Wet-chemical preparation of Ce3+-activated K2LaX5 (X = Cl, Br or I) phosphorsby D. K. Ingole, C. P. Joshi, S. V. Moharil, P. L. Muthal, S. M. Dhopte

Luminescence

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Year
2011
DOI
10.1002/bio.1319
Subject
Chemistry (miscellaneous) / Biophysics

Text

ion of Ce3+‐activated hosphors r tiva r K ou ak te be l e itu . C compared to Ce ‐doped LaBr3. For all the K2LaX5 compounds, washed repeatedly, dried, crushed to fine powders (< 72 µm) and quickly

Research article pted: 24 April 2011, Published online in Wiley Online Library: 14 June 2011 24 the light yield increases and the energy resolution (FWHM) improves with increasing Ce3+ doping. Another important application for K2LaX5 compounds is mid‐IR lasers. Rare‐earth‐ doped chloride crystals offer a broad IR window and a slow rate of multiphonon quenching of activator luminescence, which makes them candidate materials for mid‐IR lasers. In the search for mid‐IR laser materials, chloride crystals with high capacity for accommodating other rare earth ions are of special interest.

Phase diagrams of KCl–LnCl3 systems show that they contain sandwiched between quartz plates and transferred to a photoluminescence (PL) cell. The compounds formed are hygroscopic and attract moisture if left in the open; they are to be stored in tight‐capped bottles. * Correspondence to: S. V. Moharil, Department of Physics, Nagpur

University, Nagpur 440010, India. E-mail: svmoharil@yahoo.com a Physics Department, Shri Ramdeobaba K. N. Engineering College, Nagpur 440 013, Indiaenergy resolution. The possibility to discriminate between γ‐rays with slightly different energies by means of a scintillation detector is of great importance, e.g. for X‐ray astronomy, medical imaging. At present, the scintillator providing the highest energy resolution (~2.6% at 662 keV) is LaBr3:Ce, but it is highly hygroscopic and its growth is still challenging (4). Early scintillation studies on K2LaCl5:Ce 3+ are those due to vant Spijker et al. (5,6). van Loef et al. described the spectroscopic properties of K2LaCl5:Ce 3+(7). The scintillation properties of Ce3+‐activated

K2LaX5 have also been reported by van Loef et al. (8) and Roy et al. (9). Roy et al. have also recently reported K2CeBr5 and

Cs2CeBr5 scintillators (10). These systems are quite interesting 3+ activated powders of K2LaX5 become available. During our recent investigations of wet‐chemical syntheses of rare earth‐ activated fluoride phosphors, we found that Ce3+‐activated phosphors exhibited strong emissions without any post‐ synthesis high‐temperature annealing treatment (21,22). In this paper we report the synthesis of Ce3+‐activated K2LaCl5 phosphors by a wet‐chemical method.

Experimental

Samples were prepared by dissolving desired quantities of reagent‐ grade lanthanum oxide and metal carbonates in halogen acids. Ce:La ratios were adjusted at this stage. Excess acid was then boiled off and the solutions were evaporated to dryness. The resulting mass wasWet‐chemical preparat

K2LaX5 (X=Cl, Br or I) p

D. K. Ingolea, C. P. Joshia, S. V. Moha

ABSTRACT: There has been a renewed interest in Ce3+‐ac detectors, especially for positron emission tomography. Fo (FWHM) improves with increasing Ce3+ doping. K2LaX5 comp

K2LaCl5:Nd crystals show bright mid‐IR luminescence, which m in the IR range has also been reported in K2LaCl5:U 3+. A one‐s phosphor is described. Intense luminescence of Ce3+ can treatment. The availability of such powders opens up severa going to the high temperatures required for melting the const activated materials without taking recourse to crystal growth

Keywords: phosphors; chemical synthesis; photoluminescence

Introduction

There has been a renewed interest in Ce3+‐activated halide phosphors, due to applications as scintillation detectors (1), especially for positron emission tomography (2). Ce3+ exhibits intense emission, due to allowed electric dipole transitions corresponding to transitions from levels of the 5d1 configuration to 2Fj states of the 4f 1 configuration, with fast decay time in the order of several nanoseconds. In the last few years, several inorganic scintillator materials based on Ce3+ have emerged that have a high light yield (3), a fast decay time and a good

Received: 04 December 2010, Revised: 04 March 2011, Acce (wileyonlinelibrary.com) DOI 10.1002/bio.1319K2LnCl5 compounds, which melt congruently and undergo no polymorphic transformations. K2LaCl5:RE systems were studied by Vinogradova et al. (11). K2LaCl5:Nd crystals show bright mid‐

IR luminescence, which makes them candidates for IR laser

Luminescence 2012; 27: 24–27 Copyright © 2011 Johnilb*, P. L. Muthalc and S. M. Dhoptec ted halide phosphors due to applications as scintillation 2LaCl5, the light yield increases and the energy resolution nds are also important as laser hosts for the mid‐IR range. es them a candidate for IR laser materials. Efficient emission p, wet chemical process for preparing Ce3+‐activated K2LaCl5 observed in the as‐prepared powders without any heat xciting possibilities, such as growing single crystals without ent chlorides, or even obtaining processed, transparent, Ce3+‐ opyright © 2011 John Wiley & Sons, Ltd. materials. Efficient emission in the IR range has also been reported in K2LaCl5:U 3+ (12). K2LaX5:Pr crystals have been studied (13–15) and upconversion ability of Pr3+ ions has been demonstrated (16,17).

Crystal growth of these materials is somewhat difficult, due to the moisture sensitivity of lanthanum halides, especially LaBr3 and LaI3 and consequently, high vacuum and an argon atmosphere become indispensable. In some studies, crystals were encapsulated in a KCl host to overcome the problems due to their hygroscopic nature (18–20). It will be more convenient ifb Department of Physics, Nagpur University, Nagpur 440010, India c National Environmental Engineering Research Institute, Nehru Marg,

Nagpur, India

Wiley & Sons, Ltd.

No change in the PL properties was observed for the phosphors, so they were stored for several months. Samples were also found to be stable against UV irradiation, which was used for the PL measurements. No changes in spectral positions or intensities were observed during several successive PL runs. Photoluminescence spectra at room temperature were recorded in the spectral range 220–700nm on a Hitachi F‐4000 spectrofluorometer with a spectral slit width of 1.5 nm. Quantum yields were estimated using sodium salicylate as standard. X‐ray diffraction patterns were recorded on a Philips PANalytical X’pert Pro diffractometer.