Abstract:
Rare earth-doped up-conversion (UC) phosphors, as an important type of phosphors, are widely used in sensing, anti-counterfeiting, bio-imaging, photo-dynamic and photo-thermal therapy with their advantages of low auto-fluorescence, high stability and resistance to photo-bleaching. However, different application fields have different requirements for the optical properties of materials, it is necessary to effectively modulate the emission spectra of UC phosphors according to requirements. The present paper reviews the spectral modulation of Er3+ doped UC phosphors, in which traditional chemical component modulation such as the type of matrix, phosphors structure and doping concentration can be adjusted fundamentally to achieve color tunable emission.Nevertheless this method is uncertain and irreversible and requires a lot of complicated experiments. In contrast, external field modulation changes the environment of the samples and the electron population at each energy level of the rare earth ions by changing the external physical environmental conditions including the external electromagnetic field, temperature, pressure, and excitation light source parameters, thereby realizing the color of the phosphor. These methods can achieve a continuous spectral regulation of the rare earth-doped UC fluorescent material, and the color transition is repeatable and reversible. Analyzing the modulation mechanism of above mentioned methods will be conductive to understand the nature of Er3+ UC emission spectrum control, and build the solid base for designing new optical control methods.
