4f 2 to 4f5d excited state absorption in Pr 3 -doped crystals S. Nicolas a, * , E. Descroix a , Y. Guyot b , M.-F. Joubert b , R.Yu. Abdulsabirov c , S.L. Korableva c , A.K. Naumov c , V.V. Semashko c a Laboratoire du Traitement du Signal et Intrumentation, CNRS-UMR 5516, Universit e Jean Monnet, 23 Rue du Docteur Paul Michelon, 42023 Saint-Etienne, France b Laboratoire de Physico-Chimie des Mat eriaux Luminescents, CNRS-UMR 5620, Universit e Claude Bernard Lyon I, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France c Laboratory of Quantum Electronics and Radiospectroscopy, Kazan State University, 18 Kremlin Street, 420008 Kazan, Russian Federation Abstract We ®rst report one photon classical spectroscopy of Pr 3 -doped LiLuF 4 single crystals which leads to the energy level diagram for Pr 3 levels in this host and to the 1 D 2 and 3 P 0 emitting level lifetimes. Then, excited state absorption ESA) spectra from these metastable levels to 4f5d states are presented and the ESA cross-sections are in the order of 10 18 cm 2 . Subsequently, such upconversion excitation into the 4f5d states of Pr 3 is used to generate the broad band 4f5d to 4f 2 UV ¯uorescence. Moreover, an energy transfer from Pr 3 4f5d states to Ce 3 5d states is clearly identi- ®ed. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 78.50.-w; 78.55.-m Keywords: Rare earth spectroscopy; Upconversion; Excited state absorption 1. Introduction Radiative desexcitation from 4f n1 5d to 4f n con®gurations of some trivalent rare earth ions in dielectric host matrix, with wide band gap, oers the possibility of generating broad band emissions or tunable laser radiations in the near ultraviolet UV) or UV spectral domain. Until now, 4f5d to 4f 2 laser emission with Pr 3 -doped crystals has never been observed contrary to Ce 3 ions [1,2] or Nd 3 ions [3] doped ¯uoride crystals, for which 4f n1 5d to 4f n laser radiations have been obtained after direct pumping into their 4f n1 5d band. However, Pr 3 -doped oxide and specially ¯uoride crystals seem to be interesting as they can generate very intense 4f5d±4f 2 emissions in a broad spectral domain, from 220 to 450 nm approximately, de- pending on the host matrix. In addition to that, emitting 4f5d states can be excited either directly or by a two-step excitation process using meta- stable 3 P J ; 1 I 6 or 1 D 2 levels, located in the blue or orange spectral domain respectively, as interme- diate levels. These upconversion mechanisms en- able to pump 4f5d states using visible or near UV photons. This is a great advantage as it should limit gain laser decrease resulting from solarization eects created by 4f5d direct pumping with UV or Vacuum UV VUV) photons. Possible two-step excitation of the 4f5d states of Pr 3 has been Optical Materials 16 2001) 233±242 www.elsevier.nl/locate/optmat * Corresponding author. 0925-3467/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0925-346700)00083-5