Unique adjustable UC luminescence pattern and directional radiation of peculiar-shaped NaYF(4): Yb(3+)/Er(3+) microcrystal particle

A new design of peculiar-shaped β-NaYF(4): 20% Yb(3+)/2% Er(3+) hexagonal microcrystal (PSβHM) is proposed and its upconversion (UC) luminescence with adjustable color pattern is studied with near infrared excitation. Flower-like green UC luminescence emission pattern from blooming to withering process and intensive directional red emission are achieved by simply adjusting the focal point position of the excitation light. The mechanism that determines the unique UC luminescence phenomena are investigated systematically. The function of the internal light reflection and waveguide effect with annular microcavity is explored based on the structure characteristic of the hexagonal microplate. The current work may have great significant and potential applications in the development of optoelectronic device, color display, directional light and laser emission of microsystem.