Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator ...arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI
and MAPbBr
and two-dimensional (2D) (EDBE)PbCl
hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl
significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications.
High-index dielectric materials are in great demand for nanophotonic devices and applications, from ultrathin optical elements to metal-free sub-diffraction light confinement and waveguiding. Here we ...show that chalcogenide topological insulators are particularly apt candidates for dielectric nanophotonics architectures in the infrared spectral range, by reporting metamaterial resonances in chalcogenide crystals sustained well inside the mid-infrared, choosing Bi
Te
as case study within this family of materials. Strong resonant modulation of the incident electromagnetic field is achieved thanks to the exceptionally high refractive index ranging between 7 and 8 throughout the 2-10 μm region. Analysis of the complex mode structure in the metamaterial allude to the excitation of circular surface currents which could open pathways for enhanced light-matter interaction and low-loss plasmonic configurations by coupling to the spin-polarized topological surface carriers, thereby providing new opportunities to combine dielectric, plasmonic and magnetic metamaterials in a single platform.
We review principles and trends in the use of
semiconductor nanowires as gain media for stimulated
emission and lasing. Semiconductor nanowires have recently
been widely studied for use in integrated ...optoelectronic
devices, such as light-emitting diodes (LEDs),
solar cells, and transistors. Intensive research has also
been conducted in the use of nanowires for subwavelength
laser systems that take advantage of their quasione-
dimensional (1D) nature, flexibility in material choice
and combination, and intrinsic optoelectronic properties.
First, we provide an overview on using quasi-1D nanowire
systems to realize subwavelength lasers with efficient, directional,
and low-threshold emission. We then describe
the state of the art for nanowire lasers in terms of materials,
geometry, andwavelength tunability.Next,we present
the basics of lasing in semiconductor nanowires, define
the key parameters for stimulated emission, and introduce
the properties of nanowires. We then review advanced
nanowire laser designs from the literature. Finally,
we present interesting perspectives for low-threshold
nanoscale light sources and optical interconnects. We intend
to illustrate the potential of nanolasers inmany applications,
such as nanophotonic devices that integrate electronics
and photonics for next-generation optoelectronic
devices. For instance, these building blocks for nanoscale
photonics can be used for data storage and biomedical
applications when coupled to on-chip characterization
tools. These nanoscale monochromatic laser light sources
promise breakthroughs in nanophotonics, as they can operate
at room temperature, can potentially be electrically
driven, and can yield a better understanding of intrinsic
nanomaterial properties and surface-state effects in lowdimensional
semiconductor systems.
The photoconductive properties of a novel low‐bandgap conjugated polymer, poly2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta2,1‐b;3,4‐b′dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole), PCPDTBT, with an ...optical energy gap of Eg ∼ 1.5 eV, have been studied. The results of photoluminescence and photoconductivity measurements indicate efficient electron transfer from PCPDTBT to PCBM (6,6‐phenyl‐C61 butyric acid methyl ester, a fullerene derivative), where PCPDTBT acts as the electron donor and PCBM as the electron acceptor. Electron‐transfer facilitates charge separation and results in prolonged carrier lifetime, as observed by fast (t > 100 ps) transient photoconductivity measurements. The photoresponsivities of PCPDTBT and PCPDTBT:PCBM are comparable to those of poly(3‐hexylthiophene), P3HT, and P3HT:PCBM, respectively. Moreover, the spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the infrared, to 900 nm, than that of P3HT. The potential of PCPDTBT as a material for high‐efficiency polymer solar cells is discussed.
The photoconductive properties of a low‐bandgap conjugated polymer, PCPDTBT (see figure), are studied. Photoresponsivities of PCPDTBT and PCPDTBT:fullerene‐derivative (PCBM) blends are comparable to those of poly(3‐hexylthiophene), P3HT, and P3HT:PCBM. The spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the IR than that of P3HT, improving solar‐light harvesting and offering potential for use in solar cells.
ZnO nanowire (NW) visible-blind UV photodetectors with internal photoconductive gain as high as G ∼ 108 have been fabricated and characterized. The photoconduction mechanism in these devices has been ...elucidated by means of time-resolved measurements spanning a wide temporal domain, from 10-9 to 102 s, revealing the coexistence of fast (τ ∼ 20 ns) and slow (τ ∼ 10 s) components of the carrier relaxation dynamics. The extremely high photoconductive gain is attributed to the presence of oxygen-related hole-trap states at the NW surface, which prevents charge-carrier recombination and prolongs the photocarrier lifetime, as evidenced by the sensitivity of the photocurrrent to ambient conditions. Surprisingly, this mechanism appears to be effective even at the shortest time scale investigated of t < 1 ns. Despite the slow relaxation time, the extremely high internal gain of ZnO NW photodetectors results in gain-bandwidth products (GB) higher than ∼10 GHz. The high gain and low power consumption of NW photodetectors promise a new generation of phototransistors for applications such as sensing, imaging, and intrachip optical interconnects.
Photoinduced electron transfer in a small band gap bulk heterojunction material (see figure) is studied by ultrafast spectroscopic methods. In this composite, the photo excitation initiates ultrafast ...electron transfer from the polymer to the fullerene, as in most bulk heterojunction materials. From analysis of the carrier recombination dynamics, we infer the existence of an intermediate charge transferred state from which long‐lived mobile positive and negative carriers are generated.
A refractive index interface is dynamically induced in a bulk photorefractive material by biasing two adjacent regions with different electric fields, thus building up an electric wall. Effects of ...this interface on reflection, refraction and breathing of bright photorefractive solitons and their associated waveguides are numerically and experimentally studied as a function of the induced purely electric field gradient. Reflection and refraction efficiency depends on the amplitude and sign of the applied voltages that affect both the self-confining beam and the signals propagating inside the waveguide. Experimental tests are performed in nominally undoped lithium niobate samples.
Ethology has shown that animal groups or colonies can perform complex calculation distributing simple decision-making processes to the group members. For example ant colonies can optimize the ...trajectories towards the food by performing both a reinforcement (or a cancellation) of the pheromone traces and a switch from one path to another with stronger pheromone. Such ant's processes can be implemented in a photonic hardware to reproduce stigmergic signal processing. We present innovative, completely integrated X-junctions realized using solitonic waveguides which can provide both ant's decision-making processes. The proposed X-junctions can switch from symmetric (50/50) to asymmetric behaviors (80/20) using optical feedbacks, vanishing unused output channels or reinforcing the used ones.
One of the most notable manifestations of electronic properties of topological insulators is the dependence of the photocurrent direction on the helicity of circularly polarized optical excitation. ...The helicity-dependent photocurrents, underpinned by spin-momentum locking of surface Dirac electrons, are weak and easily overshadowed by bulk contributions. Here, we show that the chiral response can be enhanced by nanostructuring. The tight confinement of electromagnetic fields in the resonant nanostructure enhances the photoexcitation of spin-polarized surface states of topological insulator Bi
Sb
Te
Se
, leading to an 11-fold increase of the circular photogalvanic effect and a previously unobserved photocurrent dichroism (ρ
= 0.87) at room temperature. The control of spin transport in topological materials by structural design is a previously unrecognized ability of metamaterials that bridges the gap between nanophotonics and spin electronics, providing opportunities for developing polarization-sensitive photodetectors.
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