Quantum efficiency of 1 S 0 and 3 P 0,1 levels of Pr 3+ doped YF 3 Stefan Ku ¨ck a, * , Irena Soko ´ lska b,c , Markus Henke c , Eugen Osiac c,d a Physikalisch-Technische Bundesanstalt, Optics Division, Working Group 4.13 ‘‘Laser radiometry’’, Bundesallee 100, 38116 Braunschweig, Germany b Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław, Poland c Institut fu ¨ r Laser-Physik, Universita ¨ t Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany d Institute of Atomic Physics, P.O. Box MG-6, 76900 Bucharest, Romania Received 30 July 2004; accepted 5 October 2004 Available online 11 November 2004 Abstract We present a detailed investigation of the quantum efficiency of the 1 S 0 and 3 P 0,1 levels in Pr 3+ doped YF 3 under VUV excitation. The quantum efficiency of the 3 P 0,1 level was determined by the measurement and comparison of the photon fluxes of the 1 S 0 ! 1 I 6 transition around 400 nm with the visible emissions occurring from the 3 P 0,1 levels. It was found that already at concentrations as low as 0.01% the 3 P 0,1 emission quantum efficiency is only about 61%. The quenching process is most probable caused by an energy transfer cross relaxation process involving the 3 P 0,1 levels and the 3 H 4 ground state. For concentrations of 0.1%, 0.5%, 1% and 10%, the quantum efficiency was determined to be about 42%, 29%, 17%, and 0.4%, respectively. The total quantum efficiency of the vis- ible emission (380–750 nm) under excitation at 190 nm, determined by measurements of the total photon flux, has a maximum for a Pr 3+ concentration of 1%. At this value, the absorption efficiency of the 4f5d absorption bands is very high and the 3 P 0,1 quenching is only moderate. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Phosphors; Luminescence; Emission; Quantum efficiency; Synchrotron radiation; Quantum cutting; Photon cascade emission; Pr 3+ ; 1 S 0 ; YF 3 1. Introduction Luminescent materials with a quantum efficiency higher than unity might play a significant role for light- ing applications, especially in discharge lamps. Environ- mental reasons may force the replacement of Hg gas by Xe gas. The latter emits at wavelengths around 172 nm, thus at shorter wavelengths compared to the Hg dis- charge, where the mean emission wavelength is around 243 nm. Therefore, the phosphors to be used in the Xe-discharge lamp need to have a conversion efficiency of 140% of that for the commonly used phosphors. Since the latter have an efficiency of 90%, the total efficiency of the Xe-discharge phosphors need to have an average conversion efficiency of 125%. Thus, the aim of this ongoing research work is the development of efficient luminescent materials which compensate the additional energy required when using the Xe discharge. Suitable materials are so called ‘‘quantum cutters’’ or ‘‘photon cascade emitters’’, which generate more than one visible photon after absorbing an UV photon. The most effi- cient quantum cutter known thus far is Eu 3+ doped LiGdF 4 with down-conversion quantum efficiencies of up to 190% [1,2]. However, overall external quantum efficiencies are rather low (32% [2]) and the excitation occurred at 202 nm directly into the Gd 3+ excitation bands. Another interesting and promising material for quantum cutting is Pr 3+ doped YF 3 . In fact, this mate- rial was already investigated in the mid 1970Õs and was found to exhibit photon cascade emission by Somme- rdijk et al. [3,4] and Piper et al. [5]. For the illustration of the cascade emission process, in Fig. 1 the energy 0301-0104/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2004.10.015 * Corresponding author. Tel.: +49 531 592 4111; fax: +49 531 592 4116. E-mail address: stefan.kueck@ptb.de (S. Ku ¨ ck). www.elsevier.com/locate/chemphys Chemical Physics 310 (2005) 139–144