The Research On Cooperative Sensitization And Cooperative Reception Of Yb³⁺-clusters With Gd³⁺?Tb³⁺?Ce³⁺ Ions Andcluster Structure Destruction Fluorescence Quenching

Cooperative transitions include cooperative luminescence,cooperative sensitization luminescence,cooperative absorption and another mechanism which Dexter proposed in 1957.The last mechanism refer to a process that a sensitization ion excite two ions simultaneously that was verified in 2005.Since this mechanism can improve quantum yield,it has been a hot research topic.This mechanism is the inverse process of cooperative sensitization,we define this mechanism as cooperative reception.The above cooperative processes are based on two ions,Until 2014,the triplet cooperative luminescence of three Yb³⁺ ions(Yb³⁺-trimers)in the ultraviolet?UV?region and the emission of Gd³⁺?6P7/2?ions cooperatively sensitized by four Yb³⁺ ions(Yb³⁺-tetramers)were confirmed experimentally and theoretically by our research group,which was a great breakthrough in cooperative transition investigation.Think about it,when the cooperative reception process extended to three ions,the theoretical quantum efficiency limit can be increased to 300%.It is an efficient and feasible method to improve the quantum efficiency.In such a background,we studied the cooperation processes of Yb³⁺ ions and other Ln³⁺ ions.In this process,we found a unique fluorescence quenching process within the cooperative transitions.That is cluster structure destructive fluorescence quenching.This quenching process is a more significant mechanism in the cooperative transitions than the traditional quenching mechanisms like concentration quenching.This paper will focus on the cooperative transition processes between Yb³⁺ ion and Gd³⁺,Tb³⁺,Ce³⁺ ions.The main contents are as follows:1.We experimentally observed an unusual luminescent phenomenon of Gd³⁺ in Ca F₂:Yb³⁺/Gd³⁺.Upon excitation with a 980 nm laser,the upconversion luminescence of Gd³⁺ increases first and then decreases in the Gd³⁺ concentration range of 0-0.9 mol%,which is different from the monotonic increase of Gd³⁺ luminescence observed in the downconversion spectra by direct excitation of Gd³⁺.Correspondingly,Yb³⁺ lifetime decreases first and then increases.This special luminescent behavior is indicated to relate to energy transfer from Yb³⁺-tetramers to Gd³⁺ and destruction of Yb³⁺-clusters.In order to explain the special phenomenon,we proposed a new luminescence quenching mechanism,Yb³⁺-cluster destructive quenching,which is verified by optical inactive Y³⁺ doping experiment.This quenching mechanism is a novel static fluorescence quenching mechanism different from concentration quenching,impurity quenching,and thermal quenching.2.Yb³⁺ ions tend to form clusters when they are doped in Ca F₂ host.The clustered two Yb³⁺ ions can cooperatively emit a green light,or cooperatively sensitize a Tb³⁺ ion,or cooperatively received energy transferred from a Tb³⁺ ion.We experimentally observed the luminescence induced by the above three processes and found that the quantum yield of the luminescence of cooperative sensitization is 10–3 that is higher than the highest reported quantum yield?10–4?,which is convenient for our research.Correspondingly,we found that the down-and upconversion emissions both quenched at a very low concentration of Tb³⁺ ions.To explain the above emission quenching phenomenon,we further performed the optically inactive rare earth ion doping experiments and fluorescence dynamic measurements.Finally,we found that the cluster structural destruction quenching mechanism dominated the quench of the down-and upconversion emissions induced by cooperative transitions in Ca F₂: Yb³⁺,Tb³⁺.3.We experimentally observed a three-photon near-infrared?NIR?quantum cutting?QC?process in Ca F₂: Yb³⁺,Ce³⁺,in which three Yb³⁺ ions cooperatively received the energy transferred from a Ce³⁺ ion in 5d excited state.In the sample,three clustered Yb³⁺ ions(Yb³⁺-trimer)formed a system coupling wave function through Coulomb interaction and cooperatively emitted a 343 nm photon under 978 nm laser excitation.Fortunately,5d energy level of Ce³⁺ ions overlap well with the excited state of Yb³⁺-trimers.So,upon excitation with a 306 nm photon,one Ce³⁺ ion in excited 5d state transferred the energy to a Yb³⁺-trimer,and finally,each Yb³⁺ ion of the Yb³⁺-trimer emitted a NIR photon.We obtained a maximum efficiency as 222%.For the first time,we confirmed that three acceptor ions can cooperatively receive UV energy.This QC process can yield three 1000 nm photons and have a theoretical efficiency limit of 300%.Application of the QC materials has prospect for improving the energy efficiency of silicon solar cells.4.4f^n-15d?4fⁿ ultraviolet?UV?upconversion?UC?luminescence of Ce³⁺ ions sensitized by Tm³⁺ was observed under 980 nm laser excitation in Li YF4: Yb³⁺,Tm³⁺,Ce³⁺ microparticles.Our experiment revealed that 5d level of Ce³⁺ ions can be effectively populated through the energy transfer 1I6 ? 3H6(Tm³⁺):4f ? 5d(Ce³⁺).The influence of Ce³⁺ ions concentration on the absorption and emission intensity was investigated.We found that the 4f-5d transitions of rare earth ions sensitized by the 4f-4f transition of rare earth ions is an effective way to modulate the ultraviolet upconversion luminescence.