Upconversion Luminescence Properties Of Lithium Niobate Crystals Co-doped With Trivalent Metal And Erbium Ions

In recent years, upconversion （UC） luminescence materials have many importantpotential applications in many areas of the national economy and national defenseconstruction, thus questing for high luminous efficiency and excellent optical performanceof the UC luminescence materials, and opening out new materials have important researchsignificance. Investigation on the properties of UC luminescence of rare-earth ions underfemtosecond （fs） laser excitation can enhance the luminous efficiency and exploit newapplication of materials in being.In this paper, Sc:Er:LiNbO₃（LN） crystals and In:Er:LN crystals were grown by theCzochralski method. The influence on the spectral and UC luminous properties of Er:LNcrystal with the variety of doping concentration and [Li]/[Nb] were analysed. All of theabove laid the foundation of questing the high luminous efficiency and excellent opticalperformance UC luminescence materials.Firstly, the threshold concentration and location of doped ions were investigated byinfrared transmittance spectra and ultraviolet–visible absorption spectra. The results showthat the threshold concentration can be reached by increasing [Li]/[Nb] and theconcentration of doping third-valance metal ions. When the doping concentration is overthe threshold, all the anti-site Nb defects are replaced by Sc and In ions, and the dopingions begin to enter into the normal Li and Nb sites. The violet absorption edge will shift tothe red and the OH-peak will move distictly according to spectrum analysis. However, theincreasing of [Li]/[Nb] can reduce the doping threshold concentration. When theincreasing of the [Li]/[Nb], the OH-absorption edge will shift the shorter wavelength withthe low In doping concentration.Secondly, the UC luminescence properties and mechanisms of crystals under the fslaser excitation were investigated. The results indicate that the increase of [Li]/[Nb] cannot only enhance the optical damage resistance ability, but also increase the UCluminescence intensity. But when the doping concentration exceeds a threshold concentration, the UC luminous intensity will be decrease at the same time. Furthermore,the second harmonic generation （SHG） light of 400 nm with high intensity appears in theIn:Er:LN crystal with a [Li]/[Nb] of 1.38 （In:Er:SLN）.Finally, in order to clarify the reason of In:Er:SLN that can produce high-intensitySHG light in the case of no phase-matching, we performed a serious experiments andJudd-Oflet （J-O） theory calculation to analyse this phenomenon, and analysed the reasonthat the SHG light can be affected by fs excitation source, near-stoichiometric compositionand heavily doped trivalent metal ions.