title: Europium-doped LaF3 nanocrystals with organic 9-oxidophenalenone capping ligands that display visible light excitable steady-state blue and time-delayed red emission.
abstract: Visible light excitable and color tunable ∼5% Eu(3+)-doped LaF3 nanocrystals (NCs), containing 9-oxidophenalenone ligands bound to the surface as visible light sensitizers for Eu(3+) dopants, have been synthesized by a facile solution-based method. The crystalline phase structure, size, composition, morphology and luminescence properties of the NCs are characterized using X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and steady-state and time-resolved emission spectroscopy. The results show that these NCs are very small in size (<10 nm), display high degree of crystallinity and have pure tysonite structure of LaF3 with P3[combining macron]c1 space group. The visible light excitation of the capping ligands triggers an alternate display of steady-state, short-lived blue emission (τ < 1 ns) and time-delayed, long-lived sensitized red Eu(3+) emission (τ = 0.41 ms), allowing photoluminescence chromacity tuning as a function of delay time within a specific inorganic composition. The visible light sensitization of the dopant Eu(3+) sites proves more efficient than direct excitation of 5% Eu(3+)-doped LaF3 NCs capped by citrate ligands. The dopant Eu(3+) ions are well protected from non-radiative deactivation through high-energy vibrations of the organic capping ligands which is proved by the long lifetime of the sensitized Eu(3+) emission. The time-resolved emission spectra collected over a period of several milliseconds reveal that the dopant Eu(3+) ions occupy at least three different sites in the NC host. It is further inferred that the sensitized Eu(3+) emission primarily comes from surface dopant sites and sites just underneath the surface of the NCs. We propose that some of the interior Eu(3+) sites also display sensitized emission, which are indirectly populated via Eu(3+) → Eu(3+) energy migration from surface-sensitized Eu(3+) sites of the NCs.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India. mir.irfanullah@gmail.com mirfanullah@chem.iitb.ac.in arindam@chem.iitb.ac.in.
authors.forename: Mir
authors.initials: M
authors.lastname: Irfanullah
authors.forename: Dharmendar Kumar
authors.initials: DK
authors.lastname: Sharma
authors.forename: Ramya
authors.initials: R
authors.lastname: Chulliyil
authors.forename: Arindam
authors.initials: A
authors.lastname: Chowdhury
mesh_terms: D005063:Europium / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D007811:Lanthanum / Q000737:chemistry*; D008024:Ligands; D008027:Light; D049449:Luminescence; D053758:Nanoparticles / Q000737:chemistry*; D043803:Phenalenes / Q000737:chemistry*; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D008024:Ligands; D043803:Phenalenes; C083668:lanthanum trifluoride; D005063:Europium; C038036:phenalen-1-one; D007811:Lanthanum; D005459:Fluorides