Investigation Of Efficient Energy Transfer From Ce To Nd In Nd/Ce Codoped Yttrium Aluminum Garnet

Nd³⁺:YAG is one of the most commonly used commercial available laser material.Near-infrared （NIR） luminescence of Nd³⁺ions plays an important role in laser, fiberoptical communication. The laser made by Nd³⁺:YAG Has many advantages. Becauseits low threshold value, it can proceed long-pulse、highrepetitionrate、continuous、frequency multiplication operation at room temperature. Although thelaser-performance of Nd³⁺:YAG crystal is very good, it can’t satisfy the high power,high efficiency requirements. The reason is Nd³⁺ions in the YAG segregatedcoefficient is low. It limits the light emitting efficiency at some wavelengths. Inaddition, NIR luminescence of Nd³⁺ions originated from its f-f transition, which ispartially forbidden. The f-f transitions are usually with low direct excitation efficiencyand very long lifetime. It Can’t make full use of the optical pump energy. In view ofthis, In order to increase the luminous efficiency of infrared light of Nd³⁺:YAG lasercrystal, we doped sensitizer Ce³⁺ions in the Nd³⁺:YAG laser crystal.The reasons of Adopting Ce³⁺ions as sensitizer are: the excitation state of Ce³⁺ions is at the d shell level, while the ground state is an f shell level and the d-ftransition is an allowed transition. Hence, fluorescence of Ce³⁺ions is more efficientthan Nd³⁺ions which have forbidden f-f transition. In addition, The absorption bandof Nd³⁺ions matches well with the emission band of Ce³⁺ions, resulting in theefficient energy transfer from Ce³⁺to Nd³⁺. In this paper, In order to fully study theenergy transfer from Ce³⁺ions to Nd³⁺ions in Ce³⁺,Nd³⁺:YAG, we concretely researchon the spectral measurement, the energy level diagram analysis and the fluorescencedecay curve three aspects.It is shown that NIR-788nm luminescence of Nd³⁺in YAGcould also be very efficiently sensitized with codoped Ce³⁺ions. First, The excitation and emission spectrum of4mol%Ce³⁺:YAG,4mol%Nd³⁺:YAG and4mol%Ce³⁺,4mol%Nd³⁺:YAG Crystal sample have beeninvestigated by the Hitachi F-4500fluorescence spectrophotometer at roomtemperature. Fluorescence of Ce³⁺ions originates from its d-shell energy level, whichcan be affected by local crystal field, and the excitation band of Ce³⁺ions in YAGranges in UV. The Emission of Ce³⁺:YAG shows a broad band from500nm to650nm. It was noticed that this band overlaps well with the excitation peaks of Nd³⁺ions.We can investigate that the shape of the emission spectrum of Ce³⁺, Nd³⁺:YAG Crystalsample changes a lot. Apperance of the Nd³⁺ions absorbtion lines shows that the Ce³⁺ions fluorescence is selectively reabsorbed by Nd³⁺ions. This fearure is characteristicof radiative energy transfer between two impurity ions.The second, We use the same intensity of372nm light excitation samplesCe³⁺:YAG and Ce³⁺,Nd³⁺:YAG. respectively. We can investigate from the emissionspectrums that Ce³⁺ion doping significantly enhanced the Nd³⁺ions emission at788nm. Followed, in order to explain the energy transfer between Ce³⁺and Nd³⁺ionsintuitively, we present the part of the energy level diagram of Ce³⁺and Nd³⁺ions.Analyse the possible transition and the radiation process specifically.Finally, additional experimental support on efficient energy transfer from Ce³⁺toNd³⁺came from the lifetime experiment. The lifetime for Ce³⁺emission at535nm inCe³⁺:YAG is87ns, whereas it is41ns in Ce³⁺,Nd³⁺:YAG. And we estimated theenergy transfer efficiency is53%. The fluorescence lifetime of the sensitizer Ce³⁺ionsis shortened if nonradiative energy transfer takes place.In a word, for Nd³⁺:YAG crystal, the doping of sensitizer Ce³⁺ions improves itsutilization rate of the pump light and the luminous efficiency of infrared light. Thisconclusion has a certain reference value for Nd³⁺:YAG crystal applications ontechnology.