Why the quest of new rare earth doped phosphors deserves to go on B. Moine * , G. Bizarri Laboratoire de Physico-Chimie des Mate ´riaux Luminescents, UMR 5620 du CNRS UCBL, 10 rue Ampe `re, 69622 Villeurbanne, France Received 29 September 2004; accepted 30 September 2004 Available online 6 June 2005 Abstract The scientific research on phosphors has a long history starting more than 100 years ago. But recently the appearance of new kinds of displays and lighting devices (plasma display, fluorescent lamp without mercury...) induced an increase of the research of new phosphors with better luminous efficiency than those available up to now. It has been shown that the behaviour of ‘‘classical’’ phosphors in a plasma display panel is quite different than in a cathode ray tube and that the vacuum ultraviolet (VUV) excitation process has to be studied with care in order to improve the phosphors efficiency. It is well established now that a good phosphor for electronic or ultraviolet excitation, is not necessarily a good choice for excitation in VUV. This is probably due to the fact that the excitation process is very different in that case. We will illustrate this difference on the well-known LaPO 4 :Ce 3+ , Tb 3+ phosphor. The penetration depth of the VUV photons is extremely small inducing a large contribution of the surface of the phosphor. We have shown that, for most phosphors, only a few tens of nanometers of the phosphor grain are really useful and we propose a way to realize phosphors powders using less than 20% of doped materials. However the traps of the material play a crucial role in the fluo- rescence properties due to the fact that autoionization process is likely when dopant ions absorb high energy photons. Fast aging process is one of the main drawbacks of VUV excitation. We demonstrate this effect on BaMgAl 10 O 17 :Eu 2+ , the blue emitting phos- phor widely used up to now in Plasma Displays Panels and fluorescent lamps. Low energetic efficiency is another drawback of VUV excitation that can be solved only in the framework of fundamental studies. Quantum cutting emission may be a solution and calls new research to find good phosphors characterized by a high quantum efficiency, a high fluorescence efficiency and an adapted colorimetry. Ó 2005 Elsevier B.V. All rights reserved. PACS: 78.55.Hx; 78.60.Kn Keywords: Phosphors; Luminescence; VUV; Aging process 1. Introduction The scientific research on phosphors has a long his- tory starting more than 100 years ago. Why do we need new phosphors? Essentially because of the technological progress: From the early black and white television, in 1936, to the new 60 in. plasma display panels, the tech- nology has really changed. In the domain of lighting de- vices, also from the first lamp made by Edison to the compact fluorescent lamp used everywhere now, pro- gress and improvement are obvious. We also need to continue research in this field because the excitation sources have changed and it is known that a good phos- phor for electronic or ultraviolet excitation is not neces- sarily a good choice for excitation in vacuum ultraviolet (VUV). In a near future, we will be obliged to suppress mercury in any lighting devices because it is very harmful for the environment, and replace it by a mixing of rare gas (Xenon and Neon) which emits VUV photons from 147 nm to 190 nm instead of ultraviolet photons at k = 254 nm in order to excite the phosphor coated lamp inner surface. Therefore the fluorescence properties of 0925-3467/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.09.028 * Corresponding author. Tel.: +33 472448330; fax: +33 472431130. E-mail address: moine@pcml.univ-lyon1.fr (B. Moine). www.elsevier.com/locate/optmat Optical Materials 28 (2006) 58–63