Achieving multicolor emission readout and tunable photoswitching via multiplexing of dual lanthanides in ferroelectric oxides
For luminescent photochromic materials, the optical properties of lanthanide (Ln) ions, including emission color, excitation mode and lifetime, are extremely important in optical information storage and recording. Conventional dopants of single Ln ions generally display unicolor and unimodal emission, leading to low-level luminescence modulation and information readout. Therefore, it is urgent to develop multicolor and multimodal luminescence modulation in a single photochromic material, thus well modulating luminescent readout capability. In this study, superior multicolor emissions (red-green), multimodal properties (downshifting/upconversion) and tunable luminescent switching contrast were successfully obtained in Bi2.5Na0.5Nb2O9-based ferroelectric materials by dual-lanthanide ion doping (Pr/Er). Red/green emission ratios can be continuously tuned from red, orange and yellow to green range via controlling the excitation wavelengths and doped concentrations. Correspondingly, the luminescent switching contrast (ΔRt) gradually increases from 29% to 93% with increasing excitation wavelength upon visible irradiation (407 nm), while the ΔRt values decrease with emission wavelengths, which can be well explained by the Dexter energy transfer model. These findings offer a guide to designing tailored luminescence modulation behavior of luminescent photochromic materials for wide application in optical storage and switching devices.