Preparation And Luminescence Control Of Cr³⁺-Activated Silicate Phosphors With Near Infrared Emissions

With the advantages like low cost,broadband emission,all solid state,energy saving and environment protection,phosphor-converted light-emitting diode(pc-LED)has promising applications in spectroscopic analysis,security monitoring and food testing.However,the near-infrared phosphors currently used for pc-LED have the shortcomings such as short emission wavelength,poor thermal stability and low emission intensity.Silicate has the advantages of low cost and high thermal stability,which provides the possibility for developing efficient and stable NIR phosphors.Cr³⁺is an ideal near-infrared activator ion.Thus,this paper is based on the Li Sc Si₂O₆:Cr³⁺(LSS:Cr³⁺)phosphor.Firstly,Li Sc Si₂O₆:Cr³⁺(LSS:Cr³⁺)phosphor with higher luminescence performance is synthesized through optimization of the preparation.Then,new phosphors Li Sc_1-xIn_xSi₂O₆:Cr³⁺(LSIS:Cr³⁺,x=0?1.0)with higher emission intensity and Li Sc Si_2-yGe_yO₆:Cr³⁺(LSSG:Cr³⁺,y=0?2.0)with wavelength-tunable emission are synthesized by the ion site substitution.The specific content can be categorized into the following aspects:(1)LSS:Cr³⁺phosphor with higher luminescence performance is obtained by optimizing the sintering temperature,which eliminates the reabsorption of Cr⁴⁺at 800?900 nm,and changing the raw materials and the fluxes.As a result,the internal quantum yield and the external quantum yield are increased to 70%and 37%,respectively.Under 450 nm excitation,the phosphor shows broadband emission(700?1100 nm)peaking at 836 nm,with a full width at half maximum(FWHM)of 145 nm.The phosphor maintains 86%of the initial intensity at150°C and exhibits excellent luminescence performance.(2)Based on the LSS:Cr³⁺phosphor,new LSIS:Cr³⁺phosphor with higher emission intensity is obtained by the substitution of Sc³⁺by In³⁺ions.It is found that the crystal field engineering of ion substitution can change the surrounding crystal field environment of Cr³⁺,and realize the improvement of phosphor absorption efficiency and quantum yield.When x=0.6,the phosphor has the highest luminous intensity with the internal quantum yield of 77%and the external quantum yield of 45%,which is 7%and 8%higher than the LSS:Cr³⁺phosphor.(3)Based on the LSS:Cr³⁺phosphor,new LSSG:Cr³⁺phosphor with wavelength-tunable emission is obtained by the substitution of Si⁴⁺by Ge⁴⁺ions with a larger radius.It is found that the substitution of Ge⁴⁺can be acted as an effective strategy to control the emission wavelength.Under 450 nm excitation,the emission band gradually red-shifts from 836 nm to 900 nm covering from 700nm to 1200 nm with the increase of Ge⁴⁺concentration,which has a certain reference value for the preparation of long-wavelength and high-efficiency near-infrared phosphors.