Wavelength-tunable Photoluminescence Research Articles

Electrically Controlled Wavelength-Tunable Photoluminescence from van der Waals Heterostructures.

Achieving facile control of the wavelength of light emitters is of great significance for many key applications in optoelectronics and photonics, including on-chip interconnection, super-resolution imaging, and optical communication. The Joule heating effect caused by electric current is widely applied in modulating the refractive index of silicon-based waveguides for reconfigurable nanophotonic circuits. Here, by utilizing localized Joule heating in the biased graphene device, we demonstrate electrically controlled wavelength-tunable photoluminescence (PL) from vertical van der Waals heterostructures combined by graphene and two-dimensional transition metal dichalcogenides (2D-TMDCs). By applying a moderate electric field of 6.5 kV·cm-1 to the graphene substrate, the PL wavelength of 2D-TMDCs exhibits a continuous tuning from 662 to 690 nm, corresponding to a bandgap reduction of 76 meV. The electric control is highly reversible during sweeping the bias back and forth. The temperature dependence of Raman and PL spectroscopy reveals that the current-induced local Joule heating effect plays a leading role in reducing the optical direct bandgap of TMDCs. The bias-dependent optical reflectivity and time-resolved photoluminescence measurements show a consistent reduction of the optical band gap of 2D-TMDCs and increased PL lifetimes with the electric field over the heterostructures. Moreover, we demonstrate the consistent device operation from 2D materials grown by chemical vapor deposition, showing great advantages for the scalability.

Self-assembled CsPbBr3 quantum dots with wavelength-tunable photoluminescence for efficient active jamming.

CsPbBr3 perovskite quantum dots (QDs) show great potential in various applications due to their size-dependent and excellent optoelectronic properties. However, it is still challenging to synthesize size-tunable CsPbBr3 QDs with purple emission. Herein, CsPbBr3 nanospheres (NS) with purple emission (432 nm) and wavelength-tunable photoluminescence were synthesized using a two-step recrystallization method for the first time. A nanocube (NC) strategy resulting from CsPbBr3 nanosphere self-assembly via polar solvent-induced surface ligand mismatch was proposed. The self-assembly process endows the QDs with wavelength-tunable photoluminescence ranging from 432 to 518 nm. The significant reduction in defects during self-assembly was confirmed by transient optical spectroscopy measurements, photoluminescence quantum yields (PLQY), and the disappearance of tail bands in the long-wavelength region of the photoluminescence (PL) spectrum. This theory demonstrated that the decrease in high defect surfaces and increase in specific surface area were the reasons for the decline in defects. Most importantly, these QDs could be used for the active jamming of optical imaging systems based on charged-coupled devices (CCDs), including laser imaging radar and low light level (LLL) night vision systems. QDs significantly increase the mean square error (MSE) of the image, while the detection rate of the target by the artificial intelligence algorithm decreased by 95.17%. The wide wavelength tunable emission caused by structural changes makes it arduous for silicon-based detectors to avoid the interference of QDs by adding filters or by other means.

Indium nitride quantum dots could shine the light for next-generation fiber optics

Researchers demonstrate the first wavelength-tunable photoluminescence from N-polar InN quantum dots from 1.00 µm to longer than 1.55 µm.Researchers demonstrate the first wavelength-tunable photoluminescence from N-polar InN quantum dots from 1.00 µm to longer than 1.55 µm.

Wavelength-tunable photoluminescence of ZnSe quantum dot micelles synthesized by femtosecond laser ablation in microfluidics

Aqueous ZnSe quantum dots were synthesized by femtosecond laser ablation in microfluidics (FLAM). Hyperbranched polyethylenimine (PEI) was used to form quantum dot micelles which exhibited wavelength-tunable photoluminescence of bright visible light with the variation of pH values. The emission was attributed to the radiative deep levels introduced by the defect states. The emission peak center exhibited a blue shift as much as 25nm to the shorter band. A possible band gap expansion mechanism for the photoluminescence wavelength tunability was discussed.

The structures and properties of Si/SiO2 core/shell quantum dots studied by density-functional tight-binding calculations

Si/SiO2 core/shell quantum dots (QDs) have been shown with wavelength-tunable photoluminescence in addition to their inert, nontoxic, abundant, low-cost, biocompatible advantages. Due to their big size, here, we apply density-functional tight-binding (DFTB) method to perform calculations to study their structures and properties. We systematically investigate the effects of surface passivation, thickness of SiO2 shell, and Si/O ratio on the structures and properties of Si/SiO2 core/shell quantum dots. We find that hydroxyl passivated Si/SiO2 core/shell quantum dots are able to stabilize the quantum dots compared with hydrogen passivated Si/SiO2 core/shell quantum dots. By using DFTB method, we are able to study Si/SiO2 core/shell quantum dots of big size (3 nm) and we find that, in Si/SiO2 core/shell quantum dots, there are competing effects between quantum confinement (blueshift) and oxidation (redshift) with the decrease of the size of Si core. The transition point is when Si/SiO2 ratio is around 1:1. The effect of the thickness of SiO2 on energy gap is not as significant as the effect of the size of the Si core. Our study provides theoretical basis for designing Si quantum dots with tunable photoluminescence.

Intense and wavelength-tunable photoluminescence from surface functionalized MgO nanocrystal clusters

We report fancy brilliant photoluminescence (PL) from surface functionalized MgO nanocrystal clusters (NCs). Single-crystal-like MgO NCs were prepared by a simple one-pot pyrolysis method in the mixed organic solvent of octylamine (OTA) and oleic acid (OA) using magnesium acetate as a precursor. Under the chemical equilibrium of etching and re-growth with the assistance of OA, the MgO products were surface functionalized. It was found that such surface functionalized MgO NCs exhibited intense visible light PL with high PL thermal-stability, and the apparent quantum yield was as high as 19 ± 1%. In addition, through controlling the synthetic temperature and the reaction time, the functionalized surfaces of MgO NCs were facilely tuned, resulting in the tuneable wavelength of the PL from blue-violet to yellow. Different low-coordinated oxygen sites, capping OA and carbonate species on the surface of the MgO nanocrystals were thought to be the origin of PL at different wavelengths. Considering the intense PL, high PL stability at ambient conditions, low cost and low toxicity, such MgO NCs might have potential applications in medicine and biology as a new kind of fluorescent label.

The synthesis and structural characterization of boron-doped silicon-nanocrystals withenhanced electroconductivity

Boron (B)-doped silicon-nanocrystals (Si-NCs) with wavelength-tunable photoluminescence(PL) properties in the visible region are successfully prepared for the first time, leading tosignificant enhancement of electroconductivities. The B-doped Si-NCs are prepared on ap-type Si(100) substrate by co-deposition of p-type Si(100) chips/boron chips/silicadisk targets. As the number of the B chips used as the target is increased, theamount of doped B content increases gradually. Here the amount of doped Bcontent in the Si-NCs is controlled from 0 to 0.4, 0.7, 2.3 at.%. The B elementalstates, compositional ratios, and surface condition of the obtained Si-NCs are fullycharacterized by high-resolution transmission electron microscopy (HRTEM) observations,micro-Raman scattering spectroscopic analysis, etc. Our B-doped Si-NCs possessboth the continuous luminescence property in the visible region and enhancedelectroconductivity. The red-shift of the PL peak is confirmed by the increase of theamount of doped B content. This paper should be very important from the viewpointof application to optoelectronic devices and electroluminescent (EL) displays.

可调整发光波长之富硅氮化硅发光二极管

Wavelength tunable photoluminescence (PL) of Si-rich silicon nitride (SRSN) film with buried Si nanocrystals (Si-ncs) grown by plasma enhanced chemical vapor deposition (PECVD) under SiH4 and NH3 environment is investigated. Intense broadband visible emissions tunable from blue to red can be obtained from the as-deposited SiNx thin films with increasing NH3 flow rate from 150 to 250 sccm and detuning the SiH4/NH3 flow ratio during deposition. To date, the normalized PL wavelength of SiNx films after annealing could be detuned over the range of 385~675 nm by decreasing the NH3 flow rate, corresponding to an enlargement on Si-nc size from 1.5~2 to 4~5 nm. The PL linewidth is decreased with increasing ammonia flow rate due to the improved uniformity of Si-ncs under high NH3 flow rate condition. In addition, the PL intensity is monotonically increasing with the blue shift of PL wavelength due to the increasing density of small-size Si-ncs. The ITO/SiNx/p-Si/Al diode reveals highly resistive property with the turn-on voltage and power-voltage slope of only 20 V and 0.18 nW/V, respectively. The turn-on voltage can further reduce from 20 to 3.8 V by improving the carrier injection efficiency with p-type Si nano-rods.

Controlled chemical etching for silicon nanocrystals with wavelength-tunable photoluminescence

The size of silicon nanocrystals is finely tuned by applying a chemical etching process, leading to differently coloured visible luminescence.