Excellent enhancement of thermal stability and quantum efficiency for Na2BaCa(PO4)2:Eu2+ phosphor based on Sr doping into Ca

Abstract

High thermal stability and quantum efficiency are the two very significant factors for phosphors when concerning all kinds of related applications. Therefore, it is still main research topics as long as referencing to the luminescence phosphors. It is well known that deep trap and large band gap are beneficial to excellent thermal stability. In this work, a series of Na 2 BaCa 1- x Sr x (PO 4 ) 2 :0.03Eu 2+ phosphors have been prepared by traditional solid state reaction. When the Sr 2+ content increases, the emission intensity exhibits a blue shift phenomenon with the highest peak around 448 nm caused by the varied centroid shift ( ε c ) and the crystal field splitting ( ε cfs ). The thermal stability of Na 2 BaCa 0.2 Sr 0.8 (PO 4 ) 2 :0.03Eu 2+ phosphor still approaches to 100.3% of that room temperature at 150 °C, while the external and internal quantum efficiency are greatly enhanced from 19.92% to 62.53%. It is due to the effect of the cation disorder by introducing the high level of Sr ion, which create the deep trap and broaden the bandgap, resulting in the anti-thermal quenching behavior and enhanced quantum efficiency. Moreover, Rietveld refinements, microstructure, decay curves and thermoluminescence are also adopted to shed light on related mechanism of luminous performance. Furthermore, a pc-WLED device has been fabricated through Na 2 BaCa 0.2 Sr 0.8 (PO 4 ) 2 :0.03Eu 2+ blue phosphor mixed with commercial yellow phosphor (SrSi 2 O 2 N 2 :Eu 2+ ) and red phosphor (Sr 2 Si 5 N 8 :Eu 2+ ), which performs a color temperature of 4721 K with a high color rendering index of Ra = 91.9. In view of zero thermal quenching and favorable quantum efficiency, this new phosphor is a prospect candidate for blue phosphors in WLED application. Further, the work provides a new method and reference for the great enhancement of thermal stability and quantum efficiency of luminescence materials. Based on the crystal structure of Na2BaCa(PO4)2:Eu2+ phosphors, the PL, thermal dependent spectra and application in WLED of Na2BaCa0.2Sr0.8(PO4)2:Eu2+ phosphors have been detected. • A series of solid solution Na 2 BaCa x Sr 1 -x (PO 4 ) 2 ( x = 0–1.0) have been synthesized. • The thermal stability of Na 2 BaCa 0.2 Sr 0.8 (PO 4 ) 2 :0.03Eu 2+ is 100.3% of that room temperature at 150 °C. • The external quantum efficiency of Na 2 BaCa 0.2 Sr 0.8 (PO 4 ) 2 :0.03Eu 2+ is improved from 19.92% to 40.78%. • The fabricated white WLED shows the CIE of (0.3532, 0.3561), the CCT of 4721 K and CRI of 91.9.