We introduce white light generation using CdSe/ZnS core–shell nanocrystals of single, dual, triple and quadruple combinations hybridized with InGaN/GaN LEDs. Such hybridization of different nanocrystal combinations provides the ability to conveniently adjust white light parameters including the tristimulus coordinates (x,y), correlated colour temperature (Tc) and colour rending index (Ra). We present the design, growth, fabrication and characterization of our white hybrid nanocrystal-LEDs that incorporate combinations of (1) yellow nanocrystals (λPL = 580 nm) on a blue LED (λEL = 440 nm) with (x,y) = (0.37,0.25), Tc = 2692 K and Ra = 14.69; (2) cyan and red nanocrystals (λPL = 500 and 620 nm) on a blue LED (λEL = 440 nm) with (x,y) = (0.37,0.28), Tc = 3246 K and Ra = 19.65; (3) green, yellow and red nanocrystals (λPL = 540, 580 and 620 nm) on a blue LED (λEL = 452 nm) with (x,y) = (0.30,0.28), Tc = 7521 K and Ra = 40.95; and (4) cyan, green, yellow and red nanocrystals (λPL = 500, 540, 580 and 620 nm) on a blue LED (λEL = 452 nm) with (x,y) = (0.24,0.33), Tc = 11 171 K and Ra = 71.07. These hybrid white light sources hold promise for future lighting and display applications with their highly adjustable properties.

The authors present the design, growth, fabrication, experimental characterization, and theoretical analysis of blue quantum electroabsorption modulators that incorporate ϳ5 nm thick In 0.35 Ga 0.65 N / GaN quantum structures for operation between 420 and 430 nm. Growing on polar c plane on sapphire, they obtain quantum structures with zigzag potential profile due to alternating polarization fields and demonstrate that their optical absorption blueshifts with applied electric field, unlike the redshift of conventional quantum confined Stark effect. In InGaN / GaN quantum structures, they report the largest absorption change of 6000 cm −1 for 6 V bias swing around 424 nm, holding promise for blue optical clock generation and injection directly into silicon chips. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2424642͔ Today silicon microelectronics is limited in operating speed: the electrical interconnects suffer from the RC limitation; scaling does not mitigate this problem.1 This leads to a bottleneck in electrical clocking. Optical clocking is proposed as a remedy.2 Optical clock distribution is implemented commonly in the near infrared ͑IR͒ spectral region where optoelecronic devices are readily available.3,4 However, silicon photodetectors, for example, those fabricated in standard complementary metal-oxide-semiconductor ͑CMOS͒ process, unfavorably exhibit long absorption length and thus a diffusion tail problem in the near IR. This limits the operating speed of Si CMOS photodetectors to 1 Gbits/ s. 5 To circumvent this problem, one approach is to utilize high-speed III-V photodetectors hybrid integrated on Si chips. This, however, introduces difficulties related to post-CMOS fabrication. On the other hand, unlike in the IR, optical clock injection directly to Si is possible in the blue, where Si features a very short absorption length ͑ϳ100 nm at 400 nm͒ and thus lacks the diffusion tail. 6 However, there exists no chip-scale device to modulate optical clock signal in the blue at high speeds to date. In this letter, we propose blue InGaN / GaN based quantum electroabsorption modulators for a possible chip-scale solution in optical clock modulation in the blue. Here we present the design, epitaxial growth, fabrication, experimental characterization, and theoretical analysis of our quantum electroabsorption modulators that incorporate ϳ5 nm thick In 0.35 Ga 0.65 N / GaN quantum structures in a p-i-n diode architecture for operation in the blue spectral range, as shown in Fig. 1.We grow these quantum structures on the polar c plane of GaN on sapphire in metal organic chemical vapor deposition ͑MOCVD͒ and obtain a zigzag potential profile due to high polarization fields with alternating directions in their heterostructures. We study the electroabsorption behavior of these quantum zigzag structures for proof-of-concept demonstration of their use in blue modulation. In the blue range, using InGaN / GaN quantum structures, we experimentally demonstrate the largest optical absorption change of 6000 cm −1 wi...

Using first-principles density functional theory calculations, we systematically investigate the structural, electronic and vibrational properties of bulk and potential single-layer structures of perovskite-like CsPb 2 Br 5 crystal. It is found that while Cs atoms have no effect on the electronic structure, their presence is essential for the formation of stable CsPb 2 Br 5 crystals. Calculated vibrational spectra of the crystal reveal that not only the bulk form but also the single-layer forms of CsPb 2 Br 5 are dynamically stable. Predicted single-layer forms can exhibit either semiconducting or metallic character. Moreover, modification of the structural, electronic and magnetic properties of single-layer CsPb 2 Br 5 upon formation of vacancy defects is investigated. It is found that the formation of Br vacancy (i) has the lowest formation energy, (ii) significantly changes the electronic structure, and (iii) leads to ferromagnetic ground state in the single-layer CsPb 2 Br 5 . However, the formation of Pb and Cs vacancies leads to p-type doping of the single-layer structure. Results reported herein reveal that single-layer CsPb 2 Br 5 crystal is a novel stable perovskite with enhanced functionality and a promising candidate for nanodevice applications.

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The interest in all-inorganic halide perovskites has been increasing dramatically due to their high quantum yield, band gap tunability, and ease of fabrication in compositional and geometric diversity. In this study, we synthesized µm long and ~4 nm thick CsPbBr3 nanowires (NWs). They were, then, integrated into electrospun polyurethane (PU) fibers to examine polarization behavior of the composite fiber assembly. Aligned electrospun fibers containing CsPbBr3 nanowires show remarkable increase in degree of polarization from 0.17 to 0.30. This combination of NWs and PU fibers provides a promising composite material for various applications such as optoelectronic devices and solar cells.

Cataloged from PDF version of article.Semiconductor nanocrystal quantum dots are utilized in numerous applications in nano- and biotechnology. In device applications, where several different material components are involved, quantum dots typically need to be assembled at explicit locations for enhanced functionality. Conventional approaches cannot meet these requirements where assembly of nanocrystals is usually material-nonspecific, thereby limiting the control of their spatial distribution. Here we demonstrate directed self-assembly of quantum dot emitters at material-specific locations in a color-conversion LED containing several material components including a metal, a dielectric, and a semiconductor. We achieve a spatially selective immobilization of quantum dot emitters by using the unique material selectivity characteristics provided by the engineered solid-binding peptides as smart linkers. Peptide-decorated quantum dots exhibited several orders of magnitude higher photoluminescence compared to the control groups, thus, potentially opening up novel ways to advance these photonic platforms in applications ranging from chemical to biodetection. © 2011 American Chemical Society

In this paper, we present four GaN based polar quantum structures grown on c-plane embedded in p-i-n diode architecture as a part of high-speed electroabsorption modulators for use in optical communication (free-space non-line-of-sight optical links) in the ultraviolet (UV): the first modulator incorporates ∼4–6nm thick GaN∕AlGaN quantum structures for operation in the deep-UV spectral region and the other three incorporate ∼2–3nm thick InGaN∕GaN quantum structures tuned for operation in violet to near-UV spectral region. Here, we report on the design, epitaxial growth, fabrication, and characterization of these quantum electroabsorption modulators. In reverse bias, these devices exhibit a strong electroabsorption (optical absorption coefficient change in the range of 5500–13000cm−1 with electric field swings of 40–75V∕μm) at their specific operating wavelengths. In this work, we show that these quantum electroabsorption structures hold great promise for future applications in ultraviolet optoelectronics technology such as external modulation and data coding in secure non-line-of-sight communication systems.

As a new material system for solar cell applications, III-nitrides -InGaN alloys in particular -offer significant benefits including direct band gap covering almost the entire visible spectrum, high electron and hole mobility, high drift velocity, and radiation resistance, making InGaN/GaN one of the most promising material systems for future photovoltaics [1][2][3][4][5]. One way of making solar cells using this material system is based on the approach of conventional photovoltaics using a p -i-n diode architecture that basically relies on generating excitons in InGaN/GaN quantum wells (QWs) as a result of the optical absorption of the incident solar radiation and subsequently disassociating these excitons and separating their carriers in QWs with the help of the built-in electric field of the diode. However, the efficiency of this type of solar diodes is limited due to low light absorption by thin QW layers and undesired absorption of the incoming photons possibly in the top contact layer [6]. Alternatively, in this work, we investigate and demonstrate an electrostatically coupled hybrid system of CdSe/ZnS core/shell semiconductor quantum dots (QDs) with InGaN/GaN QWs in which colloidal QDs behave as the Förster-type nonradiative resonance energy transfer (NRET) donors to harvest incident light as an additional pathway and epitaxial QWs as the NRET acceptors to collect these harvested exciton energies. The advantage of such a hybrid system is that the enhancement of the effective absorption cross section of the quantum wells as a result of additional exciton harvesting in the quantum dots and the undesired electron-hole pairs generated in the top contact layer in a conventional solar cell can be reduced [7]. The feasibility of this type of NRET-based light harvesting into InGaN/GaN QWs offers new possibilities for InGaN material system important for future photovoltaics.Recently such incoherently coupled hybrid nanostructures have been investigated in the literature. AgranovichWe report on Förster-type nonradiative resonance energy transfer (NRET) directed from colloidal quantum dots (QDs) to epitaxial quantum wells (QWs) with an efficiency of 69.6% at a rate of 1.527 ns -1 for potential application in III-nitride based photovoltaics. This hybrid exciton generation-collection system consists of chemically-synthesized cyan CdSe/ZnS core/shell QDs (λ PL = 490 nm) intimately integrated on epitaxially-grown green InGaN/GaN QWs (λ PL = 512 nm). To demonstrate directional NRET from donor QDs to acceptor QWs, we simultaneously show the decreased photoluminescence decay lifetime of dots and increased lifetime of wells in the hybrid dipole-dipole coupled system.