Realizing Color-tunable Emission Borophosphate Phosphors Via The Anion-group Cosubstutition Strategy And Its Application In WLED

Three new types of borophosphate phosphors with color-tunable emission were successfully designed and synthesized using the cosubstitution strategy of anionic groups.The crystal structure,phase identification,luminescence properties,fluorescence lifetime,density functional theory calculation(DFT),and as-prepared WLED optical parameters of the phosphors were studied.The results are as follows:(1)We report a successful control of the site-occupation of Eu²⁺activators in well-designed borophosphate full-visible-spectrum K₂BaCa(PO₄)_2-x(BO₃)_x:0.03Eu²⁺phosphors via anion-group cosubstitution strategy.In the pristine sample,there are four crystallographic sites(Ca,Ba,K1 and K2),yet,Eu²⁺ions only occupy the K1 and K2 sites,which is confirmed by XRD Rietveld refinement,PL/PLE spectrum and lifetime decay.For the first time,using DFT and VDP in K₂BaCa(PO₄)_2-x(BO₃)_x:0.03Eu²⁺phosphors find that introduced(BO₃)^3-units not only reduces the dopant formation energy,but also decreases the resistance of(PO₄)^3-tetrahedrons acting on cationic polyhedron.This opens a new Eu²⁺-substitution pathway,rendering partial Eu²⁺ions to a new Ca site,resulting in the formation of an uncommon Eu²⁺red emission at 660 nm,and thereby realizing spectral tuning from cyan(473 nm)to white-light with striking red emission.Moreover,the photoluminescence quantum efficiency and luminescence thermal stability of the borophosphate phosphors were studied.Importantly,using only this white-light phosphor(x=0.4),as-prepared WLED shows excellent color quality(Ra=90.4 and R9=93.8).This work not only presents an in-depth investigation of site-selection of Eu²⁺,but also opens a new way to design full-visible-spectrum phosphors.(2)Based on the theory of the DFT and VDP,we choose Ba₂Ca(PO₄)₂:0.03Eu²⁺and Sr₃(PO₄)₂:0.07Eu²⁺as matrix structure by using the anion-group cosubstitution strategy,realizing two types of new borophosphates Ba₂Ca(PO₄)_2-x(BO₃)_x:0.03Eu²⁺and Sr₃(PO₄)_2-x(BO₃)_x:0.07Eu²⁺phosphors.Although the phosphates we chose have distinct space groups(P121 and R3m),the two borophosphates synthesized by substituting(PO₄)^3-with(BO₃)^3-polyhedron,without inducing phase separation.Significantly,we note that as long as(BO₃)^3-successfully substitute(PO₄)^3-units in phosphates,color point tuning of as-prepared the two phosphors would take place.Therefore,we emphasize that anion-group cosubstitution strategy based on the replacement of(PO₄)^3-with(BO₃)^3-probably is a very useful and versatile design way for developing new materials with adaptable crystalline frameworks.Of course,it is also an effective way for tuning spectral distribution and designing highly efficient phosphors.