Broadband NIR Emission Research Articles

Cr3+-Doped LiAlO2 NIR-I Emitting Phosphors with Superior Resistance to Thermal Quenching for Night Vision Monitoring and Bioimaging.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) as a new NIR light source has outstanding application potential in the fields of NIR spectroscopy analysis, sensing, imaging, and pattern recognition. Therefore, the development of NIR phosphors with good NIR luminescence thermal stability has attracted much attention. To this end, we developed LiAlO2:Cr3+ garnet-type NIR phosphors by a high-temperature solid-state reaction method. Under 405 nm excitation, the Cr3+ ions located in tetrahedrons of LiAlO2 emit NIR emission in a broadband NIR emission that covers 650-900 nm mixed with several sharp narrowband R-line emissions, which showed excellent luminescence thermal stability with integrated intensity of emission measured at 573 K is ∼90.86% of that measured at 303 K caused by good structural rigidity and low thermal expansion coefficient of the matrix material. An NIR pc-LED device assembled with the optimized LiAlO2:Cr3+ and a commercially available purple LED chip emitted NIR output power of ∼98.172 mW at a driving current of 300 mA and demonstrated an electro-optical conversion efficiency of ∼9.09%, while demonstrated it has excellent application potential in the fields of night vision monitoring and biomedical imaging.

Highly Efficient and Thermally Stable Broadband NIR Phosphors with Superlong Afterglow Performance and their Multifunctional Applications

AbstractNear‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) are considered as promising next‐generation light sources for optoelectronic and biomedical applications. Nevertheless, NIR phosphors with large bandwidths, long emission peaks, high external quantum efficiencies (EQEs) and valuable thermal stabilities are challenging to develop. Herein, this study reports a novel gallium germanate host, Ga3Al3Ge2O13 (GAGO), with a large bandgap and rigid host lattice for Cr3+ ion doping. The blue LED excitable GAGO:0.012Cr3+ phosphor can produce broadband NIR emission with a maximum intensity at 816 nm and a full‐width at half‐maximum (FWHM) of 187 nm. Notably, the phosphor also exhibits an excellent EQE of 35.8% and perfect thermal stability (I423 K/I298 K = 67.4%). Moreover, an attractive NIR afterglow duration of more than 24 h is achieved in the GAGO:0.004Cr3+ phosphor. The type and origin of the traps are discussed, and a possible long persistent luminescent (LPL) mechanism is proposed. Finally, an NIR pc‐LED based on a GAGO:0.012Cr3+ phosphor is fabricated. The results demonstrate that the obtained phosphors show great potential for use in night vision, nondestructive detection, bioimaging and information encryption. This study provides new insight into the development of broadband NIR luminescent materials with high efficiency, good thermal stability and extraordinary afterglow performance.

UV- and X-ray-activated broadband NIR garnet-type Ca3Ga2Sn3O12:Fe3+ phosphors with efficient persistent luminescence

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are compact light sources of great interest for NIR spectroscopy applications. Beyond typical Cr3+-activated NIR-emitting phosphors, there exists a strong demand for Cr3+-free alternatives with high efficiency and broadband emission to rich the landscape of NIR luminescent materials and extend their range of application fields. Here, we report a series of Fe3+-activated Ca3Ga2Sn3O12 garnet-type phosphors exhibiting broadband NIR emission in the 650–1000 nm range attributed to 4T1(G) → 6A1(S) transition, with a maximum at 754 nm and a FWHM of 89 nm upon UV excitation. The spectroscopic results were analyzed according to the Tanabe-Sugano theory from which the crystal field parameter Dq and Racah parameters B and C were obtained for the octahedrally coordinated Fe3+ ion. Notably, the NIR persistent luminescence lasting over 1 h was detected following UV or X-ray irradiation. The possible mechanism involving electron traps was proposed to explain the observed persistent luminescence. Furthermore, a NIR pc-LED was fabricated by coating synthesized phosphor on a UV chip, and its performance was evaluated to assess its potential suitability as a NIR light source. Our discovery of novel type of nontoxic Fe3+-activated broadband NIR luminescence phosphors with efficient NIR persistent luminescence paves the way for discovering Cr3+-free multifunctional NIR luminescence materials, thereby expanding their application possibilities.

Broadband NIR luminescence of Cr3+-doped Mg4Nb2O9 phosphors toward LED light source applications for NIR spectrometry

Abstract Herein, we report the photoluminescence (PL) properties of Cr3+-doped Mg4Nb2O9 phosphors for applications in NIR phosphor-converted LEDs. Trigonal Mg4Nb2O9 crystals with Cr3+ substitution at three sites were synthesized as the main phase using a solid-state reaction. X-ray photoelectron spectrometry and diffuse reflectance spectroscopy indicated that only trivalent chromium ions were present in the samples. Broadband NIR emission of Cr3+ suitable for combination with Si photodetectors was confirmed at approximately 850 nm. The maximum PL quantum yield (PLQY) was 0.62, and concentration quenching explained the Cr concentration dependence of the PLQY and PL decay time. Low-temperature PL measurements suggested that the PL spectrum comprised three distinct emission bands. The results of the phonon line simulation, low-temperature PL excitation measurements, and crystal-field parameter estimation clarified the correlation between these emission bands and the Cr3+ substitution sites.

Broadband near-infrared luminescence in a cubic pyrophosphate Al0.5Ta0.5P2O7:Cr3+ phosphor for multi-functional applications.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered as next-generation of NIR light sources for spectroscopy. However, it is still a challenge to develop an inexpensive broadband NIR phosphor with relatively long-wavelength (λem > 800 nm) emission. In this work, an octahedral Al3+-containing pyrophosphate Al0.5Ta0.5P2O7 with a cubic structure was chosen as a host for Cr3+. Synthesizing this material indicates that this phosphor exhibits a broadband NIR emission peaking at 850 nm with a full width at half maximum (FWHM) of 155 nm under 465 nm excitation. The crystal structure, morphology, local structure, and photoluminescence properties of this material were investigated in detail. The results revealed a full understanding of this new material. A NIR pc-LED device fabricated by using this material combined with a 450 nm LED chip generates a NIR output power of 10.7 mW and a NIR photoelectric conversion efficiency of 3.4% under a 100 mA driving current, which shows the possibility of this material to be utilized in NIR pc-LED applications. Moreover, this material exhibits a linear relationship between emission intensity, decay time and temperature in a wide temperature range, implying that excellent multi-model temperature sensing applications can be expected.

Realizing efficient broadband near-infrared emission under blue light excitation in Sb3+-doped zero-dimensional organic tin(iv)-based metal halides via coordination structure modulation

Here, we report a new NIR emitter of Sb3+-doped tin(iv)-based metal halides via coordination structure modulation, which can exhibit bright broadband NIR emission under blue light excitation with a PLQY of 33.2%.

Near‐Infrared Emission of Sm2+ in Oxynitrides

AbstractNear‐infrared (NIR) luminescent materials hold promising applications in NIR spectroscopy technologies, but the NIR emitters are largely limited to some transition metals with spin‐forbidden transitions that lead to low absorption efficiency of the pumping light. Exploring novel efficient NIR emitters is thus an urgent and challenging task for developing high‐efficiency NIR luminescent materials. Here, an interesting NIR emission of Sm2+ is reported in BaAlSi5O2N7, which exhibits both a line spectrum at 682 nm and a broadband centered at 778 nm with a full‐width at half maximum (FWHM) of 141 nm. Temperature‐dependent photoluminescence spectra and decay curves evidence that the thermally assisted electrons crossover (TAEC) process contributes to the enhancement of the broadband NIR emission. The fabricated NIR phosphor‐converted light‐emitting diode (pc‐LED) shows promising potential as a NIR lighting source and proves robust thermal stability under high‐temperature aging test. The present surprising NIR emission from Sm2+ in highly stable oxynitrides opens a way to explore efficient and reliable NIR phosphors that are suitable for commercial LED chips.

Efficient CrIII Ion Governed Energy Migration for Broadband Near‐Infrared Emission in Ca3Sc2Ge3O12 Garnet Phosphor

AbstractThe rapid growth in phosphor‐converted near‐infrared light‐emission diodes (NIR‐LEDs) has led to the development of NIR emitter with high efficiency, broadband emission and high thermal stability. In this work, an efficient broad NIR emission of Cr3+ in novel Ca3Sc2Ge3O12 (CSGO) garnet‐based host was developed for the first time, which located at 700 to 1000 nm peaking at 817 nm with a broad bandwidth of ~128 nm. Such a broadband NIR emission originated from the preferential occupancy of Cr3+ in Sc3+ sites with weak octahedral field, which was manifested by the luminescence spectrum and decay behaviors. The Cr3+‐doping concentration was regulated to achieve a good internal quantum efficiency (IQE) of 72.1 % and a fantastic thermal stability (at 423 K, sustained approximately 85 % of the initial intensity). The mechanism for concentration and thermal quenching was further investigated. Benefiting from the excellent luminescence features, a prototype NIR‐LEDs was assembled via integrating the optimized samples with commercial blue InGaN LED chips, which exhibited a satisfactory photoelectric property and a brilliant performance in night vision. These results demonstrated the as‐obtained sample to be a great potential candidate for NIR‐LEDs.

Achieving an ultra-high absorption efficiency in a monoclinic LiAlP2O7:Cr3+ near-infrared phosphor

Near-infrared phosphor-converted light-emitting diode (NIR pc-LED) is becoming a smart light source for portable multifunctional devices, utilizing in fields like bio-imaging, night-vision, and food-quality analysis. However, developing broadband, inexpensive, and efficient NIR phosphors are still in great challenges. Herein, we report a phosphate LiAlP2O7:Cr3+ phosphor by choosing highly distorted and inexpensive octahedral Al3+-containing compound as host. This material generates a broadband NIR emission with peak located at 844 nm and a full width at half maximum (FWHM) of 163 nm under 450 nm excitation. Amazingly, the absorption efficiency (AE) was measured to be as high as 64%, being higher than most of Cr3+-activated polycrystalline materials. Unfortunately, the internal quantum efficiency (IQE) was only 26.7%, and the emission intensity at 373 K kept only 56% of that at room temperature. The detailed reasons for these undesired properties are systematically investigated. Moreover, a prototype NIR pc-LED fabricated by using this material combining with 450 nm LED chip demonstrates a NIR output power of 9.7 mW and NIR photoelectronic conversion efficiency of 3.3% under 100 mA driving current, indicating the feasibility of this material to be applied in NIR pc-LEDs.

Near-infrared emission of Cr3+ in five-coordinated field

Cr3+-activated NIR phosphors have received increasing attention due to their versatile applications. Cr3+ generally shows tunable NIR emission by occupying a six-coordinated field (Oh). Herein, we discover broadband NIR emission of Cr3+ at the five-coordinated field in the phosphors BaXP2O7:Cr3+ (X = Mg/Zn) for the first time. The five-coordinated [MgO5] (D3h) or [ZnO5] (C4v) site provides a quasi-octahedral field. The symmetry of D3h and C4v fields is lower than that of Oh, thus leading to further splitting of the energy levels and generating the broadband NIR emission from 700 to 1100 nm. This work breaks through the traditional limitation of NIR luminescence of Cr3+ in the six-coordinated field and opens a new window to explore novel NIR phosphors of Cr3+ in five-fold coordination.

Designing and controlling the Ni2+-activated (Zn, Mg)Al2O4 spinel solid-solution for phosphor-converted broadband near-infrared illumination

Ni2+-activated Zn1−xMgxAl2O4 phosphors exhibit broadband NIR emission band of 1000–1600 nm and are utilized in the application of broadband pc-NIR LEDs.

Novel broadband NIR phosphors Y2Mg2Ga2Si2O12:xCr3+ for NIR LED applications.

The Cr3+-doped near-infrared (NIR) phosphors have been extensively investigated owing to their promising applications in biomedicine, food safety detection, and night vision surveillance. However, achieving broadband (FWHM > 160 nm) NIR emission is still challenging. In this paper, novel Y2Mg2Ga2-xSi2O12:xCr3+ (YMGS:xCr3+, x = 0.005-0.08) phosphors were prepared by a high-temperature solid-state reaction. The crystal structure, photoluminescence properties of the phosphor, and the device performance of a pc-LED were researched in detail. When excited at 440 nm, the YMGS:0.04Cr3+ phosphor exhibited broadband emission in the range of 650-1000 nm, peaking at 790 nm with a full width at half-maximum (FWHM) of up to 180 nm. The wide FWHM of YMGS:Cr3+ is conducive to its extensive application in NIR spectroscopic technology. In addition, the YMGS:0.04Cr3+ phosphor could maintain 70% of the initial emission intensity at 373 K. By combining the commercial blue chip with the YMGS:0.04Cr3+ phosphor, the resulting NIR pc-LED demonstrated a near-infrared output power of 14 mW with a photoelectric conversion efficiency of 5% at a drive current of 100 mA. This work provides a broadband emission NIR phosphor option for NIR pc-LED devices.

Simultaneous Absorption and Near‐Infrared Emission Enhancement of Cr3+ Ions in MgGa2O4 Spinel Oxide via Anionic F‐Substitution

AbstractNear‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) are newly emerging broadband NIR light sources. However, the lack of high‐performance NIR‐emitting materials limits their popularization. Herein, an anionic F‐substitution strategy is presented to regulate the light absorption and emission of MgGa2O4:Cr3+ phosphors. Accordingly, absorption enhancement as well as emission redshift and broadening are achieved for F‐substituted MgGa2O4:Cr3+ (MGOF:Cr3+) phosphors, simultaneously with high efficiency and excellent thermal stability. Upon blue light excitation, the MGOF:0.02Cr3+ phosphor exhibits a broadband NIR emission (650–1200 nm) with a peak wavelength (λmax) of 835 nm and a full width at half maximum of ≈250 nm. Furthermore, MGOF:0.02Cr3+ has a near‐unity internal quantum efficiency and its emission intensity at 150 °C maintains 94% of the initial value. A record external quantum efficiency of 60.6% is further achieved for MGOF:0.08Cr3+ with a redshifted λmax of 870 nm. The Cr3+ local structural alteration with F‐substitution is revealed to account for the outstanding NIR luminescence characteristics of MGOF:Cr3+ in view of systematic structural characterization and spectroscopic analysis. A broadband NIR pc‐LED device with good optical performance is fabricated and its application in semiconductor wafer inspection is demonstrated. This study initiates a new way to design high‐performance NIR phosphors.

A highly efficient and broadband near-infrared-emitting garnet phosphor for plant lighting realized by cation co-substitution in lutetium aluminum garnet

Near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) is developing rapidly in plant cultivation because of its low cost, compact size and high efficiency. The NIR light of 700 ∼ 760 nm is known to be beneficial for seed germination and growth. Therefore, the exploration of NIR phosphors with specific wavelength and high efficiency is essential for the development of high-performance plant cultivation pc-LEDs. In this study, a highly efficient and thermal stable Cr3+ doped Lu2CaAl4SiO12 (LCAS) phosphor with broadband NIR emission covering phytochrome Pfr absorption range was successfully realized via Ca2+-Si4+ co-substitution of Lu3+-Al3+ pairs. The LCAS:0.07 Cr3+ exhibits a major emission peak of 740 nm with a FWHM of 160 nm and its internal/external quantum yield (IQY/EQY) is as high as 80%/30.5%. The integrated emission intensity of LCAS:0.07Cr3+ at 423 K lost only 33.8% of its initial intensity, indicating that it has a good thermal stability. When the LCAS:0.07Cr3+ was packaged into a pc-LED with a driving current of 320 mA, the device output power and photoelectric efficiency reached 90.6 mW and 8.6%, respectively, demonstrating that this phosphor has potential application in plant cultivation lighting.

Efficient and Thermally Robust Broadband Near‐Infrared Emission in a Garnet Ca3MgHfGe3O12:Cr3+ Phosphor

AbstractNear‐infrared (NIR) spectroscopy based on phosphor‐converted light‐emitting‐diode (pc‐LED) has promising applications in food quality analysis, security monitoring, medical diagnosis, and bioimaging fields, stimulating the demand of developing NIR phosphors with high‐performance. Herein, a highly efficient and thermally robust Ca3MgHfGe3O12:Cr3+ NIR phosphor is discovered, which exhibits a broadband NIR emission (λem = 800 nm) covering 700 to 1100 nm region with an internal quantum efficiency as high as 90.7% when excited by 460 nm blue light. Moreover, the emission intensity at 423 K retains 84.5% of that at room temperature. The highly efficient and thermally robust luminescence of this material is mainly ascribed to the ultrawide bandgap of host, extremely weak electron–photon coupling effect, defect‐free, and highly structural rigidity. The NIR pc‐LED device fabricated by using the optimized Ca3Mg0.97Hf0.97Ge3O12:0.06Cr3+ phosphor combined with blue (λem = 455 nm) LED chip produces an excellent NIR output power of 49.5 mW @ 11.5% under a driving current of 150 mA, which indicates a superiority to the device fabricated by using the well‐known efficient ScBO3:Cr3+ phosphor under the same condition. Therefore, this work not only provides a promising broadband NIR material, but also highlights the design rules for searching high‐performance NIR materials toward spectroscopy applications.

Luminescence properties and phase transformation of broadband NIR emitting A2(WO4)3:Cr3+ (A=Al3+, Sc3+) phosphors toward NIR spectroscopy applications

The synthesis, structural, and luminescence properties have been carried out for Cr3+-activated Al2(WO4)3 (AWO) and Sc2(WO4)3 (SWO) phosphors for application in pc-NIR LED. Upon blue excitation, these compounds are capable of exhibiting broadband NIR emission stems primarily from 4T2→4A2 transition in the range of 670–1200 nm (maxima ∼808 nm, FWHM ∼140 nm) for AWO:Cr and of 700–1300 nm (maxima ∼870 nm, FWHM ∼164 nm) for SWO:Cr. The significant shift of NIR emission is attributed to the substitution of AlO6 with larger ScO6 octahedrons. To gain insight into the luminescence the crystal field strength, Racah parameters, nephelauxetic effect, and electron-phonon coupling have been analyzed based on spectroscopic results. The electron-phonon coupling parameter S for SWO:Cr was determined to be 11.5, twice as large as that for AWO:Cr, which is in accordance with its strong thermal quenching. The abrupt changes occurring at 275 K in temperature-dependent luminescence spectra and decay lifetime of AWO:Cr is associated with temperature-driven phase transformation from low-temperature monoclinic to high-temperature orthorhombic phase. Pressure induced amorphization of AWO:Cr at pressures higher than 25 kbar was confirmed by employing high pressure evolution of Raman spectra. A high-power NIR pc-LED, fabricated by coating AWO:0.04Cr on a commercial 470 nm LED chip, shows good performance with an output power of 17.1 mW driven by a current of 320 mA, revealing potential application of studied materials for NIR light source.

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.

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.

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.

Multicolor tunable and NIR broadband emission from rare-earth-codoped tantalum germanate glasses and nanostructured glass-ceramics

High photoluminescence efficiency, unusual NIR broadband and tunable emission are possible in erbium-doped and tantalum germanate glasses and nanostructured glass-ceramics. The chemical microenvironment around erbium ions and their influence on optical properties are dependent on the TaO6 clusters formation and tantalum perovskite-like bronze crystallization, which are strongly related to the tantalum oxide content and annealing. Erbium ions are preferably distributed close to tantalum-rich environment, providing an intense emission with minimized nonradiative processes and inhomogeneous broadband NIR emission with increasing site numbers. A more pronounced broadening in the nanocrystalline samples is due to the multi-sites of the tantalum perovskite-like bronze crystalline structure. Green/red tunable emission from up conversion processes was observed since the erbium ions occupy a chemical environment with low phonon energy in the tantalum germanate glass and with close neighbors in the tantalum germanate glass-ceramics. Accordingly, the highly tantalum germanate glasses and glass ceramics are promising for photonic applications in optical amplification, lighting and lasing, as well as for nonlinear optical applications and studies considering the perovskite-like bronze crystalline samples.