Midwavelength Infrared Colloidal Nanowire Laser

Abstract

Realizing bright colloidal infrared emitters in the midwavelength infrared (or mid-IR), which can be used for low-power IR light-emitting diodes (LEDs), sensors, and deep-tissue imaging, has been a challenge for the last few decades. Here, we present colloidal tellurium nanowires with strong emission intensity at room temperature and even lasing at 3.6 μm (ω) under cryotemperature. Furthermore, the second-harmonic field at 1.8 μm (2ω) and the third-harmonic field at 1.2 μm (3ω) are successfully generated thanks to the intrinsic property of the tellurium nanowire. These unique optical features have never been reported for colloidal tellurium nanocrystals. With the colloidal midwavelength infrared (MWIR) Te nanowire laser, we demonstrate its potential in biomedical applications. MWIR lasing has been clearly observed from nanowires embedded in a human neuroblastoma cell, which could further realize deep-tissue imaging and thermotherapy in the near future.

Unveiling Ultrafast Carrier Dynamics of Tellurium Microcrystals by Two-Color Asynchronous Sampling Infrared Transient Absorption Spectroscopy

“…They found that the time constant of the latter rising component depends on the power (excitation intensity) of the pump beam. They suggested that the τ 1 and τ 2 components originate from the accumulation of population in the conduction band and the stimulated emission, respectively . Similarly, the ultrafast τ 1 (∼1 ps) component in our experimental data (Figure a) could be assigned to the rapid increase or accumulation of the electronic population in the conduction band.…”

“…Previous studies on the charge carrier dynamics of Te have been carried out with steady-state spectroscopy, − transient photoconductivity, transient reflectivity, − and transient microwave conductivity at various temperatures. Recently, several studies of electronic relaxation dynamics of Te at room temperature have been reported. ,− After photoexcitation, charge carriers (electrons and holes) are generated in the conduction and valence bands, respectively, and subsequently recombine to return to the initial ground state through different relaxation channels, such as direct recombination of the free and bound exciton, recombination of trapped electron and hole, and electronic relaxation to midgap trap state or defect states . As described in ref , the radiative recombination of charges in Te crystals is the dominant process (98%) at room temperature, with the remaining charges either undergoing the Shockley–Read–Hall recombination or transitioning to deeply trapped states.…”

“…Since such MIR-transition materials are interesting for optoelectronic applications, exciton recombination processes in the intraband and interband transitions of colloidal quantum dots and chalcogenide semiconductors with a narrow bandgap have been studied extensively. Among various MIR-active materials, tellurium (Te) has attracted particular attention because its bandgap energy was found to be around 0.32 eV, and it shows interesting properties, such as optical nonlinearity, − thermoelectricity, − photoconductivity, and piezo-electricity. , In addition, it has been demonstrated that Te microcrystals and nanowires can exhibit a strong MIR emission and even a lasing property. , However, a detailed study of the carrier dynamics in photoexcited Te microcrystals has yet to be reported.…”

Enhanced Solar‐Photo(Electro)catalysis of Microwave‐Hydrothermal Synthesized BiVO4, ms‐BiVO4/Reduced Graphene Oxide/Ag3PO4 Nanohybrid: Crystalline Phase‐Dependent Interfacial Charge Carrier Dynamics

“…[ 54–56 ] The formation of built‐in electric field by the transfer of charges from the semiconductor to the electrolyte interface creates a space‐charge layer, which efficiently separates the charge carriers. [ 57 ] The amount of charge transferred influences the electric field potential and the width of the space‐charge layer ( W ), which can be quantitatively measured using Equation (11). …”

“…The decreased space‐charge‐width ( W ) further implies that the Ag 3 PO 4 contributes towards charge separation while RGO assists in charge transportation, of surface carriers, together enhancing light absorption. [ 57 ] Taking the condition of minimum recombination in the space‐charge layer, the absorption coefficient ( α ) can be estimated by Equation (12)…”