Energy Transfer And Sensitized Near-Infrared Luminescence In Yb³⁺/Er³⁺ Doped Phosphors

Rare earth ions have abundant energy level structure depended on the special electronic configuration.The electronic transitions can occur in the different energy levels,which produce large numbers of spectral information,spanning from vacuum ultraviolet to infrared area.Recently,rare earth ions doped near-infrared luminescent materials have received an extensive research.Especially,near-infrared luminescent materials doped with Yb³⁺,Er³⁺ ions have attracted considerable interests,which are widely used in the fields of optical fiber communication,solid laser,medical diagnosis,etc.However,the electronic transitions within the 4f orbit of rare earth ions are forbidden and the absorption cross section is narrow,leading to the low luminous efficiency of rare earth ions and limiting its application.In order to solve this problem,the paper try to improve near infrared light-emitting efficiency by the means of matrix or transition metal sensitizing Yb³⁺ and Er³⁺ ions.The main contents and results are as follows:1)A series of Y₂WO₆:Yb³⁺ phosphors were synthesized by the conventional high temperature solid-state reaction.The composition was characterized by XRD.And the luminescence properties of as-prepared phosphors wereinvestigated in the PLE and PL spectra.An intense infrared emission was observed from 900 to 1100 nm attributed to the ²F_5/2-?²?F_7/2 electronic transition of Yb³⁺ ions under the excitation of 340 nm UV light in Y₂WO₆:Yb³⁺ phosphors.Moreover,the mechanism of the energy transfer from WO66-group to Yb³⁺ ions in Y₂WO₆ was studied in detail.Finally,energy transfer efficiency and quantum efficiency depended on Yb³⁺ doping contents were calculated in Y₂WO₆:Yb³⁺phosphors.2)A set of LaAlO₃:Mn⁴⁺,Er³⁺ phosphors were prepared via a high temperature solid-state route.The structure and luminescence properties were characterized by X-ray diffraction?XRD?,fluorescence spectra and the fluorescence decay curves.The results show that when the Mn⁴⁺ is excited,the LaAlO₃:Mn⁴⁺,Er³⁺ phosphors exhibit strong near infrared emission,corresponded to the ⁴I_11/2?⁴I_15/2?990 nm?and ⁴I_13/2?⁴I_15/2?1552 nm?of Er³⁺respectively,indicating that there is an efficient energy transfer from Mn⁴⁺ to Er³⁺.It further reveals the existence of energy transfer from Mn⁴⁺ to Er³⁺ in the LaAlO₃:Mn⁴⁺,Er³⁺ phosphors by the fluorescence lifetime analysis of Mn⁴⁺depended on the Er³⁺ concentration.Moreover,it is confirmed that a quadrupole-quadrupole interaction is responsible for the energy transfer mechanism from Mn⁴⁺ to Er³⁺.3)A series of SrGa₁2O₁9:Cr³⁺,Er³⁺ phosphors were synthesized through the high temperature solid-state method.The phase and composition was characterized by XRD.Photoluminescence excitation?PLE?and emission?PL?spectra of phosphors were investigated in detail.It was observed that near infrared emission was centered at 1550 nm when the Cr³⁺ is excited,corresponded to the ⁴I_13/2?⁴I_15/2 of Er³⁺ in the SrGa₁2O₁9:Cr³⁺,Er³⁺ phosphors.Moreover,luminescence decay curves were measured to discuss the energy transfer process from Cr³⁺ to Er³⁺ in the phosphors,and the energy transfer mechanism was demonstrated to be electric dipole-dipole interaction.