Thermal quenching mechanisms of the Eu 3+ luminescence in Ca 9 Al(PO 4 ) 7 obtained by citric route Robert Pa ˛zik a, *, Katarzyna Zawisza a,b , Adam Watras a , Kinga Maleszka-Bagin ´ ska a , Philippe Boutinaud c , Rachid Mahiou d , Przemysław J. Deren ´ a, ** a Institute of Low Temperature and Structure Research, PAS, Okolna 2, 50-422 Wroclaw, Poland b Wroclaw University, Faculty of Chemistry, F. Joliot-Curie 14, 50-338 Wroclaw, Poland c Clermont Universite ´, ENSCCF, Institut de Chimie de Clermont-Ferrand – BP 10448, F-63000 Clermont-Ferrand, France d CNRS, UMR 6296, ICCF, F-63177 Aubie `re, France 1. Introduction Constantly growing interest in development and engineering of new phosphor materials for modern, environmentally friendly and energy saving light sources and other optical applications demands more and more detailed analysis of the luminescence properties extended to the identification of the mechanisms leading to the thermal quenching of the luminescence. Why is this issue extremely important? The answer on this question is fairly straightforward, indeed, in many devices containing phosphors (e.g. LEDs technology, lamps, projection television tubes, etc.), the operating temperature exceeds room temperature [1]. Unfortunately majority of the published scientific articles devoted to the new materials do not contain any information on the luminescence stability of phosphors at elevated temperatures being a critical parameter. Additionally extended studies could provide more facts facilitating the under- standing of the emission quenching processes. Among of variety of the phosphors based on the mixed metal oxides serving as a host-lattice for d and f metal cations phosphates of different types are nowadays attracting increased attention due to their excellent thermal and chemical stability as well as excellent luminescence performances [2] . They are interesting candidates for mercury-free lamps due to high absorption and transfer efficacies of the VUV radiation to the emitting RE 3+ dopant. In view of the EU communication concerning the usage of mercury in the lightning industry, findings of new phosphors for VUV lamps is of great importance [3]. According to our knowledge there is only one article published on the solid-state synthesis and lumines- cence characteristics of Ca 9 Al(PO 4 ) 7 (hereafter CAlP) [4], but authors did not raise the problem of thermal quenching of luminescence at all. In this paper, we report on the synthesis, structural properties and the effect of temperature on the luminescence performance of the Eu 3+ emission in CAlP powders. 2. Experimental details 2.1. Instruments The X-ray diffraction (XRD) patterns were collected in a 2u range of 5–1008 with X’Pert Pro PANalytical X-ray diffractometer (Cu, K a1 : 1.54060 A ˚ ). Raman spectra were acquired using a LabRam HR 800Horiba Jobin Yvon equipped with a 9 mW HeNe laser emitting 632.8 nm line. The microstructure and morphology of CAlP particles were investigated by high resolution transmission electron micros- copy (HRTEM) using a Philips CM-20 Super Twin microscope, operated at 200 kV. Samples for HRTEM measurements were Materials Research Bulletin 48 (2013) 337–342 A R T I C L E I N F O Article history: Received 4 August 2012 Received in revised form 8 October 2012 Accepted 22 October 2012 Available online 2 November 2012 Keywords: A. Inorganic compounds A. Optical materials B. Chemical synthesis D. Luminescence A B S T R A C T The citric route was employed for synthesis of the pure phase Ca 9 Al(PO 4 ) 7 :Eu 3+ (CAlP:Eu 3+ ) powders as an attractive alternative to the solid state reaction (no need of multistep and long thermal treatment). Structural properties of the final product were studied by means of X-ray diffraction as well as Rietveld refinement was conducted in order to calculate the cell parameters. The thermal behavior of the emission was studied using excitation line well matched with the 7 F 0 ! 5 D 4 absorption band covering broad range of temperature. Activation energy was estimated to be equal to 10,550 cm 1 . The thermal behavior of the Eu 3+ luminescence in CAlP crystal lattice shown that the almost 80% of intensity is kept up to 430 K. ß 2012 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +48 71 343 5021; fax: +48 71 344 1029. ** Co-corresponding author. E-mail addresses: R.Pazik@int.pan.wroc.pl (R. Pa ˛ zik), P.Deren@int.pan.wroc.pl (P.J. Deren ´ ). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2012.10.034