Optical properties of the rat head tissues (brain cortex, cranial bone and scalp skin) are assessed, aiming at transcranial light applications such as optical imaging and phototherapy. The spectral measurements are carried out over the wide spectral range of 350 to 2800 nm, involving visible, near-infrared (NIR) and short-wave infrared (SWIR) regions. Four tissue transparency windows are considered: ~700 to 1000 nm (NIR-I), ~1000 to 1350 nm (NIR-II), ~1550 to 1870 nm (NIR-III or SWIR) and ~2100 to 2300 nm (SWIR-II). The values of attenuation coefficient and total attenuation length are determined for all windows and tissue types. The spectra indicate transmittance peaks in NIR, NIR-II and SWIR-II, with maximum tissue permeability for SWIR light. The use of SWIR-II window for the transcranial light applications is substantiated. Furthermore, absorbance of the head tissues is investigated in details, by defining and describing the characteristic absorption peaks in NIR-SWIR.

heterojunctions have been constructed and demonstrated for controlling optical, [1] electrical, [2] mechanical [3] and magnetic characteristics. [4] In particular, semiconductor heterojunctions as the core of light-emitting diodes (LEDs) have played vital roles in electric-driven lighting and display devices. The electric potential of a semiconductor heterojunction has a strong positive effect on charge carrier transport at the interface and can tune/ control the behaviors of light emitting. [5] The advances in lighting technology have greatly promoted the development of artificial intelligence, biotechnology and flexible optoelectronics. [6] At present, almost all LEDs are driven by external power supply through wire connecting electrodes. However, the high-efficiency heterojunction material driven by Newton force to achieve the stress light-emitting devices is still limited in the present research. Thus, the exploration of such a new type of light-emitting device without wires and electrodes not only supplies advanced heterojunction systems for light-emitting but also provides a prospective reference for the future multiapproach energy conversion with extended applications.As a special type of light source, mechanoluminescence (ML) materials are capable of generating photon emissions in response to mechanical stimuli. In comparison with LEDs based on electroluminescence (EL), ML provides sustainable light output by excitation of mechanical energy ubiquitously available in nature. During the past decade, ML materials have attracted widespread interests due to their promising applications in stress sensing, display, artificial skin, bioimaging, anti-counterfeiting, structure fatigue diagnosis, night surveillance and flexible optoelectronics. [7][8][9][10] However, the recent developments of highperformance ML materials are not as fast as other luminescence systems such as photoluminescence (PL)/EL, which is attributed to the lack of rational design of ML material systems guided by the in-depth theoretical exploration in the mechanism. ML materials known to date are typically homogenous structures, which offer limited space for optimizing the ML performance. Therefore, further improving the ML performance by exploiting heterostructures remains a challenge for present research. [11,12] In this work, we fabricate a class of ZnS/CaZnOS heterostructures, which flexibly tune the efficient and reproducible Actively collecting the mechanical energy by efficient conversion to other forms of energy such as light opens a new possibility of energy-saving, which is of pivotal significance for supplying potential solutions for the present energy crisis. Such energy conversion has shown promising applications in modern sensors, actuators, and energy harvesting. However, the implementation of such technologies is being hindered because most luminescent materials show weak and non-recoverable emissions under mechanical excitation. Herein, a new class of heterojunctioned ZnS/CaZnOS piezophotonic systems is presented, which disp...

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Deep levels in metamorphic InAs/In x Ga 1−x As quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/ GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x=0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.

Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies. It was shown that the use of the InGaAs buffer spectrally shifted the maximum of the QD PL band to 1.3 μm (telecommunication range) without a decrease in the yield. Photosensitivity for the metamorphic QDs was found to be higher than that in GaAs buffer while the photoresponses for both metamorphic and pseudomorphic buffer layers were similar. The mechanisms of PV and PC were discussed for both structures. The dissimilarities in properties of the studied structures are explained in terms of the different design. A critical influence of the defects on the photoelectrical properties of both structures was observed in the spectral range from 0.68 to 1.0 eV for contact configuration (ii), i.e., in the case of electrically active GaAs wafer. No effect of such defects on the photoelectric spectra was found for configuration (i), when the structures were contacted to the top and bottom buffers; only a 0.83 eV feature was observed in the photocurrent spectrum of pseudomorphic structure and interpreted to be related to defects close to InAs/GaAs QDs.