PurposeThe purpose of this paper is to prepare calcium oxide (CaO) nanoparticles by green synthesis technique and study its structural, morphological and optical properties. The prepared samples were calcined at, 200°C, 300°C and 500°C, and the variation in the properties at different temperatures were investigated.Design/methodology/approachGreen approach has been used in the present work to synthesise the CaO nanoparticles using Murraya Koenigii leaf (curry leaves) extract as a capping agent. This technique involves the use of nontoxic reagents and natural products derived from various parts of plants.FindingsStudies reveal that CaO nanoparticles with good optical properties can be synthesized successfully by green approach. The optical absorbance spectra show a broad absorption peak around 400–500 nm. FTIR studies confirm the presence of different functional groups that help in the stabilization of CaO nanoparticles. PL emission spectra show a high intensity emission peak at around 231 nm in addition to peaks at 375 nm and 400 nm. XRD studies show planes of CaO cubic phase. SEM images show a nonuniform distribution of spherical particles along with some clusters. EDX spectra confirm the presence of calcium and oxygen.Practical implicationsCaO nanoparticles have wide applications in optical devices as well as in phototherapy. It is thus interesting to devise new and eco-friendly techniques to synthesise these nanoparticles to suit these applications.Originality/valueThis work would provide a new insight into the preparation of different metal oxide nanoparticles by a very simple and cost-effective green technique without the use of toxic reagents.

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A method of preparation of calcium sulphide phosphors doped with samarium and dysprosium is given. The electroluminescence (EL) spectra of these two phosphors in the visible region are recorded. The EL spectrum of CaS:Sm has three groups of emission bands which are well resolved into discrete lines. On the basis of crystal field parameter calculations using the measured line separation, the site of the samarium impurity in CaS is identified. CaS : Dy gives five emission bands which are further resolved into lines. The band with maximum intensity occurring a t 580 nm is found to be resolved into six lines. The splitting pattern is explained again on the basis of crystal field parameter calculations.

ZnS: Cu: Cl phosphor prepared under a vacuum fUing process i~ found t?give blue electroluminescence with emission peak at 460 nm which remams unaltered with the frequency of the excitation voltage. Addition of excess chlorine in the phosphor gives blue, green and red emissio~ at 460, 520 and 640 run. The intensity of the blue band decreases and It fmally disappears as chlorine concentration is increased. A scheme involving three energy levels attributed to Cu 2 +, eu+ and cr centres in Zns explains the experimental results completely.