Combustion synthesis and up-conversion luminescence of La2O2S:Er3+,Yb3+ nanophosphors

La2O2S:Er3+,Yb3+ nanocrystalline up-converting phosphors were synthesized by a combustion method at low temperature, using ethanol as pre-ignition fuel and thioacetamide as sulfurizing agent and organic fuel. The phosphors were characterized by powder X-ray diffractometry, scanning electron microscopy, UV/Vis/NIR spectroscopy and fluorescence spectroscopy. Pure and well-crystallized La2O2S: Er3+,Yb3+ nanoparticles, of the order of 50-200 nm, are obtained after a post-treatment in a H2S/N2 flow for 2 h at 1000 degrees C. The efficient energy transfer from Yb3+ to Er3+ results in a strong up-conversion upon excitation at 980 nm. The emission spectra show the intense green emissions corresponding to the (H-2(11/2), S-4(3/2))-> I-4(15/2) transitions and a red emission corresponding to the F-4(9/2)-> I-4(15/2) transition. Additionally, within the investigated co-doping concentrations, no significant concentration quenching effect and back energy transfer from Er3+ to Yb3+ were evidenced. This research highlights the influence of the sulfurization treatment on the purity/crystallinity/morphology of the nanocrystals and the luminescence efficiency. (C) 2015 Elsevier Inc. All rights reserved.