**3. Conclusion**

*Materials at the Nanoscale*

The energy states identified in the OA spectrum of figure x (a) belong to

*(a) Optical absorption spectra at room temperature of Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) embedded in SNAB glass matrix. For comparison purposes, the absorption spectrum of the SNAB glass matrix represents* 

*10 Dq = 2.16 eV. (b) TEM image of Bi2-xCrxTe3 NCs (x = 0.05) embedded in SNAB glass. (c) Details of the quintuple layer and the van der Waals gap in the Bi2T3 hexagonal unit cell with the substitutional doping of Bi3+ ions by Cr3+ in distorted octahedral sites. (d) EPR spectra in the X band, at 300 K for NCs of Bi2-xCrxTe3 NCs (x = 0.00; 0.01; 0.05) embedded in the SNAB glass matrix. The inset shows the split diagram of the energy* 

in **Figure 6a**) [43]. The results are typical of inter-electronic repulsion parameters (Racah) B = 0.088 eV in a crystal field strength 10 Dq (∆) = 2.16 eV of Cr3+ ions in

The exciton Bohr radius of approximately 50 nm for Bi2Te3 bulk [45] makes the semiconductor subject to strong quantum confinements. **Figure 6**(**b**) shows the TEM image of the SNAB glass matrix host of the Bi2-xCrxTe3 NCs (x = 0.05). The nanocrystal's 5 nm size confirms the formation of Bi2-xCrxTe3 quantum dots due to the strong

The quantum size of the Bi2-xCrxTe3 NCs does not change with the increase of Cr incorporation in the samples. In this way, the structure preserves due to the nonsaturation of the molar fraction of Cr doping in the Bi2-xCrxTe3 NCs. The interplanar distance d015 = 0.321 nm is evidence of Tellurobismuthite's hexagonal crystalline

Cr-doped Bi2Te3 NCs with the atomic arrangement of monoatomic planes Te - Cr - Te - Bi - Te and Te - Bi - Te - Bi - Te in terms of quintuple layers linked by weak van der Waals interactions [41]. The substitutional doping of Cr3+ ions with a smaller ionic radius (0.53 Å) in relation to Bi3+ (1.03 Å) distorts the environment of octahe-

structure [27, 41]. **Figure 6**(**c**) shows the hexagonal unit cell *Rm D*− *<sup>d</sup>*

T2g (4

*9− complex and the respective spin allowed and forbidden transitions indicated on the energy* 

G) (1.83 eV), 4

F) → <sup>4</sup>

A2g (4

T1 (4

*on the black bottom line. The inset shows the Tanabe-Sugano diagram d3*

quantum confinement of the semiconductor structure.

A2( 4 F) → <sup>2</sup>

F) (2.16 eV), 4

9−) ligands [42, 44].

F) (3.06 eV). These transitions are in accordance

of octahedral symmetry for C/B = 4.5 (see inset

Eg (2

A2g (4

F) → <sup>2</sup>

 *of octahedral symmetry (C/B = 4.5)* 

T2g (2 G)

<sup>5</sup> 3 <sup>3</sup> [41] of the

the spin allowed and forbidden d-d transitions: 4

G) (1.91 eV), 4

F) → <sup>4</sup>

coordinated octahedral sites of Te ([CrTe6]

**150**

dral symmetry [42].

A2( 4 F) → <sup>2</sup>

**Figure 6.**

*for the [CrTe6]*

(2.76 eV) and 4

*states of the system.*

T1( 2

A2 (4

with a Tanabe-Sugano diagram d3

Therefore, this chapter showed the development and applications of several doped semiconductor nanocrystals, as nanopowders or embedded in glass systems. Doped Nanocrystals show good potential to control plant diseases as controlling bacterial diseases on field crops is complex. We also demonstrate that depending on the ion incorporated in the nanocrystal structure, the biocompatibility could be improved. Additionally, we show magnetic properties generated by the domain of the Cu or Cr ions doping spins, in addition to semiconductor nanocrystals embedded in glass systems, for the development of spintronic nanodevices.
