La2O2S:Tm/Yb as a novel phosphor for highly pure near-infrared upconversion luminescence

Simple dehydration of the hydrothermally crystallized RE2(OH)(4)SO4 center dot 2H(2)O layered compound (RE = La0.97Tm0.01Yb0.02) in flowing H-2 at 1200 degrees C directly produced a La2O2S:Tm/Yb phosphor that exhibits highly pure near-infrared luminescence (similar to 802 nm, the H-3(4) -> H-3(5) transition of Tm3+) under 978 nm laser excitation, which is desired for near-infrared biological applications. Rietveld refinement confirmed the direct crystallization of solid solutions. The codoped Yb3+ ion significantly sensitizes Tm3+ luminescence, and improved the emission intensity by similar to 2000 times. Analysis of the excitation-power dependence of Tm3+ emission revealed a three photon mechanism for the observed upconversion, and the possible photon reactions were discussed. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.