Particle size influence of starting batches on phosphorescence behaviour of Sr 4 Al 14 O 25 based bluish green phosphors S. Yesilay Kaya* 1 and B. Karasu 2 Photoluminescent material with long afterglow is a kind of energy storage material that can absorb both ultraviolet (UV) and visible lights from sunlight, and gradually releases the energy in the dark at a certain wavelength. These sorts of materials have great potential for various device applications and have been widely studied by many researchers. In recent years, it has also been reported that 2SrO.3Al 2 O 3 /Eu 2z and 4SrO.7Al 2 O 3 /Eu 2z phosphors as green and blue emitters have even higher quantum efficiencies. To determine the initial particle size effect on the phosphorescence behaviour, Eu 2z /Dy 3z doped Sr 4 Al 14 O 25 phosphors were synthesised by mixing 4SrO and 7Al 2 O 3 with a flux (H 3 BO 3 ) through high temperature solid state reaction method under weak reducing atmosphere. Such an influence on the crystalline structure and emission colour of phosphorescent pigments was studied by means of X-ray diffraction, scanning electron microscope (SEM), particle size analysis, excitation and emission spectroscopy. The results showed that the emission wavelength of the phosphorescence pigments shifted from green to blue region due to the decrease in average particle sizes of the phosphor batches, forming different types of strontium aluminate crystals. Keywords: Phosphorescence, Long afterglow, Wet milling, Rare earths, Solid state reaction, Particle size Introduction Phosphorescence (or afterglow) refers to the light emission of an insulator that persists at room tempera- ture after stopping excitation [usually ultraviolet (UV) irradiation]. 1 Long lasting phosphors absorb light energy and gradually emit visible light in the absence of the source for a long period of time. 2 Among different afterglow (AGL) phosphors, europium activated stron- tium aluminates like SrAl 2 O 4 /Eu 2z , Dy 3z , SrAl 4 O 7 / Eu 2z , Dy 3z , SrAl 12 O 19 /Eu 2z , Dy 3z and Sr 4 Al 14 O 25 / Eu 2z , Dy 3z are of special interest for their efficient emissions in the visible region. 3–6 The phosphorescence emission of Eu 2z ions spreads from the UV to the red region, depending on the host lattice. This is because the phosphorescence emission is associated with the 5dR4f transition, and the 5 d excited state is influenced by crystal field effects. 7 Long lasting emission is observed in the transition of Eu 2z *REu 2z (4f 6 5d 1 R4f 7 ). In other words, Eu 2z and Dy 3z act as luminescence and hole trap centres respectively. 8 With the increasing interest in Eu 2z and Dy 3z doped SrAl 2 O 4 and Sr 4 Al 14 O 25 phosphors, researchers focused themselves on the effect of various additions, mole fractions of components and preparation methods within the development process of phosphorescence. During these studies, it was found that the shapes and sizes of phosphor particles affect the phosphorescence properties. New properties were discovered, such as the conversion of diffusion strength into blue when the particle size reaches nanolevel. If the phosphor particles are well shaped and in a plate-like structure, it is expected that their light absorption will be better, and they form a high density compact as a result of their orientations. This situation causes higher emission intensity. The particle sizes and shapes of phosphor powders may be dependent on the type of crystal formed, the grain size of starting materials and therefore the preparation process. 9,10 In the present work, the synthesis of blue–green emitting Eu 2z doped, Dy 3z and Nd 3z co-doped Sr 4 Al 14 O 25 phosphor through solid state reaction route is reported. To obtain pure Sr 4 Al 14 O 25 /Eu 2z , Dy 3z , Nd 3z phosphors, raw materials were ball milled with other reactants for various times before sintering. Photoluminescence studies have been carried out to understand the mechanism of excitation and the corresponding emission in the prepared phosphor host and also to understand the effect of the initial particle size of starting batches. 1 Department of Glass, Anadolu University, Yunusemre Campus, Eskisehir 26470, Turkey 2 Department of Materials Science and Engineering, Anadolu University, Iki Eylul Campus, Eskisehir 26555, Turkey *Corresponding author, email selvin.yesilay@gmail.com ß 2012 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 14 November 2011; accepted 4 January 2012 DOI 10.1179/1743676112Y.0000000005 Advances in Applied Ceramics 2012 VOL 0 NO 0 1