Strong Emission In Visible Region Research Articles

Sr8MSm1-xEux(PO4)7 phosphors derived by different synthesis routes: Solid state, sol-gel and hydrothermal, the comparison of properties

A series of new Sr-based phosphors Sr8M2+Sm1-х(PO4)7:xEu3+, M = Mg2+, Zn2+ with β-Ca3(PO4)2-type structure was synthesized and studied. The Sr8MgEu(PO4)7 was obtained by three types of synthetic routs: high temperature solid-state, hydrothermal and sol-gel methods. The influence of synthesis routes and annealing conditions on luminescent properties was studied and analyzed taking into account the data on average crystallite size and grain size determination. It was shown that the synthesis method has a defining role on the phosphor’s properties. The solid-state route gives the best powders crystallinity and the highest intensity of emission. The samples were characterized by strong emission in visible region at 615 nm originating from 5D0 → 7F2 transition of Eu3+ and 600 nm originating from the 5G5/2 → 4H7/2 transition of Sm3+. Also, it was revealed that Zn-substituted samples exhibit higher intensity than Mg-containing ones due to larger particle size and lower scattering of light and higher light absorption. Photoluminescence decay curves were measured and the dependence of decay times on activator concentrations was revealed. The CIE chromaticity coordinates were close to red standard. The prototypes of LED devices were characterized by strong emission with warm correlated color temperature. The investigated compounds can be used as a potential commercial phosphor for solid-state lighting application.

One-pot synthesis, crystal structure, and fluorescence property of a cadmium(II) complex based on mono salicylaldehyde Schiff base ligand

A new cadmium(II) complex [Cd(NO2-Salen)2] containing Schiff base ligand (NO2-Salen = N-mono-5-nitro-salicylideneamino ethanato) has been prepared through facile condensation reaction of sub-stituted salicylaldehyde with ethylene-diamine and has been structurally characterized by elemental analysis, IR spectra and X-ray diffraction. It is formulated as C18H20CdN6O6 crystallizes in the orthorhombic system, space group of Pccn. The ligand of 5-nitrosalicylaldehyde-ethylene-diamine exhibits unusual mono asymmetry tridentate mode. The Cd2+ ion has a coordination number of six and assumes a distorted octahedral geometry. It exhibits an offset π-π stacking interaction between the substituted benzene ligands of adjacent mononuclear complexes. The neutral monomeric units of [Cd(NO2-Salen)2] are linked into a one-dimensional (1D) array via the intermolecular hydrogen bonds and π-π stacking interactions. The complex exhibits strong emission in visible region with the maximum wavelength of 428 nm, which is tentatively assigned to the π → π* intraligand fluorescence.

Multi-band emission in a wide wavelength range from tin oxide/Au nanocomposites grown on porous anodic alumina substrate (AAO)

The photoluminescence (PL) properties of tin oxide nanostructures are investigated. Three samples of different morphology, induced by deposition process and various geometrical features of nanoporous anodic aluminum oxide (AAO) substrate, are analyzed. X-ray photoelectronic spectroscopy (XPS) analysis reveals the presence of two forms of tin oxide on the surface of all studied samples: SnO and SnO2. The former form is typical for reduced surface with bridging oxygen atoms and every other row of in-plane oxygen atoms removed. The oxygen defects give rise to a strong emission in visible region. Two intense PL peaks are observed centered at about 540 (band I) and 620 (band II)nm. The origin of these bands was ascribed to the recombination of electrons from the conduction band (band I) and shallow traps levels (band II) to the surface oxygen vacancy levels. Upon deposition of Au nanoparticles on the top of tin oxide nanostructures the emission at 540 and 620nm disappears and a new band (band III) occurs in the range >760nm. The PL mechanism operating in the studied systems is discussed. The tin oxide/Au nanocomposites can be used as efficient multi-band light emitters in a wide (from visible to near infrared) wavelength range.

Unusual and strong emission in visible region from Mn2+ and Y3+ doped ZnO nanocrystals

Unusual and strong emission in the visible region has been observed from Mn2+ and Y3+ doped ZnO nanocrystals prepared by a chemical route using CTAB (cetyltrimethylammonium bromide). Various state-of-the-art techniques including high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis), Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopy have been employed to characterize the prepared nanocrystals. On the basis of experimental results we have proposed a schematic band model to explain the emission observe in visible region. It is not possible to exactly pin down the origin of visible emission yet we believe that the creation of different mid gap states by virtue of microstructure manipulation and dopants are likely to play a major role.