Study On Upconversion Of Er³⁺ Ions Broadbandly Sensitized By Yb³⁺ And Ni²⁺

The concept of up-conversion luminescence have received extensive attention since it was proposed.Due to its unusual luminescence characteristics,upconversion have always been a research hotspot.Upconversion materials are widely used and developed rapidly in the fields of biology,lasers,anti-counterfeiting technology,three-dimensional display and photovoltaic cells,etc.As an effective means of using solar energy,photovoltaic cells have made great progress in rencent years.However,solar cells generally have the disadvantage of low photoelectric conversion efficiency.Upconversion luminescence have been proposed to improve the utilization of near-infrared photons in photovoltaic cells as a photon frequency conversion method and there is a lot of related research has been reported.Due to the shortcomings of rare earth ions such as Er³⁺,Ho³⁺single-doped upconversion systems with low absorption efficiency and narrow absorption band,a method based on energy-transfer is proposed to achieve broadband sensitized up-conversion luminescence for activator ions.In order to further expand the applications of up-conversion phosphors in photovoltaic cells,infrared detection and other fields,and get an up-conversion phosphor that can be excited within broadband near-infrared wavelengths,following work has been done in this paper:(1)Yb³⁺,Er³⁺co-doped AY(WO₄)₂(A=Na,Li,K)phosphors were prepared by high-temperature solid state method.The upconversion luminescence of these samples is studied by using 940nm,980nm and 1064nm lasers as excitation light sources.The KY(WO₄)₂:Yb³⁺,Er³⁺sample with the strongest upconversion emission is selected from Yb³⁺,Er³⁺co-doped AY(WO₄)₂(A=Na,Li,K).The spectral characteristics of Er³⁺single-doped and Yb³⁺,Er³⁺co-doped KY(WO₄)₂phosphors were studied.The up-conversion and energy transfer mechanism were analyzed and discussed.The Yb³⁺,Er³⁺co-doped KY(WO₄)₂sample may absorb the photons within range 900-1100nm,and then produces the green and red upconversion emission through the energy transfer process.The effects of concentration and excitation power for the upconversion performance have been studied.The optimal doping concentration of 1.5mol%Er³⁺and 20mol%Yb³⁺is obtained by comparing the luminescence intensity.The developed up-conversion phosphor optimizes the up conversion characteristics under multi wavelength excitation and broadens the excitation range in a certain sense.(2)In this work,The Ni²⁺and Er³⁺co-doped Mg Ga₂O₄phosphors were synthesized by the high-temperature solid-state reaction method.The photons in wavelength range 900-1700nm could be absorbed by the phosphor and then upconverted into 660 nm emission by the energy-transfer process from the Ni²⁺to Er³⁺ions as well as the excited state absorption of Er³⁺ions.The effects of Ni²⁺,Er³⁺concentration and excitation power on the upconversion performance have been investigated.The upconversion mechanism in the samples is also studied.It is found that the upconversion process is different under different excitation wavelengths.In the Mg Ga₂O₄:5%Ni²⁺,0.4%Er³⁺sample that exhibits the strongest upconversion emission,the sensitized energy transfer efficiency from Ni²⁺to Er³⁺is about 11.2%.This upconversion phosphor has a broadband near-infrared absorption band,which shows that it has great potential in optical applications and can provide a certain reference for the subsequent research on broadband sensitization upconversion.