Orthogonally Polarized Luminescence of Single Bismuth Phosphate Microcrystal Doped with Europium

Rare-earth-doped micro/nanocrystals are significant candidates for nanophotonic and quantum information elements. Nevertheless, the polarization of light emission, which serves as one of the most widely adopted optical information carriers, has been rarely studied in such micro/nanocrystals due to the random crystalline orientation of the ensemble cluster as grown. Herein the polarization-resolved spectroscopy on a single europium-doped bismuth phosphate (BiPO4:Eu) microcrystal is performed, and a series of partially linearly polarized emission in the visible spectrum is observed, which can be grouped into orthogonal pairs. Such emission features are well explained by a phenomenological model of group theory that gives rise to the existence of optical C-2 axes induced by local symmetry breaking. Such a polarization detection provides a neat optical method to distinguish single micro/nanocrystals from clusters, and confirms the tunable polarization features by selecting the suitable single microcrystal and engineering its orientation of crystalline axis. The rare-earth-doped single micro/nanocrystals, with precise positioning technique realized, can promisingly serve as controllable polarization devices on integrated photonic circuits.