Temperature-Dependent Photoluminescent Properties of PbSe Nanoplatelets

Semiconductor colloidal nanoplatelets (NPLs) are a promising new class of nanostructures that can bring much impact on lightning technologies, light-emitting diodes (LED), and laser fabrication. Indeed, great progress has been made in optimizing the optical properties of the NPLs for the visible spectral range, which has already made the implementation of a number of effective devices on their basis possible. To date, state-of-the-art near-infrared (NIR)-emitting NPLs are significantly inferior to their visible-range counterparts, although it would be fair to say that they received significantly less research attention so far. In this study, we report a comprehensive analysis of steady-state and time-dependent photoluminescence (PL) properties of four monolayered (ML) PbSe NPLs. The PL measurements are performed in a temperature range of 78–300 K, and their results are compared to those obtained for CdSe NPLs and PbSe quantum dots (QDs). We show that multiple emissive states, both band-edge and trap-related, are responsible for the formation of the NPLs’ PL band. We demonstrate that the widening of the PL band is caused by the inhomogeneous broadening rather than homogeneous one, and analyze the possible contributions to PL broadening.

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Micro-scale Realization of Compliant Mechanisms: Manufacturing Processes and Constituent Materials—A Review

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-021-00606-y ◽

2021 ◽

Vol 34 (1) ◽

Author(s):

Minchang Wang ◽

Daohan Ge ◽

Liqiang Zhang ◽

Just L. Herder

Keyword(s):

3D Printing ◽

Compliant Mechanisms ◽

State Of The Art ◽

Manufacturing Processes ◽

Mems Devices ◽

Process Selection ◽

Micro Scale ◽

Great Progress ◽

Different Types ◽

Made In

AbstractCompliant micromechanisms (CMMs) acquire mobility from the deflection of elastic members and have been proven to be robust by millions of silicon MEMS devices. However, the limited deflection of silicon impedes the realization of more sophisticated CMMs, which often require larger deflections. Recently, some novel manufacturing processes have emerged but are not well known by the community. In this paper, the realization of CMMs is reviewed, aiming to provide help to mechanical designers to quickly find the proper realization method for their CMM designs. To this end, the literature surveyed was classified and statistically analyzed, and representative processes were summarized individually to reflect the state of the art of CMM manufacturing. Furthermore, the features of each process were collected into tables to facilitate the reference of readers, and the guidelines for process selection were discussed. The review results indicate that, even though the silicon process remains dominant, great progress has been made in the development of polymer-related and composite-related processes, such as micromolding, SU-8 process, laser ablation, 3D printing, and the CNT frameworking. These processes result in constituent materials with a lower Young’s modulus and larger maximum allowable strain than silicon, and therefore allow larger deflection. The geometrical capabilities (e.g., aspect ratio) of the realization methods should also be considered, because different types of CMMs have different requirements. We conclude that the SU-8 process, 3D printing, and carbon nanotube frameworking will play more important roles in the future owing to their excellent comprehensive capabilities.

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Single Crystal Hybrid Perovskite Optoelectronics: Progress and Perspectives

10.5772/intechopen.95046 ◽

2020 ◽

Author(s):

Feng LI

Keyword(s):

Single Crystals ◽

Carrier Transport ◽

Research Attention ◽

Light Emitting ◽

Practical Applications ◽

New Class ◽

Hybrid Perovskite ◽

Device Applications ◽

Perovskite Crystal ◽

Higher Carrier Mobility

Organic–inorganic hybrid perovskites, which combine the superior optical and electronic properties and solution-processed manufacturing, have emerged as a new class of revolutionary optoelectronic devices with the potential for various practical applications. Encouraged by the advantages of longer carrier diffusion length, higher carrier mobility and lower trap densities as compared to the polycrystalline counterparts’, increasing research attention has focused on preparation and optimization of perovskite crystal candidates, via using various facile growth techniques, for the development of a wide range of optoelectronic applications. This chapter presents a comprehensive review of recent advances in the field of optoelectronic technologies based on different forms of single crystals, including bulk crystals and thin ones, with emphasis placed on the optimization of crystals and the relationship among the charge-carrier transport, operation mechanism, device architecture, and device performance. First, we introduce the main methods used to prepare bulk and thin single crystals, and analyze several aspects of their properties. Thereafter, the applications of single crystals into solar cells, photodetectors, light-emitting diodes, and lasers, are discussed in depth. Finally, we summarize the challenges of perovskite single crystals and propose further improvements in the synthesis approaches and device applications.

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Porphycene Films Grown on Highly Oriented Pyrolytic Graphite: Unveiling Structure–Property Relationship through Combined Reflectance Anisotropy Spectroscopy and Atomic Force Microscopy Investigations

Proceedings ◽

10.3390/proceedings2020056044 ◽

2021 ◽

Vol 56 (1) ◽

pp. 44

Author(s):

Marta Penconi ◽

Lorenzo Ferraro ◽

Jacek Waluk ◽

Lamberto Duò ◽

Franco Ciccacci ◽

...

Keyword(s):

Atomic Force Microscopy ◽

Near Infrared ◽

Pyrolytic Graphite ◽

Visible Spectral Range ◽

Visible Range ◽

Structure Property ◽

Force Microscopy ◽

Reflectance Anisotropy ◽

Atomic Force ◽

Proper Design

Thin organic films are widely used in sensors, solar cells, and optical devices due to their intense absorption in the visible/near-infrared (IR) region. Shifting, quenching, or reshaping of some spectral features can be achieved by chemical functionalization of the molecules, whereas an anisotropic fingerprint due to preferential molecular alignment can be induced via a proper design and/or preparation of the substrate. Recently, we investigated the optical response of thin films of porphycene to acidification. With respect to the well-known and closely related tetraphenyl porphyrin, porphycene has the clear advantage of being optically active in the full visible range, and this makes visible by naked eye the immediate change of the film from brilliant blue-turquoise to green when exposed to HCl vapors. In this work, by exploiting a homemade reflectance anisotropy spectroscopy (RAS) apparatus, we explore possible optical anisotropies in the visible spectral range of porphycene films and relate them to the film morphology analyzed by atomic force microscopy (AFM).

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Short-time speaker verification with different speaking style utterances

PLoS ONE ◽

10.1371/journal.pone.0241809 ◽

2020 ◽

Vol 15 (11) ◽

pp. e0241809

Author(s):

Hongwei Mao ◽

Yan Shi ◽

Yue Liu ◽

Linqiang Wei ◽

Yijie Li ◽

...

Keyword(s):

State Of The Art ◽

Speaker Verification ◽

Feature Space ◽

Gaussian Mixture ◽

Normal Reading ◽

Great Progress ◽

Short Time ◽

Speaking Style ◽

Target Speaker ◽

Made In

In recent years, great progress has been made in the technical aspects of automatic speaker verification (ASV). However, the promotion of ASV technology is still a very challenging issue, because most technologies are still very sensitive to new, unknown and spoofing conditions. Most previous studies focused on extracting target speaker information from natural speech. This paper aims to design a new ASV corpus with multi-speaking styles and investigate the ASV robustness to these different speaking styles. We first release this corpus in the Zenodo website for public research, in which each speaker has several text-dependent and text-independent singing, humming and normal reading speech utterances. Then, we investigate the speaker discrimination of each speaking style in the feature space. Furthermore, the intra and inter-speaker variabilities in each different speaking style and cross-speaking styles are investigated in both text-dependent and text-independent ASV tasks. Conventional Gaussian Mixture Model (GMM), and the state-of-the-art x-vector are used to build ASV systems. Experimental results show that the voiceprint information in humming and singing speech are more distinguishable than that in normal reading speech for conventional ASV systems. Furthermore, we find that combing the three speaking styles can significantly improve the x-vector based ASV system, even when only limited gains are obtained by conventional GMM-based systems.

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III-nitride photonic cavities

Nanophotonics ◽

10.1515/nanoph-2019-0442 ◽

2020 ◽

Vol 9 (3) ◽

pp. 569-598 ◽

Cited By ~ 3

Author(s):

Raphaël Butté ◽

Nicolas Grandjean

Keyword(s):

Data Storage ◽

Near Infrared ◽

Optical Data Storage ◽

Blue Laser ◽

Optical Data ◽

Light Emitting ◽

Third Harmonic ◽

Refractive Index Material ◽

Photonic Cavities ◽

Made In

AbstractOwing to their wide direct bandgap tunability, III-nitride (III-N) compound semiconductors have been proven instrumental in the development of blue light-emitting diodes that led to the so-called solid-state lighting revolution and blue laser diodes that are used for optical data storage. Beyond such conventional optoelectronic devices, in this review, we explore the progress made in the past 15 years with this low refractive index material family for the realization of microdisks as well as 2D and 1D photonic crystal (PhC) membrane cavities. Critical aspects related to their design and fabrication are first highlighted. Then, the optical properties of passive PhC structures designed for near-infrared such as their quality factor and their mode volume are addressed. Additional challenges dealing with fabrication pertaining to structures designed for shorter wavelengths, namely the visible to ultraviolet spectral range, are also critically reviewed and analyzed. Various applications ranging from second and third harmonic generation to microlasers and nanolasers are then discussed. Finally, forthcoming challenges and novel fields of application of III-N photonic cavities are commented.

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Lanthanoid β-triketonates: a new class of highly efficient NIR emitters for bright NIR-OLEDs

Chemical Communications ◽

10.1039/c4cc04961f ◽

2014 ◽

Vol 50 (78) ◽

pp. 11580-11582 ◽

Cited By ~ 29

Author(s):

Brodie L. Reid ◽

Stefano Stagni ◽

Joanna M. Malicka ◽

Massimo Cocchi ◽

Garry S. Hanan ◽

...

Keyword(s):

Near Infrared ◽

Light Emitting ◽

Light Emitting Devices ◽

New Class ◽

Highly Efficient ◽

Organic Light ◽

Organic Light Emitting Devices

A bimetallic tetranuclear Yb3+/K+ complex obtained using β-triketonate ligands was found to be a suitable precursor for the fabrication of near-infrared Organic Light Emitting Devices that outclass any other previously reported lanthanoid-based near-infrared device.

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Pushing the Band Gap Envelope of Quasi-Type II Heterostructured Nanocrystals to Blue: ZnSe/ZnSe1-XTeX/ZnSe Spherical Quantum Wells

Energy Material Advances ◽

10.34133/2021/3245731 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Jun Hyuk Chang ◽

Hak June Lee ◽

Seunghyun Rhee ◽

Donghyo Hahm ◽

Byeong Guk Jeong ◽

...

Keyword(s):

Quantum Wells ◽

Near Infrared ◽

Lattice Mismatch ◽

Charge Carriers ◽

Emission Wavelength ◽

Type Ii ◽

Shell Layer ◽

Light Emitting ◽

New Class ◽

Wide Range

Quasi-type II heterostructured nanocrystals (NCs) have been of particular interest due to their great potential for controlling the interplay of charge carriers. However, the lack of material choices for quasi-type II NCs restricts the accessible emission wavelength from red to near-infrared (NIR), which hinders their use in light-emitting applications that demand a wide range of visible colors. Herein, we demonstrate a new class of quasi-type II nanoemitters formulated in ZnSe/ZnSe1-XTeX/ZnSe seed/spherical quantum well/shell heterostructures (SQWs) whose emission wavelength ranges from blue to orange. In a given geometry, ZnSe1-XTeX emissive layers grown between the ZnSe seed and the shell layer are strained to fit into the surrounding media, and thus, the lattice mismatch between ZnSe1-XTeX and ZnSe is effectively alleviated. In addition, composition of the ZnSe1-XTeX emissive layer and the dimension of the ZnSe shell layer are engineered to tailor the distribution and energy of electron and hole wave functions. Benefitting from the capabilities to tune the charge carriers on demand and to form defect-free heterojunctions, ZnSe/ZnSe1-XTeX/ZnSe/ZnS NCs show near-unity photoluminescence quantum yield (PL QY>90%) in a broad range of emission wavelengths (peak PL from 450 nm to 600 nm). Finally, we exemplify dichromatic white NC-based light-emitting diodes (NC-LEDs) employing the mixed layer of blue- and yellow-emitting ZnSe/ZnSe1-XTeX/ZnSe/ZnS SQW NCs.

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Electronic structure studies of conducting polymers by electron energy-loss spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100163265 ◽

1996 ◽

Vol 54 ◽

pp. 160-161

Author(s):

J. Fink

Keyword(s):

Electronic Structure ◽

Conducting Polymers ◽

Conjugated Polymers ◽

Electron Acceptors ◽

Electron Donors ◽

Light Emitting ◽

One Dimensional ◽

New Class ◽

Electrical Conductivities ◽

Electron Energy Loss

Conducting polymers comprises a new class of materials achieving electrical conductivities which rival those of the best metals. The parent compounds (conjugated polymers) are quasi-one-dimensional semiconductors. These polymers can be doped by electron acceptors or electron donors. The prototype of these materials is polyacetylene (PA). There are various other conjugated polymers such as polyparaphenylene, polyphenylenevinylene, polypoyrrole or polythiophene. The doped systems, i.e. the conducting polymers, have intersting potential technological applications such as replacement of conventional metals in electronic shielding and antistatic equipment, rechargable batteries, and flexible light emitting diodes.Although these systems have been investigated almost 20 years, the electronic structure of the doped metallic systems is not clear and even the reason for the gap in undoped semiconducting systems is under discussion.

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Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Near-Infrared Light

10.26434/chemrxiv.12588965 ◽

2020 ◽

Author(s):

Alex Stafford ◽

Dowon Ahn ◽

Emily Raulerson ◽

Kun-You Chung ◽

Kaihong Sun ◽

...

Keyword(s):

Near Infrared ◽

Transient Absorption ◽

Reaction Times ◽

Infrared Light ◽

Structure Property ◽

Light Emitting ◽

Structure Property Relationships ◽

Nir Light ◽

Light Intensities ◽

Emission Quenching

Driving rapid polymerizations with visible to near-infrared (NIR) light will enable nascent technologies in the emerging fields of bio- and composite-printing. However, current photopolymerization strategies are limited by long reaction times, high light intensities, and/or large catalyst loadings. Improving efficiency remains elusive without a comprehensive, mechanistic evaluation of photocatalysis to better understand how composition relates to polymerization metrics. With this objective in mind, a series of methine- and aza-bridged boron dipyrromethene (BODIPY) derivatives were synthesized and systematically characterized to elucidate key structure-property relationships that facilitate efficient photopolymerization driven by visible to NIR light. For both BODIPY scaffolds, halogenation was shown as a general method to increase polymerization rate, quantitatively characterized using a custom real-time infrared spectroscopy setup. Furthermore, a combination of steady-state emission quenching experiments, electronic structure calculations, and ultrafast transient absorption revealed that efficient intersystem crossing to the lowest excited triplet state upon halogenation was a key mechanistic step to achieving rapid photopolymerization reactions. Unprecedented polymerization rates were achieved with extremely low light intensities (< 1 mW/cm<sup>2</sup>) and catalyst loadings (< 50 μM), exemplified by reaction completion within 60 seconds of irradiation using green, red, and NIR light-emitting diodes.

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First-Principles Evaluation of the Potential of Borophene as a Monolayer Transparent Conductor

10.26434/chemrxiv.5439880 ◽

2017 ◽

Author(s):

Lyudmyla Adamska ◽

Sridhar Sadasivam ◽

Jonathan J. Foley ◽

Pierre Darancet ◽

Sahar Sharifzadeh

Keyword(s):

First Principles ◽

Density Functional ◽

State Of The Art ◽

Transparent Electrode ◽

Visible Range ◽

Two Dimensional ◽

Transparent Conductor ◽

Many Body ◽

Functional Theory ◽

Many Body Perturbation Theory

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron-phonon and electron-electron interactions, we show that the electrical conductivity is limited by electron-phonon interactions. Our results indicate that both structures are suitable as a transparent electrode.

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