CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 1129–1134 Y 2 O 3 :Yb,Tm and Y 2 O 3 :Yb,Ho powders for low-temperature thermometry based on up-conversion fluorescence V. Lojpur a , M. Nikolic b , L. Mancic a , O. Milosevic a , M.D. Dramicanin b,n a Institute of Technical Sciences of SASA, K. Mihailova 35/IV, Belgrade, Serbia b Vincˇa Institute of Nuclear Science, University of Belgrade, P.O. Box 522, Belgrade, Serbia Received 15 June 2012; received in revised form 9 July 2012; accepted 9 July 2012 Available online 20 July 2012 Abstract Recently, trivalent rare earth doped materials have received significant attention due to the strong temperature dependence of the fluorescence emission of these materials, which can be useful in temperature sensing. Here, we investigated Y 2 O 3 ceramic powders doped with Yb 3 þ and co-doped with either Tm 3 þ or Ho 3 þ . The powders were obtained via spray pyrolysis at 900 1C and additionally thermally treated at 1100 1C for 24 h. Structural characterization using X-ray powder diffraction confirmed the cubic bixbyte structure. Scanning electron microscopy (SEM) revealed that the particles exhibit a uniform spherical morphology. The up-conversion emissions were measured using laser excitation at 978 nm, resulting in the following transitions: blue emission in the range of 450–500 nm, weak red emission in the range of 650–680 nm and near infrared emission in the range of 765–840 nm for Tm 3 þ , as well as green emission centered at 550 nm and weak near infrared emission at 755 nm for the Ho 3 þ ions. In addition, the temperature dependence of the fluorescence intensity ratios of different Stark components was analyzed in the range of 10–300 K. Significant temperature sensitivity was detected for several components, with the largest value of 0.097 K 1 related to the intensity ratio of I 536 and I 772 emissions observed for the Y 2 O 3 :Yb,Ho powder. & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: D. Y 2 O 3 ; Spray pyrolysis; Thermometry; Up-conversion 1. Introduction Phosphors are materials composed of a transparent host and an activator, typically a small quantity of a transition metal or a rare earth ion [1]. After absorbing a specific form of energy, these materials emit light in the ultraviolet (UV), visible (VIS) or infrared (IR) spectral regions. Rare earth (RE 3 þ ) ion doped materials have been widely used as fluorescent and light-emitting diodes (LED), biological labels, lasers and components in a variety of display technologies [2–5]. Because the absorption and emission properties of phosphors change with temperature, they could find applica- tions in optical temperature sensing devices [6] . Phosphor thermometry represents an optical technique for surface temperature measurements that is based on the time and temperature dependence of phosphorescence intensity. The fluorescent intensity ratio (FIR) is the foremost technique used to reduce the influence of measurement conditions and improve the sensitivity of the measurement [7, 8]. This simple, non-contact and precise method is applicable over a wide temperature range (from 10 K to 2000 K) and involves the comparison of intensities of two emission lines or areas in photoluminescent spectra. Using this technique, RE 3 þ ion doped bulk and nano- materials have been prepared in the literature, and some have been used as temperature sensors. For example, the high temperature sensing behavior of Er 3 þ or Nd 3 þ doped strontium barium niobate ceramic glasses was reported in a study [9], whereas Nikolic et al. discussed a possible applica- tion of the FIR method for Sm 3 þ doped GdVO 4 phosphors [10]. Additionally, it was shown that the same technique is useful for the determination of up-conversion in Er 3 þ /Yb 3 þ co-doped Gd 2 O 3 [11] and Er 3 þ /Yb 3 þ /Li þ doped ZrO 2 [12]. The synthesis of new rare-earth sesquioxides has gener- ated significant interest due to their excellent chemical www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2012.07.036 n Corresponding author. Tel./fax: þ381 11 3408 678. E-mail address: dramican@vinca.rs (M.D. Dramicanin).