Energy transfer between Ce 3+ → Gd 3+ or Tb 3+ in KNaSO 4 microphosphor Urvashi Manik, a S. C. Gedam b * and S. J. Dhoble c ABSTRACT: KNaSO 4 microphosphor doped with Ce,Gd and Ce,Tb and prepared by a wet chemical method was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) characterization. KNaSO 4 has a 5-μm particle size detected by SEM. KNaSO 4 :Ce 3+ ,Tb 3+ showed blue and green emission (at 494 nm, 557 nm, 590 nm) of Tb 3+ due to 5 D 4 → 7 F J ( J = 4, 5, 6) transitions. KNaSO 4 :Ce 3+ ,Gd 3+ showed luminescence in the ultraviolet (UV) light region at 314 nm for an excitation at 271nm wavelength. It was observed that efficient energy transfer took place from Ce 3+ → Gd 3+ and Ce 3+ → Tb 3+ sublattices indicating that Ce 3+ could effectively sensitize Gd 3+ or Tb 3+ ( green emission). Ce 3+ emission weakened and Gd 3+ or Tb 3+ enhanced the emission significantly in KNaSO 4 . This paper discusses the development and understanding of photoluminescence and the effect of Tb 3+ and Gd 3+ on KNaSO 4 :Ce 3+ . Copyright © 2015 John Wiley & Sons, Ltd. Keywords: luminescence; phosphor; wet chemical method; sensitizer and activator; energy transfer; spectroscopy Introduction The luminescence of rare earth ions has been investigated extensively during the past decades, especially of trivalent ions and of energy transfer between these ions (1,2). In this paper we will describe and discuss a process of energy transfer in which different luminescent centers are involved, i.e. a sensitizer Ce and activators Gd and Tb. Incorporation of Ce 3+ in the host results in emission spectra in the near ultraviolet (UV) light range (3,4). Energy transfer between pairs of rare earth ions at dilution levels below the self-quenching limits has been known to take place generally through multipolar interaction such as dipole– dipole interactions or dipole–quadrupole interactions (5–7). The Ce 3+ ion can be used as a sensitizer as well as an activator, depending on the splitting of 5d excited levels by the crystal field symmetry. Much work has been done on the energy transfer from Ce 3+ to different activator ions in different host lattices (8–11). In recent years we have reported several phosphors in rare earth (RE) ion doped mixed sulphates (12–19) and showed how those ions can exist in different valence states, as a result of irradiation, which can induce valence changes. de Hair (20) studied the energy transfer phenomenon between sensitizer Ce 3+ and activators Tb 3+ , Dy 3+ and Mn 2+ ions. X-ray diffraction (XRD) of KNaSO 4 crystals was studied by Chen et al. (21). In this study we investigated the energy transfer phenomenon in this phosphor for the first time in which Ce 3+ and Gd 3+ act as a sensitizers, whereas Tb 3+ plays the role of activator. Experimental KNaSO 4 (pure) (99.99%), KNaSO 4 :Ce and co-doped by Gd (99.99%) or Tb (99.99%) phosphors were prepared by a wet chemical method. Na 2 SO 4 (99.99%) and K 2 SO 4 (99.99%) of analar grade were taken in a stoichiometric ratio and dissolved separately in double-distilled de-ionized water, resulting in a solution of KNaSO 4 . Water-soluble sulphate salt of cerium was then added to the solution to obtain KNaSO 4 :Ce. We confirmed that no undissolved constituents were left behind and all the salts had completely dissolved in water and thus reacted. The same method was adopted to obtain KNaSO 4 :Ce,Gd and KNaSO 4 :Ce,Tb (here terbium or gadolinium was used as co-dopants): Na 2 SO 4 þ K 2 SO 4 → KNaSO 4 The compounds in their powder form were obtained by evaporating at 80°C for 8h. The dried samples were then slowly cooled at room temperature. The resultant polycrystalline mass was crushed to fine particles in a crucible and then it was fired at 750 °C for 2 h and slowly cooled at room temperature. Formation of the compound was confirmed by taking the XRD pattern (22). The diffraction peaks are found to be matched well with those in the standard profile of JCPDF 74–0394. The photoluminescence measurements of excitation and emission were recorded on a Shimadzu RFPC5301 spectrofluorophotometer fitted with a sensitive photomultiplier tube with a 150 W xenon lamp as the light source with ozone self-dissociation function. This spectro- fluorophotometer provided corrected emission and excitation spectra in the 220–400 nm and 300–700 nm ranges respectively at room temperature. The wavelength scan rate of this spectrom- eter is 2, 5, 15, 30, 120, 240, 600 nm/min (eight-step selection). Samples (2 g) were used for each measurement. Emission and excitation spectra were recorded using a 1.5-nm spectral slit (with minimum band pass resolution). * Correspondence to: S. C. Gedam, Department of Physics, K.Z.S. Science College, Kalmeshwar, Nagpur 441501, India. E-mail: gedam_sc@rediffmail.com a Department of Physics, Sardar Patel Mahavidyalaya, Chandrapur, 442402, India b Department of Physics, K.Z.S. Science College, Kalmeshwar, Nagpur, 441501, India c Department of Physics, R.T.M. Nagpur University, Nagpur, 440033, India Abbreviations: PL, photoluminescence; SEM, scanning electron microscopy; XRD, X-ray diffraction. Luminescence 2016; 31: 911–914 Copyright © 2015 John Wiley & Sons, Ltd. Short communication Received: 07 July 2014, Revised: 16 December 2014, Accepted: 30 April 2015 Published online in Wiley Online Library: 4 June 2015 (wileyonlinelibrary.com) DOI 10.1002/bio.2953 911