Redistribution of Activator Tuning of Photoluminescence by Isovalent and Aliovalent Cation Substitutions in Whitlockite Phosphors

Abstract

Many strategies, including double substitution, addition of charge compensation, cation-size-mismatch and neighboring-cation substitution, have contributed to tuning photoluminescence of phosphors for white light-emitting diodes. These strategies generally involve modification of a certain special site where the activator occupies; tuning strategy based on multiple cation sites is very rare and desirable. Here we report that isovalent (Sr 2+ ) and aliovalent (Gd 3+ ) substitutions for Ca 2+ tune the photoluminescence from one band to multiple bands in whitlockite β-Ca 3−x Sr x (PO 4 ) 2 :Eu 2+ and β-Ca 3−3y/7 Gd 2y/7 (PO 4 ) 2 :Eu 2+ phosphors. The saltatory variation of the emission spectra is caused by the removal of Eu 2+ from the site M(4) to other sites. Moreover, we found the mechanisms of dopant redistribution tuning the luminescence are different. The incorporation of Gd 3+ makes the site M(4) empty according to the scheme 3Ca 2+ = 2Gd 3+ + □, while Sr 2+ substitution causes the cation sites to be enlarged due to cation size mismatch. Additionally, the influence of the cation substitutions on the photoluminescence thermal stability of phosphors is researched. The strategies, emptying and enlarging sites, developed herein are expected to provide a general route for tuning luminescence of phosphors with multiple sites in the future.

Effect of [Ln3+–Si4+] (Ln = Y, La, Gd, Lu) Cosubstitution on the Structure and Luminescence Property of Sr9Mg1.5(PO4)7:Eu2+ Phosphor

“…Redistribution of dopant Eu 2þ after the incorporation of isovalent and aliovalent cation is a general route for tuning luminescence of phosphors with multiple sites. [20] Obviously, the redistribution of Eu 2þ ions among Sr1, Sr2, and Sr3 sites in Sr 8.95Àx Ln x Mg 1.5 (PO 4 ) 7Àx (SiO 4 ) x :0.05Eu 2þ phosphors is kinetically unfavorable and needs to overcome a significant activation barrier. Thus, the aforementioned mechanisms do not work here.…”

Effect of codoping Ce3+ on the luminescence properties of Sr9Mg1.5(PO4)7:Eu2+ orange–yellow phosphor

“…Vacancies could be produced at the Sr31 sites due to the charge mismatch between Ce 3+ and Sr 2+ . The so‐called “emptying site” effect forces the dopant Eu 2+ ions move from the Sr31 site to Sr1 and Sr32 sites in host lattice . Correspondingly, the PL spectra show a saltatory variation with increasing the Ce 3+ doping.…”

Dual energy transfer controlled photoluminescence evolution in Eu and Mn co-activated β-Ca2.7Sr0.3(PO4)2phosphors for solid-state lighting

“…28 Very recently, we proposed two new strategies, empting site and enlarging sites, to tune the photo-luminescence (PL) of the whitlockite phosphor with multiple cation sites. 29,30 That work claried the relation between the sites and PL properties of Eu 2+ .…”