Improved Up-Conversion Luminescence from Er3+:LaF3 Nanocrystals Embedded in Oxyfluoride Glass Ceramics via Simultaneous Triwavelength Excitation

Up-conversion (UC), harvesting near-infrared (NIR) sunlight, is highly desirable for photovoltaic (PV) cells. In regard to this concept, most of the reported experiments on UC materials and their applications, however, were conventionally studied on a monochromatic laser with a narrow excitation band, which is difficult to meet the requirement of solar spectrum conversion. Given the practical applications in PV cells, investigations for UC materials upon simultaneous multiwavelengths even broadband near-infrared (NIR) sunlight excitation are much more meaningful. Herein, we studied the UC luminescence properties of germanate oxyfluoride glass ceramics (GCs) containing LaF3:Er3+ nanocrystals with lower phonon energy upon simultaneous triwavelength excitation. The UC emission intensities upon simultaneous triwavelength excitation were drastically enhanced in comparison with the case of that by monochromatic excitation. The UC luminescence mechanisms were interpreted in-depth in terms of synergetic UC effect owing to the perturbation in the excited states established by different excitation wavelengths. We demonstrated the application of the simultaneous triwavelength excited GC by adding it to the rear face of thin-film hydrogenated amorphous silicon (a-Si:H) solar cells. The photoactive current generated by the reflected UC light upon simultaneous triwavelength excitation was dramatically enhanced in contrast to the case of that upon monochromatic excitation. This Er3+-doped germanate oxyfluoride GC, harvesting broader NIR sunlight photons via simultaneous multiwavelength excitation, has colossal potential to improve the power conversion efficiency in PV cells in the near future.