Luminescence properties of Yb:Nd:Tm:KY3F10 nanophosphor and thermal treatment effects

Author(s)

Gomes, Laercio ^[1] ; Linhares, Horacio Marconi da Silva M. D. ^[1] ; Ichikawa, Rodrigo Uchida ^[2] ; Martinez, Luis Gallego ^[2] ; Ranieri, Izilda Marcia ^[1]

Affiliation

^[1] IPEN CNEN SP, Ctr Lasers & Aplicacoes, Inst Pesquisas Energet & Nucl, BR-05422970 Sao Paulo - Brazil

^[2] Inst Pesquisas Energet & Nucl, Dept Ciencias Mat, Sao Paulo - Brazil

• Document type: Journal article
• Source: Journal of Luminescence; v. 157, p. 285-292, JAN 2015.
• Web of Science Citations: 6

Abstract

In this work, we present the spectroscopic properties of KY3F10 (KY3F) nanocrystals activated with thulium and codoped with ytterbium and neodymium ions. The most important processes that lead to the thulium upconversion emissions in the blue region were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the upconversion process that populates (1)G(4) (Tm3+) excited states. Analysis of the energy-transfer processes dynamics using selective pulsed-laser excitations in Yb:Nd:Tm, Nd:KY3F nanocrystals shows that the direct energy transfer from Nd3+ to Tm3+ ions is the mechanism responsible for the 78% of the blue upconversion luminescence in the Yb:Nd:Tm:KY3F when compared with the Yb:Nd:Tm:KY3F bulk crystal for an laser excitation at 802 nm. An investigation of the (1)G(4) level luminescence kinetic of Tm3+ in Yb/Nd/Tm system revealed that the luminescence efficiency ((1)G(4)) starts with a very low value (0.38%) for the synthesized nanocrystal (as grown) and strongly increases to 97% after thermal treatment at 550 degrees C for 6 h under argon flow. As a consequence of the thermal treatment at T=550 degrees C, the contributions of the (Nd x Tm) (Up(1)) and (Nd x Yb x Tm) (Up(2)) upconversion processes to the (1)G(4) luminescence are 33% (Up(1)) and 67% for Up(2). Up(2) process represented by Nd3+ (F-4(3/2))-->Yb3+ (F-2(7/2)) followed by Yb3+ (F-2(5/2))--> TM (H-3(4))--> TM3+ ((1)G(4)) was previously reported as the main mechanism to produce the blue luminescence in Yb:Nd:Tm:YLiF4 and KY3F10 bulk crystals. Results of X-ray diffraction analysis of nanopowder using the Rietveld method reveled that crystallite sizes remain unchanged (12-14 nm) after thermal treatments with T <= 400 degrees C, while the (1)G(4) luminescence efficiency strongly increases from 0.38% (T=25 degrees C) to 12% (T=400 degrees C). Results shown that the Nd3+ ions distribution has a concentration gradient increasing towards the nanoparticle surface allowing the direct (Nd x Tm) (Up(1)) (78%) in competition with the (Nd x Yb x Tm) (Up(2)) (22%) upconversions for the synthesized nanocrystals (11 nm). (C) 2014 Elsevier B.V. All rights reserved. (AU)