Development of Highest Value of the Measured Efficiency of Mesoporous Petal Shaped Europium (III) Doped Cobalt Tetroxide@Cupric Oxide Hybrid Nanomaterials for Enhanced Room Temperature Photoluminescence and Fluorescence Decay Properties.

In our work, a novel series of europium (III) (Eu) (5, 10 and 15 wt %) doped cobalt tetroxide@cupric oxide (CoO@CuO) nanomaterials (NMs) were synthesized by facile coprecipitation method. The synthesized NMs were characterized by XRD (X-ray diffraction), FT-IR (Fourier transform infrared), UV (ultraviolet)-visible absorption spectra, XPS (X-ray photoelectron), BET (Brunauer-Emmett-Teller) analytical methods. Crystal structure studies revealed the formation of polycrystalline nature with monoclinic and cubic phase. The morphology studies of Eu:CoO@CuO (x = 5, 10 and 15 wt %) showed petal shape nanoparticles (NPs) with agglomeration. Redshift in optical absorption spectra appeared with a significant impact on the optical band gap as Eu concentration increases on CoO@CuO bimetallic oxide NMs. The chemical composition and valence state of the elements confirmed from XPS studies detected the presence of Eu, Cu, Co, O and C elements. An increase in the pore size and surface area resulted as the Eu concentration increased on CoO@CuO NMs. However, room temperature photoluminescence (RTPL) spectra of CoO@CuO bimetallic oxide NMs at two different excitations (λ  = 280 nm, 320 nm) showed sharp, strong emission intensities located at near ultraviolet (NUV) region and weak emissions detected at far ultraviolet (FUV) regions of the RTPL spectrum. Further, visible range emission intensities were displayed by Eu:CoO@CuO (5, 10 and 15 wt %) NMs when exited at 280 nm. The characteristic white light emission peaks in the visible range of the RTPL spectra showed intense blue, green and orange colours. Emission intensity increases with an increase in Eu concentration on CoO@CuO bimetallic oxide NMs. The fluorescence (FL) decay spectra of Eu : CoO@CuO NMs showed a decay lifetime of 2.54 and 2.31 ns (ns) attributed to the dynamic, ultrafast excitation energy transfer between Eu (dopant) and CoO@CuO (host) NMs. It is proposed that enhanced RTPL emission intensity and FL decay behavior of Eu:CoO@CuO NMs closely related to the change in the optical band gap, variation in the crystallite size, formation of more number of oxygen vacancies in the crystal structure of hybrid nanomaterials.