Photoluminescence and magnetic investigation of ternary ion activated enhanced multicolor LaF3 nanophasphores

Abstract

The luminescence-tuneable multicolored LaF3:xCe3+,xGd3+,yEu3+ (x = 5; y = 1, 5, 10 and 15 mol%) nanoparticles have been synthesized via a new low cost polyol method. Powder X-ray diffraction and high resolution transmission electron microscopy confirms the hexagonal phase of LaF3:xCe3+,xGd3+,yEu3+ nanophosphors with average sizes (oval shape) from 5-7 nm. Energy-dispersive X-ray spectroscopy analyses show the uniform distribution of Ce3+, Gd3+ and Eu3+ dopants in the LaF3 host matrix. The photoluminescence spectra and electron paramagnetic resonance measurement guarantee the presence of Eu2+, corroborated through DC susceptibility measurements of the samples displaying the paramagnetic behavior at 300 K, whereas a weak ferromagnetic ordering at 2 K. The non-radiative energy transfer processes from the 4f1→4f5d1 state (Ce3+) (ultraviolet excitation, λex = 260 nm) to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions in visible region from the 4f65d1 (Eu2+) and 5D0 (Eu3+) emitting level, leading to overlapped broad and narrow emission bands, have been proclaimed. The energy transfer mechanism proposes involvement of Gd3+ ion sub-lattice as bridge and finally trapping by Eu2+/3+, upon excitation of Ce3+ ion. The calculation of experimental intensity parameters (2,4) have been discussed and highest emission quantum efficiency (η = 85%) of Eu3+ ion for y = 10 mol% sample is reported. The advantageous existence of Eu2+/Eu3+ ratio along with variously-doped nanomaterials described in this work, exhibit tunable emission color in the blue-white-red regions, highlighting their potential application in solid state lighting devices, scintillation, and multiplex detection.