Wanlu Zhang

High-Bandwidth White-Light System Combining a Micro-LED with Perovskite Quantum Dots for Visible Light Communication

This work proposes a high-bandwidth white-light system consisting of a blue gallium nitride (GaN) micro-LED (μLED) exciting yellow-emitting CsPbBr1.8I1.2 perovskite quantum dots (YQDs) for high-speed real-time visible light communication (VLC). The packaged 80 μm × 80 μm blue-emitting μLED has a modulation bandwidth of ∼160 MHz and a peak emission wavelength of ∼445 nm. The achievable bandwidth of the white-light system is up to 85 MHz in the absence of filters and equalization technology. Meanwhile, the bandwidth of the YQDs as a color converter is as high as 73 MHz with the blue GaN μLED as the pump source. A maximum data rate of 300 Mbps can be achieved by taking advantage of the high bandwidth of the white-light system using the non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. The resultant bit-error rate is 2.0 × 10-3, well beneath the forward error correction criterion of 3.8 × 10-3 required for error-free data transmission. In addition, the YQDs which we proposed as a color converter possess high stability for VLC. After half a year, the achievable bandwidths of the white-light system and the YQDs are still up to 83 and 70 MHz, respectively. This study provides the direction of developing high-bandwidth white-light system for both high-efficiency solid-state lighting and high-speed VLC.

Spectral optimization of color temperature tunable white LEDs based on perovskite quantum dots for ultrahigh color rendition

The spectral optimization for maximizing limited luminous efficacy (LLE) of correlated color temperature (CCT) tunable white light-emitting diodes (LEDs) with two, three and four color perovskite quantum dots (QDs) excited by a blue chip was investigated under the constraint of designated ultrahigh color rendering index (CRI) and color quality scale (CQS). The results show that high quality white lights with CRIs of 96-97, CQSs of 95-96, and LLEs of 243-225 lm/W at CCTs of 2700 K to 6500 K could be realized by the QDs-converted white LEDs (QD-WLEDs) using a blue chip and different combinations of perovskite quantum dots. The luminous efficacies of QD-WLEDs are expected to reach 114 to 122 lm/W at CCTs of 2700 K to 6500 K, if the radiant efficiency of a blue chip is 60% and the real PLQY values of perovskite QDs are 75%. These results demonstrate that perovskite QD-based LEDs are expected to be promising in next generation display and lighting technologies.

Photometric Optimization of Color Temperature Tunable Quantum Dots Converted White LEDs for Excellent Color Rendition

The photometric optimization for maximizing limited luminous efficacy (LLE) of correlated color temperature (CCT) tunable quantum dots (QDs) converted white light-emitting diode (LED) (QD-WLED) with green, yellow, and red QDs excited by a blue chip was developed under the constraints of the designated color rendering index (CRI) and color quality scale (CQS). The results show that CCT tunable (2700-6500 K) QD-WLEDs with both excellent color rendition and high luminous efficacy should use three narrow emission QDs. The optimal CCT tunable QD-WLEDs with CRI ≥ 95 and CQS ≥ 93 consist of a blue chip (461.0, 25 nm) and green (519.7, 30 nm), yellow (569.2, 30 nm), and red (622.9, 30 nm) QDs, and their LLEs could reach 270-292 lm/W. Simulation demonstrates that QD-WLEDs using a blue chip (460.0, 25 nm) and the green (521, 41 nm), yellow (562 nm, 44 nm), and red (620, 59 nm) CdTe QDs could realize CCT tunable white lights with CRIs of 95-96, CQSs of 93-94, and LLEs of 256-272 lm/W, which increase by 12-21%, compared with that of optimal phosphor-coated white LEDs (pc-W LEDs). Finally, LEs of both QD-WLED and pc-W LED were estimated. The requirements of the overall efficiency of QDs film were present if the CCT tunable QD-WLEDs were competitive to the CCT tunable pc-W LEDs.

Hydrogen Peroxide-Treated Carbon Dot Phosphor with a Bathochromic-Shifted, Aggregation-Enhanced Emission for Light-Emitting Devices and Visible Light Communication

Abstract It is demonstrated that treatment of blue‐emissive carbon dots (CDs) with aqueous hydrogen peroxide (H2O2) results in the green emissive solid state CD phosphor with photoluminescence quantum yield of 25% and short luminescence lifetime of 6 ns. The bathochromic‐shifted, enhanced green emission of H2O2‐treated CDs in the powder is ascribed to surface state changes occurring in the aggregated material. Using the green emissive H2O2‐treated CD phosphor, down‐conversion white‐light‐emitting devices with cool, pure, and warm white light are fabricated. Moreover, using the green emissive CD phosphor as a color converter, a laser‐based white‐light source is realized, and visible light communication with a high modulation bandwidth of up to 285 MHz and data transmission rate of ≈435 Mbps is demonstrated.

Microwave-Assisted Heating Method towards Multi-Color Quantum Dots-Based Phosphors with Much Improved Luminescence

Solid-state highly photoluminescent quantum dot (QD)-based phosphors attract great scientific interests as color converters because of an increasing demand for white-light-emitting devices. Herein, a microwave-assisted heating method is presented to fabricate multicolor QD-based phosphors within 30 s through microwave-assisted heating of the mixture of QDs and sodium silicate aqueous solution. In the composites, the formed cross-linked networks not only play as a matrix to prevent QD aggregation in solid state but also cause the variation of the refractive index around QDs and the QD surface optimization, which contributes to good stabilities and twice enhancement in photoluminescence quantum yields (69%) compared with the initial QD aqueous solution (33%). Using the QD-based phosphors as color conversion layers, white-light-emitting diodes were realized with controllable color temperature, high color purity, and high color-rendering index (90.3), which show a great potential in display and illumination. Furthermore, the luminescence lifetime of the QD-based phosphors is less than 25 ns. The potential application of the QD-based phosphors in visible light communication was also demonstrated, with the modulation bandwidth achieving 42 MHz.