic carbon (WSOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Cr, Ni, Mo, Cl, P, S, K, Zr, Pb, Na, Mg, Ca, and B) in PM2.5 and PM10 were analyzed to estimate their possible sources. The annual concentrations of PM2.5 and PM10 were computed as 37±12 μg m−3 and 58±18 μg m−3, respectively. In the present case, total carbonaceous species in PM2.5 and PM10 were accounted for 20.6% of PM2.5 and 18.6% of PM10, respectively, whereas trace elements in PM2.5 and PM10 were estimated to be 15% of PM2.5 and 12% of PM10, respectively. Monthly and seasonal variations in mass concentrations of carbonaceous aerosols and elements in PM2.5 and PM10 were also observed during the observational period. In PM2.5, the annual concentrations of POC and SOC were 2.35 ± 1.06 μg m−3 (66% of OC) and 1.19±0.57 μg m−3 (34% of OC), respectively, whereas annual average POC and SOC concentrations in PM10 were 3.18 ± 1.13 μg m−3 (63% of OC) and 2.05±0.98 μg m−3 (37% of OC), respectively. The seasonal contribution of POC and SOC were ranging from 55 to 77% and 33 to 45% of OC in PM2.5, respectively, whereas in PM10, the seasonal contributions of POC and SOC were ranging from 51 to 73% and 37 to 49% of OC, respectively. The positive relationship between OC & EC and OC & WSOC of PM2.5 and PM10 during all the seasons (except monsoon in case of PM10) indicates their common sources. The enrichment factors (EFs) and significant positive correlation of Al with othe crustal elements (Fe, Ca, Mg, and Ti) of fine and coarse mode aerosols indicate the influence of mineral dust at Darjeeling. Principal component analysis (PCA) resolved the four common sources (biomass burning + fossil fuel combustion (BB + FFC), crustal/soil dust, vehicular emissions (VE), and industrial emissions (IE)) of PM2.5 and PM10 in Darjeeling.

Congruent lithium niobate single crystals with a Ru:Mg co-dopant have been successfully grown using the Czochralski technique from the melt containing 0.02 mol % Ru with Mg of two varied concentrations (4.0 and 6.0 mol %). The effects of Ru and Mg co-doping on the crystalline quality were determined by high-resolution X-ray diffractometry, which confirmed that the crystalline quality is good and that the dopants are statistically distributed in the crystal. The Raman scattering analysis shows no change in the lattice vibration except a slight change in the peak width and intensity due to more asymmetry in the molecular charge, which leads to enhancement of the polarizability. The optical transmission spectra indicate that both the crystals have high optical transparency in the visible region, with a shift of the absorption edge toward shorter wavelengths, as compared to un-doped LN. The weak absorption band observed below 400 nm is attributed to Ru ions. The influence of co-doping in the electronic band gap energies is calculated by the Tauc relation. The refractive index is measured by using a prism coupler at two wavelengths (532 and 1064 nm). The calculated absorption coefficients and direct and indirect band gap energies for both the samples are found to be nearly the same within experimental error. A decrease in the birefringence is observed for the Ru:Mg(6 mol %) doped sample. The observed slight reduction in refractive indices with Ru:Mg co-doping is consistent with a rise in band gap energy, which is related to the change in absorption edge to the lower wavelength. The second harmonic generation (SHG) efficiency is measured by the Kurtz and Perry powder method, and a decrease in SHG efficiency for Ru:Mg(6 mol %) is observed.

Potassium dihydrogen phosphate (KH2PO4; KDP) is a well known nonlinear optical (NLO) material for optoelectronic, laser technology and fiber optical communication device applications. In a view to yeild better device properties, l-Phenylalanine (l-Phe) aminoacid doped KDP (LKDP) crystals with different dopant concentrations (0.5 mol%, 1 mol% and 2 mol %) were grown by slow evaporation solution technique (SEST). The grown crystals were powdered of micron size crystallites and subjected to powder X-ray diffraction (PXRD). In PXRD spectra, a few peaks with increasing intensity were observed in LKDP crystals when compared to pure KDP, revealing the effect of incorporation of dopants in the crystalline matrix of KDP and the enhancement of growth rate along [100] direction. FT-IR spectrum confirms the incorparation of dopant in KDP crystalline matrix with the presence of different vibrational modes of assignments belongs to L-Phe. To study the crystalline perfection of pure and doped crystals, the high-resolution X-ray diffraction (HRXRD) was employed and the crystalline perfection was found to be reasonably good with relatively low values of FWHM. UV–Vis-NIR spectroscopy results show significant increase in optical transmission up to ~ 80% from ~ 60% (pure KDP) in the entire visible spectrum of l-Phe doped KDP at low doping concentration. However, it was decreased to ~ 70% when we increase the dopant concentration by 2 mol% and suggests that if we increase the dopant (l-Phe) concentration above an optimal value in KDP, the transmission decreases. The Photoluminescence (PL) spectrum reveals high crystalline perfection at low concentration of dopants as observed by the sharp peaks. The weak green emission peak for sample with higher dopant concentrations indicates the segregation of doped molecules at the structural grain boundaries as observed in the HRXRD studies. The mechanical strength of pure and doped KDP crystals with increasing dopant concentration has been studied and found that the hardness was increased slightly due to doping. The powdered sample of micron size particle made from as grown crystals were subjected to Kurtz powder technique to observe the relative second harmonic generation (SHG) efficiency in comparison with the pure KDP. These results reveal significant enhancement of SHG efficiency with increasing doping concentration up to 2 mol% in KDP crystals which is 1.31 times to that of pure KDP.

This work focuses on the bulk growth of Itaconic acid (ITA) single crystal from aqueous solution by slow evaporation solution growth technique. The detailed structural, optical, laser studies have been carried out for the title compound by adopting different instrumentation techniques. The cut-off wavelength of ITA crystal was obtained at 268 nm shows good nonlinear response. From the PL measurement, the high intense emission peak was observed at 442 nm corresponds to blue emission. The dominant emission colour of the grown specimen was estimated by CIE plot. The fast and slow decay of ITA single crystal were studied by time resolved PL. The laser resistive nature was examined by Nd-YAG laser and found that it is having good laser damage threshold (LDT) property. The third-order nonlinear optical behaviour of ITA crystal has been analyzed with the help of a femto-second laser using Z-scan technique. The value of various parameters like nonlinear refractive index (n2) and nonlinear absorption coefficient (β) is estimated using the theoretical calculations. The values of n2 and β were found to be 3.13 $$\times$$ 10–17 cm2/W and 1.57 $$\times$$ 10–12 cm/W, respectively. Such values of nonlinear parameters shows that grown crystal can be useful in optoelectronics applications.

The scientific research and new innovations are associated with the accurate and precise measurements which are crucial for operation of recent civilization. In order to maintain the precision and accuracy in analytical measurements, Reference Materials and Certified Reference Materials (CRMs) play a vital role for improving the measurement capability to obtain the property value close to its true value which in turn revamps the overall growth of country for better quality of life. Certified Reference Materials are basically used to assess the performance of analytical procedures and laboratory apparatus for authentic measurement data. In recent scientific world, many sophisticated instruments are emerging with their various facets of measurement capabilities to cater the need of high end research in the field of academia and industries. In recent years, powder X-ray diffraction (PXRD) has been shown as the most powerful characterization and non-destructive technique to explore the structural investigation in terms of phase identification, size of a unit cell, volume fraction of phases, site occupancy of different elemental component, anti-site defects in materials and having many more other applications. The identification of mentioned information from PXRD instrument is a basic need in material science, geology, polymer, forensic science and environment etc. This article focuses on the importance of CRMs for calibrating the instruments and validation of analytical methods. Also the article explicitly discuss about the importance and applications of PXRD technique together with the role of National Physical Laboratory, India the national institute of measurement NMI of India.

This paper reviews the growth and properties of L-asparagine monohydrate (L-ASPM) single crystal. The growth technique by which a well-defined bulk-sized single crystal can be grown is also reported. The various reported studies done over titled crystal signify its suitability for various optoelectronic applications. This paper also includes few derivative compounds of L-asparagine (L-ASP), their structural review has also been incorporated to evaluate its structural bonding and atomic arrangement. Various advanced characterization and their outcomes were also discussed in detail from all the available reported literature which mainly emphasizes on the vast applicability of the crystal. The L-ASPM single crystal is a potential candidate to be used in various optical applications.

Optical grade semi-organic single crystal of sodium acid phthalate (NaAP) was synthesized, and the crystals were harvested by slow evaporation solution growth technique (SEST) in an ambient condition. The titled compound is a promising material for nonlinear optical (NLO) applications and crystallized in non-centrosymmetric system. The structural information of the above-mentioned crystal was investigated by powder X-ray diffraction (PXRD), which reveals that it belongs to orthorhombic structure and B2ab space group. The presence of defects in the harvested crystal was assessed by high-resolution X-ray diffraction (HRXRD) and found that grown single crystal is moderately good. The optical behaviour of NaAP crystal was examined by UV–Vis, photoluminescence (PL) and time-resolved PL (TRPL), respectively. Thermal response and stability of the title compound were tested using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The coefficient of thermal expansion (CTE) was evaluated using thermomechanical analyzer (TMA). The third-order NLO properties of NaAP single crystal had been evaluated by Z-scan method. The two-photon absorption coefficient (β) was calculated from open-aperture curve of Z-scan. The nonlinear study reveals that NaAP crystal is an appropriate choice in optical limiting usage. Terahertz (THz) time domain spectroscopy was used to study optical characteristics like refractive index and absorption coefficient of NaAP single crystal.

In the present study, we have focused on the growth of semi-organic single crystals, as they play a vital role in the generation of a terahertz pulse and its potential applications. The single crystals of l-histidine hydrochloride monohydrate (LMHCL) were grown by slow evaporation solution growth by using deionized water as a solvent in a controlled atmosphere. Good quality crystals of the required size were obtained within 2 weeks. To estimate the lattice dimensions and get the structural information, powder x-ray diffraction (PXRD) study was performed in which we have found that the crystal belongs to the orthorhombic crystal system with space group P212121. The functional groups and the corresponding vibrational mode were confirmed using Fourier transform infrared (FTIR) and Raman spectroscopy, respectively. To study the optical properties UV–Vis transmission spectrum and photoluminescence (PL) were recorded. It was observed that the single crystal has a high value of transmission over a long range of wavelength which signifies that the crystal is a good candidate for nonlinear optical (NLO) applications. The UV cut-off wavelength is found to be 236 nm. The grown single crystals were studied by time-domain terahertz spectroscopy (THz-TDS) for photonic applications and the refractive indices were calculated and it is found that the refractive index is nearly equal to 3.4.

The present work deals with the seasonal variations in the contribution of sources to PM2.5 and PM10 in Delhi, India. Samples of PM2.5 and PM10 were collected from January 2013 to December 2016 at an urban site of Delhi, India, and analyzed to evaluate their chemical components [organic carbon (OC), elemental carbon (EC), water-soluble inorganic components (WSICs), and major and trace elements]. The average concentrations of PM2.5 and PM10 were 131 ± 79 μg m−3 and 238 ± 106 μg m−3, respectively during the entire sampling period. The analyzed and seasonally segregated data sets of both PM2.5 and PM10 were used as input in the three different receptor models, i.e., principal component analysis-absolute principal component score (PCA-APCS), UNMIX, and positive matrix factorization (PMF), to achieve conjointly corroborated results. The present study deals with the implementation and comparison of results of three different multivariate receptor models (PCA-APCS, UNMIX, and PMF) on the same data sets that allowed a better understanding of the probable sources of PM2.5 and PM10 as well as the comportment of these sources with respect to different seasons. PCA-APCS, UNMIX, and PMF extracted similar sources but in different contributions to PM2.5 and PM10. All the three models extracted 7 similar sources while mutually confirmed the 4 major sources over Delhi, i.e., secondary aerosols, vehicular emissions, biomass burning, and soil dust, although the contribution of these sources varies seasonally. PCA-APCS and UNMIX analysis identified a less number of sources (besides mixed type) as compared to the PMF, which may cause erroneous interpretation of seasonal implications on source contribution to the PM mass concentration.

A semi-organic l-tyrosine hydrobromide (LTHB) nonlinear optical single crystal has been harvested using slow evaporation solution technique (SEST) at atmospheric conditions. The ingot has under gone for different characterisations to check its appropriateness for device fabrications. The structural conformation and unit cell dimensions have been estimated using powder X-ray diffraction (PXRD) method. The prominent peaks of PXRD have been indexed and it shows that crystal having non-centrosymmetric in nature with nonlinear optical application in second harmonic generation (SHG). Fourier-transform infrared spectroscopy (FTIR) analysis has been employed to characterise as grown crystal to know about the presence of various functional group in it. The crystalline quality and defects during the growth have been inspected by high resolution X-ray diffraction (HRXRD) technique. Optical studies have been carried out using UV–Vis and photoluminescence (PL) analysis. From UV–Vis measurement, we found that the material exhibits lower cut off wavelength with a high transparency window which is suitable for nonlinear optical (NLO) and optoelectronic applications. A detailed discussion of thermo gravimetric (TG) and derivative thermogravimetry (DTG) along with differential scanning calorimetry (DSC) has been presented to know about the thermal behaviour of LTHB crystal. The thermo mechanical analyser (TMA) which is useful to evaluate the coefficient of thermal expansion (CTE) of the grown crystal has been performed. Laser damage threshold (LDT) density has been noticed to check its strength for high intense laser. The optical, structural, thermal and phase matching studies of titled crystal establish the suitability of this material for optoelectronics and NLO device applications.

A bulk-sized single crystal of sulphamic acid (SA) was grown by the solution growth technique. The lattice dimensions and the plane’s identification of the grown crystal were confirmed with powder X-ray diffraction. High-resolution X-ray diffraction was employed to observe crystalline perfection that was found fairly good. The optical transmission studies reveal its suitability for optical applications in the complete UV–visible region of the electromagnetic spectrum. Bandgap calculations and other optical parameters like absorption and extinction coefficient were calculated to scrutinize its optical characteristics. The photoluminescence emission spectrum was recorded for the corresponding excitation wavelength to reveal the crystal behavior and energy gap transitions. The presence of the titled compound was examined through FTIR spectroscopy. Ellipsometry study was also carried out for the measurement of linear refractive index (n) and also for the extinction coefficient (K). Z-scan studies have been examined to reveal third-order nonlinear optical behavior and calculated the value of its nonlinear absorption coefficient (β). The Terahertz response of the grown crystal was analyzed by the terahertz time-domain spectroscopy. Observed results showed that SA crystal is a good aspirant for NLO applications.

Observations of carbonaceous species [organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), carbonaceous aerosols (CAs) and secondary organic carbon (SOC) ] and trace elements (As, Cr, Ni, Zn, Na, Mg, Al, P, K, Ca, Ti, Fe, and Mn) in PM10 are made over a high altitude site (ARIES, Nainital, 29.4° N, 79.5° E, ~1958 m amsl) in the central Himalayan region during October 2018−February 2019 to explore their possible sources. The average concentrations of PM10, OC, EC, WSOC, CA and SOC were recorded as 44±13 µg m-3, 3.66±1.26 µg m-3, 1.29±0.61 µg m-3, 2.28±0.76 µg m-3, 7.15±1.96 µg m-3 and 1.45±0.73 µg m-3, respectively during the study period. The concentrations of PM10, OC, EC, WSOC, CAs and SOC were significantly varied during autumn (October-November) and winter (December-February) seasons. During both the seasons, significant positive linear trend between OC & EC and OC & WSOC have been observed which is indicative of their common sources of carbonaceous aerosols at the study site. WSOC/OC ratio was estimated as 0.56 and 0.67 during autumn and winter, respectively suggested that the biomass burning could be one of the major sources of carbonaceous aerosols at Nainital. The significant positive correlation of PM10 with crustal elements (Al, Fe, Ca, Mg and Ti) as well as correlation of Al with other crustal elements (Fe, Ca, Mg and Ti) indicates the abundance of mineral dust at the sampling site. The observed Fe/Al ratio (1.07) also indicates mineral dust as a source at the sampling site, similarly, Ca/Al ratio (1.36) indicates that aerosols over this region is rich in Ca mineral as compared to average continental crust. Principal component analysis (PCA) identified the contribution of crustal/soil dust, biomass burning and industrial emissions to the PM10 over the central Himalayan region of India. Five days back trajectory analysis indicates that the air mass impacting the sampling site is from local surrounding area in Uttrakhand as well from Himachal Pradesh, Jammu & Kashmir, Ingo Gangetic Plain (IGP) region, Pakistan, Afghanistan region and Thar Desert.

An optical material is a fundamental in the field of information along with measurement of laser applications. Crystals of organic compounds are very well known for its highly efficient behavior towards the optical activities. In the present study, slow evaporation solution growth technique has been adopted for the growth of l-tartaric acid (LTA). The phase and structural information was assessed with powder X-ray diffraction and grown single crystal’s quality was tested through high resolution X-ray diffraction and found to be reasonably good. The composition bonding between the molecules was revealed out by Fourier-Transform Infrared Spectroscopy method. The Ultraviolet–Visible spectroscopy exposes the excellent transmittance properties of LTA crystal. Photoluminescence spectrum shows strong emission in the violet region. Optical properties are measured to know its behavior towards electromagnetic spectrum which is further analyzed by ultrafast pump probe spectrometry and the determination of non-linear optical absorption coefficient was also taken into account with respect to the absorbance spectra. Moreover, Vickers microhardness studies were carried out to check its mechanical behavior.

Nonlinear optical (NLO) single crystals with high quality are the pillars for the development of new devices that fulfil the demands of society. Nowadays, NLO single crystals are very attractive for the photonic applications particularly for terahertz (THz) photonics. The reason for their popularity is that these crystals can produce very powerful and ultra wideband THz waves due to their high nonlinear susceptibility. In this review paper, we deal with the challenges and progresses in the evolution of NLO single crystals for THz wave generation and detection. Here, we review the single crystal growth that how and by which method single crystal is grown. We summarize the structures, intermolecular and intramolecular interactions, their properties and how they generate and detect the THz waves. Widely used single crystals at present are DAST, BNA, OH1, amino acid-based single crystals, etc.