Femtosecond laser induced cross relaxation in Er³⁺ doped NaYF₄ glass ceramic

Cross relaxation (CR) plays a significant role in the luminescence of rare-earth ion doped materials. It is generally considered as a major cause of concentration quenching in bulky materials and has been intentionally adopted in selectively tuning the color output. In this work, we combine streak camera with spectrometer to investigate the CR processes in Er³⁺ doped NaYF₄ glass ceramic under a 400 nm femtosecond laser field. This combination technique incorporates the advantages of both the streak camera with high time-resolution and the spectrometer with good wavelength-resolution, and can provide the luminescence information in both the temporal and spectral dimensions. A new CR process is experimentally observed in the higher doping concentration, and its excitation mechanism is justified by comparing the luminescence lifetimes and intensities in low and high doping concentrations. This study will contribute to a better understanding of the luminescence mechanisms in the rare earth ion doped materials and its color output tuning.