# Progress of Organic/Inorganic Luminescent Materials for Optical Wireless Communication Systems
## 3 Applications of Luminescent Materials in VLC  
The preparation PNCs with versatile surface chemistry were adequate for the VLC applications, such as Li-Fi (Light Fidelity) systems, which, unlike conventional Wi-Fi (Wireless Fidelity), are bidirectional wireless communication processes mediated using visible light. A typical Li-Fi system is based on a couple of high quantity of transmitters (LEDs) and signal receivers that match the demand of high-speed wireless communication and multiuser interaction [96; 97]. As they make data transference as fast as possible, electroluminescent fibers are the most important communication line between the emitter diode and the receptor in the wireless optical system, offering a high emission color quality and the fabrication of an inexpensive process. Organic materials and polymers were employed as OLEDs to obtain efficient Li-Fi; however, these tools require a high turn-on voltage to mobilize ions into the device, slowing the data transmission. Therefore, the use of PNCs inks represents a low-cost alternative to create light-emitting/detecting bifunctional fibers, as shown in Figure 5a, with narrow electroluminescence linewidth, as shown in Figure 5b,c; as well as creating a small exciton binding energy, which mediates a favored carrier transport to enable the fast travel of information into the wireless tools [97]. As depicted above, LEDs based on orange- or red-light emission develop 0.7-1 GHz modulation bandwidths and a real-time data transmission near to 2 Gbps.  
Another type of wireless application is related to the underwater optical communication (UWOC), which attends to the fact that radio frequency suffers from a high attenuation in water, and, therefore, the infrared signal cannot propagate effectively in this medium [98]. In this context, stable underwater emitters with good PL properties, fast radiative recombination pathway and low light attenuation are key factors that influence the transmission distance, frequency bandwidth and data rate [99]. However, the ionic nature of the PNCs  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Luminescent Material** & **PLQY (\%)** & **Integrated System** & **Maximum Frequency** & **Data Rate** & **Ref.** \\  & & **for VLC** & **Bandwidth (MHz)** & **(Mbps)** & **Ref.** \\ \hline Al-DBA MOF & 12 & MOF-WLED & 3.6 & 3.6 & [27] \\ Zr-based MOFs & - & MMM & 80 & 215 & [29] \\ BCP and PTCBI & - & OPD & 430 & - & [58] \\ Poly p-phenylene vinylene & 60 & OVLC & 200 & 1680 & [17] \\ copolymer & & & & & \\ TBPe and BDAVBi & - & OLED & 245 & 1000 & [32] \\ MDMO-PPV & - & PLED & 0.27 & 10 & [49] \\ BBEHP-PPV and MEH-PPV & 25 & OVLC & 200 & 350 & [7] \\ BODDIPY & 55–75 & OVLC & 39 & 100 & [4] \\ Y-BODIPY & 49 & OVLC & 73 & 370 & [69] \\ Dialkylfluorene/bicyclic 2,1,3- & 87–95 & OVLC & 55 & 207–218 & [72] \\ benzothiadiazole-BODIPY & & Inorganic & & & \\ CsPbBr\({}_{3}\) PNCs & 70 & \(\mu\)-LED & 491 & 2000 & [8] \\ PMMA-coated CsPbBr\({}_{1.5}\)I\({}_{1.5}\) & - & Inorganic & & & \\ and CsPbI\({}_{3}\) PNCs & & \(\mu\)-LED & 1005–1100 & 1700 & [9] \\ CsPbBr\({}_{1.8}\)I\({}_{1.2}\) PNCs & 78 & \(\mu\)-LED & 85 & 300 & [13] \\ \hline \hline \end{tabular}
\end{table}
Table 1: VLC parameters obtained using different light converters in potential wireless optical systems.  
hinders their applicability in polar solvents, causing a rapid quenching of their emission features. In this way, it was reported the introduction of PNCs into the amorphous glass avoided direct interaction between water and the nanoparticles, making them viable for use in a UWOC system [100]. For instance, CsPbBr\({}_{3}\) films, as shown in Figure 5d, can provide a PLQY \(\sim\)69%, which decreases to 53% after 2 weeks in the polar environment. At this point, the high refraction index of the glass accelerates the carrier radiative channel of the perovskite, obtaining a bandwidth of 180 MHz and data rate of 185 Mbps, as shown in Figure 5e,f.