**8. Conclusion**

**Figure 15.** The decay curves for the 5

D4 →<sup>7</sup> F5

then relaxes nonradiatively and populates the emitting 5

D4

**Figure 14.** Photoluminescence spectra of Tb3+ ions (A), Tb3+ ions with Bi NPs (B), and (Tb(Sal)<sup>3</sup>

5 D4

(Tb(Sal)<sup>3</sup>

142 Acrylic Polymers in Healthcare

The increase in the lifetime of the 5

ting 5 D4

the <sup>5</sup> D4 →<sup>7</sup> F5

complex with and without Bi NPs in PVA using 355 nm radiation (reproduced from Kaur et al. [24].

transition at 544 nm of Tb3+ ions with and without NPs and the (Tb(Sal)<sup>3</sup>

D4

level of Tb3+ ion is clearly observed in the decay curves for

energy absorbed by the Sal ligand is also transferred to the resonating Tb3+ ions populating the

Bi NPs (C) in PVA in the range of 375–700 nm on excitation with 355 nm radiation (reproduced from Kaur et al. [24]).

is the fundamental basis for the enhancement in intensity as shown in the inset of **Figure 14**.

Herein, the point to mention is that different transitions of Tb3+ ion respond differently to the

 level via intersystem crossing and the consequent energy transfer process that is the reason for enhancing the emission intensity. Also, the Bi NPs form a local plasmonic field around the

(Phen)) complex, and the high-field gradients of NPs increase the lifetime of the emit-

level of Tb3+ ions [42]. The coupling between the radiative transitions, and the field effect

transition of Tb3+ ions in the presence and absence of Bi NPs (as seen in **Figure 15**).

level. Along with this, the optical

(Phen)) complex with

(Phen))

To recapitulate, bismuth nanoparticles have been prepared by laser ablation technique at in different aqueous solutions, namely water, water + sodium hydroxide, and water + hydrochloric acid. TEM micrographs confirm the formation of spherical, core shell, and hollow spheres in H, HN, and HC, respectively, with variation in size. Further, the Bi NPs were subsequently scattered with Tb3+ ions and their complex with salicylic acid (Sal) and 1,10-phenanthroline in aqueous solution of polyvinyl alcohol to get thin polymer films. Then the photoluminescence properties of Tb3+ ions and the (Tb(Sal)<sup>3</sup> (Phen)) complex were studied using 266 and 355 nm as excitation wavelengths. The emission efficiency of Tb3+ ions and their complex is seen to be enhanced in the presence of Bi NPs on excitation with both the radiations. On 266 nm excitation, a comprehensive photoluminescence emission spectrum of Tb3+ ions is observed for Tb(Sal)<sup>3</sup> (Phen) complex with Bi NPs spanning the region between 375 and 700 nm depicting transitions from 5 D3 / 5 D4 levels to diverse 7 FJ levels. It is worthy to mention that the luminescence enhancement is better for (Tb(Sal)<sup>3</sup> (Phen)) complex with 355 nm excitation radiation. The augmentation in intensity is ascribed to the coupling of plasmonic and local field effect of Bi nanoparticles on Tb3+ ion that influence the lifetime of radiative level of Tb3+ ion in addition to transfer of energy from Sal to Tb3+ ion.
