Ultra-broadband Emission Research Articles

Two-stage ultra-broadband luminescence of Cr3+-doped multisite layered phosphor Sr3Ga2Ge4O14 and its application in pc-LEDs

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have enormous potential for all kinds of applications, both non-destructive testing and biological applications. The development of broadband NIR phosphors with good thermal stability for a wide range of applications remains a challenge. This work successfully synthesized a layered structure ultra-broadband NIR phosphor Sr3Ga2Ge4O14:Cr3+ (SGGO:Cr3+) under 431 nm excitation and achieved a spectrum adjusted from 750 nm to 900 nm in a two-stage ultra-broadband emission with a full width at half maximum (FWHM) varying between 257 and 336 nm by controlling the Cr3+ concentration. In particular, SGGO:0.15Cr3+ has a FWHM of 257 nm and the internal quantum efficiency (IQE) of 36.67%, while the emission intensity at 423 K remained at 76% of room temperature. Finally, SGGO:0.03Cr3+ and SGGO:0.15Cr3+ phosphors were used with 430 nm blue light chips to produce NIR pc-LEDs devices and applied to night vision and human palm penetration, as well as plant illumination, revealing the potential of SGGO:Cr3+ for multiple applications. The potential of SGGO:Cr3+ for a variety of applications was demonstrated.

Ultra-Broadband Random Laser and White-Light Emissive Carbon Dots/Crystal In-Situ Hybrids.

The continuous white-light emission of carbon dots (CDs) can be applied to producing multicolor laser emissions by one single medium. Meanwhile, the solid-state emission greatly contributes to its practical application. In this work, a strategy to realize the in-situ hybridization of silane-functionalized CDs (SiCDs) and 1,3,5-benzenetricarboxylic acid trimethyl ester (Et3BTC) by a one-pot solvothermal method is reported. Significantly, the SiCDs/Et3BTC hybrid crystals exhibit ultra-broadband random laser emission over the near ultraviolet-visible region under 265nm nanosecond pulsed laser excitation. The wavelength region of laser emission is achieved from 315 to 600nm within an emission band of CDs-based materials. It is worth noting that the wavelength range of the laser is wider than the previously reported works. It is proposed that the continuous white-light emission of SiCDs caused by multiple fluorescence centers mainly gives rise to the broadband random laser emission. Moreover, the crystals are conducive to forming resonance and realizing solid-state laser emission. This in-situ method is expected to enable a more convenient, cheaper, and greener approach to prepare luminescent hybrids for application in multicolor laser displays, multi-level laser anti-counterfeiting, supercontinuum light sources, and so on.

Ultra-broadband near infrared phosphor with wide spectral range and long peak wavelength achieved by double-site occupation

The miniaturization and intelligence of near infrared (NIR) devices urgently require an excellent broadband NIR phosphor. However, emission spectra of most NIR phosphors cover less than 1200 nm with a full width at half maximum (FWHM) less than 200 nm and a peak wavelength less than 900 nm. Here, we successfully developed ultra-broadband NIR phosphors ScNbO4:Cr3+ which can overcome the above shortcomings based on a double-site occupancy strategy. The phosphors achieve ultra-broadband NIR emission from 800 to 1400 nm with a peak wavelength at 980 nm. Its FWHM is up to 217 nm. The valence state of Cr ions in phosphors was analyzed. The double-site occupancy of Cr3+ ions in the host and the relationship between host structure and optical properties are discussed in detail. NIR light transmission experiments show that phosphors have potential application value in non-destructive analysis. This work develops an excellent NIR luminescent material and provides an efficient method to obtain ultra-broadband NIR phosphors with longer peak wavelength.

Optimizing Broadband Near-Infrared Emission in Bi/Sn-Doped Aluminosilicate Glass by Modulating Glass Composition.

The Bi/Sn-doped aluminosilicate glass samples were prepared using a melting–quenching method and their near-infrared (NIR) emission properties were studied. An ultra-broadband NIR emission ranging from 950 nm to 1600 nm was observed in all samples under 480 nm excitation, which covered the whole fiber low-loss window. The NIR emission spectrum showed that the maximum emission peak was about 1206 nm and the full width at half maximum (FWHM) was about 220 nm. Furthermore, the NIR emission intensity strongly depends on the composition of the glass, which can be optimized by modulating the glass composition. The Bi0 and Bi+ ions were the NIR luminescence source of the glass samples in this paper. The Bi/Sn-doped aluminosilicate glass has the potential to become a new type of core fiber material and to be applied to optical fiber amplifiers (OFAs), based on its excellent performance in ultra-broadband NIR emission.

Novel luminescence of bismuth in silica glass and fiber based on nanoporous glass

The ultra-broadband emission spectrum of Bi-doped fiber brings new hope for improving communication rate, while there are still many obstacles on the road to its full commercialization. The method of preparing Bi-doped fiber based on nanoporous silica glass (NPSG) is expected to be the key to breaking through the bottleneck of Bi-doped fiber. In this article, we conduct an in-depth study on the luminescence behavior and up-conversion of Bi in NPSG and its fabricated fibers. It was found that aluminum and germanium ions compete for Bi active centers (BACs) in glass, and more BAC-Al is formed when the aluminum-germanium ratio is increased, and more BAC-Ge is formed when the aluminum-germanium ratio is decreased. It is verified that the luminescence principle of bismuth originates from the defects in the glass. Bismuth up-conversion occurs in glasses which possess both BAC-Al and BAC-Ge. Bi-doped fibers were fabricated using the sleeve method, and excited-state absorption was found in the fibers. The energy level diagrams of BAC-Al and BAC-Ge are drawn. This work brings us one step to the near-infrared (NIR) luminescence principle of Bi, and lays a solid foundation for Bi-doped fiber amplifiers.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission

AbstractChiroptical hybrid organic–inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white‐emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)‐ and (S)‐(H2MPz)PbBr4 (R/S‐MPz=(R)‐(−)/(S)‐(+)‐2‐methylpiperazine) (1 and 2), (R)‐ and (S)‐(H2MPz)3Pb2Br10⋅2 DMAc (3 and 4), (R)‐ and (S)‐(H2MPz)PbBr4⋅0.5 MeCN (5 and 6) and (R)‐ and (S)‐(H2MPz)2Pb2Br8⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3–6 even achieve white circularly polarized emission with a high dissymmetric factor (glum) (±3×10−3 for 3 and 4; ±8×10−3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission.

Chiroptical hybrid organic-inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white-emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)- and (S)-(H2 MPz)PbBr4 (R/S-MPz=(R)-(-)/(S)-(+)-2-methylpiperazine) (1 and 2), (R)- and (S)-(H2 MPz)3 Pb2 Br10 ⋅2 DMAc (3 and 4), (R)- and (S)-(H2 MPz)PbBr4 ⋅0.5 MeCN (5 and 6) and (R)- and (S)-(H2 MPz)2 Pb2 Br8 ⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3-6 even achieve white circularly polarized emission with a high dissymmetric factor (glum ) (±3×10-3 for 3 and 4; ±8×10-3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

Broadband NIR-emitting Te cluster-doped glass for smart light source towards night-vision and NIR spectroscopy applications

Broadband near-infrared (NIR)-emitting materials are crucial components of the next generation of smart NIR light sources based on blue light-emitting diodes (LEDs). Here, we report a Te cluster-doped borate glass, which exhibits ultra-broadband emission around 980 nm with a full-width at half-maximum (FWHM) of 306 nm under blue light excitation. We propose adjustments of glass chemistry and processing condition as a means for topo-chemical tailoring of the NIR photoemission characteristics in such materials. Through implementing strongly reducing conditions during glass melting, Te clusters with broad NIR photoluminescence can be generated and stabilized once the melt is vitrified to the glassy state. Tunability of the NIR emission peak over the wavelength range of 904 to 1026 nm is possible in this way, allowing for fine adjustments of spectral properties relative to the stretching vibrations of common chemical bonds, for example, in water, proteins, and fats. This potentially enables high sensitivity in NIR spectroscopy. We further demonstrate potential application of glass-converted LEDs in night vision.

Single Bi3+ Ultrabroadband White Luminescence in Double Perovskite via Crystal Lattice Engineering toward Light‐Emitting Diode Applications

AbstractSingle‐phase white luminescence phosphors are emerging for potential phosphor‐converted white light‐emitting diodes (pc‐WLEDs) and alternatives to trichromatic phosphor blends. In this work, Ba2ZnWO6:Bi3+ phosphors are prepared by a high‐temperature solid‐state reaction method and the luminescent properties are investigated. The broadband excitation from 250 to 400 nm is perfectly matched with the emission of nearly ultraviolet (n‐UV) InGaN chip, which ultrabroadband emission band (full width at half maximum = 217 nm) can cover a wider luminescence region. Li+/Na+/K+ codoping is more desirable for the ultrabroadband emission of Ba2ZnWO6:0.006Bi3+ due to the charge compensation and rationally designed lattice distortion while improving the thermal stability of the phosphor. Furthermore, tunable emissions can be achieved either by changing the content of doped ions or the excitation wavelength due to the different occupation of Ba2+ and Zn2+ sites by Bi3+ ions. Finally, single‐phase warm WLED ((x, y) = (0.4170, 0.4035)) devices with a correlated color temperature of 3329 K and color rendering index of Ra = 75.3 are successfully prepared using Ba2ZnWO6:0.006Bi3+, 0.03Na+ phosphor, and 365 nm InGaN chips. These results indicate that Ba2ZnWO6:Bi3+ has excellent potential as phosphor for n‐UV pc‐WLEDs and provides new ideas for the application of ultrabroadband emitting phosphors in WLEDs.

Automatic target detection and localization using ultra-wideband radar

<span>The pulse ultra-wide band (UWB) radar consists of switching of energy of very short duration in an ultra-broadband emission chain, and the UWB signal emitted is an ultrashort pulse, of the order of nanoseconds, without a carrier. These systems can indicate the presence and distances of a distant object, call a target, and determine its size, shape, speed, and trajectory. In this paper, we present a UWB radar system allowing the detection of the presence of a target and its localization in a road environment based on the principle of correlation of the reflected signal with the reference and the determination of its correlation peak.</span>

Efficient red photoluminescence in holmium-doped Cs2NaInCl6 double perovskite

Metal halide perovskites with efficient and stable self-trapped exciton emission have attracted considerable attention for next-generation solid-state lighting owing to their ultrabroadband emission. However, it remains challenging to widen the color gamut and realize high color-rendering index due to the lack of highly saturated red color-emitting inorganic lead-free perovskite materials with narrow full width at half-maximum. Here, we report a lanthanide-codoped system (Cs2NaInCl6:Sb3+/Ho3+) that enables efficient blue and red emissions with photoluminescence quantum yields of up to 99% and 72%, respectively. The energy transfer efficiency in Ho3+-doped Cs2NaInCl6:Sb is up to 73%, which can overcome the weak absorption cross-section of the f-f transition of lanthanide ion and improve its luminescence performance. Benefitting from the efficient energy-transfer channel from the self-trapped excitons to Ho3+, the emission color is continuously tuned from blue to red by controlling the Ho3+-doping concentration.

MxLa1–xSiO2–yNz (M = Ca/Sr/Ba): Elucidating and Tuning the Structure and Eu2+ Local Environments to Develop Full-Visible Spectrum Phosphors

The local environments of rare-earth activators have profound effects on the luminescent properties of phosphors. Here, we elucidate the crystal structure of the LaSiO2N phosphor host using a combination of density functional theory calculations and synchrotron X-ray diffraction. We determine that LaSiO2N crystallizes in the monoclinic C2/c instead of the hexagonal P6̅c2 space group. To improve the luminescence performance, divalent cations M (M = Ca/Sr/Ba) were introduced into LaSiO2N to eliminate Eu3+. A family of apatite M1+xLa4–xSi3O13–x/2:Eu2+ (x ∼ 1.5, M = Ca/Sr/Ba) phosphors was further developed with unprecedented ultra-broadband (290 nm) emission spectra and excellent thermal stability. Detailed local environment investigations reveal that the formation of oxygen vacancies within and beyond the first-shell environment of Eu2+ is responsible for the redshift and broadening of the emission spectra via geometrical alteration of the Eu2+ local environment. This work provides new insights for understanding and optimizing the luminescence of rare-earth phosphors.

Compact ultrabroadband light-emitting diodes based on lanthanide-doped lead-free double perovskites

Impurity doping is an effective approach to tuning the optoelectronic performance of host materials by imparting extrinsic electronic channels. Herein, a family of lanthanide (Ln3+) ions was successfully incorporated into a Bi:Cs2AgInCl6 lead-free double-perovskite (DP) semiconductor, expanding the spectral range from visible (Vis) to near-infrared (NIR) and improving the photoluminescence quantum yield (PLQY). After multidoping with Nd, Yb, Er and Tm, Bi/Ln:Cs2AgInCl6 yielded an ultrabroadband continuous emission spectrum with a full width at half-maximum of ~365 nm originating from intrinsic self-trapped exciton recombination and abundant 4f–4f transitions of the Ln3+ dopants. Steady-state and transient-state spectra were used to ascertain the energy transfer and emissive processes. To avoid adverse energy interactions between the various Ln3+ ions in a single DP host, a heterogeneous architecture was designed to spatially confine different Ln3+ dopants via a “DP-in-glass composite” (DiG) structure. This bottom-up strategy endowed the prepared Ln3+-doped DIG with a high PLQY of 40% (nearly three times as high as that of the multidoped DP) and superior long-term stability. Finally, a compact Vis–NIR ultrabroadband (400~2000 nm) light source was easily fabricated by coupling the DiG with a commercial UV LED chip, and this light source has promising applications in nondestructive spectroscopic analyses and multifunctional lighting.

PbS quantum dots and BaF2:Tm3+ nanocrystals co-doped glass for ultra-broadband near-infrared emission [Invited

With the rapid growth of optical communications traffic, the demand for broadband optical amplifiers continues to increase. It is necessary to develop a gain medium that covers more optical communication bands. We precipitated PbS quantum dots (QDs) and BaF2:Tm3+ nanocrystals (NCs) in the same glass to form two independent emission centers. The BaF2 NCs in the glass can provide a crystal field environment with low phonon energy for rare earth (RE) ions and prevent the energy transfer between RE ions and PbS QDs. By adjusting the heat treatment schedule, the emission of the two luminescence centers from PbS QDs and Tm3+ ions perfectly splices and covers the ultra-broadband near-infrared emission from 1200 nm to 2000 nm with bandwidth over 430 nm. Therefore, it is expected to be a promising broadband gain medium for fiber amplifiers.

Achieving a tunable and ultra-broadband near-infrared emission in the Ga2-2xZnxGexO3:Cr3+ phosphor.

Near-infrared (NIR) spectroscopy (700-1100 nm) based on a phosphor-converted light-emitting diode (pc-LED) has multi-functional applications in bio-imaging, night-vision, and food quality analysis, simulating the development of efficient and ultra-broadband NIR phosphors. Herein, a series of tunable and ultra-broadband NIR phosphor Ga2-2xZnxGexO3:Cr3+ was successfully produced by a [Zn2+-Ge4+] unit co-substituting a [Ga3+-Ga3+] unit in Ga2O3:Cr3+. With the increasing amount of [Zn2+-Ge4+] incorporation, the emission peak can be tuned from 726 to 808 nm, and the maximum FWHM can be extended from 126 to 190 nm. However, the excitation peak position remained nearly unchanged in the blue light region, enabling this material to perfectly match the InGaN blue LED chip. Although the gradually enhanced electron-lattice coupling and low energy barrier for thermal quenching caused by this co-substitution lead to a decrease in the photoluminescence quantum yield (PLQY) and thermal stability, respectively, the absolute values of these two criteria can be well maintained. Finally, to evaluate the practical applications, prototype NIR pc-LEDs were fabricated using these materials combined with 450 nm LED chips. Under the same conditions, the NIR output power and photoelectronic conversion efficiency of these devices are superior to those fabricated using the well-known ScBO3:Cr3+ phosphor. These results demonstrate that this series of materials with tunable and ultra-broadband NIR emissions has great potential for NIR pc-LED applications.

Ultra-broadband NIR luminescence in chromium doped magnesium aluminosilicate glass as future light sources for spectroscopy applications

The discovery of high-efficiency and ultra-broadband near-infrared (NIR)-emitting material is crucial for constructing NIR lighting sources and emerging applications. Herein, a series of NIR-emission Cr3+-doped glasses were successfully prepared. The results indicated that the glasses mainly consisted of [SiO4] and [AlO4], the optical band gap and Urbach energy were in the range of 3.806–2.195 eV and 0.445–0.704 eV. Meanwhile, it can be concluded that the Cr3+ ions are located in distorted octahedral sites in the glass, and the parameter Dq/B was less than 2.3. Under the excitation of 466 nm light, an ultra-broadband emission peak centered at ∼1000 nm with a full width at half maximum (FWHM) of 220–310 nm was found, which is crucial for improving the imaging resolution of the prepared light source. This work shows the potential advantages of glass as a NIR light source in NIR spectroscopy, which can encourage further studies on ultra-broadband NIR-emitting glass materials.

Mid infrared fluorescence characteristics and application of Co2+:ZnS doped chalcogenide glass-ceramics

A Co2+:ZnS-doped chalcogenide glass with broadband mid-infrared emission was prepared by using a hot uniaxial pressing process. The refractive index difference (Δn) between matrix glass (As2S5) and crystal (Co2+:ZnS) was controlled to be 0.0042 in the emission spectral range of Co2+ to minimize the scattering effect. An ultrabroadband mid-infrared emission of 2–4 μm was observed at room temperature in the samples after excitation by using a commercially available laser diode of 1550 nm. The significant changes in the lifetime and fluorescence intensity of Co2+:ZnS-doped chalcogenide glass were measured in the temperature range of 90–290 K. A resolution of approximately 0.18 K was observed when used as a temperature detector. Furthermore, a gas-sensing device was built by using the strong and broad emissions of the sample, and the detection sensitivity of butane reached 56 ppm. These results show that this glass-ceramics can be used as optical sensing of gas and temperature.

Efficient ∼4 µm emission from Pr3+/Yb3+ co-doped fluoroindate glass.

Pr3+/Yb3+ co-doped fluoroindate (InF3) glasses were prepared by using a traditional melt-quenching method in dry N2 atmosphere. Pumped by a 976 or 1570 nm laser diode, efficient emissions at ∼4µm were obtained from the Pr3+/Yb3+ co-doped glasses, which could be ascribed to the transition 3F4→3H6 of Pr3+ ions. The relative stimulated emission cross section was calculated to be ∼1.44×10-24m2 at 4 µm, which was ∼4.2 times larger than that of transition Ho3+:5I5→5I6 (3.4×10-25m2). In addition, combined with transitions 1G4→3F3 and 1G4→3F4 of Pr3+ ions, ultra-broadband emission ranging from 2.7 to 4.2 µm was also obtained. Our results indicate that Pr3+/Yb3+:InF3 glasses could be used to develop efficient ∼4µm lasers and widely tunable mid-infrared lasers.

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.

Antimony‐Doped Lead‐Free Zero‐Dimensional Tin(IV)‐Based Organic–Inorganic Metal Halide Hybrids with High Photoluminescence Quantum Yield and Remarkable Stability

AbstractLead‐free organic–inorganic metal halide perovskites have attracted wide attention owing to their outstanding photophysical properties. Herein, a new type of antimony‐doped 0D tin(IV)‐based organic–inorganic metal halide hybrid (C10H16N2)SnCl6:Sb with highly efficient luminescence and remarkable stability is reported. Upon photoexcitation, the prepared samples exhibit an ultrabroadband emission ranging from 400 to 900 nm with two centers at 500 and 660 nm, which originate from free excitons and self‐trapped excitons, respectively. Such 0D metal halide hybrids with ultrabroadband emission covering the entire visible spectrum are rare. Especially, the photoluminescence quantum yield (PLQY) of red emission is as high as 77% upon 345 nm ultraviolet excitation. More importantly, (C10H16N2)SnCl6:Sb exhibits relatively good stability. It can still maintain 90% photoluminescence intensity after one week of 365 nm ultraviolet irradiation. Simultaneously, its PL intensity still retains 61% of room temperature emission intensity at 400 K. This work provides a new direction for the development of 0D organic–inorganic metal halide hybrids with excellent performance.