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The emission properties of the 3 P0 state of praseodymium ions in lithium niobate crystal have been studied. Blue-green emission at 510 nm corresponding to the 3 P0 3 H4 transition in Pr3+ :LiNbO3 crystals was generated after direct and up-conversion excitation with orange and infrared radiation around 920 nm. The up-conversion mechanisms were shown to be energy transfer and excited state absorption for orange and infrared excitation, respectively. The processes responsible for non-radiative relaxation of the 3 P0 state were also determined.

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Abstract. Nonequivalent Er 3+ sites in LiNbO3 crystals have been evidenced by low-temperature optical absorption measurements. The radiative transition rates for the 4S3/2, 4F9/2, 419/2, "111/2, and 4/13/2 levels have been evaluated by the Judd-Ofelt method, and the contribution of multiphonon relaxation to the decay of excited states has been estimated. The quantum efficiency of the 4/11/2 level has been estimated to be 6 % only, thus the excitation of levels lower than 4S3/2 is expected to populate efficiently the 4/13/2 level. 78.55.Hx, 42.70.Hj Growing interest in rare earth doped LiNbO3 is stimulated by attempts to endow the sophisticated integrated optics structures based on lithium niobate with the ability to produce and amplify light. The most extensively studied compound is lithium niobate doped with neodymium, particularly after the demonstration that the introduction of MgO into LiNbO3 substantially reduces the photorefractive damage and increases the distribution coefficient of neodymium [1,2]. However, the erbium ion as a dopant seems to be more interesting for telecommunication purposes because of the long lifetime of the 4113/2 level from which an efficient emission at about 1,56 gm occurs. Literature concerning erbium doped LiNbO3 is not exhaustive. Energy levels of Er 3 + in LiNbO3 have been reported for the first time by Gabrielyan et al. [3]. More recently, room temperature luminescence spectra and lifetimes for several excited states of Er 3 + in this matrix have been studied by Babadjanian et al. [4], and the Er 3 + lattice sites have been investigated by Kovacs et al. [5]. In this paper we attempt to determine the dynamics of excited state relaxation and the contribution of radiative and nonradiative transitions to the decay of excited states relevant to laser action in LiNbO3:Er. As in previous published works, we investigate bulk-doped crystals which are not the optimal solution for guided-wave optics, but they can furnish reliable information useful for characterization of locally doped materials. It has been shown recently [6], that the bulk-grown Er 3 +-doped LiNbO3 and locally doped LiNbO3 by diffusion of Er 3+ have essentially the same structural and emission properties. PACS: ExperimentalSingle crystals of LiNbO3 : Er 3 + were grown from a congruent melt (i.e., Li/Nb=0.945) by the Czochralski method. Uniformly doped, good quality crystals have been obtained at a pulling rate of 2 mm/h and rotation rate of 8 r.p.m. Two samples were used in this study. One sample had 1.88x 1019ions/cm 3 and the other had 5.64 x 1019 ions/cm 3 of Er 3+. Examination of samples with an X-ray microprobe indicated that in contrast to neodymium-doped LiNbO3, the actual concentration of erbium at this doping level is essentially the same as the nominal concentration. Absorption spectra were measured with a Varian model 2300 absorption spectrophotometer. Luminescence spectra were excited by an argon-ion laser, analyzed by a grating monochromator (Zeiss, model GDM 1000 or Optel, model M-56, depending on spe...