Ruiqian Guo

Density-Controlled Growth of ZnO Nanowires Via Nanoparticle-Assisted Pulsed-Laser Deposition and Their Optical Properties

Vertically aligned ZnO nanowires with controllable density were successfully synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD), by which nanoparticles formed in the gas phase by the condensation of the ablated species are transported onto the substrate, and nanoparticles play an important role in density control. The effects of synthesis conditions on the density and optical properties of ZnO nanowires were investigated in detail. With the increase in repetition rate and laser energy, ZnO nanowires with a higher density can be obtained as a result of a larger quantity of nanoparticles formed in the gas phase. The density-controlled growth also depends on substrate–target distance. UV emission was observed from all the obtained nanowires at about 390 nm without visible fluorescence near 500 nm due to their excellent crystallinity and the oxygen-deficient defect.

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.

Vertically Aligned Growth of ZnO Nanonails by Nanoparticle-Assisted Pulsed-Laser Ablation Deposition

Vertically aligned ZnO nanonails have been successfully grown on annealed sapphire substrates using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The growth behavior of the ZnO nanonails has been investigated by variation of the ablation time, and a three-step growth mechanism for ZnO nanonails is proposed.

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.

Controlled Growth of ZnO Nanowires by Nanoparticle-Assisted Laser Ablation Deposition

Vertically aligned ZnO nanowires have been successfully synthesized on c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in a background gas by laser ablation are used as a starting material for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which are accomplished by changing the energy of the ablation laser, the repetition rate of the laser and so on. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire. These nanowires were used as building blocks for an ultraviolet light emitting diode with a structure of n-ZnO/ZnO nanowire/p-GaN.

Aligned growth of ZnO nanowires by laser ablation and their applications

Vertically aligned ZnO nanowires have been successfully synthesized on c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in the background gas by laser ablation are used as a starting material for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which are accomplished by changing the energy of the ablation laser, the repetition rate of the laser and so on. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire. These nanowires were used as building blocks for an ultraviolet photo-sensor, field emitters and an ultraviolet light emitting diode with a structure of n-ZnO/ZnO nanowire/p-GaN.Vertically aligned ZnO nanowires have been successfully synthesized on c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in the background gas by laser ablation are used as a starting material for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which are accomplished by changing the energy of the ablation laser, the repetition rate of the laser and so on. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire. These nanowires were used as building blocks for an ultraviolet photo-sensor, field emitters and an ultraviolet light emitting diode with a structure of n-ZnO/ZnO nanowire/p-GaN.

Optical Characteristics of ZnO Nanowires Synthesized by Nano-Particles Assisted Pulsed Laser Deposition

ZnO nanowires were synthesized by the nanoparticle-assisted pulsed-laser deposition. The optical properties of the nanowires were investigated. It was confirmed that the nanowires act as an optical waveguide. The stimulated emission was also observed, when single ZnO nanowire was excited by the nanosecond laser pulse at 355 nm.