Luminescent color modulation of Zn/BaAl2O4:0.2%Eu phosphors for LED application

Abstract

Spinel-type aluminate (ZnAl2O4) doped with europium (Eu) ions has garnered considerable attention in the field of luminescence. This study explores a series of Zn/BaAl2O4:0.2%Eu phosphors (x=0∼0.25, x is for the mole fraction of BaAl2O4), fabricated through a high temperature solid-phase reaction method in air or reduction environment. In the case of phosphors synthesized in air, the photoluminescence emission (PL) spectra show a series of sharp emission peaks at 570nm, 589nm, 620nm, 660nm, and 710nm, which are generated by the 5D0-7FJ (J = 0, 1, 2, 3, 4) level transitions in Eu3+. Time-resolved photoluminescence and X-ray photoelectron spectroscopy (XPS) characteristics also validate the presence of Eu3+ in samples synthesized in air. An intriguing observation is the abnormally strong emission peak at 570nm under 346nm excitation, originating from the Eu3+5D0-7F0 level transition. For x=0.15, the corresponding CIE color coordinate is (0.3246, 0.3449), suggesting its potential application as a mono-doped and uni-matrix white phosphor. On the other hand, phosphors synthesized in reduction environment exhibit PL spectra with a wide emission band spanning from 400nm to 550nm, resulting from the electric-dipole-allowed transition of f-d state of Eu2+. The partial substitution of Zn2+ with Ba2+ significantly enhances the Eu2+ luminescence intensity. Moreover, an elevation of the mole fraction of Zn/BaAl2O4:0.2%Eu leads to a notable redshift (450nm→500nm) in the emission peaks of Eu2+ caused by lattice expansion, providing the adjustability of emitting color.