Comment on "A universal approach for calculating the Judd-Ofelt parameters of RE in powdered phosphors and its application for the β-NaYF4:Er/Yb phosphor derived from auto-combustion-assisted fluoridation" by B. Chen, S. Xu et al., Phys. Chem. Chem. Phys., 2018, 20, 15876.

A recent paper [Y. Q. Zhang, B. J. Chen, S. Xu, X. P. Li, J. S. Zhang, J. S. Sun, X. Q. Zhang, H. P. Xia and R. N. Hua, A universal approach for calculating the Judd-Ofelt parameters of RE3+ in powdered phosphors and its application for the β-NaYF4:Er3+/Yb3+ phosphor derived from auto-combustion-assisted fluoridation, Phys. Chem. Chem. Phys., 2018, 20, 15876-15883] used the Er3+/Yb3+:β-NaYF4 phosphor as an example to demonstrate a method used for evaluating Judd-Ofelt parameters of rare-earth-ion-doped powder. The method is actually established on the basis of a measured diffuse reflectance spectrum and fluorescence lifetime of Er3+ emission at 1.5 μm. The paper compared the Judd-Ofelt parameters obtained from two least-squares fitting processes with and without inclusion of two strong Er3+ absorption transitions from 4I15/2 to 2H11/2 and 4G11/2, and erroneously concluded that the values of the Judd-Ofelt parameters depend mainly on the majority of transitions with even weak intensities rather than on a few strong transitions. We have repeated the two fitting processes and the reverse conclusion has been made. Moreover, we have studied the effects of the transitions selected for the analysis and comprehensive explanations are given for the effects. In addition, the previously reported methods, including the aforementioned one, are reviewed, compared and discussed in detail.