Ultra-broadband Emission Research Articles

A novel broadband near-infrared phosphor Ca3MgTiGe3O12:Cr3+

Near-infrared spectroscopy (NIRS) is a rapid, non-destructive analytical characterization tool. In this study, we report near-infrared (NIR) phosphor Ca3MgTiGe3O12:Cr3+ in garnet system, achieving ultra-broadband NIR emission. The emission spectrum of the phosphor ranges from 690 nm–1100 nm with a full width of half maximum (FWHM) value of ∼127 nm. The emission peak is observed at 786 nm when the excitation wavelength is 463 nm. The broadband emission seen in this study was identified as a result of 4T2 → 4A2 transition of Cr3+ in host lattice. The internal quantum efficiency (IQE) of the material was found to be as high as 66.5 %. The energy transfer mechanism, quantum yield, thermal stability and preparation conditions of the material were further investigated. These studies show that these materials with highly-efficient ultra-brosd near-infrared emissions are promising candidates for high-quality near-infrared light sources.

Efficient and ultra-broadband near-infrared emission in perovskite-like Mg4Sb2O9:Cr3+ phosphor

Near-infrared (NIR) spectroscopy based on phosphor-converted NIR light-emitting-diode (LED) has extensive applications in modern life, stimulating the exploration of ultra-broadband NIR phosphors with high efficiency. Herein, Cr3+-doped perovskite-like Mg4Sb2O9 phosphor was synthesized, which exhibits a NIR emission with peak wavelength of 855 nm, and a full width at half maximum (FWHM) of about 207 nm. Upon 442 nm excitation, the quantum efficiency (QY) and absorption efficiency (AE) were determined to be 59.1 % and 48.3 %, respectively; while the luminescence intensity remained 61.5 % of room temperature at 373 K, indicating an excellent efficient and a moderate thermal stability of this material. The fabricated NIR pc-LED through combining the optimized phosphor with a 455 nm LED chip presents an output power of 20.1 mW and a photoelectronic conversion efficiency of 3.6 % under a driving current of 175 mA. These results suggest that Mg4Sb2O9:Cr3+ phosphor with excellent luminescent performance may have good potential for applications in NIR pc-LEDs.

Synergistic effect of dual-site occupation and activators confinement realizing an efficient ultra-broadband NIR emitter

Broadband near-infrared (NIR) phosphor-conversion light-emitting diode (pc-LED) devices have an extensive application prospect in night vision monitoring, nondestructive testing, and biomedical imaging. In this work, the ultra-broadband NIR emission produced by the chromium-activated NaZn(PO3)3 phosphor with two-site occupation peaks at around 900 nm with a full width at half-maximum (FWHM) of 218 nm. Time-resolved spectroscopic techniques and steady-state fluorescence spectra coupled with crystal structure confirm the multiple occupations of the chromium ion. Notably, the NaZn(PO3)3: Cr3+ phosphors exhibit an internal quantum efficiency (IQY) of 80.6 % and an external quantum efficiency (EQY) of 35.4 %, which may originate from the activators confinement, direct band-gap property, and high absorbance. To better comprehend the connection between structure and luminescence capabilities, the band structure, crystal field strength parameters, fluorescence lifetime, and thermal stability were all thoroughly investigated. Finally, the optimal sample has demonstrated its application in the quantitative analysis of ethanol/water mixtures. The results provide a novel perspective for the rational design of desired emitters.

Selective enrichment strategy induces ultra-broadband NIR emission in Cr3+-doped multi-phase glass-ceramics for NIR spectroscopy applications

Near-infrared (NIR) spectroscopy has gained widespread application in food analysis, disease diagnosis, fingerprint analysis, and security monitoring. However, the lack of efficient, broadband NIR luminescent materials hinders the full potential of this technology. Here, an ultra-broadband and high-efficiency Cr3+-doped multi-phase glass-ceramics containing MgAl2O4, Al2SiO5, and SiO2 nanocrystals was discovered, which exhibited an ultra-broadband NIR emission (λem ∼ 900 nm) with a full width at half maximum more than 300 nm and a high internal quantum yield of 50.9% under the excitation of 465 nm blue light. Moreover, the integrated emission intensity at 100 °C and 150 °C can keep 88% and 77% of that at room temperature. The ultra-broadband, high efficiency, and thermally robust luminescence of this Cr3+-doped multi-phase glass-ceramics can be attributed to the selective enrichment of Cr3+ ions into different nanocrystals with octahedral sites, and medium electron-photon coupling effect. The NIR glass-ceramics-converted light-emitting diode constructed by the glass-ceramics combined with 465 blue LED chip produced an excellent NIR output and photoelectric conversion efficiency of 274 mW/1007 mW and 3.43%/2.79% at 100 mA/320 mA drive current, which demonstrated superior overall performance to the NIR device built by using the well-known NIR phosphors. Additionally, the NIR camera can capture the image of license plate and nectarine, as well as identify the residual drug content in the bottle under the irradiation of the NIR device constructed by the glass-ceramics. This work not only presented an ultra-broadband and high-efficiency NIR material but also highlights a design strategy to effectively enhance the efficiency and broadband characteristics of NIR glass-ceramics.

Ultra-broadband near-infrared Cr3+-doped multi-phase glass-ceramics realized by the selective enrichment strategy for near-infrared spectroscopy applications

As a very important component of NIR spectroscopy, the enhancement of luminescent efficiency and the broadening of bandwidth for NIR light sources are still considered to be a challenge. Hereon, a novel Cr3+-doped MgO-Al2O3-SiO2 multi-phase glass-ceramics was successfully constructed. Upon excitation of 400 nm, the glass-ceramics presented an ultra-broadband NIR emission peaking at ∼910 nm with full width at half maximum of >270 nm, and the internal/external quantum efficiency of 60.4 %/28.8 %. The integrated emission intensity remained at ∼86.6 %/80.9 % at 100 ℃/150 ℃ compared to the intensity at room temperature. Furthermore, a NIR device was made by encapsulating the glass-ceramics on 405 nm LED, which presented a NIR output power and photoelectric conversion efficiency of 322 mW/1117 mW and 2.72 %/2.39 % at the driven current of 100 mA/320 mA, respectively. This work realized simultaneous adjustment of luminescent efficiency and bandwidth by selective enrichment of Cr3+ ions into different crystal phases, which provides an effective strategy for improving the luminescent efficiency and bandwidth of NIR glass-ceramics.

Luminescence characteristics of ultra-broadband near-infrared emission Li3Mg2SbO6:Cr3+ phosphors and their applications in light-emitting diodes

In this study, a Li3Mg2SbO6:Cr3+ phosphor was prepared by high-temperature solid-phase reaction. The phosphors doped with 0.03Cr3+ showed broadband emission at 805 nm, a wide spectral band of 200 nm at 435 nm excitation, an internal quantum efficiency of 80.8%, and the integrated emission intensity at 423 K of Li3Mg2SbO6:Cr3+ is about 50% of that at room temperature. The phosphors conversion (pc) - light-emitting diodes (LEDs) with broadband near-infrared (NIR) emission were prepared using the Li3Mg2SbO6:Cr3+ phosphor coating on blue LED chips. They achieved 10.4% photoelectric efficiency and 60.2 mW NIR output power at 210 mA. All results showed that the Li3Mg2SbO6:Cr3+ phosphors had considerable potential in NIR spectroscopy applications.

Near-Infrared LuCa2ScZrGa2GeO12:Cr3+ Garnet Phosphor with Ultra-broadband Emission for NIR LED Applications.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs), as a new generation of NIR lighting sources, have wide prospects in the areas of food analysis and biological and night vision imaging. Nevertheless, NIR phosphors are still limited by short-wave and narrowband emissions as well as low efficiency. Herein, a series of NIR phosphors, LuCa2ScZrGa2GeO12:Cr3+ (LCSZGG:Cr3+), with broadband emissions have been developed and first reported. At 456 nm excitation, the optimized LCSZGG:0.005Cr3+ phosphor represents an ultra-broadband emission within the range of 650-1100 nm, peaking near 815 nm with a full width at half maximum of 166 nm. Furthermore, the LCSZGG:0.005Cr3+ phosphor possesses good internal quantum efficiency of 68.75%, and its integrated emission intensity at 423 K still retains about 64.17% of that at room temperature. By combining the optimized sample with a blue chip, a NIR pc-LED device is fabricated, which has an excellent NIR output power of 37.88 mW with an NIR photoelectric conversion efficiency of 12.44% under a 100 mA driving current. The aforementioned results demonstrate that these LCSZGG:Cr3+ broadband NIR phosphors are expected as NIR light sources.

Enhancing Infrared Photoluminescence Performance via Li+ Substitution and Yb3+ Codoping in Na3ScSi3O9:Cr3+ Phosphor

Cr3+-doped broadband infrared luminescent materials have attracted growing attention in consideration of their potential applications in phosphor-converted infrared light sources. However, discovering infrared-emitting luminescent materials with ultrabroadband emission and excellent thermal stability still remains a challenge. In this work, we report the significant improvement of infrared photoluminescence properties in Na3ScSi3O9:Cr3+ phosphor via Li+ substitution and Yb3+ codoping. The prepared Na3ScSi3O9:Cr3+ phosphor can produce broad infrared emission over 650–1350 nm with a peak maximum at 898 nm under the excitation of blue light. Through the substitution of Li+ for Na+, the maximum infrared emission peak can be tuned from 898 nm to 850 nm. When the Li+ content is 0.5, the integrated infrared luminescence intensity of the obtained Na2.5Li0.5ScSi3O9:Cr3+ phosphor increases by 4.2 times compared with that of the Na3ScSi3O9:Cr3+ phosphor, and the luminescence thermal stability is also improved significantly (58.5%@100 °C). Moreover, Yb3+ codoping can simultaneously realize the characteristic infrared luminescence of Cr3+ and Yb3+, resulting in a broadened spectral width due to efficient energy transfer from Cr3+ to Yb3+. Finally, an ultrabroadband infrared light-emitting diode prototype is fabricated through a combination of the optimized Na2.5Li0.5ScSi3O9:2%Cr3+,0.5%Yb3+ phosphor with a commercial 490 nm LED chip, giving an infrared output power of 5.2 mW at 320 mA drive current. This work provides an effective way to optimize the infrared photoluminescence performance of Cr3+-doped Na3ScSi3O9 infrared phosphors.

Ultra-Broadband Near-Infrared Phosphors Realized by the Heterovalent Substitution Strategy.

Near-infrared (NIR) phosphor-converted light-emitting diodes with broadband emission have received considerable interest. However, there remains a challenge in the construction of ultra-broadband NIR phosphors, hindering their further application. In this work, a heterovalent substitution strategy is proposed to construct a novel ultra-broadband NIR-emitting LaTiTaO6:Cr3+ phosphor with a full width at half maximum of ∼300 nm. Crystal structure, time-resolved emission spectroscopy, and electron paramagnetic resonance analyses confirm that only one crystallographic site of Cr3+ with separated ions exists. Electron and phonon coupling (EPC) evaluated by the Huang-Rhys factor (S) reveals that the heterovalent substitution strategy contributes to strong EPC with S = 9.185, resulting in ultra-broadband emission. Interestingly, a remarkable blue shift of emission from 1050 to 922 nm with increasing temperature is observed. Moreover, the application of LaTiTaO6:Cr3+ phosphor is demonstrated in the qualitative analysis of ethanol/water mixtures. The work will enrich the toolbox for designing broadband NIR-emitting materials.

Efficient ultra-broadband NIR-II emission achieved by multi-site occupancy in Mg3Ga2GeO8: Ni2+ phosphor

It is an important and urgent task to improve the luminous efficiency and emission bandwidth of existing luminescent materials with emission in near infrared (NIR) spectral region (especially for NIR-II spectral region from 1000 to 1700 nm). Herein, we report a novel Ni2+ doped phosphor Mg3Ga2GeO8: 0.8 %Ni2+ which exhibits ultra-broadband emission (from 1100 to 1700 nm, the full width at half maximum (FWHM) is up to 300 nm) with high quantum efficiency (The internal quantum efficiency (36.7 %) and external quantum efficiency (7.3 %) are relatively high in the reported Ni2+ dope NIR-II emitting phosphors). The phosphor presents desirable thermal stability of luminescence (At 373 K, it remains 56.2 % of the initial intensity at room temperature). This work not only provides an advanced NIR-II emitting phosphor which can be effectively pumped by commercial near ultraviolet light emitting diode chips, but also introduces a new strategy (that is to explore a suitable host in which there exists many different crystalline sites for the occupation of activators) for the exploration of efficient ultra-broadband NIR-II emitting phosphors.

Ultrabroadband Emission from CsCu2I3/Cs3Cu2I5 Dual-Phase Glass-Ceramics with Long-Term Stability

Metal halides (MHs) show great potential in photovoltaic and optoelectronic applications, but their lack of long-term stability limits their applications for their sensitivity to oxygen, moisture, strong light irradiation, and high temperature. In this report, lead-free MHs CsCu2I3/Cs3Cu2I5 dual-phase glass-ceramics were prepared with a traditional melting-quenching method by using solid reductive agent Si3N4. Ultrabroadband emission from violet to near-infrared (350–800 nm) can be obtained from these CsCu2I3/Cs3Cu2I5 dual-phase glass-ceramics with long-term water-resistance stability. Detailed analysis of microstructure, spectra, and calculation reveals that the ultrabroadband nature can be ascribed to the intense emission of CsCu2I3 NCs, Cu+ ions, and Cs3Cu2I5 NCs together, and especially, the emission from Cs3Cu2I5 NCs and Cu+ ions presents a cyan color. Our work not only demonstrates that CsCu2I3/Cs3Cu2I5 glass-ceramic is a promising fluorescent material, but also develops a method to prepare lead-free metal halides CsCu2I3/Cs3Cu2I5 dual-phase glass-ceramics with high stability, paving the way for their applications.

Achieving Narrowed Bandgaps and Blue‐Light Excitability in Zero‐Dimensional Hybrid Metal Halide Phosphors via Introducing Cation–Cation Bonding

Zero‐dimensional (0D) hybrid metal halides, which consist of organic cations and isolated inorganic metal halide anions, have emerged as phosphors with efficient broadband emissions. However, these materials generally have too wide bandgaps and thus cannot be excited by blue light, which hinders their applications for efficient white light‐emitting diodes (WLEDs). The key to achieving a blue‐light‐excitable 0D hybrid metal halide phosphor is to reduce the fundamental bandgap by rational chemical design. In this work, we report two designed hybrid copper(I) iodides, (Ph3MeP)2Cu4I6 and (Cy3MeP)2Cu4I6, as blue‐light‐excitable yellow phosphors with ultrabroadband emission. In these compounds, the [Cu4I6]2− anion forms an I6 octahedron centered on a cationic Cu4 tetrahedron. The strong cation–cation bonding within the unique cationic Cu4 tetrahedra enables significantly lowered conduction band minimums and thus narrowed bandgaps, as compared to other reported hybrid copper(I) iodides. The ultrabroadband emission is attributed to the coexistence of free and self‐trapped excitons. The WLED using the [Cu4I6]2− anion‐based single phosphor shows warm white light emission, with a high luminous efficiency of 65 lm W−1 and a high color rendering index of 88. This work provides strategies to design narrow‐bandgap 0D hybrid metal halides and presents two first examples of blue‐light‐excitable 0D hybrid metal halide phosphors for efficient WLEDs.

Singlet exciton and singlet/triplet self-trapped excitons for ultra-broadband white-light emission in a zero-dimensional cadmium bromide hybrid

A new zero-dimensional hybrid Cd-based metal halide featuring isolated CdBr4 tetrahedra segregated by luminescent organic templates shows UV-excited ultra-broadband white light emission with a CRI of 98 and a PLQY of 23.46%.

Dopant and compositional modulation triggered long-wavelength ultra-broadband and tunable NIR emission in MgO: Cr3+ phosphor for NIR spectroscopy applications

Efficient ultra-broadband near-infrared (NIR) phosphors with long-wavelength ( λ max > 850 nm) and wide full width at half-maximum (FWHM, >200 nm) have sparked tremendous interest, demonstrating their immense potential in NIR spectroscopy technology. Nevertheless, the development of NIR spectroscopy technology suffers from the restricted capability to efficiently emit the ultra-broadband NIR light. Herein, the synergetic enhancement strategy of heterogeneous substitution and compositional modulation was applied to create a novel Cr 3+ doped long-wavelength ultra-broadband MgO: Cr 3+ , Ga 3+ phosphor, which exhibited a long-wavelength ultra-broadband NIR emission ( λ max = 850 nm) covering the range of 650–1300 nm on the electromagnetic spectrum with the FWHM of more than 200 nm under the excitation of 468 nm light. Furthermore, the tunable NIR emission from 818 nm to 862 nm with an optimized quantum efficiency of 30% was accomplished by the Ga 3+ ions substitution and Cr 3+ ions modulation. The phosphor exhibited remarkable thermal stability up to 100 °C, remaining 83% of the integrated emission intensity at room temperature. A prototype of the NIR phosphor-converted LED (pc-LED) demonstrated that the novel MgO: Cr 3+ , Ga 3+ phosphor possessed a relatively strong NIR output power (15.05 mW at 100 mA driven current) with a photoelectric conversion efficiency of 5.53%, which is impressive compared with other Cr 3+ -doped long-wavelength ultra-broadband phosphors. This work not only proposes a novel long-wavelength ultra-broadband NIR phosphors with industrialization and great application prospect in night vision but highlights a synergetic enhancement strategy to effectively boost the performance of long-wavelength ultra-broadband NIR pc-LED light sources.

Luminescence properties and spectral modulation of the ultra-broadband, highly efficient near-infrared luminescent material CaGa4O7:Cr3+, Cr4+, Yb3+

Recently, near-infrared phosphors have received a lot of attention due to their wide application in the field of detection and analysis, and it is urgent to develop efficient broadband NIR phosphors. In this paper, a conventional high-temperature solid-phase method was used to prepare a novel near-infrared phosphor CaGa4O7:Cr3+, Cr4+, which provides two emission bands ranging from 600 to 1000 nm and 1100–1600 nm. Although there are only four and five coordination sites in the CaGa4O7 (CGO) lattice, the doping of the Cr3+ ions in the CGO causes the Ga–O tetrahedral distortion into an octahedron, providing a favorable environment for the emission of the Cr3+ ions. Under blue light excitation, Cr3+ emits luminescence in the NIR I region from 600 to 1000 nm with a half-height width of up to 148 nm. With increasing Cr ion concentration, more and more Cr4+ preferentially occupy the four coordinated Ga3+ sites, and the intensity of the ultra-broad emission band in the NIR II region (1100 nm–1600 nm) increases with a full width at half maximum (FWHM) of 262 nm. To further optimize the emission spectrum, Yb3+ was codoped into CGO: Cr3+, Cr4+, the energy transfers from Cr3+ to Yb3+ in CGO was found, thus filling the gap between 1000 and 1100 nm in the CGO emission spectrum and obtaining a more complete ultra-wide spectrum. Moreover, the luminescence mechanism, energy transfer efficiency, and quantum yield are also studied in detail, and the ability of CaGa4O7:Cr3+, Cr4+, and Yb3+ luminescent materials to achieve ultra-broadband efficient near-infrared emission was demonstrated.

Ultra-broadband near-infrared emission in the double-perovskite Ca2InTaO6:Cr3+ phosphor for light-emitting-diode applications

Broadband near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have extensive applications basing on spectroscopy technology, which promote the exploration of broadband NIR phosphors. However, there are still lack of efficient ultra-broadband NIR phosphors with peak emission wavelength over 850 nm. In this work, a series of double-perovskite-type Ca2InTaO6:Cr3+ NIR phosphors were successfully prepared through a conventional high-temperature solid-state reaction process. Optimizing the Cr3+ doping concentration, the obtained phosphor exhibits an ultra-broadband emission covering 700–1300 nm with peak wavelength located at 880 nm. The full width at half maximum (FWHM) of this phosphor reaches 200 nm ascribing to the two crystallographic sites in this compound that are available for Cr3+ substitution. Upon 480 nm excitation, the photoluminescence quantum yield (PLQY) and absorption efficiency are determined to be 33.6% and 30.6%, respectively, indicating an excellent efficiency within this emission range among ultra-broadband NIR phosphors. Thus, this work provides an alternative Cr3+-activated ultra-broadband and long-wavelength NIR phosphor Ca2InTaO6:Cr3+ for the upcoming smart spectroscopy applications.

Site-selective occupation of Cr3+ ions toward ultra-broadband near-infrared emission stannate phosphors

Cr3+-activated near-infrared (NIR) luminescent materials with broadband emission have attracted extensive attentions for multipurpose NIR phosphor-converted light-emitting diodes (LED). It is widely believed that broadband NIR-emitting from optical center Cr3+ could merely made in crystal-filed caused six-coordinated sites or four-coordinated sites. Herein, taking La3Ga5SnO14 compound with six-coordinated Sn and four-coordinated Ga sites as host, we design and synthesize a new ultra-broad NIR-emitting La3Ga5Sn1-xO14:xCr3+ (LGSn1-x:xCr3+) phosphor ranging from 700 to 1500 nm via solid-state reaction. Structural analysis, low-temperature spectra investigations, and density functional theory calculations demonstrate that, in La3Ga5SnO14 (LGSn) host lattice, six-coordinated Sn sites and four-coordinated Ga sites can be successfully occupied by Cr3+ ions, leading to two distinct Cr3+ centers and an impressive broadband with full width at half maximum of up to 275 nm. At 373 K, emission intensity of LGSn0.97:3%Cr3+ phosphor maintains 43% of that at room temperature. We fabricate a NIR phosphor-converted LED device by using as-prepared LGSn0.97:3%Cr3+ phosphor and a blue LED chip and demonstrate its potential applications in night vision and food analysis. These findings provide not only an in-deep insight on site-occupation of Cr3+ residing in compounds with six-coordinated sites and four-coordinated sites but also feasible method of designing ultra-broadband NIR phosphors.

Broadening and enhancing emission of Cr3+ simultaneously by co-doping Yb3+ in Ga1.4In0.6SnO5

Cr3+ doped broadband near-infrared (NIR) emitting phosphors are currently the focus of research. Researchers have developed a variety of strategies to achieve broad and strong NIR emission. However, it is a conundrum to simultaneously broaden and enhance the emission of Cr3+ with a single strategy. In this work, we solved this problem by co-doping Yb3+. Under 452 nm excitation, Ga1.4In0.6SnO5 (GISO):0.01Cr3+ shows ultrabroadband NIR emission covering 650–1300 nm with a peak of 884 nm. The full width half maximum (FWHM) of the emission is 215 nm and the internal quantum yield (IQY) is 25%. This indicates that the double sites occupation strategy is favorable to achieve ultra-broadband NIR emission. The co-doping of Yb3+ can effectively broaden and enhance the emission of Cr3+. The FWHM for GISO:0.01Cr3+,0.002Yb3+ extends to 245 nm, and the IQY increases to 28%. Further increasing the concentration of Yb3+ to 0.005, the IQY is lifted to 32%. Finally, a phosphor-converted light emitting diode (pc-LED) was prepared by integrating the GISO:0.01Cr3+,0.002Yb3+ with a blue light chip. Under the current drive of 40 mA, the maximum output power of pc-LED is 4.54 mW, and the photoelectric conversion efficiency is 4.12%. These results indicate that Yb3+ ions can simultaneously broaden the emission band and improve the emission efficiency. This work provides an effective strategy for the design of efficient broadband NIR phosphors in the future.

Achieving the ultra-broadband near-infrared La3SnGa5O14:Cr3+ phosphor via multiple lattice sites occupation for biological nondestructive detection and night-vision technology

Currently, near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have become a research hotspot, however, the NIR phosphors continue to face the problems of narrowband emission and poor thermal stability. Therefore, in order to solve these problems, La3SnGa5O14:xCr3+ phosphors with ultra-broadband NIR emission were obtained by multiple lattice sites occupation, featuring ultra-broadband emission in the range of 650–1300 nm with full width at half-maximum (FWHM) up to 333 nm under 437 nm excitation. By tuning the concentration of Cr3+, the FWHM value can reach 333–417 nm La3SnGa5O14:Cr3+ also exhibits favorable thermal stability, maintaining 90.5% and 67% of the initial intensity at 373 K and 423 K, respectively. The NIR pc-LEDs were manufactured by combining the blue light chip with La3SnGa5O14:Cr3+ phosphor. When the NIR pc-LED was switched off, no image could be generated from the infrared camera. Instead, the image captured by the infrared camera was visible in the light of the NIR pc-LED lamp. Such results imply that La3SnGa5O14:Cr3+ may be a prospective candidate for future biological accurate nondestructive detection and night-vision technology.

Ultra-broad NIR emission from two-site Cr3+ occupation in fluoride phosphor via composition-driven structural transformation

Cr3+-activated fluoride-based near-infrared (NIR) phosphors have attracted wide attention from researchers due to their high luminous efficiency and high thermal stability. However, the practical application of this type of phosphors is severely hindered by their narrow emission. In this work, a structural transformation from Li3GaF6 to LiMgGaF6 was successfully obtained by stoichiometric control during hydrothermal process, leading to an NIR phosphor LiMgGaF6:Cr3+ with broadband emission ranging from 650 to 1150 nm. With the replacement of Li by Mg atom of Li3-2xMgxGaF6:Cr3+(0 ≤ x ≤ 1), the full width at half maximum of emission band can be broaden to 189.9 nm from 140 nm. This ultra-wide NIR emission of fluoride phosphor is caused by double-site Cr3+ occupation, which is verified by activator concentration-dependent spectra, Rietveld structural refinement, and density functional theory first-principles calculations. Despite the wide-band NIR emission, the LiMgGaF6:Cr3+ phosphor shows relatively high quantum efficiency of 42.3% and high thermal stability, which maintains 50% of its initial intensity at 400 K. The ultra-broadband NIR emission of LiMgGaF6:Cr3+ has potential applications as a light source in ingredient identification, and the strategy of multisite occupation of Cr3+ through compositional regulation opens a new way for the exploration of Cr3+-doped broadband NIR fluoride phosphors.