Preparation and luminescence characteristics of monazite Eu3+:LaPO4 nanocrystals in NH4NO3 molten salt

Molten-salt method and NH4NO3 flux were developed to fabricate monoclinic monazite Eu3+:LaPO4 nanocrystals for the first time. The products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, excitation spectra, emission spectra and luminescence decay curves. The as-obtained products were quasihexagonal Eu3+:LaPO4 nanocrystals with the mean size of 30 nm. The room temperature charge transfer bands (CTB) exhibited red-shift and spectral broadening in comparison with 10 K CTB. The optimal Eu3+ concentration was determined to be 8 mol% by a comparative study of the relative emission intensities for different Eu3+ doping concentrations. The higher concentration quenching could be caused by the possible nonradiative energy transfer (electric multipole-multipole interaction). The relationship between the FL lifetime of D-5(0) energy level and Eu3+ concentration was investigated based on Auzel's model. This work is important not only to understand the unique physical properties of Eu3+:LaPO4 nanocrystals but also to bring an opportunity for the development of the other nanocrystals via the molten salt synthesis in NH4NO3 flux. (C) 2015 Elsevier B.V. All rights reserved.