Luminescent nanoparticles for anti-counterfeiting applications: determination of dopant concentrations

Counterfeiting of documents and currency is an enhancing high-tech crime which requires high-tech solutions to inhibit counterfeiting. In present data detailed study on synthesis of NaYF₄-Yb-Er (core), NaYF₄-Yb-Er (core)@NaYF₄ (shell), NaYF₄-Yb-Er (core)@NaYF₄-Yb-Nd(shell-1) @NaYF₄(shell-2), NaGdF₄-Yb-Tm (core)@NaGdF₄-X(shell-1, X = Ho³⁺, Eu³⁺, Tb³⁺, Dy³⁺)@NaYF₄(shell-2) will be performed. X-ray diffraction (XRD) and transmission electron microscopy (TEM) will be used for structural morphology and microstructural characterization of synthesized nanoparticles. FullProf program employed for Rietveld refinement will be used to refine simultaneously the structural parameters such as lattice constants, atomic positions, occupancies and micro structural parameters as crystallite size and strain present in the crystal and for the determination of dopant amounts in host lattice. Surface functionalization and elemental compositional will be carried out using Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDX). Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA) to measure the change in sample weight as a function of temperature (and/or time) under controlled gas atmosphere and temperature will be used. Study of up-conversion (UC), down-conversion (DC), optical heating behavior and energy transfer (ET) mechanism photoluminescence studies will be performed. The characterizations of lanthanide doped UCNM for the fabrication and design of luminescent security inks for their anti-counterfeiting applications, surface and morphological characterizations, ink designing and electroluminescence and chemiluminescence properties will be reported. The synthesized LA doped UCNM based inks can be formulate and produce the accurate color rendering index only for specific excitation power densities, which will make them harder to copy. However, determination of dopant concentration is required to understand properties of materials. Dopant concentrations in nanoparticles will be determined by nuclear techniques such NAA, PIXE, PIGE, etc. (author)