Photoluminescence Properties of AScSi2O6:Cr3+ (A = Na and Li) Phosphors with High Efficiency and Thermal Stability for Near-Infrared Phosphor-Converted Light-Emitting Diode Light Sources

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.

Unlocking Cr3+-Cr3+ Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) hold promising potential as next-generation compact, portable, and intelligent NIR light sources. Nonetheless, the lack of high-performance broadband NIR phosphors with an emission peak beyond 900 nm has severely hindered the development and widespread application of NIR pc-LEDs. This study presents a strategy for precise control of energy-state coupling in spinel solid solutions composed of MgxZn1-xGa2O4 to tune the NIR emissions of Cr3+ activators. By combining crystal field engineering and heavy doping, the Cr3+-Cr3+ ion pair emission from the 4T2 state is unlocked, giving rise to unusual broadband NIR emission spanning 650 and 1400 nm with an emission maximum of 913 nm and a full width at half-maximum (fwhm) of 213 nm. Under an optimal Mg/Zn ratio of 4:1, the sample achieves record-breaking performance, including high internal and external quantum efficiency (IQE = 83.9% and EQE = 35.7%) and excellent thermal stability (I423 K/I298 K = 75.8%). Encapsulating the as-obtained phosphors into prototype pc-LEDs yields an overwhelming NIR output power of 124.2 mW at a driving current of 840 mA and a photoelectric conversion efficiency (PCE) of 10.5% at 30 mA, rendering high performance in NIR imaging applications.

Two-Site Occupation for Constructing Double Perovskite BaLaMgNbO6:Cr3+ Ultrabroadband NIR Phosphors

Given the escalating significance of near-infrared (NIR) spectroscopy across industries, agriculture, and various domains, there is an imminent need to address the development of a novel generation of intelligent NIR light sources. Here, a series of Cr3+-doped BaLaMgNbO6 (BLMN) ultrabroadband NIR phosphor with a coverage range of 650-1300 nm were developed. The emission peak locates at 830 nm with a full width at half maximum of 210 nm. This ultrabroadband emission originates from the 4T2→4A2 transition of Cr3+ and the simultaneous occupation of [MgO6] and [NbO6] octahedral sites confirmed by low photoluminescence spectra (77-250 K), time-resolved photoluminescence spectra, and electron paramagnetic resonance spectra. The fluxing strategy improves the luminescence intensity and thermal stability of BLMN:0.02Cr3+ phosphors. The internal quantum efficiency (IQE) is 51%, external quantum efficiency (EQE) can reach 33%, and thermal stability can be maintained at 60%@100 °C. Finally, we successfully demonstrated the application of BLMN:Cr3+ ultrabroadband in the qualitative analysis of organic matter and food freshness detection.

Comprehensive Review on Downconversion/Downshifting Silicate-Based Phosphors for Solar Cell Applications

Insufficient utilization of the solar spectrum in commonly employed solar cells, stemming from a spectral mismatch between the solar spectrum and the solar cell's band gap, poses a barrier to enhancing solar cell efficiency. To overcome this challenge, downconverting silicate phosphors are employed in solar cells to capture the infrared spectrum of sunlight, thereby augmenting solar cell efficiency. Downconversion/downshifting involves in converting high-energy photons into one or two near-infrared (NIR) photons. Remarkably, silicate-based downconverting phosphors enhance solar cell sensitization, light scattering, antireflectivity, and stability. This review delves into the various energy transfer mechanisms utilized in silicate phosphors. The key aspects covered in this review encompass the development of silicate phosphors that emit NIR light and their synthesis process. The working principle of the solar cell and its parameters are discussed. The impacts of silicate phosphor size, coverage, volume concentration, and arrangement on solar cell performance are also explored. Furthermore, the study addresses several intriguing approaches for developing innovative silicate phosphors to enhance solar cell performance.

Thermally Stable Red-Emitting Ca18K3Sc(PO4)14:Mn2+ Phosphor and Enhanced Luminescence by Energy Transfer Between Ce3+-Eu2+-Mn2

It is significant and valuable to investigate novel and high-performance red-emitting phosphors for high-quality wLED applications. Based on this consideration, we developed a novel Mn2+-doped red Ca18K3Sc(PO4)14:Mn2+ (CKSP:Mn2+) phosphor. The emission peak of CKSP:Mn2+ is located at 640 nm, presenting a broadband red emission with a fwhm of 79 nm under 405 nm excitation. The CKSP:1.0Mn2+ phosphor shows superior thermal stability. At 150 °C, the integrated PL intensity and peak intensity of the CKSP:1.0Mn2+ phosphor maintain 93.2 and 85.7% of those at 25 °C, respectively. Through the strategy of energy transfer among Ce3+-Eu2+-Mn2+, the PL intensity of Mn2+ has increased by nearly 118 times, and the quantum yield has improved from 6 up to 72%. The structure-related photoluminescence and energy transfer mechanisms are discussed in detail. The as-fabricated wLED pumped by a 370 nm LED chip combining commercial the green (Sr,Ba)2SiO4:Eu2+ phosphor, blue BaMgAl10O17:Eu2+ phosphor, and the as-synthesized CKSP:1.0Mn2+, 0.02Eu2+, 0.40Ce3+ phosphor shows excellent color quality (CCT = 5555 K, Ra = 87), which indicates that the CKSP:1.0Mn2+, 0.02Eu2+, 0.40Ce3+ phosphor has extraordinary broad prospects in future wLED applications.

Broadband near-infrared (NIR) emitting Cr3+ -doped La3 Ga5 SnO14 phosphor with long persistent and photostimulated persistent luminescence

Recently, long persistent phosphors (LPPs) have attracted significant attention as promising candidates for biomedical applications. However, the serious decrease in luminescence intensity in tissue still remains a major challenge. Therefore, exploring more competitive LPPs and achieving reproducible tissue imaging is crucial. In this study, a new series of near-infrared (NIR) phosphors La3 Ga5 Sn1-x O14 :xCr3+ (x = 0.005-0.05) were synthesized using a high-temperature solid-state method. The as-synthesized samples were characterized using X-ray diffraction, diffuse/photoluminescence spectroscopy, fluorescence decay curves, and thermoluminescence spectroscopy. Upon excitation with ultraviolet light, strong emission bands were observed in the range 600-1200 nm with an optimal doping concentration of x = 0.02 mol. Moreover, La3 Ga5 SnO14 :Cr3+ exhibits persistent luminescence due to the presence of suitable energy traps, which prompted the phosphor to emit NIR light even after the removal of the excitation source.

Advancing Near-Infrared Light Sources: Enhancing Chromium Emission through Cation Substitution in Ultra-Broadband Near-Infrared Phosphors

The growing interest in the use of near-infrared (NIR) radiation for spectroscopy, optical communication, and medical applications spanning both NIR-I (700-900 nm) and NIR-II (900-1700 nm) has driven the need for new NIR light sources. NIR phosphor-converted light-emitting diodes (pc-LEDs) are expected to replace traditional lamps mainly due to their high efficiency and compact design. Broadband NIR phosphors activated by Cr3+ and Cr4+ have attracted significant research interest, offering emission across a wide range from 700 to 1700 nm. In this work, we synthesized a series of Sc2(1-x)Ga2xO3:Cr3+/4+ materials (x = 0-0.2) with broadband NIR-I (Cr3+) and NIR-II (Cr4+) emission. We observed a substantial increase in the intensity of Cr3+ (approximately 77 times) by incorporating Ga3+ ions. Additionally, our investigation revealed that energy transfer occurred between Cr3+ and Cr4+ ions. Configuration diagrams are presented to elucidate the behavior of Cr3+ and Cr4+ ions within the Sc2O3 matrix. We also observed a phase transition at a pressure of 20.2 GPa, resulting in a new unknown phase where Cr3+ luminescence exhibited a high-symmetry environment. Notably, this study presents the pressure-induced shift of NIR Cr4+ luminescence in Sc2(1-x)Ga2xO3:Cr3+/4+. The linear shifts were estimated at 83 ± 3 and 61 ± 6 cm-1/GPa before and after the phase transition. Overall, our findings shed light on the synthesis, luminescent properties, temperature, and high-pressure behavior within the Sc2(1-x)Ga2xO3:Cr3+/4+ materials. This research contributes to the understanding and potential applications of these materials in the development of efficient NIR light sources and other optical devices.

The broadband emission of Cr3+-doped CaY2Mg2Ge3O12 and its applications for NIR detectors

A phosphor-converted light-emitting diode (pc-LED) is a prime light source in smart broadband near-infrared (NIR) spectroscopy. The performance of NIR pc-LEDs crucially depends on the employed NIR luminescent materials. In this study, we synthesized a novel high-efficiency broadband NIR phosphor, CaY2Mg2Ge3O12:Cr3+ (CYMG:Cr3+). Under 450 nm excitation, CYMG:Cr3+ exhibited remarkable broadband NIR emission from 650 to 900 nm with a full width at half maximum (FWHM) of 115 nm. Within the CYMG lattice, the Cr3+ ion occupies Ca/Y sites in the dodecahedron Ca/YO8 and Mg sites in the octahedron MgO6, giving rise to two distinct Cr3+ luminescence centers. Remarkably, the emission at 100 °C remained at 92% of its room temperature intensity and 81% at 150 °C, showcasing its exceptional thermal stability. The internal quantum efficiency (IQE) reached an impressive 81.1%, with an activation energy ΔE of 0.324 eV. Furthermore, we integrated the CYMG:Cr3+ phosphor with a commercial 450 nm blue chip to fabricate a micro NIR pc-LED, which exhibited stable NIR emission across different driving currents, with a NIR output power of 49.65 mW@400 mA and a photoelectric conversion efficiency of 10.52% at 20 mA. All findings highlight CYMG:Cr3+ as a stable and efficient broadband luminescent material for high-performance NIR LEDs.

Realization of Broadband Near-Infrared Emission with High Thermal Stability in YGa3(BO3)4: Cr3+ Borate Phosphor

As a key material for phosphor-converted light-emitting diodes (pc-LEDs) applications, broadband near-infrared (NIR) phosphors currently face poor thermal stability issues. In this work, we synthesized a broadband near-infrared phosphor YGa3(BO3)4: Cr3+ (YGBO: Cr3+) with a high thermal stability. The YGBO: Cr3+ sample exhibits a broadband near-infrared emission centered at 770 nm with a full width at half-maximum (fwhm) of 2130 cm-1 under blue light excitation. Benefiting from the borate host crystal's strong structural rigidity, wide optical band gap, and weak electron-phonon coupling strength, YGBO: Cr3+ demonstrates strong luminescence thermal stability, and the corresponding luminescence intensity can maintain 80% at 150 °C compared to room temperature. Furthermore, we fabricated a pc-LED device using a blue light chip and YGBO: Cr3+ phosphor, and confirmed its application potential as a near-infrared light source in the spectral analysis of fruit freshness.

Spectrally tunable near-infrared photoluminescence in MP3O9:Cr3+ (M = Al, Ga, In) phosphate phosphors

Modulation of the octahedral crystal field environment of Cr3+ is an effective approach to achieve tunable emission. Here, we prepared a series of broadband MP3O9:Cr3+ (M = Al, Ga, In) near-infrared (NIR) phosphors, and cubic AlP3O9:Cr3+ (APO-c:Cr3+) and monoclinic AlP3O9:Cr3+ (APO-m:Cr3+) phosphors were prepared by controlling the synthesis temperature. The emission wavelength was tuned from 787 nm for APO-c:Cr3+ to 894 nm for monoclinic InP3O9:Cr3+ (IPO:Cr3+) by regulating the M ion and reducing the crystal field intensity. Excitingly, the MP3O9:Cr3+ (M = Al, Ga, In) family shows excellent thermal stability; the emission intensity of APO-c:Cr3+, APO-m:Cr3+ and monoclinic GaP3O9:Cr3+ (GPO:Cr3+) can still maintain 95.6%, 86% and 86% of that at room temperature when heating to 423 K, respectively. An NIR LED device was prepared by incorporating GPO:Cr3+ and a blue light LED, demonstrating the potential application in night vision and non-destructive testing.

Isolated Coordination Polyhedron Confinement in ABP2O7:Mn2+ (A = Ba/Sr; B = Mg/Zn)

Many research efforts have focused on designing new inorganic phosphors to meet different application requirements. The structure-photoluminescence relationship between activator ions and the matrix lattice plays an irreparable role in designing target phosphors. Herein, a series of ABP2O7:Mn2+ (A = Ba/Sr; B = Mg/Zn) phosphors are prepared for a detailed study on the relationship between the luminescence performance and spatial structure and symmetry of the doping site of Mn2+. Due to the weak interaction between nearest B-B pairs, [BO5] is defined as an isolated coordination polyhedron whose structure and symmetry directly influence the photoluminescence of Mn2+. The emission wavelength of Mn2+ is ∼620 nm when it occupies the triangular bipyramid [MgO5] in BaMgP2O7. When Mn2+ occupies the quadrangular pyramid-typed [MgO5] or [ZnO5] in SrMgP2O7, SrZnP2O7, and BaZnP2O7, the emission wavelengths peak at ∼670 nm. We propose a conception of isolated coordination polyhedral confinement to clarify the luminescence performance of Mn2+ in the fivefold coordination configuration with different geometries, which has great theoretical research significance for designing inorganic phosphors.

Regulating Luminescence Thermal Quenching of Praseodymium-Doped Niobo-Tantalate Phosphor through Intervalence Charge Transfer Band Displacement

Pr3+-related intervalence charge transfer (IVCT) bands are a research hotspot owing to their amelioration in the luminescence thermal quenching of Pr3+-activated phosphors. Here, a typical IVCT band displacement strategy via a topological chemical scheme is reported to optimize the luminescence thermal quenching performance of praseodymium-doped niobo-tantalate. The substitution of Ta5+ ions for Nb5+ ions reduces the valence-weighted average cation optical electronegativity and increases the bond lengths of the activator (Pr3+) to the ligand cations (Nb5+ and Ta5+) via adjusting the crystal structure, leading to an increase in the IVCT energy level position from 3.521 to 4.139 eV. The increase in the IVCT energy level leads to an increase in the number of electrons located in the Pr3+ 3P0 energy level, which compensates for the emission of 1D2 during warming. Especially, the energy gap value of the IVCT band is positively correlated with the thermal quenching activation energy ΔE2. ΔE2 increases, the crossover point rises, and the nonradiative transition decreases, further enhancing the Pr3+ 1D2 emission. At 503 K, the 1D2 emission integral intensity increases from 14 to 224% relative to the 303 K original integral intensity. This IVCT band displacement strategy can be used as a scheme for designing antithermal quenching luminescence materials.

Deep-red-emitting phosphors of Mn4+-activated tantalite for high-sensitivity lifetime thermometry and security films

Herein, single monoclinic phase Mn⁴⁺-doped Sr₂InTaO₆ (SITO) phosphors were reported in terms of both luminescence behaviors and potential applications. The optimal Mn⁴⁺-doped SITO (0.3 mol%) exhibited a good color purity of 92.9% in a deep-red region with a chromaticity coordinate of (0.707, 0.293). In addition, the local structure of Mn⁴⁺ in the SITO matrix was determined. The crystal-field strength was calculated to be approximately 1781.7 cm^-1 whereas the nephelauxetic ratio was determined to be 1.04. Furthermore, the flexible SITO:Mn⁴⁺-YAG:Ce³⁺ security film was fabricated for use in anti-counterfeiting applications, which could emit different colors under various lighting sources. The SITO:Mn⁴⁺ phosphors exhibited a high sensing sensitivity based on the luminescence lifetime. Consequently, the SITO:Mn⁴⁺ phosphors can be employed in bifunctional platforms of luminescence lifetime thermometry and anti-counterfeiting applications.

Enhanced Luminescence of Long-Wavelength Broadband Near-Infrared Germanate Phosphors

Long-wavelength broadband near-infrared (NIR) phosphors have attracted considerable interest in the fields of medical cosmetology and organic detection because of their special emission band. Herein, Ca₂GeO₄(CGO): Cr⁴⁺ NIR phosphor, presenting a broadband emission with longer wavelength ranging from 1100 to 1600 nm, has been synthesized. Further, the luminescence intensity and quantum efficiency of Cr⁴⁺ could be obviously improved via the energy transfer from Eu³⁺ to Cr⁴⁺. The energy transfer is dominated by the dipole-dipole mechanism, which can be inferred from the spectra and the decay curves. Furthermore, in order to evaluate the potential application, an NIR phosphor-converted light-emitting diode (pc-LED) based on blue chip has been prepared. Consequently, CGO: Eu³⁺, Cr⁴⁺ exhibits proper output power and wider half-width than the NIR LED chip, indicating its great prospect for long-wavelength NIR pc-LED applications.

Broadband Near-Infrared Luminescence in Garnet Y3Ga3MgSiO12: Cr3+ Phosphors

Broadband near-infrared (NIR) phosphors are the critical component of phosphor converted NIR light-emitting diode (LED) light sources. However, there are still a lack of NIR phosphors with excellent external quantum efficiency (EQE) and thermal stability. Here, we report a highly efficient broadband NIR phosphor Y₃Ga₃MgSiO₁₂: Cr³⁺. The optimized phosphor yields an internal quantum efficiency (IQE) and an EQE of 79.9 and 33.7%, respectively. The integrated emission intensity still remains at 84.4% of that at room temperature when heated to 423 K. A broadband NIR LED lamp was made by combining as-prepared phosphor and a blue InGaN LED chip, which shows an output power of 89.8 mW with a photoelectric conversion efficiency of 17.1% driven at 525 mW input power. Our research provides a promising NIR phosphor with high efficiency broadband for the NIR light source.

An efficient and thermally stable near-infrared phosphor derived from the Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) garnet family

A broadband near-infrared (NIR) light source based on a phosphor-converted light-emitting diode (pc-LED) has attracted increasing interest to be used in non-destructive examination, security-monitoring and medical diagnosis fields, which stimulates the exploration of NIR phosphors with high performance. Herein, a series of Cr³⁺-activated garnet Ln₃ScInGa₃O₁₂:Cr³⁺ (Ln = La, Gd, Y, and Lu) phosphors were reported, allowing an emission peak ranging from 726 to 822 nm. Among them, Y₃ScInGa₃O₁₂:Cr³⁺ with an optimized Cr³⁺-doping concentration of 6 mol% exhibits a high internal quantum efficiency (IQE = 83.1%) and excellent absorption efficiency (AE = 44.2%) under 450 nm blue light excitation, enabling an external quantum efficiency as high as 36.7%. Moreover, this material can maintain 93.0% of the initial intensity when heated up to 423 K, implying outstanding thermal stability. Finally, a prototype NIR pc-LED device was fabricated by coating the optimized phosphor on a 455 nm LED chip, which generates a broadband NIR emission with a peak located at 765 nm and a full width at half maximum of 127 nm. The NIR output power and NIR photoelectric conversion efficiency of this device were found to be 38.01 mW and 11.0%, respectively, under 100 mA driving current, demonstrating the feasibility of this material to be applied in NIR pc-LEDs.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr³⁺-activated Mg₂SiO₄ infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr³⁺ emitters in two different Mg sites in the Mg₂SiO₄ lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg₂SiO₄:Cr³⁺ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr³⁺-doped phosphors.

Luminescence properties and energy transfer of the near-infrared phosphor Ca3In2Ge3O12:Cr3+,Nd3

The double doping strategy based on energy transfer is an effective way to regulate the NIR spectral distribution. In this work, Ca₃In₂Ge₃O₁₂:xNd³⁺ (CIG:xNd³⁺) and Ca_3−xIn_1.93Ge₃O₁₂:0.07Cr³⁺,yNd³⁺ (CIG:0.07Cr³⁺,yNd³⁺) phosphors are successfully prepared via a high-temperature solid-state method. CIG:0.07Cr³⁺ shows broadband emission centered at 804 nm, which covers most of the excitation peaks of Nd³⁺ ions. Under excitation at 480 nm, Cr³⁺ can provide effective energy transfer to Nd³⁺. In addition, CIG:0.07Cr³⁺,0.15Nd³⁺ has good temperature stability, and maintains 68.98% of the room-temperature intensity at 150 °C. The phosphors can convert short-wave photons to long-wave photons and enhance solar cell utilization, demonstrating the potential application of this material in solar spectral conversion technology.

Improvement of the luminescence properties of Ca₃In₂Ge₃O₁₂:Cr³⁺,Nd³⁺via energy transfer and its potential application in silicon solar cells.

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

A series of tunable and ultra-broadband NIR phosphor Ga2−2xZnxGexO3:Cr3+ was successfully achieved by [Zn2+–Ge4+] unit co-substituting [Ga3+–Ga3+] unit in Ga2O3:Cr3+.

Luminescence properties of Cr3+-doped near-infrared emissive fluoroyttrates for light-emitting diodes

In this work, a series of Cr3+-doped A2NaYF6 (denoted as ANYF:Cr; A = K, Rb, Cs) fluoroyttrate double-perovskites with broad blue excitation and near-infrared (NIR) emission bands was fabricated using...