Cyan-Emitting Sialon-Polytypoid Phosphor Discovered by a Single-Particle-Diagnosis Approach

Benefiting from a novel phosphor screening method based on single crystal X-ray diffractometry and single-particle spectroscopy, i.e., the single-particle-diagnosis approach, a new Eu2+-activated cyan-emitting oxynitride phosphor (Si2.5Al9.5O0.5N12.5:Eu2+) was discovered. Single crystal X-ray diffraction analysis of the particle revealed that this sialon-polytypoid crystallizes in the Cmcm space group (No. 63) with a=3.0704 A, b=18.6697 A, c=35.7178 A, and Z=8. The analyzed orthorhombic structure is built up of highly condensed networks that constructed from linked [MX4] (M=Si, Al; X=O, N) tetrahedra. Although there are no obvious crystalline sites able to accommodate larger Eu2+ ions in the host, the time-resolved streak imaging of a single crystalline particle indicates that the cyan-emitting band peaking at ~500 nm with a relatively narrow full-width at half-maximum (FWHM) of ~61 nm exhibits a typical Eu2+ fluorescent lifetime (~0.39 μs) in oxynitrides. Besides, slight lifetime variation (0.32 μs vs. 0.47 μs) between shorter wavelength region (450-500 nm) and longer wavelength region (500-550 nm) of the Eu2+ emission band may suggest two different crystalline environments around Eu2+. This sialon-polytypoid cyan-emitting phosphor with efficient excitability at 365 nm may find its potential application as an all-inorganic color-converter in near-ultraviolet (NUV) excited wLEDs.