Near-infrared Electroluminescence Research Articles

A light emitting device with TiO2:Er3+/ZnO heterostructure for enhanced near-infrared electroluminescence

Near-infrared (NIR) electroluminescence (EL) devices based on Er3+ ions doped TiO2 emitting layer have been fabricated by employing a facile sol–gel method. The effect of Er3+ ion doping concentration on the EL performance of TiO2:Er3+ thin film devices was investigated. Moreover, a novel device with the core of TiO2:1%Er3+/ZnO heterostructure was designed and fabricated. The EL performance of the device with optimized Er3+ ion doping concentration and improved structure was significantly improved. The NIR EL-enabling voltage of the improved device is as low as ∼5 V. The attenuated concentration quenching effect and the ZnO film as an electron blocking layer should contribute to the improved EL performance of the optimized device.

1530-nm electroluminescence from p-Ga2S3:Er/n+-Si heterojunctions induced by Zener tunneling

Silicon-based near-infrared (NIR) light sources with a simple structure are significant for circuit integration and fiber optic communications. Herein, 1530-nm electroluminescence (EL) from p-Ga2S3:Er/n+-Si junction light-emitting devices (LEDs) is reported with Er-doped Ga2S3 nanofilms as the photoemission layer and heavily doped n-type silicon as the substrate. The 1530-nm EL emission is attributed to the energy transfer between the Ga2S3 host and the Er3+ dopant, and it reaches its maximum at Er-doping concentration of 1 mol. % as the device works at −4.8 mA. The Er-related NIR EL occurs only at reverse voltages because the holes and electrons for recombination in Ga2S3:Er come from the Zener tunneling in the depletion region and the direct ITO injection, respectively. The realization of 1530-nm p-Ga2S3:Er/n+-Si LEDs offers opportunities for silicon-based integrated light sources.

Synergistic Enhancement of Near-Infrared Emission in CsPbCl3 Host via Co-Doping with Yb3+ and Nd3+ for Perovskite Light Emitting Diodes.

Perovskite nanocrystals (PeNCs) have emerged as a promising class of luminescent materials offering size and composition-tunable luminescence with high efficiency and color purity in the visible range. PeNCs doped with Yb3+ ions, known for their near-infrared (NIR) emission properties, have gained significant attention due to their potential applications. However, these materials still face challenges with weak NIR electroluminescence (EL) emission and low external quantum efficiency (EQE), primarily due to undesired resonance energy transfer (RET) occurring between the host and Yb3+ ions, which adversely affects their emission efficiency and device performance. Herein, we report the synergistic enhancement of NIR emission in a CsPbCl3 host through co-doping with Yb3+/Nd3+ ions for perovskite LEDs (PeLEDs). The co-doping of Yb3+/Nd3+ ions in a CsPbCl3 host resulted in enhanced NIR emission above 1000 nm, which is highly desirable for NIR optoelectronic applications. This cooperative energy transfer between Yb3+ and Nd3+ can enhance the overall efficiency of energy conversion. Furthermore, the PeLEDs incorporating the co-doped CsPbCl3/Yb3+/Nd3+ PeNCs as an emitting layer exhibited significantly enhanced NIR EL compared to the single doped PeLEDs. The optimized co-doped PeLEDs showed improved device performance, including increased EQE of 6.2% at 1035 nm wavelength and low turn-on voltage. Our findings highlight the potential of co-doping with Yb3+ and Nd3+ ions as a strategy for achieving synergistic enhancement of NIR emission in CsPbCl3 perovskite materials, which could pave the way for the development of highly efficient perovskite LEDs for NIR optoelectronic applications.

Near-infrared (λ ∼ 1.2 μm) intersubband electroluminescence in Si/CaF2 quantum cascade structures

A clear electroluminescence (EL) from a Si/CaF2 quantum cascade structure has been successfully observed. The structure was equipped with 15 periods of an active region comprising of Si/CaF2 multi-quantum wells and a waveguide grown on the silicon-on-insulator substrate by MBE-based technique. As a result of an optical spectrum measurement by Fourier transform IR spectroscopy, a clear EL spectrum with a peak at λ ∼ 1.2 μm was observed. The EL spectrum is reasonably explained by fitting it with a Lorentzian model that considers the thickness fluctuation of a single monoatomic layer of a Si quantum well, the intra- and inter-subband scattering times, and the carrier escape time. These results indicate that the EL was generated by intersubband transitions in the Si quantum well.

Achieving near-infrared electroluminescence around 780 nm based on butterfly-shaped dinuclear platinum(ii) complexes

An effective method to build high efficiency long wavelength emission NIR phosphors using butterfly-shaped dinuclear platinum complexes by cyanidation.

Near-Infrared Electroluminescence Based on Nd-Doped Ga2O3 Nanolaminates Fabricated by Atomic Layer Deposition for Optoelectronic Applications

Near-Infrared Electroluminescence Based on Nd-Doped Ga₂O₃ Nanolaminates Fabricated by Atomic Layer Deposition for Optoelectronic Applications

Trion emission from frozen p-n junctions in networks of electrolyte-gated (6,5) single-walled carbon nanotubes

We demonstrate exciton and charged exciton (trion) electroluminescence from frozen p-n junctions in networks of polymer-sorted, semiconducting (6,5) single-walled carbon nanotubes. Electrolyte-gating with an ionic liquid was employed to achieve injection and accumulation of high densities of holes and electrons in the nanotube network at low applied voltages. Static p-n junctions were formed by cooling the devices below the melting point of the ionic liquid while in the ambipolar regime. These frozen junctions showed diode-like rectification and enabled the investigation of electron-hole recombination and near-infrared electroluminescence under controlled conditions. The contributions of exciton and red-shifted trion emission to the electroluminescence spectra were influenced by the initial parameters of the p-n junction formation (balanced or unbalanced) and the applied lateral bias, but did not depend on temperature (30–200 K). The tilted potential profile along the fixed junction and consequently the number of excess carriers within the recombination zone were found to predominantly determine the emission intensity and observed trion to exciton ratio.

Electroluminescence from Silicon-Based Light-Emitting Devices with Erbium-Doped ZnO Films: Strong Enhancement Effect of Titanium Codoping.

We report on the visible and near-infrared electroluminescence (EL) from the light-emitting device (LED) based on the erbium (Er)-doped ZnO (ZnO:Er)/SiO2/n+-Si heterostructure, wherein an ∼10 nm thick SiO2 intermediate layer serves as the energy plateau for producing hot electrons, which come from n+-Si via the trap-assisted tunneling mechanism. These hot electrons excite the doped Er3+ ions by inelastic collision, enabling the Er-related EL from the aforementioned LED. More importantly, by means of codoping the appropriate content of titanium (Ti) into the ZnO:Er film, the aforementioned Er-related emissions can be significantly enhanced. The density functional theory calculations indicate that the Ti-codoping improves rather than degrades the symmetry of the crystal field around the optically active Er3+ ions, hence not increasing the intra-4f transition probabilities of Er3+ ions. However, it is found that Ti-codoping nearly eliminates the segregation of Er3+ ions near the ZnO/SiO2 interface. Moreover, Ti-codoping is derived to result in a number of Zn vacancies, which provide the sites for incorporating Er3+ ions in the ZnO matrix. For the above two reasons, the Ti-codoping promotes the incorporation of optically active Er3+ ions into the ZnO matrix, thus enhancing the EL from the aforementioned LED.

852 nm near-infrared emission from iridium (III) complex based on an enlarging rigid coordinated core of Tribenzo[a,c]phenazine

Near-infrared (NIR) luminescent materials based on transition metal complexes have made great progress in recent years. However, there are few reports on pure NIR-emitting iridium complexes with rigid coordinated core and their organic light-emitting devices with an emission peak more than 800 nm. Herein, we designed and synthesized a NIR-emitting iridium (III) complex based on an enlarging rigid coordinated core of tribenzo[a,c] phenazine (TPz), namely (tBuTPA-TPz)2Ir(acac), in which di(tert-butyl) triphenylamine (tBuTPA) is used as a peripheral shield and appended in TPz. The effect of the enlarging rigid coordinated core and peripheral shields on the emissive property was primarily studied. A significantly red-shifted photoluminescent emission peak from 710 nm to 860 nm was exhibited in this iridium complex by enlarging rigid coordinated core from dibenzo[a,c]phenazine to TPz in dichloromethane. Furthermore, a pure NIR electroluminescence peaked at 852 nm with a shoulder at 952 nm was observed in the (tBuTPA-TPz)2Ir(acac)-doped polymer light-emitting diodes. An increasing external quantum efficiency of 0.079% and radiant emittance of 879 mW Sr−1m−2 were obtained in the optimized devices. This study provides a feasible strategy to develop pure NIR-emitting iridium complexes with an emissive peak more than 800 nm by enlarging rigid coordinated core.

Interface engineering enhanced near-infrared electroluminescence in an n-ZnO microwire/p-GaAs heterojunction.

Interface engineering in the fabrication of low-dimensional optoelectronic devices has been highlighted in recent decades to enhance device characteristics such as reducing leakage current, optimizing charge transport, and modulating the energy-band structure. In this paper, we report a dielectric interface approach to realize one-dimensional (1D) wire near-infrared light-emitting devices with high brightness and enhanced emission efficiency. The light-emitting diode is composed of a zinc oxide microwire covered by a silver nanolayer (Ag@ZnO MW), magnesium oxide (MgO) buffer layer, and p-type gallium arsenide (GaAs) substrate. In the device structure, the insertion of a MgO dielectric layer in the n-ZnO MW/p-GaAs heterojunction can be used to modulate the device features, such as changing the charge transport properties, reducing the leakage current and engineering the band alignment. Furthermore, the cladding of the Ag nanolayer on the ZnO MW can optimize the junction interface quality, thus reducing the turn-on voltage and increasing the current injection and electroluminescence (EL) efficiency. The combination of MgO buffer layer and Ag nanolayer cladding can be utilized to achieve modulating the carrier recombination path, interfacial engineering of heterojunction with optimized band alignment and electronic structure in these carefully designed emission devices. Besides, the enhanced near-infrared EL and improved physical contact were also obtained. The study of current transport modulation and energy-band engineering proposes an original and efficient route for improving the device performances of 1D wire-type heterojunction light sources.

Tetradentate cyclometalated platinum complex enables high-performance near-infrared electroluminescence with excellent device stability

Due to the high decay rate of the non-radiative transition of long wavelengths, the molecular design of efficient and stable near-infrared (NIR) electroluminescent materials remains a big challenge. Herein, a new tetradentate cyclometalated platinum(II) complex with an N∧C∧C∧N coordinated framework has been developed and used as a dopant for NIR organic light-emitting diodes (OLEDs). The complex exhibited a short-lived (0.5–1.5 µs) metal-to-ligand charge transfer (MLCT) excited state in doped and neat films. The resulting NIR OLEDs (λEL = 730 nm) achieved maximum external quantum efficiency (EQEmax) of 5.2% and radiance of 74626 mW sr−1 m–2. Of note, the device exhibited excellent stability with operational lifetime of 119 h for LT90. This work demonstrated the great potential of tetradentate platinum(II) complexes in the field of NIR OLEDs.

Electroluminescence from light-emitting device with erbium-doped TiO2 film sputtered onp+-Si substrate: Enhancement effect of codoping zirconium

In our previous report, the erbium (Er)-related visible and near-infrared (NIR, ∼1.54 μm) electroluminescence (EL) from the light-emitting device (LED) with Er-doped TiO2 (TiO2:Er) film sputtered on the heavily boron-doped p-type silicon (p+-Si) substrate thus forming the so-called TiO2:Er/p+-Si heterostructure was realized. However, it is still a challenge to enhance the Er-related emissions from the above-structured LED. In this work, we have adopted the strategy of codoping zirconium (Zr) into TiO2 host to significantly enhance the Er-related visible and NIR EL from the TiO2:Er/p+-Si heterostructured LED. It is revealed that the oversize Zr4+ ions substantially substitute for Ti4+ ions in TiO2 lattice. Such substitution results in somewhat distorted crystal field of Er3+ ions incorporated into TiO2 host, which increases the intra-4f transition probabilities of Er3+ ions thus enhancing the characteristic visible and NIR emissions.

Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X.

We present a study of aggregate excited states formed by complexes of the type Pt(N^C^N)X, where N^C^N represents a tridentate cyclometallating ligand, and X = SCN or I. These materials display near-infrared (NIR) photoluminescence in film and electroluminescence in NIR OLEDs with λ max EL = 720-944 nm. We demonstrate that the use of X = SCN or I modulates aggregate formation compared to the parent complexes where X = Cl. While the identity of the monodentate ligand affects the energy of Pt-Pt excimers in solution in only a subtle way, it strongly influences aggregation in film. Detailed calculations on aggregates of different sizes support the experimental conclusions from steady-state and time-resolved luminescence studies at variable temperatures. The use of X = I appears to limit aggregation to the formation of dimers, while X = SCN promotes the formation of larger aggregates, such as tetramers and pentamers, leading in turn to NIR photo- and electroluminescence > 850 nm. A possible explanation for the contrasting influence of the monodentate ligands is the lesser steric hindrance associated with the SCN group compared to the bulkier I ligand. By exploiting the propensity of the SCN complexes to form extended aggregates, we have prepared an NIR-emitting OLED that shows very long wavelength electroluminescence, with λ max EL = 944 nm and a maximum EQE = 0.3 ± 0.1%. Such data appear to be unprecedented for a device relying on a Pt(ii) complex aggregate as the emitter.

Thermally activated delayed fluorescence exciplexes with phosphor components realizing deep-red to near-infrared electroluminescence

Compared with single-molecule TADF emitters, exciplexes can simplify the complicated molecule design and synthesis and have the superiority of conveniently realizing spectra with a bathochromic shift via mixing donor and acceptor components.

Near-infrared electroluminescence of AlGaN capped InGaN quantum dots formed by controlled growth on photoelectrochemical etched quantum dot templates

Near-infrared electroluminescence of InGaN quantum dots (QDs) formed by controlled growth on photoelectrochemical (PEC) etched QD templates is demonstrated. The QD template consists of PEC InGaN QDs with high density and controlled sizes, an AlGaN capping layer to protect the QDs, and a GaN barrier layer to planarize the surface. Scanning transmission electron microscopy (STEM) of Stranski–Krastanov (SK) growth on the QD template shows high-In-content InGaN QDs that align vertically to the PEC QDs due to localized strain. A high-Al-content Al 0.9 Ga 0.1 N capping layer prevents the collapse of the SK QDs due to intermixing or decomposition during higher temperature GaN growth as verified by STEM. Growth of low-temperature (830°C) p-type layers is used to complete the p-n junction and further ensure QD integrity. Finally, electroluminescence shows a significant wavelength shift (800 nm to 500 nm), caused by the SK QDs’ tall height, high In content, and strong polarization-induced electric fields.

Rigid Bridge-Confined Double-Decker Platinum(II) Complexes Towards High-Performance Red and Near-Infrared Electroluminescence.

A molecular design to high-performance red and near-infrared (NIR) organic light-emitting diodes (OLEDs) emitters remains demanding. Herein a series of dinuclear platinum(II) complexes featuring strong intramolecular Pt⋅⋅⋅Pt and π-π interactions has been developed by using N-deprotonated α-carboline as a bridging ligand. The complexes in doped thin films exhibit efficient red to NIR emission from short-lived (τ=0.9-2.1 μs) triplet metal-metal-to-ligand charge transfer (3 MMLCT) excited states. Red OLEDs demonstrate high maximum external quantum efficiencies (EQEs) of up to 23.3 % among the best PtII -complex-doped devices. The maximum EQE of 15.0 % and radiance of 285 W sr-1 m-2 for NIR OLEDs (λEL =725 nm) are unprecedented for devices based on discrete molecular emitters. Both red and NIR devices show very small efficiency roll-off at high brightness. Appealing operational lifetimes have also been revealed for the devices. This work sheds light on the potential of intramolecular metallophilicity for long-wavelength molecular emitters and electroluminescence.

Electroluminescence from the light-emitting devices with erbium-doped SrTiO3 films on oxidized silicon substrate

We report on the visible and near-infrared (NIR) electroluminescence (EL) from the light-emitting devices (LEDs) with erbium-doped SrTiO3 (SrTiO3:Er) films on oxidized silicon substrate, namely, with the structure of SrTiO3:Er/SiO2/Si in abbreviation. It is found that the 900 °C-annealed SrTiO3:Er films are most desirable for the SrTiO3:Er/SiO2/Si structured LEDs. In the EL-enabling voltage range, the electron transportation through the SiO2 layer of SrTiO3:Er/SiO2/Si structured LED is revealed to be compliant with the trap-assisted tunneling (TAT) mechanism. Based on the energy band diagram of the SrTiO3:Er/SiO2/Si structured LED under the EL-enabling forward bias where the negative voltage is connected with Si substrate, it is believed that a number of conduction electrons in Si can tunnel into the conduction band of SiO2 layer via the aforementioned TAT mechanism and then jump down to the conduction band of SrTiO3 host. Because the conduction band offset of SiO2 and SrTiO3 host is larger than 3 eV, the conduction electrons reaching the SrTiO3 host gain considerably high energies so that they become the so-called hot electrons. The Er3+ ions incorporated into the SrTiO3 host are impact-excited by the hot electrons, ultimately emanating the characteristic visible and NIR light.

Room temperature near-infrared electroluminescence of Si/CaF2 quantum cascade laser structures grown on an SOI substrate

Room temperature near-infrared electroluminescence (EL) from Si/CaF2 quantum cascade laser structures has been demonstrated. The structure was equipped with 25 periods of the active region comprised of Si/CaF2 multi quantum-wells and single-mode waveguide grown by molecular beam epitaxy-based technique on the silicon-on-insulator (SOI) substrate. EL spectra with multiple peaks around the near-infrared region were obtained at room temperature and the EL intensity response with injection current clearly confirmed the EL emission was originated from the current injection. Moreover, it was found that EL peak shift by changing applied bias was reasonably explained by energy shift due to the electric field applied to the Si quantum-well of the active region.

An Electron-Accepting aza-BODIPY-Based Donor-Acceptor-Donor Architecture for Bright NIR Emission.

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor-acceptor-donor (D-A-D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D-A-D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104 m-1 cm-1 , whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D-A-D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 μJ cm-2 , indicating the high potential for NIR optoelectronic applications.

Electroluminescence from 4-nitroaryl organic color centers in semiconducting single-wall carbon nanotubes

Organic color-centers (OCCs) on single-wall carbon nanotubes are quantum defects that demonstrate intriguing near-infrared emission properties with potential for bioimaging, chemical sensing, and quantum communication. Many of these applications will require electrical pumping rather than optical excitation to deterministically access the near-infrared emission properties of OCCs, though this has yet to be achieved. In this work, we report experimental observation of near-infrared electroluminescence from 4-nitroaryl OCCs intentionally introduced on (6,5)-single-wall carbon nanotubes that are aligned across a pair of gold electrodes. Spatially correlated photoluminescence and electroluminescence spectroscopy reveal direct evidence of the localized electroluminescence from the OCCs on the semiconducting nanotube hosts. The electroluminescence intensity displays an exponential dependence on the source–drain current, suggesting that impact excitation by unipolar carriers at the quantum defects is the origin of the observed emission. These electroluminescent quantum defects may pave the way to enable on-chip integration for potential applications of OCCs in display, sensor, and spin-based devices, as well as other quantum technologies.