Multiple Spectral Tunability in Single Eu2+-Doped (Ba,Sr)5(PO4)3Br Phosphor
Spectral modification is crucial for luminescent materials. A variety of strategies have been proposed in the literatures including the selection of activator ions with characteristic electron configurations, the modification of local crystal field, and the design of emissive center pair and energy transfer. The Eu2+-activated haloapatites are considered as candidates for phosphor converted light emitting devices due to their excellent stabilities, easy preparation, and high efficiency. In this work, the single-phased, single-doped (Ba,Sr)5(PO4)3Br: Eu2+ is selected and multiple approaches are applied leading to multicolor tunabilities of the phosphors, including crystal field strength controlled spectral shift, occupuancy selectivity induced spectral saltation, defect-driven color tunability, and irradiation dependent dynamic chromaticity. In the high Eu2+ concentration doped Ba5-mSrm(PO4)3Br phosphor, the main emission band shifts from 448 to 452 nm with increasing Sr2+/Ba2+ ratio, and a second emission band around green region uplifts in the binary metal solid solution phosphors, leading to variable emission colors from blue to cyan under near UV excitation. Moreover, oxygen vacancy (VO) defects formed in a synthetic reducing condition enable the bromoapatites with bright self-activated luminescence. In the low Eu2+ concentration doped Ba2Sr3(PO4)3Br, the combination of the broad yellow-green emission from VO and bluish emission from Eu2+ contributes to a full spectrum feature. The gradual increase of Eu2+ concentrations regulates the tunable emissions from yellow-green, through white, to blue under short UV excitation. Furthermore, due to the different absorption preferences of these two centers, Ba2Sr3(PO4)3Br: 0.01Eu2+ shows white light emitting under 254 nm irradiation while blue emitting when exposed to 365 nm ray. The materials with multicolor luminescence show promising versatile applications in lighting, biological detection and anti-counterfeiting. The cooperated effects of multiple strategies provides a promising approach to regulate the optical properties of inorganic phosphors.