Photoluminescence properties and preferable site occupancy of Ce3+ in apatite-like RbSr4(BO3)3 blue-emitting phosphors for white LEDs

Abstract

A near-ultraviolet (n-UV) pumped blue-emitting apatite-like phosphor RbSr₄(BO₃)₃:Ce³⁺ (RSBO:Ce³⁺) was synthesized using a high temperature solid-state reaction method. Rietveld refinement on the structure indicates that Ce³⁺ ions are apt to occupy the Sr1²⁺ (8c) site, in spite of one Rb⁺ and three different crystallographic Sr²⁺ ions in the structure. The Ce³⁺ ion activated RbSr₄(BO₃)₃ (RSBO) material can be excited by a relatively broad absorption band ranging from 320 to 365 nm, which matches well with the light from the commercial n-UV white light emitting diode (w-LED) chips, and generates a strong blue emission spectrum peaking at 415 nm due to the electronic transitions from 5d to 4f of the Ce³⁺ ion. And the color purity of RSBO:Ce³⁺ is comparable to that of the blue-emitting commercial phosphor BAM:Eu²⁺. The temperature-dependent spectra show that its luminescence intensity at 100 °C can remain about 85% of the initial value at room temperature. A w-LED device was fabricated by combining the RSBO:Ce³⁺, commercial (Sr,Ba)₂SiO₄:Eu²⁺ and (Ca,Sr)SiAlN₃:Eu²⁺ phosphors with a 365 nm n-UV chip. The w-LED device generates white light with CIE chromaticity coordinates, correlated color temperature (CCT) and color-rendering index R_a are (x, y) = (0.3315, 0.3402), 5540 K and 72.9, respectively. The experimental results indicate that the RSBO:Ce³⁺ phosphor is a promising candidate as a blue component for application in w-LEDs.