Study On The Luminescence Properties Of Borate Excited By Ultraviolet-Near Ultraviolet Broadband

Fluorescent conversion light-emitting diodes（pc-LEDs）are an indispensable artificial light source that is widely used in many areas of life.As an important component of pc-LED devices,fluorescent materials are highly sought after by researchers.Based on this,this paper mainly focuses on borate-based fluorescent materials,and three new luminescent color-tunable phosphors have been developed and obtained,and the results are as follows:1.Rare-earth borates are well known good photoluminescent materials due to the easy manipulation of activator concentration.K₇Ca Y₂(B₅O₁₀)₃ belongs to a recently discovered borate family with outstanding nonlinear optical performances.A systematic study on Bi³⁺and Eu³⁺doped phosphors was performed to explore their potential in photoluminescence.K₇Ca(Y_1-xBi_x)₂(B₅O₁₀)₃（0.01≤x≤0.06）,K₇Ca(Y_1-yEu_y)₂(B₅O₁₀)₃（0.10≤y≤1）and K₇Ca(Y_0.99-zBi_0.01Eu_z)₂(B₅O₁₀)₃（0.05≤z≤0.90）were prepared by high temperature solid state reactions.Rietveld refinements reveal an 8%anti-site occupancy of Ca²⁺and Eu³⁺in K₇Ca Eu₂(B₅O₁₀)₃,and two sets of Bi³⁺emission and excitation spectra are also observed once Bi³⁺is introduced.For instance,the two strongest ¹S₀→³P₁ excitations at 270 nm and 281 nm correspond to two ³P₁→¹S₀ emissions at 383 and 334 nm,respectively.The Eu³⁺emission shows a maximal intensity at y=0.50 under charge transfer excitation,while there is no concentration quenching effect under f–f excitation.The Bi³⁺-to-Eu³⁺energy transfer is firmly supported by the steady photoluminescence spectra and the decreased lifetime of Bi³⁺upon increasing the Eu³⁺content in K₇Ca(Y_0.99-zBi_0.01Eu_z)₂(B₅O₁₀)₃.This energy transfer mechanism occurs through the electric dipole–dipole interaction.Under excitation at 281 nm,the emission is tunable from deep blue(Bi³⁺)to pink and finally to red(Eu³⁺)all with high quantum yields（>80%）.2.Based on the above borate K₇Ca Y₂(B₅O₁₀)₃ is a good luminescent host material,we found its isomeric compound K_7.5Y_2.5(B₅O₁₀)₃,in which Ce³⁺,Tb³⁺single doped and Ce³⁺/Tb³⁺co-doped.The K_7.5(Y_1-xCe_x)_2.5(B₅O₁₀)₃（0.01≤x≤0.20）phosphors doped with Ce³⁺ions alone have a broad excitation band at 352 nm in the 220-400 nm spectral range,and they have a broad blue emission band in the 365-600 nm wavelength range at352 nm excitation and the maximum is reached at 425 nm.In contrast,the Tb³⁺single-doped K_7.5Y_2.5(B₅O₁₀)₃ phosphors have no concentration quenching phenomenon in their emission spectra under either f-d or f-f excitation,and the near-ultraviolet absorption in the Tb³⁺emission spectra is relatively weak.So the energy transfer process from Ce³⁺to Tb³⁺ions by introducing the sensitizer Ce³⁺ions in the Tb³⁺-doped phosphor,this process not only enhances the f-f emission of Tb³⁺,but also realizes the luminescent color coverage area from purple to green.In the Ce³⁺/Tb³⁺co-doped sample,a broad excitation luminescence spectrum from 200 to 400 nm is available to match with the n-UV LED chip.3.In Ce³⁺/Tb³⁺co-doped Li Ca Y₅（BO₃）₆,we have studied in detail the phase purity,photoluminescence properties,energy transfer mechanism and efficiency of the synthesized samples.Under the excitation at 336 nm,the Li Ca Y₅（BO₃）₆:Ce³⁺,Tb³⁺sample can emit highly efficient tunable blue-green light with a quantum efficiency of88.69%by controlling the ratio of dopant concentration.The spectral overlap and the variation pattern of fluorescence lifetime indicate that there is a significant energy transfer between Ce³⁺and Tb³⁺in the Li Ca Y₅（BO₃）₆ matrix,and the energy transfer mechanism is proved to be a electric dipole-dipole interaction with an energy transfer efficiency of 70.95%.