La1-xLnxH(O3PCH3)2 (Ln = Tb, Eu; 0 < x ≤ 1): an organic-inorganic hybrid with lanthanide chains and tunable luminescence properties

The organic/inorganic La1-xLnxH(O3PCH3)2 (Ln = Eu, Tb) hybrids have been synthesized by hydrothermal synthesis. The crystal structure of LaH(O3PCH3)2 consists of chains of edge-sharing LaO8 polyhedra linked through PO3C tetrahedra. Photoluminescence of Eu(3+), Tb(3+) and Eu(3+)/Tb(3+) co-doped materials have been investigated. The Eu and Tb hybrids show no concentration quenching versus doping rate suggesting energy migration through a percolation model. The Eu hybrids exhibit a red emission while the Tb ones exhibit, with the Tb rate increasing, a blue to green emission under a 378 nm excitation wavelength and a cyan to green emission under a 262 nm excitation wavelength. The doping rate dependent red shift results from a cross relaxation phenomenon between closed Tb(3+) ions. The blue to cyan shift observed for the slightly doped materials, when excitation wavelength shifts from 378 nm to 262 nm, is due to different relaxation phenomena, from the (5)D3 level for a 378 nm excitation wavelength and from the (5)D4 level via the 4f5d level for a 262 nm excitation wavelength. Under a 378 nm wavelength, the co-doped La0.93Eu0.03Tb0.04H(O3PCH3)2 hybrid exhibits a white/cyan emission with CIE coordinates equal to x = 0.29, y = 0.37.

Characterization by Fourier Transform Infrared Spectroscopy (FT-IR) and 2D IR Correlation Spectroscopy of PAMAM Dendrimer

FT-IR and 2D correlation spectroscopy were employed to study the microstructural changes occurring during phase transitions of a liquid crystal poly(amidoamine) codendrimer (PAMAM (L1)16(L2)16) generation 3, functionalized on the terminal groups by one-chain promesogenic calamitic units (4-(4'-decyloxybenzoyloxy)salicylaldehyde (L1)) and two-chain promesogenic calamitic units (4-(3',4'-didecyloxybenzoyloxy)salicylaldehyde (L2)). Spectral modifications associated with molecular conformation rearrangements allowing for molecular shape change on going from a liquid-crystalline organization to another were found. The transition temperatures were calculated, and they are in good agreement with the DSC data. Spectral analysis gives evidence of the LC phase transitions and to an additional transition associated with the existence of conformers. Various types of hydrogen bonding have been established.