Efficient multicolor tunability of ultrasmall ternary-doped LaF3 nanoparticles: energy conversion and magnetic behavior. Issue 28 (11th July 2017) - Shrivastava, Navadeep
Abstract : Visible color tunability in ultrasmall LaF3 : x Ce 3+, x Gd 3+, y Eu 3+ ( x = 5; y = 1, 5, 10, and 15 mol%) NPs depending on the ratio Eu 2+ /Eu 3+ . Abstract : Luminescence-tunable multicolored LaF3 : x Ce 3+, x Gd 3+, y Eu 3+ ( x = 5; y = 1, 5, 10, and 15 mol%) nanoparticles have been synthesized via a low cost polyol method. Powder X-ray diffraction and high-resolution transmission electron microscopy studies confirm the hexagonal phase of the LaF3 : x Ce 3+, x Gd 3+, y Eu 3+ nanophosphors with average sizes (oval shape) ranging from 5 to 7 nm. Energy-dispersive X-ray spectroscopy analyses show the uniform distribution of Ce 3+, Gd 3+, and Eu 3+ dopants in the LaF3 host matrix. The photoluminescence spectra and electron paramagnetic resonance measurements guarantee the presence of Eu 2+, corroborated through DC susceptibility measurements of the samples displaying paramagnetic behavior at 300 K, whereas weak ferromagnetic ordering is shown at 2 K. The non-radiative energy transfer processes from the 4f( 2 F5/2 ) → 5d state (Ce 3+ ) to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions in the visible region from the 4f 6 5d 1 (Eu 2+ ) and 5 D0 (Eu 3+ ) emitting levels, leading to overlapped broad and narrow emission bands, have been proclaimed. The energy transfer mechanism proposes involvement of the Gd 3+ ion sub-lattice as the bridge and finally trapping by Eu 2+/3+, upon excitation of the Ce 3+ ion. The calculation of experimental intensity parameters ( Ω 2, 4 ) has been discussed and the highest emission quantum efficiency ( η = 85%) of the Eu 3+ ion for the y = 10 mol% sample is reported. The advantageous existence of the Eu 2+ /Eu 3+ ratio along with variously doped nanomaterials described in this work, results in tunable emission color in the blue-white-red regions, highlighting the potential application of the samples in solid-state lighting devices, scintillation devices, and multiplex detection.