**2. Materials and experiments**

by means of energy transfer amid nanoparticles and the active rare earth ions. The second available option for the augmentation effect is via local energy field of NPs acting on the lanthanide ions positioned in their propinquity. This effect is prominent in particular when there is a matching of the surface plasmon resonance wavelength of the NPs and the incident light beam wavelength or luminescence wavelength [7, 26]. High surface-to-volume ratio and local phenomena such as absorption or changes in the surface electronic state may contribute

Metallic and semimetallic NPs are striking examples to be explored nowadays. The phenomenon of quantum size effect has a great influence on the physical properties that are very different from those of the bulk ones. Bismuth is a semimetal with a small energy overlap between the conduction and the valence bands. The size-induced semimetal to semiconductor transition and the related quantum confinement effects are potentially useful for optical and electro-optical device applications [2, 10, 16, 36, 37]. It has a high carrier mobility, a highly anisotropic Fermi surface, and miniature effective mass [2, 24, 46]. Below the size of 30 nm, the Bi NPs behave as semiconductors [44]. The formations of semimetal to semiconductor materials are being used in different scientific devices such as in optic and electro optic devices [39]. Bi NPs exhibit absorption in the UV region [27–29, 43]. The absorption peak shifts toward lower wavelengths in the case of smaller Bi NPs and, vice versa. The stability of Bi NPs decreases with a decrease in its particle size (due to enhanced surface to volume ratio). Nevertheless, these demonstrate strong reactive morphology. There are various methods to produce NPs. Among the diverse techniques used to fabricate NPs, laser ablation synthesis in solution (LASiS) generates pure NPs free from any type of contamination and thus, is matchless. In this technique, numerous factors, namely, laser power and wavelength, repetition rate of pulsed laser, spot size of laser beam, and most importantly the medium (solvent) used, etc., control the fabrication of NPs. The medium used for the preparation of NPs in LASiS decides the nature and steadiness of the colloidal NPs that can be further altered/improved by means of varying the pH of the solution. In numerous cases, laser-induced colloidal NPs are extremely reactive as they may react with the media and/or amidst themselves heading for the formation of multifarious configurations and varied agglomerated structures at room temperature provided there exists suitable liquid environment. But one can overcome this agglomeration by the inclusion of certain smart comparable ionic materials that could errand Coulomb repulsion [1], or else the NPs can be enclosed through dissimilar polarity layer that should favor Coulomb repulsion. The tuning of the structure of NPs from core shell to hollow nano structures is also achievable by pH variation. The researchers ought to use metallic nanoparticles for tuning the optical properties of the chosen host or activator (here the lanthanide ions), and for this intention, the sensitivity of NPs is crucial, which predominantly depends on the surface or volume plasmon frequency of NPs along with very negligible involvement of the local field effect. Thus, a deep knowledge and a clear understanding of the comprehensive mechanism of formation of NPs under diverse pH environments is a must. Bismuth-induced nanomaterials encompass exhaustive investigations to become the focal point of further research owing to their new applications (due to its semiconducting

significantly to special properties.

130 Acrylic Polymers in Healthcare

properties).

All the ingredients terbium oxide, salicylic acid, and 1,10-phenanthroline used were all purchased from Sigma Aldrich. Tb<sup>4</sup> O7 and Sal were 99.9% pure. 1,10-phenanthroline was 99.5% pure. Bismuth plate with purity 99.0% was obtained from the same company and used for ablation and preparation of NPs.

#### **2.1. Laser ablation technique to prepare Bi NPs**

Laser ablation technique was used to prepare Bi NPs at different pH in different aqueous solutions (namely, water (H), water + sodium hydroxide (HN), and water + hydrochloric acid (HC)). **Figure 4** shows the experimental set up used for laser ablation for the production of Bi nanoparticles.

The irradiation source was the different wavelengths of an Nd:YAG laser with 7 ns pulse duration. The laser beam was tightly focused with the help of a short focal length (10 cm focal

**Figure 4.** Experimental setup of laser ablation for preparation of Bi nanoparticles.

length) convergent lens on the copper plate (thickness: 0.6 mm, size: 18 × 30 mm2 ) kept in a beaker with water 2.5 mm deep from the top surface. The liquid was continuously stirred using a magnetic stirrer. Laser ablation was continued for 45 min. The Bi plate was taken out of the liquid, and the sample was used for optical measurements and preparation of thin film samples. The same procedure was repeated for water + sodium hydroxide (HN), and water + hydrochloric acid.

#### **2.2. Preparation of Tb(Sal)3 (Phen) complex**

0.010 mmol Tb<sup>4</sup> O7 was obtained by dissolving Tb<sup>4</sup> O7 in hydrochloric acid to obtain TbCl<sup>3</sup> solution. 0.015 mmol of salicylic acid and 0.005 mmol 1,10-phenanthroline were independently dissolved in 2.0 ml ethanol to get its ethanolic solution. Both were added and stirred rigorously for an hour to achieve Tb(Sal)<sup>3</sup> (Phen) complex as explained by Kaur et al. [21].
