Upconversion Emission Of Cu²⁺,Pb²⁺ Ions Sensitized By Yb³⁺-trimers And Fluorescence Quenching Induced By Structural Destruction

Cooperative transition phenomena usually means the physical processes in which identical ions or atoms simultaneously make transitions by absorbing or emitting one photon with the sum of transition energies,or transferring their energies to another ion.Cooperative quantum transitions include cooperative absorption?CA?,cooperative energy transfer?CET?,and cooperative luminescence?CL?.The CL originating from ytterbium ions was first observed in Yb PO4 by Nakazawa and Shionoya.On the other hand,CL is fundamentally fascinating from a purely theoretical perspective.We reported a triplet cooperative luminescence?TCL?at³43nm from three excited Yb³⁺ ions(Yb³⁺-trimer)in 2013.From the basic physical process,material conditions for the multi-photon fission,we have established cooperative transition theory of rare earth ion clusters.This thesis is consisted of seven parts.1.Under 978 nm near infrared?NIR?excitation,ultraviolet?UV?upconversion?UC?emissions from Pb²⁺ ions in CaF₂:Pb²⁺,Yb³⁺ were first observed at room temperature.The UC emission centered at ³83 nm was ascribed to the 3P0 ? ¹A_1g?¹So?transition of Pb²⁺ ions.From transient measurements,the UC process was found to be dominated by the energy transfer process: three excited Yb³⁺ ions simultaneously transfer their energy to one Pb²⁺ ion.With the increase of Pb²⁺ concentration,the cooperative luminescence from 3-Yb³⁺ clusters decreased gradually and until to extinguished.The cooperative sensitizationto one Pb²⁺ ion comes from three excited Yb³⁺ ions,which is a four-ion process and exhibits a third power dependence on the NIR pumping power.2.Under 978 nm near-infrared?NIR?excitation,blue upconversion?UC?emissions from CaF₂:Cu²⁺,Yb³⁺ was first observed at ⁴20 nm.It was ascribed to the 3d84s1 ? 3d9 transition of Cu²⁺ ions.From transient measurements,the UC process was found to be dominated by the energy transfer process that three excited Yb³⁺ ions simultaneously transfer their energy to one Cu²⁺ ion.The influence of Cu²⁺concentration and temperature on the UC emission as well as Jahn-Teller effect was also investigated.3.The triplet cooperative luminescence?TCL?of Yb³⁺-doped AF2?A= Ca,Sr?was studied under excitation of near infrared?NIR?light.First,the TCL from Yb³⁺ ions in the SrF₂:Yb³⁺ was studied for the first time under NIR excitation.Next,the TCL and dimer cooperative luminescence?DCL?intensities in the CaF₂ and SrF₂ are compared at room temperature.Finally,we discuss why the cooperative luminescence intensities of CaF₂: 1%Yb³⁺ in the ultraviolet?UV?and visible region is much stronger than the SrF₂: 1%Yb³⁺.4.The cooperative luminescence of Yb³⁺-trimers and Yb³⁺-dimers were observed in Yb³⁺-doped CaF₂ under excitation of near infrared?NIR?light at room temperature.With the increase of doped Al³⁺ or La³⁺concentration,the cooperative luminescence from 3-Yb³⁺ trimers and 2-Yb2+ dimers decreased gradually and until to extinguished.In order to explain the phenomenon,in this paper,we propose a new fluorescence quenching mechanism,structure-destroyedfluorescence quenching.This new fluorescence quenching belongs to the static quenching.5.The cooperative luminescence of Yb³⁺-trimers and Yb³⁺-dimers were observed in Yb³⁺-doped CaF₂ under excitation of near infrared?NIR?light at room temperature.With the increase of A+?A+ = Li⁺,Na⁺,K⁺?concentration,thecooperative luminescence from 3-Yb³⁺ and 2-Yb2+ clusters first increases,then decreases in CaF₂:Yb³⁺,A+.The doped A+ ions induce luminescence quenching that comes from the destruction of Yb³⁺-trimers and Yb³⁺-dimers structures.This luminescence quenching belong to the static quenching in that luminescence centers were changed.6.The cooperative luminescence of Yb³⁺-dimers were observed in Yb³⁺-doped fluorite?CaF₂?under excitation of NIRlight at room temperature.We discuss why theemissions were from 2-Yb2+ clusters but from the 3-Yb³⁺ clusters in the samples of fluorite: Yb³⁺.However,the UC luminescence of most reported crystals and glasses,until recently no systematic studies on natural minerals upconversion systems were reported.7.The upconversion luminescence properties of natural sodalite?Na₈Al₆Si₆O₂4Cl₂?co-doped with Eu³⁺ and Yb³⁺ was studied for the first time under excitation of NIR light.The efficient energy transfers from Yb³⁺-dimers to Eu³⁺ were observed.The fitting result is approximately 1.79 ± 0.03 for 613 nm emission.This result shows that the two photon process is responsible for the red UC.