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Anharmonicity and impurities have a significant impact on the dynamic and optical properties of crystalline solids. In this report, we have performed temperature-dependent Raman spectroscopy in the range of 300–800 K for hydrothermally synthesized titanium dioxide (TiO2) nanorod composed microflowers doped with Cu. X-ray diffraction and high resolution transmission electron microscopy confirm the pure rutile phase of both pristine and Cu doped TiO2. The most intense Eg and A1g modes exhibit a frequency redshift, and the linewidth increases with temperature, which leads to Fano line shape type asymmetry. The anharmonicity induced phonon frequency shift as a function of temperature was well fitted using the Klemens model by combining three and four-phonon coupling processes. The Raman modes soften with the increasing concentration of Cu doping. The Cu dopant acts as an impurity, which manifests defect states to tune the bandgap and shorten the phonon lifetime and anharmonicity. Such an anharmonic effect can lead to applications in the sensing devices with suitable thermal and electrical conductivities.

Zinc oxide nanoparticles (ZnO NPs) were synthesised using Tabernaemontana divaricata flower extract (TFE) in different weight percentages by facile, eco-friendly and cost-effective green synthesis method. Formation and structure of the ZnO NPs were studied by powder XRD, FT−IR, Raman and TEM studies. The crystals formed are of hexagonal wurtzite structure with biological functional groups attached. Average crystallite size of the ZnO NPs (17.5−23.3 nm) was obtained from the analysis of powder XRD data which increased with increase of TFE amount while the estimated values of dislocation density and micro-strain exhibited an opposite behaviour. The optical (direct and indirect) energy band gap values estimated using UV–vis DRS spectral data decreased with increasing amount of TFE. The photoluminescence spectra for the ZnO NPs exhibited multiple peaks spread over the visible region with one peak in the NIR region indicating the existence of various defect levels of Zn and O. Position of these defect levels within the band gap was assigned which is significantly modulated by TFE. TFE amount-dependent peak shift and/or peak broadening were observed in the Raman spectra of the ZnO NPs which were correlated with the growing disorder in the crystals induced by the extract molecules. FESEM study showed the agglomerated NPs with quasi-spherical morphology. Particle size of the ZnO NPs was estimated from FESEM images. EDX study indicated that increased presence of TFE in ZnO decreased the oxygen content in the synthesised material. HRTEM study revealed the agglomeration of nanoparticles with single crystalline nature. Present study convincingly established that flower extract used for the green synthesis efficiently modified the structure and optical property, defect levels and morphology of the potentially useful ZnO nanoparticles.