Wavelength-selective Enhancement Research Articles

Spectrally selective modification in the emission lifetimes of nitrogen-vacancy centers in nanodiamonds

The nitrogen-vacancy (NV) center is one of the most prominent candidates for quantum technologies, and its efficient utilization requires control over its spontaneous emission rate. Here, we report the wavelength-selective enhancement and suppression of NV center emission lifetime at room temperature by modifying the local density of optical states (LDOS) around them. The results are explained using the Barnett–Loudon sum rule and also supported by the LDOS calculations. Two complementary measurement geometries are employed to study the direction-dependent emission behavior from the nanodiamonds decorated on the top of photonic crystals. The lifetime distributions are compared with a proper reference sample using the Kolmogorov–Smirnov test to verify the distinct nature of lifetime distributions. The wavelength-selective enhancement or suppression of emission rates would be useful for NV center-based high-resolution imaging and effective readout of its charge states.

Wavelength-selective enhancement of terahertz absorption of metallic grating/GaAs-based hybrid photoconductive detector

Terahertz (THz) technology has attracted significant research attention because it can be used for a host of applications, such as astronomical observations, security checks, material optimization, and biomedical treatment. In this work, we fabricate an extrinsic n-type GaAs photoconductive detector whose peak photoelectric response is demonstrated to be at about 255 μm. To improve device performance in a long-wave (>350 μm) domain and overcome the epitaxial-growth bottleneck, we designed hybrid structural GaAs-based photoconductive detectors on the surface of which we add subwavelength one-dimensional metallic gratings (i.e., with grating periods that range from 100 to 125 μm) and investigated the wavelength-selective enhancement of their absorption in the THz regime by using a finite-different time-domain simulation. The simulation results indicate that selective enhancement of antireflection and absorption occurs in the reflection and absorption spectra so that the peak wavelength of photoelectric response can be extended to over 400 μm and the thickness of absorption layer can be reduced to 50 μm. The electric-field intensity of the incident THz wave can be significantly enhanced near the interface between the metal gates and the absorption layer. This work can thus provide a potential scheme to fabricate high-performance THz detectors for numerous applications.

A Dual-Band Multilayer InSe Self-Powered Photodetector with High Performance Induced by Surface Plasmon Resonance and Asymmetric Schottky Junction.

A dual-band self-powered photodetector (SPPD) with high sensitivity is realized by a facile combination of InSe Schottky diode and Au plasmonic nanoparticle (NP) arrays. Comparing with pristine InSe devices, InSe/Au photodetectors possess an additional capability of photodetection in visible to near-infrared (NIR) region. This intriguing phenomenon is attributed to the wavelength selective enhancement of pristine responsivities by hybridized quadrupole plasmons resonance of Au NPs. It is worth pointing out that the maximum of enhancement ratio in responsivity reaches up to ∼1200% at a wavelength of 685 nm. In addition, owing to a large Schottky barrier difference formed between active layer and two asymmetric electrodes, the responsivities of dual-band InSe/Au photodetector could reach up to 369 and 244 mA/W at the wavelength of 365 and 685 nm under zero bias voltage, respectively. This work would provide an additional opportunity for developing multifunctional photodetectors with high performance based on two-dimensional materials, upgrading their capacity of photodetection in a complex environment.

Tunable broadband wavelength-selective enhancement of responsivity in ordered Au-nanorod array-modified PbS photodetectors

A PbS-based photodetector integrated with ordered Au-nanorod arrays exhibited high wavelength-selective enhancement in the visible and infrared region.

Wavelength-selective enhancement of photo-responsivity in metal-gated multi-layer MoS2 phototransistors

The responsivities of MoS2 based photodetectors or phototransistors have been improved by integrating additional layers or implementing a hetero-structure. Despite complicated processes, these methods only improve the overall responsivity and are not capable of wavelength selective enhancement. This study reports the wavelength-selective enhancement of photo-responsivity in a multi-layer MoS2 phototransistor by employing a reflective Al metal gate. We have observed that the photo-responsivities are enhanced at a wavelength of ∼500 nm (FWHM = 140 nm) in the Al metal-gated multi-layer MoS2 phototransistors. The finite difference time domain method also confirmed that the wavelength for enhanced responsivity can be adjusted according to the thicknesses of the MoS2 and gate insulating layer. Using this effect, the Al metal-gated multi-layer MoS2 phototransistors can be tuned for specific applications.

Aluminum ultraviolet–visible plasmonic arrays for broadband and wavelength-selective enhancements of quantum dot emission

Enhancement of spontaneous emission can be achieved by the interaction between quantum emitters and the free electrons on metal surfaces, which creates additional energy relaxation channels through plasmon excitations. It can also be realized by extra near-field excitation of quantum emitters through surface plasmons created by absorption of far-field illumination. By using aluminum dimple arrays with their surface plasmon resonances (SPRs) tunable to span from the visible to UV regions, we demonstrate the control of the quantum dot (QD)-SPR coupling routes to realize either wavelength-selective enhancement of QD emission or broadband enhancement of multicolor QDs. The cost effective Al plasmonic structures enable enhancement of light emission and excitation at tailorable wavelengths and could advance the performance and design flexibility of light-emitting devices and photovoltaic technologies.

Highly Wavelength-Selective Enhancement of Responsivity in Ag Nanoparticle-Modified ZnO UV Photodetector.

We proposed and demonstrated Ag nanoparticles (NPs)-decorated ZnO photodetectors for UV light sensing. After decoration of their surface with random Ag NPs, the dark current density of ZnO UV photodetectors decreases obviously. Moreover, the device exhibits an obvious increase in peak responsivity at around 380 nm, which can be attributed to the narrow-band quadrupole plasmon resonance of Ag NPs in the UV range. Meanwhile, the responsivity at the other wavelengths decreases a lot. As a result, the response peak becomes more significant, and the response of the devices presents an excellent wavelength selectivity after covering with Ag NPs. The detailed mechanism for this phenomenon was explained. We believe that our findings would open a way to harness the high-order plasmon modes in the field of UV optoelectronic devices.

Surface Plasmon-Enhanced Optical Properties of Composite Materials Containing Metal Nanoparticles: Birefringence and Laser Oscillation

We report on two types of optical properties enhanced by surface plasmons of metal nanoparticles. One of them is wavelength-selective enhancement of birefringence in ZnO thin films with anisotropic microstructure in which Ag nanoparticles are dispersed. The other is random laser oscillation and amplified spontaneous emission in Au core-SiO2 shell nanoparticles combined with rhodamine 6G. The mechanism of the phenomena is discussed.

Enhancement of optical birefringence in tellurite glasses containing silver nanoparticles induced via thermal poling

Wavelength-selective enhancement of optical birefringence has been observed in a tellurite glass containing silver nanoparticles (Ag NPs) induced via thermal poling. The birefringence appears as an optical rotation of linearly polarized light; a large optical rotation is observed at around the wavelength of localized surface plasmon resonance (LSPR) of Ag NPs. The optic axis is oriented along the electric field applied during the thermal poling, suggesting that birefringence induced in the glass matrix through the thermal poling is drastically enhanced by the NPs at around the LSPR. Because of the birefringence of the matrix, the wavelength of LSPR shifts depending on the polarization state of the incident light, which in turn induces the polarization dependence of the real part of the refractive index via the Kramers–Kronig relation.

Wavelength-selective enhancement of the intensity of visible photoluminescence in hydrogen-ion-implanted silicon-on-insulator structures annealed under high pressure

Characteristic features of the visible photoluminescence (PL) spectra were studied in silicon-on-insulator (SOI) wafers following high-dose (3×1017cm−2) ion implantation of hydrogen and annealing at high hydrostatic pressures. The PL behavior of the SOI material was compared with that of hydrogen-implanted bulk Si. Annealing at a pressure above 6kbars produced a wavelength-selective increase (∼37 times) in the intensity of the visible PL from the implanted SOI structures. The results are explained in terms of the effect of an optical resonant cavity formed between the air/SOI and the Si∕SiO2 interfaces as a result of the high-pressure annealing.

Spectral tuning of plasmon-enhanced silicon quantum dot luminescence

In the presence of nanoscale silver island arrays, silicon quantum dots exhibit up to sevenfold luminescence enhancements at emission frequencies that correspond to the collective dipole plasmon resonance frequency of the Ag island array. Using electron-beam lithography to alter the pitch and particle diameter, this wavelength-selective enhancement can be varied as the metal array resonance wavelength is tuned from 600to900nm. The luminescence intensity enhancement upon coupling is attributed to an increase in the radiative decay rate of the silicon quantum dots.

Wavelength-selective absorption enhancement in thin-film solar cells

We present the general principle of wavelength-selective enhancement of absorption in thin-film solar cells by a periodic grating substrate. By exact numerical calculation we demonstrate that substantial short-circuit current gains are realizable in thin-film amorphous silicon (a-SiHx) solar cells. In particular, for a 0.5-μm-thick a-SiHx solar cell, optimal texturing of an Ag substrate to form a one-dimensional reflective grating can yield a 2-mA/cm2 enhancement over the flat substrate case. For a two-dimensional cross-hatched grating substrate the enhancement is estimated to be 3.5–4 mA/cm2.