**7. Time-resolved photoluminescence spectroscopy**

**Figure 15** represents the decay curves for the 5 D4 →<sup>7</sup> F5 transition monitored at 544 nm of Tb3+ ions with and without Bi NPs and the (Tb(Sal)<sup>3</sup> (Phen)) complex with Bi NPs in PVA using 355 nm radiation.

The decay curves were fitted with first-order exponential fits that lead to a larger lifetime of 5 D4 level of Tb3+ ions in the presence of NPs. The values obtained for lifetimes are tabulated in **Table 2**.

This increase in lifetime is explained due to the local surface fields of Bi NPs as given in the inset of **Figure 13**. Thus, photoluminescence properties of polymer-doped RE complexes can be improved by adding NPs [22]. There is a substantial improvement in the lifetime values when Bi NPs are added to the TbCl<sup>3</sup> in PVA and, alternatively, for the (Tb(Sal)<sup>3</sup> (Phen)) complex, there is just a small increase in the lifetime.


**Table 2.** The values for the lifetime of Tb3+ ions, Tb3+ ions with Bi NPs, (Tb(Sal)<sup>3</sup> (Phen)) complex with Bi NPs, and (Tb(Sal)<sup>3</sup> (Phen)) with Bi NPs in PVA.
