Near-infrared Phosphor Research Articles

Efficient Broadband Near‐Infrared Emitters in Lead‐Free Metal Halides with Record Photoluminescence Quantum Yield Under Blue Light Excitation

AbstractRealizing ultra‐efficient broadband near‐infrared (NIR) luminescence, especially under blue light excitation, remains an enormous challenge in lead‐free metal halides. Herein, the efficient NIR emission under blue light excitation is achieved in Sb3+‐doped 0D (ETPP)2ZnCl4xBr4‐4x (x = 0–1) (ETPP+ = (Ethyl)triphenylphosphonium) through coordination structure modulation and halogen substitution. Compared with the visible light emission of Sb(III)‐based compounds, the emission in Sb3+‐doped (ETPP)2ZnCl4xBr4‐4x shifts to the NIR region due to the large excited state lattice distortion. Parallelly, the excitation bands gradually shift from 376 to 450 nm as Br gradually replaces Cl, and the emission bands can further shift from 702 to 763 nm. Thus, the broadband NIR emission at 763 nm with a record luminous efficiency of 55.4% under 450 nm excitation can be achieved in Sb3+‐doped compounds. Moreover, the large‐scale synthesis technique of Sb3+‐doped (ETPP)2ZnBr4: NIR phosphors at room temperature is further developed and this compound exhibits impressive thermal and chemical‐stabilities. Finally, a high‐performance NIR light‐emitting‐diode is fabricated by combining a commercial blue chip and (ETPP)2ZnBr4:10%Sb3+ phosphors, which shows the most advanced photoelectric efficiency (17.8%) and output power (67.7 mW) in lead‐free metal halides. Thus, the as‐fabricated device is further demonstrated in the applications of night vision and biomedical imaging.

Efficient and Near-Zero Thermal Quenching Cr3+-Doped Garnet-Type Phosphor for High-Performance Near-Infrared Light-Emitting Diode Applications.

In recent years, near-infrared (NIR) phosphors have attracted great research interest due to their unique physical properties and broad application prospects. However, obtaining NIR phosphors with both high quantum efficiency and excellent thermal stability remains a great challenge. In this study, novel NIR Ca3Mg2ZrGe3O12:Cr3+ phosphors were successfully prepared using a high-temperature solid-phase method, and the structure and luminescent properties of the material were systematically investigated. Ca3Mg2ZrGe3O12:0.01Cr3+ emits NIR light in the range of 600 to 900 nm with a peak at 758 nm and a half-height width of 89 nm under the excitation of 457 nm blue light. NIR luminescence shows considerable quantum efficiency, and the internal quantum efficiency of the optimized sample is up to 68.7%. Remarkably, the Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor exhibits a near-zero thermal quenching behavior, and the luminescence intensity of the sample at 250 °C maintains 92% of its intensity at room temperature. The mechanism of high thermal stability has been elucidated by calculating the Huang Kun factor and activation energy. Finally, NIR pc-LED devices prepared from Ca3Mg2ZrGe3O12:0.01Cr3+ phosphor with commercial blue LED chips have good performance, proving that this Ca3Mg2ZrGe3O12:0.01Cr3+ NIR phosphor has potential applications in night vision and biomedical imaging.

Co-training machine learning enables interpretable discovery of near-infrared phosphors with high performance

Near-infrared (NIR) phosphors based on Cr3+ doped garnets present great potential in the next generation of NIR light sources. Nevertheless, the huge searching space for the garnet composition makes the rapid discovery of NIR phosphors with high performance remain a great challenge for the scientific community. Herein, a generalizable machine learning (ML) strategy is designed to accelerate the exploration of innovative NIR phosphors via establishing the relationship between key parameters and emission peak wavelength (EPW). We propose a semi-supervised co-training model based on kernel ridge regression (KRR) and support vector regression (SVR), which successfully establishes an expanded dataset with unlabeled dataset (previously unidentified garnets), addressing the overfitting issue resulted from a small dataset and greatly improving the model generalization capability. The model is then interpreted to extract valuable insights into the contribution originated from different features. And a new type NIR luminescent material of Lu3Y2Ga3O12: Cr3+ (EPW~750 nm) is efficiently screened, which demonstrates a high internal (external) quantum efficiency of 97.1% (38.8%) and good thermal stability, particularly exhibiting promising application in the NIR phosphor-converted LEDs (pc-LED). These results suggest the strategy proposed in this work could provide new viewpoint and direction for developing NIR luminescence materials.

Improvement of luminescence properties in Zn2.1Mg0.9Ta2O8:Cr3+ by the cation substitution and its application in biological nondestructive testing and night vision lighting.

Recently, it is of great significance to explore near-infrared (NIR) phosphor with more application prospects. In this work, a series of Zn2.1 Mg(0.9 - y)GaySnyTa(2 - y)O8:0.003Cr3+ NIR broadband phosphors with high quantum yields and high thermal stability are discovered by uniquely replacing [Mg2+-Ta5+] in Zn2.1Mg0.9Ta2O8 with [Ga3+-Sn4+]. Under 460 nm excitation, Zn2.1Mg0.85Ga0.05Sn0.05Ta1.95O8: 0.003Cr3+ depicts the 600-1100 nm broadband emission with a full-width at half maximum (FWHM) of 210 nm, and the quantum yields can reach 61.2%. Finally, the phosphor was mixed with epoxy resin and encapsulated in a 460 nm blue light emitting diode (LED) chip to convert the NIR LED by phosphor (NIR pc-LED), which was applied in the field of biological nondestructive testing and night vision lighting.

The highly efficient and stable near-infrared phosphor Ca3MgSnGe3O12: Cr3+ for multifunctional application

The investigation of efficient and stable near-infrared (NIR) luminescent materials is crucial for rapidly developing near-infrared spectroscopic techniques. Herein, NIR phosphors Ca3MgSnGe3O12: Cr3+ with ultra thermal stability and high internal quantum yield (IQY) are explored. The emission intensity remained at 91.75 %@423 K of room temperature and the IQY/EQE reaches 91.41 %/34.04 % after doping the H3BO3 flux agent for optimization. Moreover, a single luminescence center was identified by cryogenic photo luminescence spectroscopy (PL) from 4 K to 300 K and lifetime decay curve. Importantly, NIR light can easily removes all kinds of background interference that cannot be easily eliminated by visible light, which is not only widely used in night vision and biological tissue penetration, but also has higher application prospects in NIR fingerprint detection. Moreover, it clearly displays high level of fingerprint details under high temperature conditions and after water immersion, thus it is perfectly suited for using in Automatic Fingerprint Identification System (AFIS) systems. Therefore, Ca3MgSnGe3O12: Cr3+ NIR pc-LEDs have great potential for latent fingerprint detection at actual crime scenes.

La3Sc2Ga3O12:Cr3+, Nd3+ near-infrared phosphor for nondestructive detection and luminescence thermometry

To develop continuous broadband emission near-infrared (NIR) phosphors compatible with blue LED chips, numerous Cr3+-Yb3+ co-doped phosphors have been synthesized. However, the emission spectra of Cr3+ vary significantly across different matrix materials, while Yb3+ maintains a relatively stable emission spectrum. This variation leads to notable luminescence depressions between 850 and 900 nm in many Cr3+-Yb3+ co-doped phosphors. To address this emission spectrum gap, we utilized Cr3+ as a sensitizer and introduced Nd3+ as the luminescence center within the La3Sc2Ga3O12 matrix material, establishing a Cr3+-Nd3+ energy transfer channel. Under 480 nm excitation, we tuned emission peaks at 800 nm (Cr3+) and 881 nm (Nd3+). The stable NIR emission of Nd3+ effectively compensates for the missing spectrum in Cr3+-Yb3+ co-doping. The Cr3+-Nd3+ energy transfer process was thoroughly analyzed using diffuse reflection spectrum, excitation spectrum, and fluorescence decay curves. The LSGO:0.125Cr3+, 0.03Nd3+ compound with the best optical performance was packaged with a 480 nm LED chip to create a NIR light source. At a working current of 10 mA, it achieved a photoelectric conversion efficiency of 9.45 %, demonstrating its potential for applications in non-destructive detection and luminescence thermometry. This work presents a novel strategy for tuning NIR spectral distribution and developing continuous broadband NIR phosphors.

Activator Heavy Solid Solution in Rigid Framework: An Effective Strategy Toward Highly Efficient and Thermally Stable Near‐Infrared Emission for Wireless Communication

AbstractBroadband near‐infrared (NIR) phosphors are crucial components of next‐generation NIR lighting sources. However, the design of high‐efficiency and thermally stable NIR phosphors still poses a significant challenge, whose quantum efficiencies (QEs) are directly limited by their absorption efficiency (AE) toward incident light. Here, an efficient and thermally stable NIR emission with AE up to 64.9% and emission keeping of 91.23% at 423 K is demonstrated via Cr3+ heavy solid solution in rigid framework LiCaGaF6:Cr3+ (LCGFC). Isomorphic LiCaAlF6:Cr3+ also exhibits thermal robustness, while traps in low doping concentration and low QEs. Comparative studies on crystal structure, formation energy, and Helmholtz free energy disclose that Cr3+ substitution on equivalent and equiradius Ga3+ site versus radii differential Al3+ site generates heavier solid solution and sustainable structural rigidity with acquirement of higher AE and better thermal stability. Incorporating LCGFC with a blue InGaN chip, a NIR phosphor‐converted light‐emitting diode is fabricated to realize stable wireless optical communication with good penetrability through biological tissue and some organic products. These findings develop a strategy based on activator heavy solid solutions in a rigid framework to achieve high‐efficiency and thermally stable NIR phosphors but also advance their novel optoelectronic applications.

Enhanced Thermally Stability and Broadened Emission for Gd3Ga5O12:Cr3+ Phosphors via Si3N4 Substitution

AbstractFar‐red (FR) and near‐infrared (NIR) spectroscopy technologies have attracted extensive attention. How to obtain luminescent materials suitable to FR‐NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) is a crucial challenge. Herein, a Si3N4‐substitution strategy is employed to regulate the luminescence of Gd3Ga5O12:Cr3+ (GGG:Cr3+) phosphors. The bandwidth of GGG:Cr3+ is 95 nm, and then it is broadened to 116 nm due to the Si3N4‐substitution. Furthermore, at 423 K the thermal stability is enhanced to 98.7% of that at room temperature, which is higher than the reported 92.7%@423 K for the Si3N4‐free sample. The intensity of the optimal specimen is elevated 2.9 times compared with the Si3N4‐free sample sintered at the same condition. The FR pc‐LED is manufactured by using the optimized sample, and its FR output power is 47.1 mW with a conversion efficiency of 15.9% driven by 100 mA. This work paves a new way to design high‐performance NIR phosphors.

High-Performance Tunable Near-Infrared Emitters of Cr3+-Activated Garnet Phosphor Enabled by Chemical Unit Co-Substitution.

The escalating demand for portable near-infrared (NIR) light sources has posed a formidable challenge to the development of NIR phosphors characterized by high efficiency and exceptional thermal stability. Taking inspiration from the chemical unit co-substitution strategy, high-performance tunable (Lu3- xCax)(Ga5- xGex)O12:6%Cr3+ (x = 0-3) phosphors are designed with an emission center from 704 to 780nm and a broadest full width at half maximum (FWHM) of up to 172nm by introducing Ca2+ and Ge4+ ions into the garnet structure. In particular, Lu3Ga5O12:6%Cr3+ demonstrates an anti-thermal quenching phenomenon (I423K = 113.1%). Compared to Lu3Ga5O12:6%Cr3+, Lu2CaGa4GeO12:6%Cr3+ exhibits significantly improved FWHM and IQE by 108nm and 25.5%, respectively, while maintaining good thermal stability (I423K = 80.4%). Finally, Lu2CaGa4GeO12:6%Cr3+ phosphor is combined with a 465nm blue LED chip to fabricate NIR LED devices, exhibiting a NIR electroluminescence efficiency of 13.31%@100mA and demonstrating successful applications in nocturnal illumination and biomedical imaging technology. This work offers a fresh perspective on the design of highly efficient NIR garnet phosphors.

Study on the Performance of Deep Red to Near-Infrared pc-LEDs by the Simulation Method Considering the Distribution of Phosphor Particles.

Effectively utilizing deep red to near-infrared (DR-NIR) phosphors to achieve the optimal performance of NIR phosphor-converted white LEDs (DR-NIR pc-wLEDs) is currently a research hotspot. In this study, an optical model of DR-NIR pc-wLEDs with virtual multilayer fluorescent films was established based on the Monte Carlo ray-tracing method. Different gradient distributions of the particles were assigned within the fluorescent film to explore their impact on the optical performance of pc-LEDs. The results show that, for the case with single-type particles, distributing more DR-NIR particles far from the blue LED chip increased the overall radiant power. The distribution of more DR-NIR particles near the chip increased the conversion ratio from blue to DR-NIR light. The ratio of the 707 nm fluorescence emission intensity to the 450 nm excitation light intensity increased from 1:0.51 to 1:0.28. For multiple-type particles, changes in the gradient distribution resulted in dual-nature changes, leading to a deterioration in the color rendering index and an increase in the correlated color temperature, while also improving the DR-NIR band ratio. The reabsorption caused by the partial overlap between the excitation band of the DR-NIR particles and the emission band of the other particles enhanced the radiant power at 707 nm. Distributing DR-NIR phosphor particles closer to the chip effectively amplified this effect. The proposed model and its results provide a solution for the forward design of particle distributions in fluorescent films to improve the luminous performance of DR-NIR pc-wLEDs.

The synthesis and application of Ni2+-doped NIR-II Phosphors composed of MgAl2-xGaxO4 solid-solution

Near-infrared (NIR) light has been widely used in fields, such as biometrics recognition, security monitoring, lighting for indoor agriculture, food safety inspection and biomedical imaging. NIR phosphors are crucial components for NIR phosphor-conversion light-emitting diodes (NIR pc-LED). Compared with the traditional high-temperature solid phase method for spinel-type phosphors, the synthesis by the sol-gel combustion method is rapid, more efficient, and requires lower temperatures, with good homogeneity and uniformed nano-size particle. Here we report the synthesis of a panel of NIR phosphors that are composed of nano-sized Ni2+-doped MgAl2-xGaxO4 solid-solution of spinal crystals with high phase purity. By adjusting the ratios of Al/Ga, the Ni2+-doped phosphors with spinel (MgAl2O4) to hybrid-spinel (MgGa2O4) crystal structures were obtained. The phosphor with the Al/Ga ratio of 0.8–1.2 showed the maximal NIR emission intensity, which was 5.9 times higher than that of the MgAl2O4 spinel structure, with an internal photoluminescence quantum efficiency of 31.63 %. The phase transformation of the crystal form from spinel to hybrid-spinel resulted in a shift of the emission peak from 1223 nm to 1287 nm, realizing a ∼ 64 nm structure-dependent tunability of NIR luminescence. We assembled a NIR pc-LED device using the optimal phosphor and a commercially available near ultraviolet LED, and experimentally demonstrated its application for night-vision monitoring and bioimaging of veins in a human hand.

Remarkable broadband NIR emission of BaCa2MgSi2O8:Cr3+ phosphors and Eu2+ co-doping modulation

Developing high-performance broadband NIR (near-infrared) phosphors remains a crucial pursuit for the next-generation smart NIR light source. This study demonstrates the successful synthesis of BaCa2MgSi2O8:Cr3+ phosphors exhibiting exceptional broadband NIR emission via a high-temperature solid-state reaction. Notably, the 0.03Cr3+ doped composition, under 485 nm excitation, shines with a remarkable broadband emission spanning 700 nm–1100 nm and boasts a full width at half maximum (FWHM) of 134 nm. This work meticulously explores the intricate interplay between Cr3+ doping concentration, temperature, crystal field strength, and the Huang-Rhys parameter, shedding light on the underlying luminescence mechanisms. Moreover, the BaCa2MgSi2O8:0.03Cr3+ phosphor exhibits exceptional thermal stability, retaining approximately 70 % of its integrated emission intensity at 425 K compared to room temperature. To further expand the excitation range, Eu2+ was introduced as a co-dopant, successfully broadening the excitation spectrum to encompass nearly the entire ultraviolet–visible region (ranging from 250 nm to 750 nm). The presence of Eu2+→Cr3+ energy transfer was elucidated, and the impact of Eu2+ doping was thoroughly investigated. Moreover, the synthesized phosphor has been successfully integrated into a NIR phosphor-converted light-emitting diode (pc-LED), showcasing their potential application in the realms of night vision and NIR vascular imaging. These findings offer invaluable insights into Cr3+ luminescence behavior and pave the way for the development of novel NIR phosphors with enhanced functionalities, propelling us closer to the realization of next-generation smart lighting solutions.

Efficient and Tunable Near-Infrared Luminescence in Cubic Phosphate K2AlTi(PO4)3:Cr3+ for Spectroscopy Applications.

Broadband near-infrared (NIR) phosphors are crucial components of NIR phosphor-converted light-emitting diode (pc-LED) sources for various smart spectroscopy applications. However, developing an efficient, tunable, and inexpensive broadband NIR phosphor with sufficient spectral coverage remains a great challenge. In this work, a cubic phosphate K2AlTi(PO4)3 with highly structural rigidity was chosen as host material for Cr3+ substitution to create an efficient NIR emission. Synthesizing this compound, the obtained material exhibits a broadband NIR emission covering 700-1200 nm with a peak wavelength ranging from 820 to 860 nm depending on the Cr3+ substituting concentration. The Cr3+ concentration optimized sample possesses a photoluminescence quantum yield (PLQY) of 76.4% with an emission peak centered at 857 nm and a full width at half-maximum (fwhm) of 184 nm under 464 nm exaction, demonstrating an efficient and relatively long-wavelength NIR emission with wide spectral coverage. This broadband NIR emission is mainly derived from a single kind of emission center deduced from spectral analysis, luminescence dynamics, and first-principle calculations. Using this material, the fabricated NIR pc-LED device presents an excellent NIR output power and NIR photoelectric conversion efficiency, making this material attractive in practical applications of night-vision and bioimaging. Therefore, this work not only provides a broadband NIR material with superiorities of low cost, high efficiency, wide-range tunability, wide spectral coverage, and relatively long-wavelength NIR emission for spectroscopy applications but also highlights some clues to discover this kind of materials.

Ni2+ activated broadband near-infrared II germanate phosphor for pc-LED applications

The broadband near-infrared (NIR) pc-LED is considered as a new generation of light source for substance measurements based on NIR spectroscopy. The most studied Cr3+ doped broadband NIR phosphors emit in the near-infrared I region. However, there is a demand for broadband near-infrared II solid-state light sources for expanding the variety of detected substances. Herein, Ni2+ activated NIR II Mg14Ge5O24 phosphor is synthesized by high-temperature solid-state method. The phosphor shows a asymmetric broad NIR emission band peaked at 1420 nm, that is assigned to the 3T2(3F)→3A2(3F) transition of Ni2+. It is observed that the asymmetric emission band is contributed from two Ni2+ centers, Ni2+(I) and Ni2+(II), occupying Ge4+ site with the emission peaked at 1313 nm and Mg2+ site with the emission peaked at 1435 nm, respectively. It is found that the addition of Ti4+ and B3+ can significantly change the intensity ratio of the two Ni2+ centers and enhance the overall emission intensity. Moreover, the addition of Mn4+ results in only Ni2+(II) emission. The origin of the unique features mentioned above is discussed. The temperature dependence of the NIR emissions is also studied. Finally a broadband NIR II pc-LED with a moderate electro-optical conversion efficiency of 1.4 % is fabricated based on a 400 nm LED chip. The results indicate that the modified Mg14Ge5O24:Ni2+ is a potential broadband NIR II phosphor for pc-LED applications.

An energy transfer strategy towards versatile sensing applications from Cr3+ and Yb3+ codoped near infrared phosphors

Near-infrared (NIR) phosphors have garnered notable attention for their extensive applications in anti-counterfeiting, optical imaging, non-invasive medical diagnosis and detection. Nevertheless, the quest for NIR phosphors with outstanding detection and sensing capabilities remains a challenge. In this study, we have successfully prepared Ga1.6Mg0.2Ge0.2O3:Cr3+,Yb3+ NIR phosphors by codoping and substitutation strategies. When incorporated into polydimethylsiloxane films, these phosphors demonstrated a direct correlation between luminescence intensity ratio and applied stress under 450 nm excitation. Moreover, variations in luminescence spectra occurred with different compositions and concentrations of liquids coated on the film, facilitating both force measurement and composition analysis. Furthermore, a NIR phosphor-converted light-emitting diode (pc-LED) was fabricated by integrating phosphor with a blue LED chip, exhibiting excellent performance. Utilizing the prepared NIR pc-LED as a light source, we facilitated non-destructive imaging, night vision, and anti-counterfeiting applications with an infrared camera. These findings suggest that the synthesized NIR phosphors possess hold promise for diverse detection and sensing applications.

Multifunctional Near-Infrared Phosphors Cr3+/Ni2+ Codoped Mg3Ga2GeO8 Based on Energy Transfer from Cr3+ to Ni2.

Currently, near-infrared (NIR) light-emitting materials have been widely used in many fields, such as night vision, bioimaging, and nondestructive analysis. However, it is difficult to achieve multifunction in certain NIR light emitting phosphor. Herein, we propose a new near-infrared phosphor Mg3Ga2GeO8:Cr3+,Ni2+ that can be applied to at least three fields, i.e., identification of compounds, temperature sensing, anticounterfeiting, and other applications. The multifunctional material exhibited efficient broadband emission of 650-1650 nm under 420 nm excitation. The emission intensity of Ni2+ in Mg3Ga2GeO8:Cr3+,Ni2+ is enhanced by two times compared with that of Ni2+ in Mg3Ga2GeO8:Ni2+ due to the energy transfer process. Compared with phosphor single doped with Ni2+, Mg3Ga2GeO8:Cr3+,Ni2+ is more convincing in organic compound recognition because it is based on two emission bands: 600-1100 nm and 1100-1650 nm. As a temperature sensor, Mg3Ga2GeO8:Cr3+,Ni2+ is an ideal temperature-sensing material. This work not only provides a super broadband NIR emitting phosphor with multiple functions but also presents a practical approach for the development of high-efficiency and multifunctional NIR phosphors.

Achieving Ultrahigh Thermal Stability in Cr3+-Activated Garnet Phosphors through Electron Migration between Thermally Coupled Levels.

Recently, Cr3+-activated near-infrared (NIR) phosphors have received much more attention due to their excellent photoluminescence (PL) properties. However, most of them suffer from poor thermal stability which limits further application. Herein, a novel Lu2CaGa4SnO12:Cr3+ phosphor with broadband NIR emission (λem = 750 nm) is synthesized successfully. Despite the good luminescence property, its PL intensity decreases obviously with temperature (I425K = 79%). To improve the thermal stability, a series of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ (x = 0-1.0) solid solutions with tunable thermal quenching performance have been designed. It is found that the fluorescence intensity ratio (FIR) of 4T2 → 4A2 to 2E → 4A2 [I(4T2)/I(2E)] transitions (i.e. electron occupation) decreases monotonously with increasing [Lu3+-Ga3+] co-substitution, resulting from a strengthened crystal field strength and increased energy difference between 4T2 and 2E energy levels. Benefiting from the various thermal population and energy difference Δ', the PL thermal quenching behavior of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ can be adjusted easily, and the corresponding mechanism is explored in detail. Most notably, the emission intensity of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ at 425 K can reach up to 142% compared with that at 300 K, which may be the best for Cr3+-activated NIR phosphors. This work may provide an alternative path for the development of thermally stable broadband NIR phosphors.

Near-infrared optical properties of Cs2KScF6:Cr3+ phosphor for high-power light-emitting diodes

The recent years have witnessed a great leap for near-infrared (NIR) spectroscopy technology in multifunctional application fields. In this study, a double-perovskite structured Cr3+-doped Cs2KScF6 fluoride NIR phosphor with peak location at 778 nm and full-width at half maximum (FWHM) of 95 nm was synthesized by a co-precipitation method. The integral emission intensity at 423 K retains 70 % of that at room temperature (RT), showing good luminescent thermal stability. Combining the obtained phosphor in an NIR phosphor converted light-emitting diode (NIR pc-LED) device, the output power and photoelectric conversion efficiency can reach 72.28 mW and 6.83 % at 320 mA. By virtue of the good optical performance, clear structural images of different fruits were visualized by using the NIR pc-LED as light source, suggesting the potential of Cs2KScF6:Cr3+ phosphor to be used in high-power LED devices.

Ruddlesden-Popper type Sr(La,Gd)2Al2O7:Cr3+ layered perovskite new phosphors for NIR pc-LED application

Near-infrared phosphor converted light-emitting diodes (NIR pc-LEDs), as a state-of-the-art type of NIR sources, are finding multifaceted applications, where phosphor is a crucial component. In hope to provide new choices for NIR lighting, we synthesized in this work the two series of Ruddlesden -Popper type layered perovskite phosphors of SrLa2Al2-xO7:xCr3+ (x = 0–0.02) and SrLa2-yGdyAl1.984O7:0.016Cr3+ (y = 0–2), followed by detailed structure and luminescence investigation. SrLa2Al2-xO7:xCr3+ was found to emit ∼700–800 nm NIR light under UV excitation and be able to maintain ∼54.3 % of its room temperature intensity at 423 K, which is remarkably higher than those (∼25–30 %@423 K) of the Mn4+ activated perovskite NIR phosphors. Luminescence regulation was achieved by substituting La3+ with Gd3+, and it was revealed that Gd3+ may act as a sensitizer to significantly enhance Cr3+ luminescence (∼346 % at 77 K) through Gd3+ → Cr3+ energy transfer, which was confirmed by spectral and fluorescence lifetime analysis. The observed spectral features and the influence of Gd3+ were rationalized by considering crystal structure, local coordination, and crystal field. Finally, an NIR pc-LED device showing strong ∼700–900 nm luminescence was fabricated to show potential application of the phosphor in night vision and plant lighting.

Broadband near-infrared luminescence in spinel Zn4InSbO8:Cr3+ phosphor for light-emitting diodes application

Near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) has been considered as a smart light source for NIR spectroscopy applications, leading to a growing need of developing broadband NIR phosphors. Herein, a new composition Zn4InSbO8:Cr3+ phosphor with classical spinel-type structure was synthesized, which emits a broadband NIR light covering a region of 700–1200 nm with a peak centered at 860 nm under 460 nm excitation. The sample with an optimized Cr3+ concentration possesses a full width at half maximum (FWHM) as broad as 180 nm mainly ascribing to multi crystallographic sites occupation. Moreover, the absorption efficiency (AE), internal quantum efficiency (IQE) and thermal stability were investigated to estimate the practicality. The relatively long-wavelength NIR emission produced by Cr3+ in this spinel make it suitable for multi-functional applications. Finally, the asprepared phosphor combining with blue LED chip is used to fabricate a prototype NIR pc-LED, giving a NIR output power of 4.8 mW under 100 mA forward bias current with a photoelectric efficiency of 1.63%, showcasing the potential use of this material as a luminescent converter in the application of NIR pc-LEDs.