Upconversion properties of a transparent Er3þ–Yb3þ co-doped LaF3–SiO2 glass-ceramics prepared by sol–gel method

Transparent 0.1ErF3–0.1YbF3–5LaF3–94.8SiO2 (mol%) glass-ceramics was prepared by sol–gel method. Efficient upconversion emissions at 379, 407, 450, 490, 520, 540 and 660 nm were observed under 973 nm excitation. The signal at 379 nm is only 4.5 times weaker than the signal at 520 nm, that is readily visible by the naked eyes even with a pump power of 27 mW, indicating that this sample is a very good infrared-to-ultraviolet upconverter. The data obtained from transmission electron microscopy and X-ray diffraction studies indicate that the rare-earth ions were partitioned in the low phonon energy LaF3 nanocrystals embedded in silica glass. The analysis of the dynamics of the upconversion emissions from level S3=2 ( 540 nm) and level F9=2 ( 660 nm) of Er3þ suggest that distinct energy transfer excitation pathways are responsible for populating these luminescent levels. 2003 Elsevier Science B.V. All rights reserved. Rare-earth doped fluoride glasses are highly desirable materials for optical amplification [1,2], upconversion lasers [3] and display devices [4]. However, poor chemical and mechanical properties and low laser damage threshold make them unsuitable for practical use [5]. Silica based glasses, on the other hand, show excellent durability and optical quality. Unfortunately, large phonon energy of these oxide glasses increases the nonradiative decay rate that reduces the luminescence efficiency [6,7]. Recently a new class of transparent glassceramics known as oxyfluoride glasses attracted much attention in which rare-earth doped fluoride nanocrystallites are dispersed in an oxide network [8]. The optical properties of the rare-earth ions in oxyfluoride glasses depend on the fluoride host while the mechanical properties of the glasses depend predominantly on the oxide host. Wang and Ohwaki [9] first reported ErF3–YbF3 doped transparent oxyfluoride glass. They found that the green upconversion emission from oxyfluoride glass is 10 times brighter than that observed from fluoride glass. Kawamoto et al. [10] and Chen et al. [11] also reported strong upconversion emission from Er3þ doped oxyfluoride glass-ceramics. Corresponding author. Present address: Center for High Technology Materials, 1313 Goddard SE, Albuquerque, NM 87106, USA. Tel.: +1-505 272 7093; fax: +1-505 272 7801. E-mail address: [email protected] (A. Biswas). 1 Present address: Departamento de Fisica, Universidade Federal Pernambuco, 50670-901 Recife, PE, Brazil. 0022-3093/03/$ see front matter 2003 Elsevier Science B.V. All rights reserved. PII: S0022-3093 (02 )01951-8 Journal of Non-Crystalline Solids 316 (2003) 393–397 www.elsevier.com/locate/jnoncrysol LETTER TO THE EDITOR