Two-site occupancy induced the broad-band emission in the Ba4−x−ySryLa6O(SiO4)6:xEu2+ phosphor for white LEDs and anti-counterfeiting

Abstract

With the increasing demand for new inorganic functional materials, more and more attention is paid to rare earth ion doped luminescent materials. In this work, an Eu²⁺ doped Ba₄La₆O(SiO₄)₆ phosphor was synthesized by the high temperature solid-phase method. In the phosphor, two Ba²⁺ sites could be occupied by Eu²⁺ cations to provide two different kinds of coordination environments, resulting in broad emitting bands in the range of 450–630 nm and ultra-wide excitation bands in the range of 250–500 nm. The presence of two different Eu²⁺ emitting centers is verified by measuring the photoluminescence spectra and decay curves in Ba₄La₆O(SiO₄)₆ phosphors. The temperature dependence of emission intensity and full width at half maximum of Eu²⁺ in the range of 293–453 K were investigated systematically. The substitution of Ba²⁺ by Sr²⁺ can adjust the crystal field; thus, the luminous intensity was improved by 2.07 times and T₅₀ was increased from 380 K to 453 K. Due to the Sr²⁺ ion doping, some of the Eu³⁺ ions cannot be reduced and remain in the trivalent state. In addition, by integrating the as-prepared Ba_1.42Sr_2.5La₆O(SiO₄)₆:Eu phosphor, commercial blue and red phosphors, and a 385 nm LED chip, a white-LED lamp was made, which realized an applicable color rendering index (R_a = 94.6). For the Ba_0.42Sr_3.5La₆O(SiO₄)₆ phosphor, the emission can be shifted from yellow to green and to yellow by excitation wavelength variation from 250 to 360 and 480 nm, which proves that the phosphor is a promising candidate for anti-counterfeiting applications.