External current-controlled dynamic display by integrating upconversion micro-disks with power density-dependent color into NIR luminescent diodes†

Abstract

An externally controlled color-tunable light-emitting device is always the frontier of color display. However, multiple colors are usually realized using different materials with variable composition, phase or structure. Developing materials, which can emit tunable colors on changing external stimuli in a fixed composition, will avoid the energy loss by mixing different materials emitting a single color. Here, we designed a core–shell upconversion micro-disk structure with high concentration of Yb3+ doped in the core. Fine-tuning color output is achieved by varying the power density of the excitation light within a range of 0.8–12.9 W cm−2, which is lower than most of the reported ones and can be realized by commercial NIR-LED. Importantly, we designed a dynamic display device by integrating the micro-disks in a series of NIR-LEDs. For the first time, the dynamic red, orange, yellow and green colors can be demonstrated by simply changing the external current. A red shape of a standing human and a green shape of human with walking step can be dynamically realized in a LED array by varying the external current.