JournalofLuminescence102–103(2003)283–286 Comparativeanalysisofnon-radiativerelaxationofCr 3+ in LiCaAlF 6 andAl 2 O 3 crystals M.G.Brik a ,C.N.Avram b, * a Chemical Physics Department, Weizmann Institute of Science, Rehovot 76100, Israel b Department of Physics, University of the West Timisoara, Bd. V. Parvan, No. 4, 1900 Timisoara, Romania Abstract Temperature dependence of the non-radiative relaxation of the octahedral coordinated Cr 3+ ion in two laser crystals—LiCaAlF 6 and Al 2 O 3 —has been considered using two models of non-radiative transitions. The model of linearelectron–phononinteraction,whichconsiderscollectivevibrationsofthecrystallattice,andtheoscillatingfield model, which takes into account the local vibrations of an impurity center only, have been used to calculate the transitionprobabilitiesofnon-radiativetransitions.Theobtainedresultshavebeencomparedwithexperiments. r 2002ElsevierScienceB.V.Allrightsreserved. PACS: 33.50.Hv;42.70.H;63.20.K;33.20.W Keywords: LiCaAlF 6 :Cr 3+ ;Al 2 O 3 ;Non-radiativetransitions;Crystalfield 1. Introduction Non-radiative relaxation of the excited states determinessignificantlytheefficiencyofsolid-state laseroperation.Thismakestheproblemofunder- standing different mechanisms of non-radiative transitions(NRT)averyimportanttask. Thesimplestmodeldescribingthemechanismof NRT in isolated center in crystals has been proposed by Mott [1] who related the non- radiativede-excitationprocesstothecrossoverof the configuration-coordinate energy surfaces of the excited and ground states. A more sophisti- cated approach was given by Struck and Fonger [2,3],whosuggestedtunnelingthroughthebarrier asaneffectproportionaltotheoverlapintegralsof the vibronic wave function of the excited and ground manifolds, using the single-configuration- coordinate model. Later on, an important devel- opmentintheapproachofStruckandFongerhas been presented by Bartram et al. [4,5] who described the non-radiative processes in a more accurateway,includingtheeffectofJahn–Teller- typedistortions.Anexcellentreviewofthemodels basedontheconfiguration-coordinateschemecan be found in Englman [6] and more recently in HendersonandBartram [7]. Inthispaper,wepresentacomparativeanalysis of non-radiative properties of impurity centers formedbyCr 3+ ionsintwocrystalsLiCaAlF 6 and Al 2 O 3 using two models of NRT, namely the model of linear electron-vibration interaction (EVI)andtheoscillatingfieldmodel. ThetheoryoflinearEVIisgiveninRef. [8] and partially the oscillating field model is founded in *Correspondingauthor.Fax:+40-256-220786. E-mail address: acalin@quasar.physics.uvt.ro(C.N.Avram). 0022-2313/02/$-seefrontmatter r 2002ElsevierScienceB.V.Allrightsreserved. PII:S0022-2313(02)00509-4