Lyoluminescence, thermoluminescence and photodecomposition in microcrystalline powder of KCl, KBr, KI and KI:KNO 3 crystals S.J. Dhoble a, * , P.M. Bhujbal b , N.S. Dhoble c , S.V. Moharil b a Kamla Nehru College, Sakkardara Square, Nagpur 440 009, India b Department of Physics, Nagpur University, Nagpur 440 010, India c Sevadal Women’s Science College, Sakkardara Square, Nagpur 440 009, India Received 5 April 2001; received in revised form 25 September 2001 Abstract Particle size effect in c-radiolysis of KCl, KBr, KI and KI:KNO 3 single crystal and microcrystalline powders has been studied using optical absorption, thermoluminescence and lyoluminescence (LL) techniques. Colouration char- acteristicsinKCl,KBrmicrocrystallinepowdersarereportedtobedifferentfromKIandKI:KNO 3 forvariousparticle sizes. F centre concentration decreases with decreasing particle size in KCl and KBr. While in KI and KI:KNO 3 ,V centreconcentrationincreases,ontheotherhandFcentreconcentrationdecreaseswithdecreasingparticlesize.Rateof formationofI  3 is100timeslessinKI:KNO 3 ascomparedtoKIcrystalandpowders.Thisisattributedtothehigher rate of F-H recombination due to the impurity ions in KI:KNO 3 . Colour centre concentration, particle size and dis- solution rate, all three factors affect LL intensity together. The results presented here may be considered as of only academic interest in solid state materials. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction Colour centres in alkali halides have now been studied for 50 years. It is known that the colour- ationproducedbyelectrolysisisverystable[1].In thelasttwodecades,wehaveshown[2–6]thatthe colouration in microcrystalline powders obtained by crushing the electrolytically coloured single crystal is not stable. In case of potassium halides, all the colouration was lost within a day [7] and Deshmukh and his co-workers established a cor- relation between microhardness, dislocation mo- bility and the stability of colouration in microcrystalline powders [2–6]. Recently a theo- retical approach has been made to the stability of colourcentresinmicrocrystallinepowdersofalkali halides [8]. The emission of visible glow during the disso- lution of irradiated crystal, known as lyolumines- cence (LL), was first reported in sodium chloride by Westermark and Grapinyieser [9]. Later on alternative mechanisms proposed for the emis- sion by Annstrom [10] and Arnikar et al. [11] also supported the formation of hydrated elec- tron (e aq ) as the first step during dissolution. The Nuclear Instruments and Methods in Physics Research B 192 (2002) 280–290 www.elsevier.com/locate/nimb * Corresponding author. 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(02)00477-9