RESUMEN
Carbon Dots (CDs), fabricated by hydrothermal bottom-up synthesis, are complex materials, whose optical properties are influenced by multiple factors. The presence of domains of conjugated sp2 carbon, which are formed upon carbonization of precursors at high temperature; nitrogen doping; and as recently shown, the presence of molecular fluorophores, are contributing to the emission of such CDs. We conducted a series of syntheses, each designed with specific precursors and reaction conditions that reveal the contribution of the above-mentioned factors. Specifically, we enforced carbonization by using graphene oxide as a precursor material; favored the formation of molecular fluorophores by conducting the synthesis at lower temperature and ambient pressure; and employed two different nitrogen precursors, namely ethylenediamine and triethanolamine. We compared and analyzed the distinct optical properties of the resulting products; furthermore, to address the relationship of CDs and molecular fluorophores, we examined photobleaching characteristics of these materials, under exposure to UV irradiation. From the analysis of the emission lifetimes, we revealed the quenching of the molecular fluorophores, whereas species with a higher degree of carbonization offer protection through incorporation into a carbon matrix. Based on a detailed comparison of different carbon dot species, our study provides novel physical insights into the origin of the luminescence properties of carbon dot derived nanomaterials.
RESUMEN
Strongly emissive (photoluminescence quantum yield up to 65%), thermally stable aluminum hydroxide blue phosphors are synthesized by a single-source precursor-decomposition approach. Blue-emitting UV-pumped light-emitting diodes (LEDs) based on the aluminum hydroxide phosphor reach luminous efficiency of 27.5 lm W-1 , while UV-white-LEDs integrating blue-emitting aluminum hydroxide and red-emitting CuInS2 nanocrystals achieve high color-rendering-index values of 94.3 and luminous efficiency of 23.5 lm W-1 .
RESUMEN
Most of the present-day down-conversion white light-emitting devices (WLEDs) utilize rare-earth elements, which are expensive and facing the problem of shortage in supply. WLEDs based on the combination of orange and blue emitting copper nanoclusters are introduced, which are easy to produce and low in cost. Orange emitting Cu nanoclusters (NCs) are synthesized using glutathione as both the reduction agent and stabilizer, followed by solvent induced aggregation leading to the emission enhancement. Photoluminescence quantum yields (PL QY) of 24% and 43% in solution and solid state are achieved, respectively. Blue emitting Cu nanoclusters are synthesized by reduction of polyvinylpyrrolidone supported Cu(II) ions using ascorbic acid, followed by surface treatment with sodium citrate which improves both the emission intensity and stability of the clusters, resulting in the PL QY of 14% both in solution and solid state. All-copper nanocluster based down-conversion WLEDs are fabricated by integrating powdered orange and blue emitting Cu NC samples on a commercial GaN LED chip providing 370 nm excitation. They show favorable white light characteristics with Commission Internationale de l'Eclairage color coordinates, color rendering index, and correlated color temperature of (0.36, 0.31), 92, and 4163 K, respectively.
RESUMEN
Organometallic halide perovskites have recently drawn considerable attention for applications in light emission diodes (LEDs). However, the small exciton binding energy of the CH3NH3PbI3 perovskite has the concerns of large exciton dissociation and low radiative recombination on its use in near-infrared LEDs (NIR-LEDs). Herein, we propose and demonstrate that the introduction of poly(2-ethyl-2-oxazoline) (PEtOz) into the perovskite can simultaneously improve the recombination rate and radiative decay rate for improving perovskite LED performances. Additionally, our approach results in smooth perovskite films with increased thickness, reduced roughness, and pin-hole free, which facilitates other film deposition on top for practical device fabrication, and reduces current leakage. After optimizing the perovskite-PEtOz nanocomposite emission layer in NIR-LEDs (emission peak at 760 nm), a high radiance of 12.3 W sr-1 m-2 and 70-fold enhancement of the external quantum efficiency (EQE) compared to that of the pristine perovskite case are achieved. The maximum EQE reaches 0.76%, which is the highest EQE reported so far for the CH3NH3PbI3 based NIR-LEDs. The simplicity of our fabrication approach combined with the outstanding device performances further highlights the enormous potential of perovskite-based LEDs.
RESUMEN
While methylammonium lead iodide (MAPbI3) with interesting properties, such as a direct band gap, high and well-balanced electron/hole mobilities, as well as long electron/hole diffusion length, is a potential candidate to become the light absorbers in photodetectors, the challenges for realizing efficient perovskite photodetectors are to suppress dark current, to increase linear dynamic range, and to achieve high specific detectivity and fast response speed. Here, we demonstrate NiOx:PbI2 nanocomposite structures, which can offer dual roles of functioning as an efficient hole extraction layer and favoring the formation of high-quality MAPbI3 to address these challenges. We introduce a room-temperature solution process to form the NiOx:PbI2 nanocomposite structures. The nanocomposite structures facilitate the growth of the compact and ordered MAPbI3 crystalline films, which is essential for efficient photodetectors. Furthermore, the nanocomposite structures work as an effective hole extraction layer, which provides a large electron injection barrier and favorable hole extraction as well as passivates the surface of the perovskite, leading to suppressed dark current and enhanced photocurrent. By optimizing the NiOx:PbI2 nanocomposite structures, a low dark current density of 2 × 10(-10) A/cm(2) at -200 mV and a large linear dynamic range of 112 dB are achieved. Meanwhile, a high responsivity in the visible spectral range of 450-750 nm, a large measured specific detectivity approaching 10(13) Jones, and a fast fall time of 168 ns are demonstrated. The high-performance perovskite photodetectors demonstrated here offer a promising candidate for low-cost and high-performance near-ultraviolet-visible photodetection.
