The Study Of Upconversion Of Tm³⁺,Er³⁺broadbandly Sensitized By Ni²⁺in LiGa₅O₈

Solar energy has a character of green,safe,poliution-free and inexhaustible.At present,the development of solar cells technology is very rapid.However,there are some disadvantage.For example,photons with energy lower than the bandgap of semiconductor can not be used directly.Upconversion can convert photons whose energy is less than the bandgap of semiconductor into photons which can be absorbed and utilized by semiconductor.Today,the main sensitizer for up conversion is Yb³⁺,However,Yb³⁺ions show narrow absorption bandwidth and low absorption efficiency in the infrared region due to the parity forbidden 4f-4f transitions,which limits their practical application in solar cells.Therefore,the realization of broadband up conversion for photons lower than the energy band gap will greatly improve the utilization efficiency of solar cells.In this paper,we will investigate the upconversion of Tm³⁺,Er³⁺broadbandly sensitized by Ni²⁺in LiGa₅O₈.First,Ni²⁺,Tm³⁺co-doped LiGa₅O₈ phosphors have been synthesized by solid state reaction method.It is found that In the LiGa₅O₈ Stroma,Ni²⁺has a wide absorption band in the near infrared region?850-1300nm?with high quantum efficiency.Moreover,the emission spectrum of Ni²⁺?³T₂?³F??³A₂?³F??matches the absorption spectrum of Tm³⁺?³H₆?³H₅?.so it can be used as the sensitizer of Tm³⁺to absorb photons in a wide near-infrared range?850-1300nm?,and then transfer its energy to Tm³⁺by successive radiation–reabsorption to realize the up conversion luminescence at 800 nm.The novel broadband-sensitive near infrared up-conversion material developed in this work offers a possible route towards surpassing the limiting conversion efficiency of GaAs or CdTe based single junction solar cells.And it may have new application in infrared detection.Second,Ni²⁺,Er³⁺co-doped phosphor samples were synthesized in LiGa₅O₈matrix by high temperature solid-state method.The crystal structure of the samples is analyzed,and the up-conversion and near-infrared emission spectra of the samples were measured.Because the emission spectrum of Ni²⁺?³T₂?³F??³A₂?³F??matches the absorption spectrum of Er³⁺(⁴I_15/2?⁴I_13/2)to some extent,Ni²⁺can absorb excitation light and sensitize Er³⁺to achieve upconversion luminescence.We observed the upconversion luminescence of Er³⁺at 670 nm under the excitation of1064 nm laser.The doping concentration of Ni²⁺,Er³⁺has been further adjusted.The optimum doping molar concentration of samples for upconversion is Ni²⁺:2%,Er³⁺:0.15%,and the chemical expression determined to be Li(Ga_0.9785Ni_0.02Er_0.0015)₅O₈.The energy transfer modes and mechanism Between Ni²⁺and Er³⁺were analyzed and discussed.