Sensors and Actuators B 202 (2014) 1305–1312 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo ur nal home page: www.elsevier.com/locate/snb Enhanced upconversion and temperature sensing study of Er 3+ –Yb 3+ codoped tungsten–tellurite glass Anurag Pandey a,∗ , S. Som a , Vijay Kumar a , Vinod Kumar a , Kaushal Kumar b , Vineet Kumar Rai b , H.C. Swart a,∗ a Department of Physics, University of the Free State, Box 339, Bloemfontein 9300, South Africa b Department of Applied Physics, Indian School of Mines, Dhanbad 826004, India a r t i c l e i n f o Article history: Received 10 May 2014 Received in revised form 19 June 2014 Accepted 21 June 2014 Available online 28 June 2014 Keywords: Rare earth doped glass Upconversion emission Temperature sensor a b s t r a c t This article reports on the visible upconversion and temperature sensing behaviour of Er 3+ –Yb 3+ doped/codoped TeO 2 –WO 3 glasses prepared by a melting and quenching method. The upconversion emissions have been observed throughout the visible and infrared region upon 980 nm and 808 nm exci- tations and assigned suitably from different transitions of the Er 3+ ion. The emission intensities of the most intense green band have been enhanced on the co-doping with theYb 3+ ions with about 5.92 and 3.99 times upon 980 and 808 nm excitations, respectively. The reason behind this improvement is explained on the basis of a power dependence study and an energy level structure. The colour tunability behaviour of the codoped glass has also been investigated upon both excitations. The temperature sensing perfor- mance of the prepared glass has been studied by using the fluorescence intensity ratio technique up to 745 K. The results suggested that the present glass is a suitable candidate for making a high temperature sensor up to 690 K with a sensitivity of about 28.72 × 10 -4 K -1 . © 2014 Elsevier B.V. All rights reserved. 1. Introduction Luminescence observed from rare earth (RE) doped glasses are promising components owing to their broad area of applications in photonics, such as frequency upconverters, optical amplifiers, eye safe lasers, radar range finders, temperature sensors, etc. [1–6]. The photoluminescence (PL) mechanisms in fluorescent materi- als may be studied by down conversion (DC) and upconversion (UC). The generation of high-energy photons upon low energy excitation is known as UC while the reverse process is called DC [7]. Visible UC emissions upon suitable near infrared (NIR) excitations from RE doped materials have attracted considerable attention of researchers during the last two decades. The NIR excitations prevailed over ultraviolet (UV) excitation sources due to their commercial availability, high power and low cost [8]. Mainly three colours, blue, green and red lights of visible emis- sion are demanded due to their direct application in behaviour life. Among them green is more sensitive to the human eyes [8]. Till now, lots of green UC emitting glasses have been investi- gated and amongst them triply ionized erbium has been used for ∗ Corresponding authors. Tel.: +27 51 401 3852/58 718 5308; fax: +27 58 718 444. E-mail addresses: anuragpandey439@gmail.com (A. Pandey), swarthc@ufs.ac.za (H.C. Swart). doping purposes [3,9–12]. Triply ionized erbium is more functional rather than the other RE ions because of its abundant energy level structure and can easily be pumped with 980 nm excitation [13]. The oxide glasses are well known as excellent hosts for the rare earths doping and better performance of the optical properties [14–16]. Among the oxides, the tellurite based glasses are of partic- ular interest due to their promising optical and physical properties viz. metallic character, low cut-off phonon energy, low fusion tem- perature, large refractive index, long transmission window, high thermal and mechanical stability, etc. [17,18]. The UC emission from Er 3+ , Yb 3+ doped/codoped tellurite glasses have been reported with other former and modifier but by using tungsten as a for- mer/modifiers only a very few was reported [9,19–21]. Guoa et al. have reported about the 2.7 m emission property of Er 3+ , Yb 3+ codoped tungsten–tellurite glass. Tungsten–tellurite based glasses having a high transition temperature and a better thermal stabil- ity which are key parameters of a material to be used for high temperature sensing purposes. UC based temperature sensing has been done in several RE ions doped/codoped glasses by different researchers using the fluorescence intensity ratio (FIR) technique [22]. It has been found that the temperature range and sensitivity of the reported glassy materials are quite low and its improvement seems to be needed. The development of high temperature sensing glasses with appreciable sensitivity is a challenging task among modern researchers working in the area of RE doped glasses. http://dx.doi.org/10.1016/j.snb.2014.06.074 0925-4005/© 2014 Elsevier B.V. All rights reserved.