Study On The Relationship Between Structure And Luminescence Properties Of Inorganic Materials Doped With Rare Earths And Transition Ions

Because rare earth ions have rich energy level structures and unique f-layer electrons that can leap to emit different colors of light,rare earth doped phosphors are excellent visible light materials.In addition to visible light materials,near-infrared materials also have a wide range of applications in production life.The research on near-infrared materials mainly focuses on transition metal ions,among which Cr³⁺has a low energy at 3d energy level,so it generally has strong emission in the near-infrared region.Single substrate doped phosphors have a better prospect in achieving broadband emission and tunable emission because of their simple synthesis process and cheap price.In this paper,a variety of broadband luminescent materials with a single matrix singly or co-doped with rare earth ions or transition metal ions are presented,and in the preparation of these phosphors,the synthesis methods are high-temperature solid-phase methods.These phosphors include Eu³⁺/Bi³⁺activated Ca Sr Ga₄O₈,Eu³⁺/Eu²⁺/Ce³⁺activated K₃YSi₂O₇,Cr³⁺doped phosphors withβ-Ga₂O₃ as the main matrix,and Eu²⁺/Eu³⁺co-doped Li₄Ca₂B₈O₁₆.XRD,diffuse reflectance spectroscopy,photoluminescence emission and excitation spectroscopy were used to characterize these samples.1.A variety of Eu³⁺,Bi³⁺and co-doped Ca Sr Ga₄O₈ phosphors were prepared by high-temperature solid-state reaction.Luminescence properties of samples were characterized by a photoluminescence instrument.Under 393 nm excitation,Ca Sr Ga₄O₈:Eu³⁺phosphor exhibits comparative stronger ⁵D₀→⁷F₂（618 nm）red emission and abnormal intensity ⁵D₀→⁷F₄（702nm）emission.The refractive index of the Ca Sr Ga₄O₈ is estimated to be 1.731.The intensity of the ⁵D₀→⁷F₂（618 nm）and ⁵D₀→⁷F₄（702 nm）transition peaks in the emission spectra were analyzed by Judd-Ofelt theory.The intensity parameterΩ₂ of Ca Sr Ga₄O₈:4%Eu³⁺is 5.0(10^-20cm²),andΩ₄ is 4.5(10^-20cm²).For the Ca Sr Ga₄O₈:Bi³⁺phosphor,the emission peak at 450 nm is displayed under excitation at 320 nm.The photoluminescence and fluorescence lifetime decay curves of Ca Sr Ga₄O₈:0.5%Eu³⁺,y%Bi³⁺（y=1.5-4.5）demonstrate the energy transfer from Bi³⁺to Eu³⁺.For the co-doped system,changing the concentration of Bi³⁺can achieve a color change from yellow to blue.2.Eu³⁺,Eu²⁺and Ce³⁺doped K₃YSi₂O₇ phosphors are synthesized under reducing atmosphere.Photoluminescence properties show K₃YSi₂O₇:1%Ce,1%Eu at 330 nm excitation（FWHM=211 nm,where FWHM stands for the full width at half maximum）can produce broadband emission,its light-emitting area covers the entire visible region.The preferential occupation sites of Ce and Eu ions in K₃YSi₂O₇ are calculated using the bond energy theory.Eu²⁺,Eu³⁺,Ce³⁺ions preferentially occupy K3,Y2,K1 sites,respectively.The broadband emission of the phosphor is caused by the dopant ions’selective site occupancy.3.A series of Cr³⁺-doped luminescent materials withβ-Ga₂O₃ as the main substrate at different temperatures were prepared by high-temperature solid-state method.The Ga₂O₃:Cr synthesized at 700°C can achieve a peculiar broadband double-centered emission from 350 to800 nm.Upon increasing the synthesis temperature,Ga₂O₃:Cr exhibits broadband emission mainly in the near-infrared region.The photoluminescence（PL）spectra of Ga₂O₃:0.3%Cr at260 nm excitation showed a blue shift from 770 to 730 nm with increasing synthesis temperature（700,900,1000°C）.Tuning of Ga₂O₃:Cr spectra was achieved by replacing Ga³⁺with In³⁺through main group element substitution,but replacing Ga³⁺with Al³⁺did not achieve tuning of Ga₂O₃:Cr spectra.4.A series of Eu²⁺/Eu³⁺co-doped Li₄Ca₂B₈O₁₆ phosphors were synthesized using a high-temperature solid-state method under air and reducing atmospheres,respectively.The photoluminescence emission spectra and excitation spectra were used to verify the"self-reduction"phenomenon of Eu³⁺to Eu²⁺conversion in Li₄Ca₂B₈O₁₆.The lattice site occupation and the"self-reduction"behavior of the doped ions were analyzed by using the bond energy method.For Li₄Ca₂B₈O₁₆:10Eu synthesized under reducing atmosphere,the chromaticity coordinates at 365 nm excitation are（0.3346,0.3107）,which is located in the white region,and therefore its application value exists in the WLED.