lithium-fluoride and barium-fluoride

This paper reports the synthesis of high quality LiYF4, BaYF5, and NaLaF4 nanocrystals by high-temperature co-decomposition of precursors in organic solvents. Their bulk counterparts have long been used as efficient luminescent hosts for various applications including lasers, upconversion fluorescence, and quantum cutters. The particles were characterized using TEM, XRD, dynamic light scattering (DLS), and fluorescence spectrometry. Trifluoroacetic acid (CF3COOH) and the reaction temperature were crucial for the formation of NaLaF4 and LiYF4 nanoparticles. NaLaF4 was not formed without using CF3COOH, only LaF3 and NaF mixture was formed. NaLaF4 nanoparticles were obtained only when CF3COOH was added in the reaction solution and the temperature was > or =330 degrees C. For the synthesis of LiYF4,, in the absence of CF3COOH in the reaction, a mixture of YOF and LiYF4 nanoparticles was formed. Pure LiYF4 particles were obtained only until CF3COOH was added in the reaction at 340 degrees C or above. The nanoparticles were easily dispersed in organic solvents include hexane, toluene, and chloroform and formed transparent colloidal solutions. The ease of doping of these as-synthesized host nanoparticles for designed optical properties was assessed. The LiYF4, BaYF5, and NaLaF4 nanoparticles, co-doped with 20% Ytterbium (Yb) and 2% Erbium (Er), showed bright upconversion fluorescence upon 980 nm NIR excitation, confirming the high quality of as-synthesized nanoparticles. These nanoparticles are potential candidates for nano-optical devices, thin films, telecommunication, and bio-probes.

Topics: Barium Compounds; Chemistry, Organic; Crystallization; Electrochemistry; Fluorides; Lanthanum; Lithium Compounds; Metal Nanoparticles; Microscopy, Electron, Transmission; Models, Chemical; Nanoparticles; Nanotechnology; Sodium; Solvents; Temperature; X-Ray Diffraction

An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF3:Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F(A) and F centres, leading to both the hopping migration and recombination of F centres and the thermoactivated dissociation of the F(A) centres.

Topics: Barium Compounds; Color; Europium; Fluorides; Iron; Lithium Compounds; Radiochemistry; Spectrum Analysis; Temperature; Thermoluminescent Dosimetry