he time-averaged ($T_{000}$) photon index $\alpha_{\rm PL}$ (for the bursts that are better fitted by the simple PL model) as a function of redshift $z$. Bursts with photometric redshifts are marked in blue specifically, due to the large uncertainties in their redshift measurements. The uncertainties for redshifts are also shown when available. However, note that these uncertainties are adopted from different references and might refer to different confidence ranges (see table \[tab:redshift\_list\] for the original sources). []{data-label="fig: