Journal of Crystal Growth 229 (2001) 497–500 Fluoridecrystals:2 mmHo 3þ laseremissionandenergytransfer mechanisms in Er 3þ P. Maroni, L. Palatella, A. Toncelli, M. Tonelli* Department of Physics}INFM, University of Pisa, Via Buonarroti 2, 56127 Pisa, Italy Abstract A spectroscopic analysis of nonlinear energy transfer in BaY 2 F 8 and LiYF 4 doped with Er 3þ is reported. We developedanewmethodtomeasuretheupconversionparameterbasedonthesinusoidalmodulationofthepumpbeam intensityandontheintensityspectrumanalysisofthegreenfluorescence.Wealsopresentcwlaserresultsinthe2 mm wavelengthregionofaTm,Ho:LiYF 4 crystalwith30%slopeefficiencyatroomtemperature. # 2001ElsevierScience B.V. All rights reserved. PACS: 81.10; 42.65.K; 78.55 Keywords: A1. Characterization; A2. Czochralski method; B1. Yttrium compounds; B2. Nonlinear optic materials; B3. Solid state lasers 1. Introduction Fluoridesareanimportantclassofcrystalsthat show peculiar chemical and physical characteris- tics: low refraction index, low phonon energy and wide-in-wavelength transmission region [1]. These features, together with the spectroscopic charac- teristics of rare earths and transition metals used as doping ions, make these crystals particularly appealing for laser and frequency conversion applications [2]. For this reason, we set up a Czochralskifurnaceforfluoridecrystalgrowth.In this paper we study both the energy transfer mechanismsandlaserapplicationsofthesecrystals inthevisibleandnear-infraredwavelengthregions (500nmand2 mm): (a)energytransferinrare-earthdopedcrystalsis characterizedbymanynonlinearprocesses;oneof the most relevant is upconversion (UPC) [3]. This process is responsible for the near infrared to visible wavelength conversion and often deter- mines the population dynamics of the levels involved in laser transitions. We studied the population dynamics of Er 3þ :LiYF 4 (YLF) and Er 3þ :BaY 2 F 8 (BaYF) by means of rate equation formalism and developed a new method to measure the upconversion parameter a. This method is based on the sinusoidal modulation of thepumplaser(at800nm)andontheanalysisof the green fluorescence intensity spectrum. (b) The near-infrared wavelength region (2 mm) is very interesting both for the basic and applied research. Several authors have reported laser action in this wavelength region both in pulsed *Corresponding author. E-mail address: tonelli@df.unipi.it (M. Tonelli). 0022-0248/01/$-see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)01216-7