# Progress of Organic/Inorganic Luminescent Materials for Optical Wireless Communication Systems
## 4 Current Challenges of Using Luminescent Materials for Visible-Light Communication  
As we highlighted in the earlier sections, interesting systems, such as MOFs, polymers, complex organic molecules, dyes, and perovskite nanoparticles, are the most promising luminescent materials in terms of making possible the faster transmission and consumption of information/data through VLC compared to the traditional IR-frequency systems. Nevertheless, although these materials exhibit improved PL properties, some issues impede the achievement of a suitable frequency bandwidth and, therefore, the obtainment of an extended response in the UV-vis-NIR spectrum. Firstly, the preparation of some organic molecules or more complex structures, such as MOFs, requires multiple reaction steps, and the amount obtained from these products is usually relatively small, hindering their industrial projection. Moreover, most products do not offer a high PLQY, deducing both that the non-radiative recombination is facilitated (loss of expected emission features) and the PL lifetime of some light converters is in the scale of microseconds. This disadvantage delays the radiative recombination, making it difficult to generate a frequency response at longer wavelengths. Therefore, after depositing visible-light emitters, such as yellow  
Figure 5: (**a**) Luminescent fibers fabricated from CsPbI\({}_{3}\), CsPbBr\({}_{3}\) and mixed halide CsPb(Br/Cl)\({}_{3}\) sinks arranged in a NUST pattern, before being exposed to UV light. Inset of Figure 1a shows emitting PNCs deposited on Zn and Ag wires. Typical electroluminescence (EL) spectra of (**b**) green- and (**c**) red-emitting PNCs fibers. Insets of Figure 5b,c exhibit EL and corresponding chromaticity coordinates of PNCs-based fibers under operation. Reproduced under terms of the CC-BY license [97]. Copyright 2020, Authors, Springer Nature. (**d**) Photograph of green-emitting CsPbBr\({}_{3}\) PNCs embedded into amorphous glass at diverse sizes under UV light. (**e**) Frequency response and (**f**) BERs measurements of CsPbBr\({}_{3}\)–glass material by varying date rate. Reproduced with permission [100]. Copyright 2021, Authors, John Wiley and Sons, Inc.  
phosphors on blue-emitting LEDs, the yellow emission is filtered to overpass the long carrier radiative recombination dynamics and accelerate the data travelling. In addition, some issues associated with photobleaching, sensitivity of environmental factors (pH, humidity, temperature, etc.), and a low signal-to-noise ratio hamper the performance of VLCs [101]. Lastly, some organics show low carrier mobility, indicating high capacitance feature, which leads to a lower frequency bandwidth.  
Concerning inorganic materials, such as PNCs, iodide-based nanoparticles can suffer an \(\alpha\)-to-\(\delta\) phase transformation [102], quenching their emission properties and any possibility of data mobility via wireless light communication. In this context, future studies should be focused on the preparation of luminescent materials with high PLQY and improved color quality, which can mediate the generation of white light emission by enhancing illumination quality (higher CRI). Besides these characteristics, the PL lifetime response of the materials should be in the range of nanoseconds (1-10 ns), with PNCs being the candidates used to satisfy fast data transmission demand. As reported in optoelectronics and photovoltaics, the confinement effect of the PNCs can avoid the phase transformation in iodide perovskites, opening the door to cover the entire UV-vis-NIR spectrum, accelerating the radiative recombination and expanding the frequency bandwidth. In this line, stable light converters would be incorporated into the actual technologies, such as efficient LEDs for phone and lighting companies, promoting their commercialization.