A blue and Red Bicolor Emission Phosphor Excited by a Single n-UV and Its Self-reduction of Eu3+ → Eu2+ in Na2Al2B2O7

Abstract

It has great significance to find a path on generating multicolor with one n-UV chip coated with single phosphor. Herein, Eu doped Na2Al2B2O7 (NAB) phosphor is synthesized by solid state reaction in air atmosphere. Both 4f65d1 → 4f7 transitions of Eu2+ (445 nm) and f–f transitions as 5D0 → 7FJ (J = 0, 1, and 2) of Eu3+ (570–650 nm) have been observed. When increasing Eu doping concentration, both the luminescence intensity and lifetime of Eu3+ are increased and no obvious concentration quenching is observed, while the emission strength of Eu2+ does not change monotonically but with two remarkable peak values. The optimum doping concentration of Eu is 16%. Furthermore, Eu3+ is determined to be from Eu(BO3) matrix itself, and Eu2+ testified by ESR and XPS is created by self-reduction of Eu3+ to Eu2+ in NAB due to charge compensation. When x ≥ 0.16, the Eu3+ ion would rather bond with BO3 triangles in Eu(BO3) than stay as Eu2+ in AlO4 tetrahedral in NAB. Furthermore, the as prepared sample shows an excellent thermal stability and the PL quantum efficiencies of NAB: 0.16Eu sample excited by 341 nm and 393 nm are 11.99% and 9.39%, respectively. Additionally, the calculated CIE chromaticity coordinates signify that a couple of colors can be generated by adjusting the excitation wavelength owing to the strength changes between blue and red emissions. Therefore, this novel bicolor phosphor can serve as a potential candidate for w-LEDs applications.