Local Enhancement Effect Of Microhole Induced Rare-earth Upconversion Luminescence

Rare earth plays an important role in science and technology, at present, especially for visual display. However, the low upconversion luminescence efficiency makes it difficult to be applied to our real life. Improving the upconversion luminescence efficiency becomes a focused research direction. Several methods were proposed previously, and achieved good results. This thesis presents a new method for improving the upconversion luminescence efficiency, which could be practically extended to a series of rare earth doped materials.Laser-Etched microhole structures were made on the surface of a rare-earth doped nanocrystal disk by high energy-focused laser. And the microhole architecture exhibited the enhancement effects for the surface upconversion luminescence. Compared with the upconversion luminescence of the original flat surface, the microhole-modified surface achieved 163-fold enhancements at most. The theoretical model was built for the preparation of the laser-etched microhole architecture and the enhancement effects of the the microhole-modified surface, respectively. Furthermore, the experiments were carried out to verify the theoretical model by employing Yb-Tm codoped samples. We measured the upconversion infrared-visible spectra and analyzed the multiphoton upconversion mechanisms by use of the popular 1gP-1gI relationship. Moreover, the spatial distribution of the luminescence intensity was also measured and verified to strictly obey the properties of a standard Lambert emitter. The systematical experiments for the laser-etched microhole architectures were made for a series of different samples in terms of different host materials,different synthetic methods, various rare-earth dopants and the dopant concentrations.Under the pump excitation of 973 nm laser, the enhanced upconversion luminescence from microhole-modified Yb-Tm doped samples was observed distinctly in contrast to the original surface. The high contrast ratios of the fluorescence display were also achieved. By employing this laser-etching technique, the specific words "HEU" were prepared on the surface of several samples,such as 6Yb:8Er (Y2O3),2Yb:3Ho:2Tm (ZrO2) and 4Yb:0.3Tm(ZrO2) disks. The display contrast and the chromaticity of the bright colorful "HEU" were analyzed correspondingly. Our work would be useful to perform the microscale two-dimensional fluorescence displays.