Broadband NIR Research Articles

High efficiency luminescence from PbS quantum dots embedded glasses for near-infrared light emitting diodes

PbS quantum dots (QDs) embedded glasses have been investigated for decades, but their applications are limited to the color filters and saturable absorbers for laser pulse generation so far, mainly due to the low photoluminescence quantum yield (PL QY) induced by the surface defects. Here, by increasing the sulfur to lead molar ratio in the glasses, surface defects of PbS QDs can be partially passivated and the fast trapping of charge carriers is reduced. As a result, PL QY of PbS QDs embedded glasses increases with larger sulfur to lead molar ratio, and PL QY as high as 46.9% is achieved. The improved PL QY along with good thermal and photo-stability makes the PbS QDs embedded glasses promising for near-infrared light generation. By integrating the PbS QDs embedded glass slab with light emitting diode (LED) chip, NIR LEDs with external quantum efficiency of 4.47% (@ ∼1.4 μm) with full width at half maximum larger than 140 nm are realized. Using this approach, it is also versatile to fabricate high-performance and broadband NIR LEDs with PbS QDs embedded glasses as light converters.

Heavily Er2O3 doped TeO2 based glass-ceramics with large grain size and high transparency for broadband ∼1.55 and efficient ∼3.5 μm fluorescence

In this work, heavily Er2O3 doped TeO2 glass was employed for the fabrication of transparent glass ceramics with broadband NIR and efficient MIR emissions. The simple composition of the glass was to minimize the refractive index difference between the glass and precipitated crystal to obtain high transmittance glass ceramics with large grain size. The heavily doping concentration was favor to obtain broadband NIR and efficient MIR emissions. The influence of the temperature and duration of the heat treatment on the size of the precipitated Er2Te5O13 crystal was investigated. The transmittance of the glass-ceramics was higher than 80%/mm when the size of the precipitated crystal increased up to 6.82 μm. The XRD patterns of the surface and bulk glass-ceramic demonstrated the crystallization was surface indued crystallization. The NIR and MIR fluorescence properties were discussed.

Structural induced tunable NIR luminescence of (Y,Lu)3(Mg,Al)2(Al,Si)3O12: Cr3+ phosphors

Garnet-type (Y,Lu)3(Mg,Al)2(Al,Si)3O12: Cr3+ compounds were successfully synthesized by high-temperature solid-phase reaction method. Starting from Y3Al5O12, Mg2+-Si4+ pairs were used to replace Al(1)3+-Al(2)3+ in octahedral and tetrahedral site, respectively, and then Y3+ was substituted by Lu3+ in dodecahedra of Y3(MgAl)(Al2Si)O12: Cr3+. Narrow-band to broad-band tunable NIR luminescence was achieved by ionic substitution at different polyhedral positions. The peak emission wavelength can be tuned from 705 to 770 nm, and the full width at half maximum (FWHM) can be extended from 27 to 160 nm. The results indicate that Y3(MgAl)(Al2Si)O12: 0.06Cr3+ is a promising NIR material. Under the excitation of blue light, the peak wavelength of Y3(MgAl)(Al2Si)O12: 0.06Cr3+ is about 760 nm with a FWHM of ∼160 nm and an IQE of 64%. Furthermore, the luminescence intensity at 150 °C remains at 84.2% of that at room temperature. Additionally, packaging performance was studied to evaluate its practical application in LEDs.

Realizing Broadband NIR Photodetection and Ultrahigh Responsivity with Ternary Blend Organic Photodetector.

With the advancement of portable optoelectronics, organic semiconductors have been attracting attention for their use in the sensing of white and near-infrared light. Ideally, an organic photodiode (OPD) should simultaneously display high responsivity and a high response frequency. In this study we used a ternary blend strategy to prepare PM6: BTP-eC9: PCBM–based OPDs with a broad bandwidth (350–950 nm), ultrahigh responsivity, and a high response frequency. We monitored the dark currents of the OPDs prepared at various PC71BM blend ratios and evaluated their blend film morphologies using optical microscopy, atomic force microscopy, and grazing-incidence wide-angle X-ray scattering. Optimization of the morphology and energy level alignment of the blend films resulted in the OPD prepared with a PM6:BTP-eC9:PC71BM ternary blend weight ratio of 1:1.2:0.5 displaying an extremely low dark current (3.27 × 10−9 A cm−2) under reverse bias at −1 V, with an ultrahigh cut-off frequency (610 kHz, at 530 nm), high responsivity (0.59 A W–1, at −1.5 V), and high detectivity (1.10 × 1013 Jones, under a reverse bias of −1 V at 860 nm). Furthermore, the rise and fall times of this OPD were rapid (114 and 110 ns), respectively.

Broadband near-infrared emission in the NaInP2O7:Cr3+ phosphor for light-emitting-diode applications

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have attracted more and more attention for the applications in spectroscopic technology, promoting the demand of searching broad-band near-infrared phosphors. In this work, Cr3+-doped NaInP2O7 phosphors with broadband NIR emission were synthesized via conventional high-temperature solid-state reaction method. The crystal, photoluminescence, and the performance of fabricated device were investigated in detail. The photoluminescence demonstrates this material exhibits an intense absorption in blue light region, matching well with the blue LED chip; while the emission spectra peaking at 870 nm covers 650–1150 nm region with a full width at half maximum (FWHM) of about 150 nm. The quantum yield (QY) and absorption efficiency was determined to be 28.2% and 49.82%, respectively, under 460 nm blue light excitation. Finally, a NIR pc-LED device was fabricated by using a commercial 455 nm blue LED combined with as-prepared NaInP2O7:Cr3+ phosphor, which has an output power of 9.08 mW and photoelectronic conversion efficiency of 2.98% under a driving current of 100 mA, indicating that the as-prepared phosphors might have a good potential for application in NIR pc-LEDs.

Physical properties and luminescence of highly stable erbium-doped antimony glasses for NIR broadband amplification

Glasses with compositions (0.8-x)Sb2O3−0.2Na2O-(x)WO3-(0.0025) Er2O3, (0 ≤ x ≤ 0.4 mol) has been synthesized by the melt-quenching technique. Physical, optical characteristics and spectroscopy have been identified and investigated. As the glass composition changes, definite variations in physio-optical properties can be observed as well as the temperature of the glass transition (Tg), the density (ρ), molar volume (Vm), bandgap energy (Eg), and the refractive index (n). The Judd-Ofelt theory has been performed using a UV–VIS-NIR absorption spectrum to examine the compositional effect on Er3+ spectroscopic properties. Some basic spectroscopic parameters including electric dipole line strengths, Judd-Ofelt parameters, the rate of radiative probability, and the lifetime of radiative levels, are determined. A high NIR emission at 1.53 μm was observed when exciting glasses at 980 nm. The FWHM, the effective line-width (Δλeff), the emission cross-section (σem), and the gain bandwidth values were calculated using the theory of Füchtbauer–Ladenburg, and the findings were critically analyzed. the decay of fluorescence spectra for the 4I13/2 level was registered, and the lifetime for the studied glasses was calculated. Upconversion luminescence was observed in the green and red regions under 980 nm excitation, with a relative increase in emission intensity due to the added tungsten content. Based on the results obtained, the studied glasses are favorable materials for broadband amplifiers in WDM systems and optical devices.

Cr3+ and Nd3+ co-activated garnet phosphor for NIR super broadband pc-LED application

Near-infrared phosphor converted light emitting diodes (NIR pc-LEDs), as a compact light source, play a constructive role in wearable optical biosensing devices. In order to detect the properties of different substances, the NIR emission should be as wide as possible. The typical strategy for broadening the band is the superposition emission of Cr3+ and Yb3+, the bandwidth of which is 300–320 nm, and it needs to be further broadened. In this paper, NIR Ca2LuZr2Al3O12 garnet phosphor, co-activated by Cr3+ and Nd3+, is prepared. The emission quantum efficiencies of Nd3+ at 900 nm and 1060 nm are close to 100%, and the emission band is complementary to that of Yb3+ at 1030 nm. An efficient super broadband NIR pc-LEDs (47.6 mW@100 mA), with the bandwidth of 350 nm, are achieved. The bandwidth and the efficiency of the pc-LEDs are improved greatly, compared with other reported ones.

Novel broadband near-infrared emitting phosphor LiGe2(PO4)3:Cr3+ with tuning and enhancement of NIR emission by codoping Sb5+

A highly efficient novel broadband NIR emission peaking at 814 nm with a large full width at half maximum (FWHM) of 170 nm was realized in novel LiGe2(PO4)3:Cr3+ (LGP:Cr3+) with internal quantum efficiency about 90% (IQE). An innovative strategy of Sb5+ codoped phosphor (LGP:Cr3+,Sb5+) led to the increases in the luminescence intensity and thermal stability. Moreover, tunable NIR emission from 814 to 743 nm was achieved which can be ascribed to the attenuation of electron-phonon coupling with increasing Sb5+-concentration. The output powers of phosphor-converted lighting emitting diodes (pc-LEDs) by combining 460 nm chips with LGP:0.01Cr3+ and LGP:0.05Cr3+,0.05Sb5+ phosphors reached 34.68 mW @ 300 mA and 40.36 mW @ 250 mA, respectively. Our results prove that the codoped strategy can provides a new idea for research on tunable NIR phosphors.

Cr3+-doped broadband near infrared diopside phosphor for NIR pc-LED

Broadband Near-infrared phosphors have attracted great attention for its potential applications in pc-LED as a novel light source for substance measurements based on NIR spectroscopy. Here, CaMgSi2O6:xCr3+ diopside phosphor were prepared by high temperature solid-state reaction. The Cr3+emission band undergoes a red-shift from 772 nm to 822 nm followed with band broadening from 132 nm to 197 nm with the increase of x from 0.25% to 6%. Highly thermal stability with the quenching temperature as high as 355 °C for 1% and 236 °C for 4% Cr3+ concentrations are observed. NIR pc-LEDs were fabricated and high NIR output power of 42.04 mW for the bandwidth of 150 nm and 23.73 mW for a more broaden bandwidth of 187 nm are achieved at 100 mA drive current, respectively. Our results suggest that CaMgSi2O6:Cr3+phosphors have great potential for applications in broadband NIR pc-LED applications.

Cr3+-doped borate phosphors for broadband near-infrared LED applications

A novel broadband NIR phosphor K6Li0.9Na0.1CaSc2(B5O10)3:Cr3+ with a single luminescence center has been successfully synthesized, and the relationship between the crystal structure and the luminescence properties was systematically investigated.

Design, luminescence properties and applications of Cr3+-doped ScTaO4: a broadband near-infrared phosphor.

Near-infrared (NIR) emitting LED devices have broad applications. Using a visible light LED chip to excite Cr3+-activated phosphors to obtain NIR light has attracted extensive attention. In this study, a near-infrared luminescent material, Cr3+-doped Sc1-xTaO4, was synthesized by the element substitution method. It demonstrated a long emission wavelength (940 nm) and wide full width at half maximum (FWHM) (186 nm). The morphology, structure and photoluminescence of the samples were investigated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy techniques. Moreover, the relationship between the NIR emission properties of Cr3+ and the substituted ions in the crystal matrix was studied. Based on this material, we fabricated near-infrared LED devices, which exhibited good near-infrared luminescence properties.

Highly efficient and thermally stable broadband near-infrared emitting fluoride Cs2KGaF6:Cr3+ for multiple LED applications

A highly efficient (IQE = 90.2%) and thermally stable (I150 °C = 88.7%) broadband NIR emitting fluoride Cs2KGaF6:Cr3+ is explored. Meanwhile, a multipurpose high-performance NIR pc-LED with a photoelectric conversion efficiency of 22.05% is achieved.

A simple and generic post-treatment strategy for highly efficient Cr3+-activated broadband NIR emitting phosphors for high-power NIR light sources

A simple and generic post-treatment strategy is reported to improve the luminescence efficiency of Cr3+-activated NIR-emitting phosphors.

Dual near infrared emission in Ag2Se quantum dots via Pb doping for broadband mini light-emitting diodes.

Dual emission almost covering the entire NIR-II region with the maximum full width at half maximum of 542 nm was achieved by doping small amounts of Pb ions into Ag2Se quantum dots, which to the best of our knowledge has not been realized for continuous tunable dual NIR emission in Ag-based QDs. The fabricated broadband NIR mini light-emitting diodes based on the Pb-doped Ag2Se QDs exhibit potential applications for highly sensitive and multispectral non-invasive imaging and NIR lighting.

Chemical unit co-substitution enabling broadband and tunable near-infrared emission in garnet-type Lu3Sc2Ga3O12:Cr3+ phosphors

Although near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are desired for non-visible light source applications, the design of broadband NIR phosphors remains a challenge. Inspired by the chemical unit co-substitution strategy for the modification of composition and local structure, we realize a tunable redshift emission from 706 to 765 nm in garnet-type Lu3Sc2Ga3O12:Cr3+ with a broadened full width at half maximum and enhanced photoluminescence intensity by introducing a [Mg2+-Si4+] unit into the [Sc3+-Ga3+] couple. Structural and spectral analyzes demonstrate that the co-substitution reduces the local symmetry and crystal field strength of the [CrO6] octahedra, thus leading to inhomogeneous widening of the 4T2→4A2 emission and enhanced blue absorption. Furthermore, the 4T2→4A2 emission exhibits a phonon-assisted character at low temperatures due to the thermal coupling effect with the 2E level. The fabricated NIR pc-LED based on the optimized NIR phosphor exhibits excellent potential in night vision and imaging applications.

Efficient Cr3+-activated NaInP2O7 phosphor for broadband near-infrared LED applications

A novel efficient broadband NIR phosphor NaInP2O7:Cr3+ (in brief NIP:Cr3+) for NIR pc-LEDs has been successfully synthesized and systematically investigated.

Wafer‐Scale Growth of Vertical‐Structured SnSe2 Nanosheets for Highly Sensitive, Fast‐Response UV–Vis–NIR Broadband Photodetectors

AbstractOwing to the strong light–matter interactions, 2D semiconducting thin films have shown their great potential in the development of high‐performance ultraviolet–visible–near infrared (UV–Vis–NIR) broadband photodetectors (PDs). However, the planar 2D semiconducting thin films via conventional growth method are often in the form of isolated flakes and/or suffering from low absorption efficiency of light, which hinders the UV–Vis–NIR optoelectronics from widespread applications. Herein are reported high‐performance nonplanar UV–Vis–NIR broadband PD arrays, based on wafer‐scale, vertical‐structured SnSe2 nanosheet arrays (NSAs) via low‐temperature molecular beam epitaxy method. The vertical‐structured SnSe2 NSAs possess light absorption efficiency of >90% covering the wave range from 340 to 650 nm. Benefiting from the excellent light trapping ability and uniformity of waferscaled SnSe2 NSAs as well as relatively short channel, the broadband PD arrays exhibit superior comprehensive performance. They achieve a high responsivity of 31.94 A W‐1, fast speed (≈63 μs), and high uniformity. In addition, the responsivity of the broadband PD arrays is further improved via Zn‐doping technique.

Achieving an ultra-broadband infrared emission through efficient energy transfer in LiInP2O7: Cr3+, Yb3+ phosphor

Spectral coverage and saturability within 700–1100 nm of phosphor-converted near infrared light-emitting-diodes (pc-NIR LEDs) are crucial for the practical applications in bioimaging, food quality analysis and night vision fields, while developing ultra-broadband NIR phosphors are still a challenge. Herein, we reported a broadband NIR phosphor LiInP2O7: Cr3+ in phosphate system. The emission spectrum of this phosphor covers 700–1200 nm with a full width at half maximum (FWHM) of 165 nm and an emission peak centering at 860 nm under 460 nm excitation. This broadband emission is verified to be derived from 4T2 g → 4A2 g transition of Cr3+ in a single crystal site. To further expand the emission spectrum, Cr3+→Yb3+ energy transfer in LiInP2O7 was designed, and an ultra-broadband emission with a FWHM of 225 nm was obtained through appropriate amount of Yb3+ codoping. The energy transfer efficiency can reach as high as 81% in this material. Furthermore, the energy transfer mechanism, quantum yield, thermal stability and fabrication performance were investigated in detail, demonstrating the ability of achieving ultra-broadband and efficient NIR emission of LiInP2O7: Cr3+, Yb3+ phosphor material.

Enhanced broadband NIR emission of low Bi-doped borate glass by carbon reduction

The NIR efficiency was greatly enhanced both in ultra-low and high Bi-doped borate glasses with the addition of a little carbon. By further adjusting the Bi-doping concentration, it is found that the optimal Bi2O3 doping concentration is 0.06 mol% under the carbon reduction (0.1 mol%). Our results indicate that the Bi-doped glass with very low doping concentration can achieve stronger broadband NIR emission than that with high doping concentration under the effect of reducing agent.

UV–Vis–NIR broadband response of GaAs-based photocathode with multilayer graded-band cascade structure

To improve the lattice matching, quantum efficiency and response range of the transmission-mode GaAs-based photocathode , a novel photocathode with multilayer graded-band cascade emission layer is proposed. The one-dimensional steady-state continuity equations and finite-difference time-domain methods are utilized to obtain the quantum efficiency and optical absorption characteristics of the proposed photocathode, respectively. The results show that, the built-in electric fields generated by the varying-composition and varying-doping structure can assist the photoelectrons generated in the sublayer itself and the front sublayers to transport towards the emitting surface and escape to the vacuum. Compared with the conventional AlGaAs/InGaAs structure, the proposed structure possesses better lattice matching and enhanced quantum efficiency in the UV and NIR wavelength range. A three-fold increase of quantum efficiency can be realized at 400 nm and the theoretical quantum efficiency at 1064 nm can reach 2%. Besides, the integral absorptivity is increased by 6.8% in the visible wavelength range, and 12.9% in the NIR wavelength range. It is found that the increase of the thickness of AlGaAs sublayer and GaAs sublayer mainly reduces the quantum efficiency in the UV–Vis wavelength range. When the InGaAs sublayer is thin enough, the increase of thickness would enhance the quantum efficiency in the NIR wavelength range and deteriorate that in the UV–Vis wavelength range. This work can contribute to the performance improvement of UV–Vis–NIR broadband GaAs-based photocathode. • A transmission-mode photocathode with multilayer graded-band cascade structure is proposed. • The quantum efficiency model of the proposed multilayer structure is deduced. • The quantum efficiency and optical absorption characteristics are investigated. • The lattice matching, quantum efficiency and response range are improved.