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

Abstract

The organic/inorganic La_1−xLn_xH(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 Eu³⁺, Tb³⁺ and Eu³⁺/Tb³⁺ 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 Tb³⁺ 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 ⁵D₃ level for a 378 nm excitation wavelength and from the ⁵D₄ level via the 4f5d level for a 262 nm excitation wavelength. Under a 378 nm wavelength, the co-doped La_0.93Eu_0.03Tb_0.04H(O₃PCH₃)₂ hybrid exhibits a white/cyan emission with CIE coordinates equal to x = 0.29, y = 0.37.