Remarkable flux effect of Li-codoping on highly enhanced luminescence of orthosilicate Ba2SiO4:Eu2+ phosphors for NUV-LEDs: autonomous impurity purification by eutectic Li2CO3 melts

Abstract

We report large photoluminescence (PL) enhancement of green-emitting Ba₂SiO₄:Eu²⁺ phosphors prepared in an eutectic Li₂CO₃ melt as a flux. Among the phosphor materials synthesized using low-purity precursors (99%-pure BaCO₃ and 99.6%-pure SiO₂), the emission intensity of Ba₂SiO₄:(Li_0.02,Eu_0.02) (Li = 200% excess) is found to be 470% as high as that of Ba₂SiO₄:Eu_0.02 (no-Li) and in fact is almost equivalent to that of Li-undoped Ba₂SiO₄:Eu²⁺ synthesized using ultrapure precursors (99.98%-pure BaCO₃ and 99.995%-pure SiO₂). In combination with the results from PL measurements and inductively coupled plasma mass spectrometry (ICP-MS), the elemental distribution of the products and melts found from time-of-flight secondary ion mass spectrometry (TOF-SIMS) directly indicates that the excess Li₂CO₃ autonomously removes the impurities that were originally contained in the low-purity precursors, in particular SiO₂, and thus critically improves the photoluminescence efficiency of the material. The newly found Li flux effect on large PL enhancement may not only contribute to more economic production of phosphors but provide a platform for discovery of new efficient phosphors for solid state lighting.