Reusable temperature-sensitive luminescent material based on vitrified film of europium(III) b-diketonate complex Dmitry V. Lapaev a, * , Victor G. Nikiforov a , Vladimir S. Lobkov a , Andrey A. Knyazev b , Yury G. Galyametdinov a, b a Zavoisky Physical-Technical Institute of Kazan Scientific Center of Russian Academy of Sciences, 420029 Kazan, Russia b Kazan National Research Technological University, 420015 Kazan, Russia article info Article history: Received 15 June 2017 Received in revised form 8 November 2017 Accepted 27 November 2017 Keywords: Lanthanide(III) b-diketonate complexes Reversible temperature-dependent luminescent properties Temperature-sensitive material Photostability Vitrified film abstract We have proposed a novel temperature-sensitive luminescent material which is a 20 mm thick vitrified film (sandwiched between two quartz plates) fabricated from an amorphous powder of a mesogenic europium(III) b-diketonate complex through a melt-processing technique. The film photoexcited by a 337 nm pulsed nitrogen laser displays a typical Eu 3þ ion luminescence bands with the strongest peak at 612 nm and with the decay time of 537 ms at 298 K. It is obtained that both the mean luminescence intensity and the luminescence decay time at 612 nm decrease significantly with temperature increasing from 298 to 348 K; the average values of the relative and absolute temperature sensitivities of the luminescence decay time in the range of 298e348 K are 1.2%$K 1 and 6.5 ms$K 1 , respectively. The thermal quenching mechanism of the luminescent properties was analyzed and discussed. The experi- ments showed that, the luminescent properties of the film is insensitive to oxygen, the film is photo- stable under UV light, there is full reversibility of the temperature-dependent luminescence intensity and the decay time, and the high luminescence brightness of the film can be observed with violet light excitation. These factors indicated that the film is promising material for reusable luminescent ther- mometers, suitable for long-term monitoring in the range of 298e348 K. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Currently, a temperature control is in demand in many areas of science and technology [1]. Among many different types of ther- mometers [2], the most widely used applications are temperature sensors based on temperature-dependent luminescence intensity and/or decay time [1,3]. Their advantages are miniaturization, high sensitivity and accuracy, fast response, non-contact monitoring of surface temperature distributions and function even in strong electromagnetic fields [1,3]. The main criteria for selection of the temperature-sensitive luminescent materials are no or low oxygen sensitivity, high tem- perature sensitivity, strong luminescence, excitation of lumines- cence by visible light and high photostability [1,3]. Europium(III) b- diketonate complexes are characterized by unique photophysical properties such as large Stokes shifts, very narrow-band lumines- cence with a high quantum yield in the red region, a long lumi- nescence decay time [4], low sensitivity to oxygen [5e10] and attractive chemical characteristics (relatively easy synthesis, good solubility in many basic solvents, possibility of incorporation into different matrices, etc) [1,3,4,8,12]. Further, some of these com- plexes display a highly temperature-dependent luminescence [1,3,5e14]. Because of these properties the europium(III) b-diket- onate complexes are very promising for luminescent sensor and temperature imaging [1,3,12]. In the past decades the luminescent temperature sensors based on isolated complexes [3,12] along with complexes embedded into different matrices [1,3,6e8,10,13,14] and organic-inorganic hybrid materials [1,3,12] were proposed. Main applied problems of the europium(III) b-diketonate com- plexes as the luminescent thermometers are absorption bands localized in the UV region [5,6,10,13,14] and poor photostability under UV irradiation [3,5,8,10e12,15e17] making them not suitable for long-term monitoring. The photostability of the europium(III) b- diketonate complexes can be enhanced by their doping into * Corresponding author. Kazan Physical-Technical Institute, Kazan Scientific Center, Russian Academy of Sciences, Laboratory of Fast Molecular Processes, Sibirsky trakt, 10/7, Kazan, 420029, Russia. E-mail address: d_lapaev@mail.ru (D.V. Lapaev). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2017.11.042 0925-3467/© 2017 Elsevier B.V. All rights reserved. Optical Materials 75 (2018) 787e795