Near-infrared Phosphor Research Articles

Achievement of broadband NIR emission in double perovskite NaLaMgWO6 via non-equivalent substitution of Cr3+

Low-cost and high-efficient broadband near-infrared (NIR) phosphor converted light-emitting diodes (pc-LEDs) are desirable for the compact NIR spectrum system. In this work, a broadband NIR emission with a large full width at half maximum (FWHM) up to ∼160 nm is achieved in double perovskite NaLaMgWO6 phosphor via the non-equivalent substitution of Cr3+. The crystal structure analysis and first-principle calculation have revealed that Cr3+ prefers to substitute Mg2+. In order to keep charge balance, the random-distributed Na+ vacancies are formed. This behavior has constructed two different crystallographic sites for Cr3+ substitution and their effect on the NIR luminescence performances of NaLaMgWO6:Cr3+ is investigated in detail. Within the weak crystal field, the zero phonon line and broadband emissions ascribed to 4T2 → 4A2 transition are present simultaneously, which ensure the large FWHM acquired in NaLaMgWO6:Cr3+. The broadband NIR pc-LED prototype fabricated with the as-prepared phosphor and blue LED chip is achieved, which demonstrates that the NaLaMgWO6:Cr3+ is a new candidate for the broadband NIR phosphor applied in the miniaturized optical devices.

Improvement the near-infrared luminescence properties of double perovskite phosphor La(Mg0.5Sn0.5In0.5Sc0.5)0.5O3:Cr3+ via co-doping Yb3+

In recent years, the broadband near-infrared (NIR) spectroscopy technology has been widely used in the field of nondestructive testing. However, these existing NIR phosphors showed relatively short emission wavelengths, narrower half-maximum full-width (FWHM), and narrower half-peak widths, importantly, few phosphors presented the emission from 950 nm to 1100 nm. In order to solve these problems, the Yb3+/Cr3+ ions codoped La(Mg0.5Sn0.5In0.5Sc0.5)0.5O3 (LMSIS) was synthesized by the solid-state method, and the emission spectrum of LMSIS:Cr3+ can be extended to the NIR long-wave region due to the energy transfer of Yb3+ and Cr3+, and the thermal stability of the phosphor can be improved due to the inherent temperature stability of the Yb3+ f-f transition. The NIR phosphor converted light emitting diodes (pc-LEDs) were fabricated by combining the LMSIS:0.003Cr3+, 0.0015Yb3+ with blue LED chip, which can be expected to be used in the field of broadband near-infrared non-destructive detection.

Engineering the local structure of ZnGa2O4: Cr3+ via Mg substitution to realize superior luminescence

Recently, near-infrared (NIR) light-emitting diodes (LED) have attracted much research attention globally. To advance this technology, NIR phosphors with high efficiency, thermal stability, and broad bands are required. In this work, we modified ZnGa2O4:Cr3+ phosphor with Mg2+ ions. Results show that this method improves the luminescence intensity of ZnGa2O4:Cr3+ phosphor, and the emission wavelength of the sample can be changed by doping different Mg2+ concentrations. This method also improved the thermal stability of the samples. The quantum yield of Mg-modified ZnGa2O4:Cr3+ phosphors reached 87.12%, and the white LED fabricated with Zn0.4Mg0.6Ga2O4:0.01Cr3+ phosphor and commercial Y3Al5O12:Ce3+ phosphor demonstrated good performance. The NIR-LED fabricated with Zn0.4Mg0.6Ga2O4:0.01Cr3+ phosphor achieved a photoelectric conversion efficiency of 7.17%. The lines on the surface of an orange taken by a NIR camera reveal that phosphor can be used in night vision lighting. Meanwhile, the distribution of blood vessels in the human palm highlights the promising biological applications of the Zn0.4Mg0.6Ga2O4:0.01Cr3+ phosphor.

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.

Rapid Discovery of Efficient Long-Wavelength Emission Garnet:Cr NIR Phosphors via Multi-Objective Optimization.

High-efficiency long-wavelength emission near-infrared (NIR) phosphors are the key to next-generation LED light sources. However, high-efficiency phosphors usually exhibit narrow-band emission at shorter wavelengths due to the crystal field intensity. In this paper, we utilize multi-objective optimization to discover the NIR phosphor Gd3Mg0.5Al1.5Ga2.5Ge0.5O12:0.04Cr3+. It exhibits a broadband NIR emission from 650 to 1100 nm peaking at 763 nm, with a full width at half maximum (FWHM) of 150 nm, an internal quantum efficiency (IQE)/external quantum efficiency (EQE) of 90%/53.1%, and good thermal stability (85.3% @ 150 °C). The packaging results show that ∼53.2 mW of output power is achieved at 915 mW input power, which suggests promising applications for NIR pc-LED. Our approach is based on the data of emission wavelength (WL) and IQE for garnet:Cr NIR phosphors to construct machine learning models. An active learning strategy is used to make tradeoffs between WL and IQE, and we are able to find the targeted phosphor after only four iterations of synthesis and characterization.

Producing Tunable Broadband Near-Infrared Emission through Co-Substitution in (Ga1-xMgx)(Ga1-xGex)O3:Cr3.

Broadband near-infrared (NIR) phosphors are in high demand for creating "smart" NIR phosphor-converted light-emitting diode (pc-LED) sources. In this work, a series of Cr3+-substituted NIR-emitting materials with highly efficient, broad, tunable emission spectra are achieved by modifying the simple oxide Ga2O3 using [Mg2+-Ge4+] and [Ga3+-Ga3+] co-unit substitution. The results show that the emission peak can be shifted from 726 to 830 nm while maintaining a constant excitation peak in the blue light region, enabling extensive application. The optical properties stem from changes in the Cr3+ crystal field environment upon substitution. Intriguingly, the temperature-dependent photoluminescence emission peak position shows virtually no change in the [Mg2+-Ge4+] co-substituted materials. This abnormal phenomenon is found to be a comprehensive embodiment of a weakening crystal field environment (red-shift) as the temperature increases and reduced local structure distortion (blue-shift) with increasing temperature. The high quantum yield, NIR emission, and net-zero emission shift as a function of temperature make this phosphor class optimal for device incorporation. As a result, their performance was studied by coating the phosphor on a 450 nm emitting LED chip. The fabricated device demonstrates an excellent NIR output power and NIR photoelectric conversion efficiency. This study provides a series of efficient, tunable, broadband NIR materials for spectroscopy applications and contributes to the basic foundation of Cr3+-activated NIR phosphors.

Ultra-broadband near-infrared Gd3MgScGa2SiO12: Cr, Yb phosphors: Photoluminescence properties and LED applications

Developing novel broadband near-infrared (NIR) phosphors is crucial to promote NIR phosphor-converted light emitting diodes (pc-LEDs) development. In this work, a new ultra-broadband NIR phosphor Gd 3 MgScGa 2 SiO 12 : Cr 3+ (GMSGS) was achieved by replacing Sc 3+ -Ga 3+ in Gd 3 Sc 2 Ga 3 O 12 with Mg 2+ -Si 4+ . Under the excitation of blue light, the peak emission wavelength of GMSGS: 0.04Cr 3+ is about 820 nm with a full width at half maximum (FWHM) of ∼180 nm and an internal quantum efficiency (IQE) of 50 %. Benefited from the superposition of Cr 3+ emission and highly efficient Yb 3+ emission excited by energy transfer (ET) from Cr 3+ , the codoped GMSGS: 0.04Cr 3+ , 0.007Yb 3+ phosphor shows an ultra-broadband of 300 nm. Moreover, Yb 3+ -codoping improves the thermal stability due to the ET from Cr 3+ to more thermally stable Yb 3+ emitters, and the integrated intensity of GMSGS: 0.04Cr 3+ , 0.007Yb 3+ at 400 K was 63 % of that at room temperature. The packaging results exhibit that ~20 mW output power was achieved at 100 mA input current, which suggests promising potential of GMSGS: Cr 3+ , Yb 3+ phosphor in NIR pc-LED applications. • A novel broadband NIR garnet phosphor Gd 3 MgScGa 2 SiO 12 :Cr 3+ is developed. • The phosphor shows broadband NIR emissions in 700–1100 nm (λ max = 820 nm). • The phosphor exhibits high quantum yield (~50 %) and good thermal stability. • An ultra-broadband GMSGS: Cr 3+ , Yb 3+ phosphor was achieved owing to the energy transfer from Cr 3+ to Yb 3+ . • The NIR phosphor-converted LED with the NIR output power with ~20 mW at 100 mA drive current is achieved.

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.

Multifunctional optical sensing applications of luminescent ions doped perovskite structured LaGaO3 phosphors in near-infrared spectroscopy

Near-infrared (NIR) phosphor have attracted great attention due to its promising applications in bioimaging, night vision, medical diagnosis and food safety. However, the development of NIR phosphors with excellent sensing properties still remains a challenge. In this study, NIR phosphor LaGaO3: Nd/Cr has been successfully synthesized. Excitation at 460 nm the phosphor can exhibit excellent temperature sensing performance with the maximum absolute sensitivity 0.6043% K−1. The NIR phosphor also displays distinguished anti-thermal quenching performance with the emission intensity at 573 K retaining 78.34% of that at room temperature. In addition, there is a linear fitting relationship between the luminescence intensity ratio and applying stress. More importantly, NIR phosphor-converted light-emitting diode (pc-LED) has been fabricated by combining LaGaO3: Nd/Cr phosphors with blue LED chips, which shows a NIR output power of 979 mW and a photoelectric conversion efficiency up to 7.79% at 280 mA. Utilizing the prepared NIR pc-LED as a light source, the distribution of blood vessels and bones in human palms can be clearly observed with the assistance of infrared camera. These results indicate that the produced NIR phosphors have a wide range of optical sensing applications.

Ultra-broadband of up to 200 nm near-infrared phosphors based on one-site occupation strategy for multipurpose applications in light-emitting diodes

Portable near-infrared (NIR) lighting source stimulates great efforts to exploit NIR phosphor-converted LEDs (pc-LEDs) that push the rapid development of broadband NIR-emitting phosphors. Although Cr3+-activated NIR phosphors designed by multisites occupation strategy show significant potential in emission bandwidth, poor spectral stability caused by different thermal quenching behaviors is a brake on practical application due to different local structure around Cr centers. One-site-based NIR phosphors seem to be an effective method to solve aforementioned problem. Herein, we report a type of new ultra-broadband one-site-based NIR-emitting phosphors NaSc1-xP2O7:xCr3+ (NSP:xCr3+) with emission at 910 nm and full width at half maximum (FWHM) of up to ∼200 nm. Their FWHM value exceeds all one-site-based Cr3+-activated phosphors and some multiple-sites ones. Structural analysis and low-temperature spectra demonstrate that such impressive broadband NIR emission originates from Cr3+ occupying at single octahedral Sc site. At 425 K, integrated emission intensity of NSP:0.04Cr3+ phosphor maintains 53.8% of room temperature. A NIR pc-LED prototype is fabricated by using NSP:0.04Cr3+ phosphor with a blue LED chip, and its multipurpose applications in non-destructive detection, night vision and analysis of foodstuff are demonstrated. These findings indicate that broadband NSP:0.04Cr3+ NIR phosphor enabled by one-site occupation strategy has potential prospect for multipurpose NIR pc-LEDs applications.

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.

Mn5+-activated Ca6Ba(PO4)4O near-infrared phosphor and its application in luminescence thermometry

The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited into the broad and strong absorption band that spans the 500–1000 nm spectral range, this phosphor provides an ultranarrow (FWHM = 5 nm) emission centered at 1140 nm that originates from a spin-forbidden 1E → 3A2 transition with a 37.5% internal quantum efficiency and an excited-state lifetime of about 350 μs. We derived the crystal field and Racah parameters and calculated the appropriate Tanabe–Sugano diagram for this phosphor. We found that 1E emission quenches due to the thermally-assisted cross-over with the 3T2 state and that the relatively high Debye temperature of 783 K of Ca6Ba(PO4)4O facilitates efficient emission. Since Ca6Ba(PO4)4O also provides efficient yellow emission of the Eu2+ dopant, we calculated and explained its electronic band structure, the partial and total density of states, effective Mulliken charges of all ions, elastic constants, Debye temperature, and vibrational spectra. Finally, we demonstrated the application of phosphor in a luminescence intensity ratio thermometry and obtained a relative sensitivity of 1.92%K−1 and a temperature resolution of 0.2 K in the range of physiological temperatures.

Thermally Robust Broadband Near-Infrared Luminescence in the NaGaP2O7:Cr3+ Phosphor

The near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) is an emerging portable light source and has multifunctional applications based on spectroscopic technology. Nevertheless, it is still difficult to develop broadband NIR materials with strong resistance toward thermal quenching. In this work, a thermally robust broadband NIR phosphor NaGaP2O7:Cr3+ was reported, which has an emission peak located at 793 nm, and the emission spectrum covers 650–1100 nm with a full width at half-maximum (fwhm) of 115 nm. The emission intensity at 150 °C was surprisingly maintained as 85.45% of that at 25 °C, indicating an outstanding ability to resist thermal quenching. A systematic investigation of aspects such as structural rigidity, the band gap of the host, and the electron phonon coupling effect was carried out to understand the mechanism of thermally robust luminescence in this material. Finally, the NaGa0.94Cr0.06P2O7 NIR phosphor and 450 nm InGaN LED chip were combined to produce a prototype NIR light source. This device generates a NIR output power of 44.43 mW and a photoelectric conversion efficiency of 10.4% when driven at 150 mA, demonstrating a good performance of this material for practical applications.

Rigid phenanthro[4,5-abc]phenazine-cored iridium(III) complexes for high-performance near-infrared emission at about 800 nm in solution-processed OLEDs

Simultaneously achieving high-efficiency and long-wavelength emission in near-infrared (NIR)-emitting iridium(III) complexes remains a huge challenge yet due to non-radiative decay of their susceptible excited states according to the energy-gap law. Herein, three new NIR-emitting iridium(III) complexes, namely TPAIr, HTIr and DPTAIr with donor-acceptor-donor (D-A-D) cheating architecture, are rationally designed and synthesized to address this issue. In these complexes, π-extended and electron-deficient phenanthro[4,5-abc]phenazine (PPz) are employed as the rigid acceptor core. Triphenylamine (TPA), n-hexylthiophene (HT) and diphenyl thiophen-2-amine (DPTA) are used as peripheral donor units, respectively. The effect of donor types on their photophysical, electrochemical and electroluminescent properties is primarily studied. It is found that the combined effect of the rigid central acceptor and peripheral donors together endow these complexes with high photoluminescence quantum yield (PLQYs) and a variational wavelength. Real NIR emission from 774 to 798 nm with PLQYs of 9–15 % and decay lifetimes as short as 0.32 μs are observed in solutions. Solution-processed organic light-emitting diodes with DPTAIr as an emitter reveals an intense NIR emission at 800 nm with an outstanding EQE of 2.98 % and a high radiance of 17,083 mW Sr−1 m−2. More importantly, the efficiency roll-off is efficiently alleviated in the devices at high current density. Our study provides a feasible molecular design strategy to develop NIR phosphors for long-wavelength, highly efficient and small efficiency roll-off NIR-OLEDs.

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 near-infrared phosphor Li3Sc2(PO4)3:Cr3+ realized by two-sites occupation

The near-infrared phosphor converted light-emitting diodes (NIR pc-LEDs) have been broadly used in the fields of night vision, biomedicine, nondestructive testing and food analysis. Over the past few years, many Cr3+ doped NIR phosphorus has been reported. However, the realization of ultra-broad band NIR emission with high quantum efficiency remains a great challenge. Here, we report an ultra-broadband NIR emitting phosphor Li3Sc1.92(PO4)3:0.08Cr3+ with a full width at half maximum (FWHM) of 240 nm. The reason for the ultra-broad emission band is that the host Li3Sc2(PO4)3 provides two different kinds of ScO6 octahedral sites for Cr3+ ions to occupy. This FWHM is better than most NIR emitting phosphors reported so far. Our research indicates that Li3Sc2(PO4)3:Cr3+ phosphors have great potential in night vision and NIR spectroscopy.

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.

Molten Salt Synthesis of Broad-Band Near-Infrared InBO3:Cr3+ Submicron Phosphor and Its Luminescent Enhancement by Lanthanide Ion Codoping.

Phosphor materials with small particle sizes and high luminescent efficiency are desired for the fabrication of phosphor-converted light-emitting diodes (pc-LEDs). Near-infrared (NIR) pc-LED light sources have great application potential in the food industry and medical fields, which stimulate the extensive exploration of NIR phosphors. In this work, broad-band NIR-emitting InBO3:Cr3+ phosphors with submicron size and spherical morphology are successfully synthesized via the molten salt method. The InBO3:Cr3+ phosphor exhibits a broad emission band covering 700-1000 nm and peaking at ∼820 nm. The maximum emission intensity is obtained for InBO3:0.02Cr3+ with an internal quantum yield (IQY) of ∼62%, which is higher than that of microsized counterparts derived from solid-state reaction. Furthermore, the absorption and emission enhancements are achieved by codoping lanthanide ions into InBO3:Cr3+ submicron phosphors. The codoping of inert La3+ ions can increase the absorption efficiency of InBO3:Cr3+, due to the increased octahedral distortion of Cr3+ sites. The codoping of active Yb3+ ions can significantly enhance the NIR emissions of InBO3:Cr3+ between 950 and 1100 nm. Meanwhile, the increased IQY of ∼73% is achieved for InBO3:0.02Cr3+,0.005Yb3+ simultaneously with suppressed thermal quenching, originating from the effective energy transfer from Cr3+ to Yb3+ ions.

Spectral Regulation and Efficiency Optimization in Cr3+‐Doped Gadolinium Aluminum Gallium Garnet Near‐Infrared Ceramic Phosphors via Crystal‐Field Engineering

AbstractThe near‐infrared (NIR) phosphor‐converted light‐emitting diode (pc‐LED) is a new NIR light source with both compact structure and high efficiency, and its performances is greatly depended on the NIR phosphors. Herein, this work presents a Cr3+‐doped gadolinium aluminum gallium garnet (GAGG:Cr3+) NIR ceramic phosphor with a broadband emission in the range of 650–850 nm, and optical performances that can be regulated via crystal‐field engineering. By optimizing the Al/Ga ratio, an external quantum efficiency as high as 65% is observed. The thermal stability is enhanced with the increase of Al content, which is attributed to the broadening of bandgap and the weakening of electron–phonon coupling effect. The NIR light output powers of the fabricated device based on the GAGG:Cr3+ ceramic are up to 88.9 mW @ 10 mA and 1247.7 mW @ 200 mA, while the electro‐optical conversion efficiencies were 28.5% @ 10 mA and 17.7% @ 200 mA, respectively. In addition, the NIR pc‐LED exhibited a strong penetrability such that the veins in a palm could be clearly identified, allowing for its potential use in biosecurity applications.