Self-suspended rare-earth doped up-conversion luminescent waveguide: propagating and directional radiation

Near-infrared excited rare-earth (RE)-doped up-conversion (UC)-luminescent materials have attracted enormous attention because of their unique emission properties, such as narrow emission bands, long luminescence lifetimes, and multiple colors. However, current development of RE-doped luminescent material is hindered by weak and narrowband absorption problems and low photon-conversion quantum efficiencies. In addition to conventional approaches to enhance fluorescence intensity, controlling emission directivity to improve detection efficiency has become a promising approach to obtain higher luminescence brightnesses. In this paper, a self-suspended RE-doped UC luminescent waveguide is designed to realize directional emissions. Benefitting from the special morphology of the crown-like NaYF4:Yb3+/Er3+ microparticle, the points contact between the waveguide and substrate can be obtained to decrease energy loss. An attractive UC luminescent pattern accompanied by powerful and controllable directional emissions is observed, and the spatial emission angle and intensity distribution are explored and analyzed in detail by introducing Fourier imaging detection and simulation. This work provides a new method for achieving controllable directional fluorescence emissions and obtaining improved detection efficiency by narrowing emission directivity, which has potential applications in 3-dimensional displays and micro-optoelectronic devices, especially when fabricating self-fluorescence micron lasers.