## 3 Results and Discussion
### Visible Light Communication and Solid-State Lighting  
Before the construction of the white-light system, two kinds of color-conversion materials (R-PQDs and G-PQDs) were utilized separately to generate monochromatic light for communication, and the properties of both PQDs are discussed in the following. Figure 5a presents the spectrum of R-PQDs under excitation of the \(\mu\)LED, where one peak wavelength was at 445 nm from the \(\mu\)LED and another peak wavelength was at 611 nm from R-PQDs. Likewise, the spectrum of G-PQDs excited by \(\mu\)LED is shown in Figure 5b, with two peak wavelengths representing \(\mu\)LED and G-PQDs at 445 nm and 531 nm, respectively. The FWHMs of the R-PQDs and G-PQDs were 34 nm and 21 nm, manifesting the outstanding narrow emission of PQDs. The normalized responses of R-PQDs and G-PQDs excited by the blue InGaN-\(\mu\)LEDs were measured, which are exhibited in Figure 6. The bandwidth of the square InGaN-\(\mu\)LED with the size of 80 \(\upmu\)m was up to \(\sim\)162 MHz, and under the excitation of the \(\mu\)LED, the bandwidths of R-PQDs (\(\mu\)LED + R-PQDs) and G-PQDs (\(\mu\)LED + G-PQDs) were \(\sim\)90 MHz and \(\sim\)64 MHz, respectively. Meanwhile, the R-PQDs showed better stability and higher bandwidth than the G-PQDs as the curve declined more slowly and smoothly. The superiority of PQDs can be supported by drawing a comparison with the slow frequency responses of conventional YAG:Ce\({}^{3+}\) phosphors (2.5 MHz) [25]. As shown in Figure 7a,b, the eye diagrams were measured at a data rate of 100 Mbps for \(\mu\)LED + R-PQDs and \(\mu\)LED + G-PQDs, respectively. Attributed to the higher frequency response and signal-to-noise ratio of the R-PQDs, the eye diagram is not only open and clear but also less noisy in comparison with that of the G-PQDs. The maximum data rate of the R-PQDs shown in Figure 7c was achieved at 200 Mbps with a BER of 3.3 \(\times\) 10\({}^{-3}\), beneath the forward error correction (FEC) criterion of 3.8 \(\times\) 10\({}^{-3}\). Similarly, in Figure 7d, the maximum achievable data rate of the G-PQDs system was 170 Mbps with a BER of 3.5 \(\times\) 10\({}^{-3}\), below the FEC threshold. Therefore, both R-PQDs and G-PQDs show excellent potential in optical wireless communication. Figure 5: PL spectra of light generated by \(\mu\)LEDs exciting two kinds of luminescent materials: (**a**) R-PQDs (**b**) and G-PQDs. To verify high-efficiency illumination and high-speed wireless communication at the same time, the characteristics of the WL-VLC system based on GaN-based white-light LED were further studied. Based on the abovementioned systems, the green light was emitted from the G-PQDs under excitation of the blue light from \(\mu\)LED, and then the mixed light was used to excite the R-PQDs. Consequently, as the blue light, green light, and red light merged, the white light was obtained. The performances of the white-light system were measured and discussed in our further experiments. As exhibited in Figure 8a, the CIE color coordinates of the WL-VLC system were (0.3327, 0.3114) and the color temperature was 5474 K. Note that compared with the CIE of (0.27, 0.30) in our previous study [38], a better-quality white light of our WL-VLC system  
Figure 6: Frequency responses of the square \(\mu\)LED, R-PQDs, and G-PQDs. The \(-3\) dB modulation bandwidth is marked by a dashed line. Figure 7: Eye diagrams versus data rates at 100 Mbps of (**a**) \(\mu\)LED + R-PQDs and (**b**) \(\mu\)LED + G-PQDs. BER at different data rates of (**c**) \(\mu\)LED + R-PQDs and (**d**) \(\mu\)LED + G-PQDs. The dashed line shows the FEC threshold. was generated, which is very close to the CIE of (0.33, 0.33) for standard white light. As presented in Figure 8b, the maximum bandwidth achieved for the proposed WL-VLC system was 57.5 MHz. The eye diagram of the WL-VLC system at 90 Mbps is shown in the inset of Figure 8b. The above results reveal that the WL-VLC system proposed in this work implemented a high-performance SSL and VLC based on the white-light GaN-based \(\mu\)LED.