Phosphor-converted Light-emitting Diodes Research Articles

Constructing Broadband Near-Infrared Garnet Emitters CaGd2Ga4SiO12:Cr3+ with Unity Quantum Efficiency and High Thermal Stability for Versatile Applications.

The pursuit of broadband near-infrared (NIR) phosphors for next-generation smart NIR light sources has garnered extensive interest. However, developing phosphors efficiently excitable by blue light to produce thermally stable and highly efficient broadband NIR emission surpassing 830 nm remains a formidable challenge. Herein, a novel CaGd2Ga4SiO12 garnet is reported, designed through a structure reconstruction approach to host Cr3+ ions for developing a high-performance broadband NIR phosphor. By strategically introducing Jahn-Teller distortion at the octahedral sites via chemical pressure, Cr3+ is endowed with a super-broadband NIR emission spanning 600-1300 nm centered at 837 nm. The full-width at half maximum (FWHM) varies from 187 to 223 nm across Cr3+ doping concentrations, with the highest internal quantum efficiency (IQE) of 99.01%. Remarkable luminescence thermal stability (90.37%@423 K) is bolstered by a weak electron-phonon coupling (EPC) effect and trap-mediated energy compensation, a result of the heterovalent ion substitutions in dodecahedral and tetrahedral sites. Furthermore, a prototype broadband NIR phosphor-converted light-emitting diode (pc-LED) is fabricated, delivering a substantial NIR output power of 287.7 mW at 1100 mA and a power conversion efficiency (PCE) of 24.4% at 30 mA, enabling impressive performance in versatile applications, including component analysis, non-destructive testing, NIR imaging, and night vision.

Red-emitting phosphors NaLiXF6:Mn4+ (X = Ti, Si) for white LEDs with high color rendering index and low correlated color temperature

White light-emitting diodes (WLEDs) are widely used in various lighting applications due to their high brightness and energy efficiency. However, commercial WLEDs, which typically combine YAG:Ce3+ phosphors with blue light-emitting diode chips, often lack red components, resulting in a high correlated color temperature (CCT) and a low color rendering index (CRI). To address this issue, two novel Mn4+-doped red-emitting phosphors, NaLiTiF6 and NaLiSiF6, were synthesized using an ion exchange method. Both phosphors exhibit strong red light with a pronounced zero-phonon line (ZPL) emission under blue light excitation. Optimal photoluminescence emission intensities were observed at Mn4+ concentrations of 6% for NaLiTiF6 and 9% for NaLiSiF6. When the temperature increased from 303 K to 413 K, both phosphors demonstrated outstanding brightness and chromatic stability. Integrated into phosphor-converted light-emitting diodes (pc-LEDs), the device incorporating NaLiTiF6:6%Mn4+ achieved a CRI of 95.1 and a CCT of 3172 K, while the device with NaLiSiF6:9%Mn4+ showed a CRI of 87.9 and a CCT of 3784 K. In addition, the luminous efficacy, CRI, and CCT of both prototype pc-LEDs maintained minimal variation with increasing driving current. These results indicate the stability and suitability of the synthesized phosphors for enhancing the performance of warm WLEDs applications.

Research note: On relation between photopic luminous efficacy and colour rendering of LED strips

Light-emitting diode (LED) strips have recently become a top-rated light source, used primarily in interior lighting applications. This increase is mainly due to increased performance in technical parameters, primarily photopic luminous efficacy (PLE) and the CIE general colour rendering index ( Ra). The relation between PLE and Ra was investigated for several types of light sources in the past and was found to be inversely related. However, confirming if a similar relation exists for the newest phosphor-converted LED strips based on up-to-date colour rendering metrics, such as TM-30-18 Rf (ANSI/IES), is essential. This study was based on measurements of 105 different phosphor-converted LED strips with correlated colour temperatures (CCTs) from 2500 K to 5000 K. The results showed that lower PLE and higher Ra usually characterize the group with lower CCTs than those with higher CCTs. In the group of LED strips below 3500 K, there is a strong negative linear correlation ( R2 = 0.51, p < 0.001) between PLE and Ra. However, in the group with CCTs above 3500 K, the linear correlation between PLE and Ra is weaker ( R2 = 0.29, p < 0.001). Moreover, the analysis of the relationship between PLE and TM-30-18 Rf showed no association between those variables. Results suggest the need to rethink the influence of PLE on colour rendering in the case of using modern metrics for LED lighting. Finally, the results are a reasonable basis for the further analysis of such associations, which should be done periodically according to the rapid development of LED light sources.

Pressure treatment enables white-light emission in Zn-IPA MOF via asymmetrical metal-ligand chelate coordination

Metal-organic frameworks that feature hybrid fluorescence and phosphorescence offer unique advantages in white-emitting communities based on their multiple emission centers and high exciton utilization. However, it poses a substantial challenge to realize superior white-light emission in single-component metal-organic frameworks without encapsulating varying chromophores or integrating multiple phosphor subunits. Here, we achieve a high-performance white-light emission with photoluminescence quantum yield of 81.3% via boosting triplet excitons distribution through pressure treatment in single-component Zn-IPA metal-organic frameworks. A novel metal-ligand asymmetrical chelate coordination is successfully integrated into the Zn-IPA after a high-pressure treatment over ~20.0 GPa. This modification unexpectedly endows the targeted sample with a new emergent electronic state to narrow the singlet-triplet energy gap, which effectively accelerates the spin-flipping process for boosted triplet excitons population. Time delay phosphor-converted light-emitting diodes are fabricated with long emission time up to ~7 s after switching off, providing significant advancements for white-light and time-delay lighting applications.

Achieving an efficient near-infrared luminescence and wide-range spectral tunability in garnet Na2CaHf2Ge3O12:Cr3+ phosphor.

Near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) has emerged as the most promising NIR light source, highlighting the importance of exploring phosphors with excellent efficiency and sufficient spectral coverage. Herein, a garnet Na2CaHf2Ge3O12:Cr3+ phosphor with an internal quantum efficiency (IQE) of 79.2% has been developed, which exhibits a relatively long wavelength NIR emission peak at 830 nm and a full width at half maximum (FWHM) of 144 nm. Moreover, the emission peak can be gradually tuned to 903 nm with an emission intensity maintaining over 60% utilizing a chemical unit co-substitution strategy. Thus, the developed material in this work has an excellent efficiency with a relatively long wavelength NIR emission and wide-range spectral tunability, being promising for multifunctional spectroscopy applications.

Improving the near-infrared luminescence of Ca3MgSnGe3O12:Cr3+ using cation modulation and energy transfer for night-vision and nondestructive testing.

A series of Ca3Mg1-x Sr x SnGe3O12:0.05Cr3+ (x = 0.005-0.3) phosphors were synthesized in this study; varying the Cr3+-ion crystal-field strength through Sr2+-concentration variation resulted in a luminescence-center redshift. Nd3+-ion co-doping resulted in a broad-spectrum emissive material with a 468 nm excitation wavelength, expanded full width at half maximum (FWHM) (195 nm), Cr-Nd energy transfer, and an ultra-high temperature stability (99.59% at 423 K). Combining Ca3Mg0.7Sr0.3SnGe3O12:0.05Cr3+, 0.05Nd3+ with blue LED chips resulted in near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) for night-vision and nondestructive testing applications. This study reports what we believe is a novel method for designing NIR light-emitting materials with excellent luminescence properties that could guide future research on NIR phosphors with widespread applicability.

Phosphor-converted light-emitting diodes in the marine environment: current status and future trends.

The exploitation and utilization of resources in marine environments have ignited a demand for advanced illumination and optical communication technologies. Light-emitting diodes (LEDs), heralded as "green lighting sources", offer a compelling solution to the technical challenges of marine exploration due to their inherent advantages. Among the myriad of LED technologies, phosphor-converted light-emitting diodes (pc-LEDs) have emerged as frontrunners in marine applications. At the heart of pc-LEDs lie phosphor materials, colour-converters that orchestrate the emission of light. In the marine environment, blue-green light with a wavelength of 440-570 nm exhibits the deepest penetration depth, while other wavelengths are rapidly attenuated in the shallow layer. Additionally, specific wavelengths of light are crucial for particular applications. However, the moist marine environment as well as the demand for continuous and stable lighting pose a formidable challenge to the environmental stability of the phosphors. Therefore, developing blue-green phosphors with exceptional colour purity and high thermal and moisture stability is paramount for marine applications. Herein, this review delves into the application of LED and pc-LED technology in underwater optical communication and marine fishery, exploring the development strategies of phosphors tailored for the marine environment. The insights presented serve as a valuable reference for further research on phosphors and pc-LED devices.

Broadband Shortwave Infrared-Emitting Cr3+- and Ni2+-Codoped Y3Al2Ga3O12 Phosphor with Excellent Thermal Stability for Multifunctional Applications.

Shortwave infrared (SWIR)-emitting materials have emerged as superior light sources with increasing demand for potential applications in noninvasive analysis, night vision illumination, and medical diagnosis. For developing next-generation SWIR phosphor-converted light-emitting diodes (pc-LEDs), the scarcity of intense blue-light-pumped broadband SWIR luminescent materials and poor thermal stability of current Ni2+-activated phosphors are the ongoing challenges. Here, a blue-light-excitable (440 nm) Y3Al2Ga3O12:Cr3+,Ni2+ phosphor with ultrawide SWIR emission centered at ∼1430 nm (FWHM ∼264 nm) is reported. The efficient Cr3+ → Ni2+ energy transfer is exploited for a remarkable enhancement of 18-fold in SWIR emission under blue-light excitation. Significantly, the excellent thermal stability (90% at 440 K) of the SWIR band is obtained in the codoped phosphor which is the best among reported SWIR phosphors. Besides, the experimental techniques (XANES and EXAFS) and density functional theory calculations are employed to investigate the local structure and propose [GaO6] octahedrons as favorable occupation sites for Ni2+/Cr3+ ions. A SWIR pc-LED is fabricated using a blue chip as a proof of concept for invisible illumination technology, nondestructive spectroscopic analysis, anticounterfeiting, and imaging applications. This work offers effective insights into energy transfer-assisted SWIR enhancement and presents a thermally robust Cr3+-Ni2+-codoped phosphor for designing future mini-SWIR pc-LEDs for spectroscopy applications.

Achieving an Improved NIR Performance of Ca4-xSc2xZr1-xGe3O12:Cr3+ via [Sc3+-Sc3+]→[Ca2+-Zr4+

High-performance near-infrared (NIR) light sources are highly sought after in advanced spectroscopy techniques, driving the development of NIR phosphor-converted light-emitting diodes (pc-LEDs). Escalating the luminescence intensity and thermal stability of NIR-emitting phosphors, which is a core component of NIR pc-LEDs, is of paramount importance. Herein, chemical unit cosubstitution and cosolvent addition tactics were implemented to simultaneously boost the NIR luminescence performance of the synthesized phosphors. The replacement of [Sc3+-Sc3+] for [Ca2+-Zr4+] in Ca4ZrGe3O12:Cr3+ likely reduces the antisite defects and offers a more rigid crystal structure. As a result, the emitting intensity is reinforced significantly, along with a remarkable improvement in thermal stability, acquiring 65% of the initial luminescence at 423 K compared with 42% for the primal sample. Moreover, the introduction of H3BO3 further enhances NIR luminescence while maintaining a favorable thermal resistance. The encapsulated NIR pc-LED carries an impressive output power of 71.8 mW at 300 mA and a conversion efficiency up to 15.6% at 10 mA. The practical presentations in food checking, imaging, and detection manifest that Ca3.5ScZr0.5Ge3O12:Cr3+,H3BO3 is a promising material for spectroscopy-based technologies.

Achieving Thermally Stable YAl3-xGax(BO3)4:Cr3+ Near-Infrared Emitting Phosphors via Chemical Substitution for Plant Growth LEDs.

Indoor plant cultivation has been receiving increased attention due to concerns about sustainable agricultural production. Phosphor-converted light-emitting diodes (pc-LEDs) offer substantial promise as lighting solutions for regulating plant growth. However, the quest for high-performance phosphors with precise responsiveness to far-red phytochromes poses a challenge. Our study proposes a chemical substitution strategy to develop near-infrared (NIR) phosphors, YAl3-xGax(BO3)4:Cr3+. Benefiting from Ga3+ replacement of Al3+, a red shift in the NIR emission of YAl3-xGax(BO3)4:Cr3+ is realized to attain a good alignment with far-red phytochrome absorption centering at 730 nm. The optimized YAl2.5Ga0.5(BO3)4:Cr3+ exhibits a favorable quantum yield of 71.8% and robust thermal stability of 101.0%@423 K, owing to local structural distortion and thermal repopulation caused by Ga3+ incorporation. The fabricated pc-LED combined with the phosphor yields an NIR output power of 40.9 mW and a photoelectric conversion efficiency of 15.4% at 100 mA. Plant growth experiments demonstrate that under NIR illumination from the devices, the average lengths of pea roots and stems gain 127 and 225% promotion, respectively, further highlighting the potential of YAl2.5Ga0.5(BO3)4:Cr3+ phosphors for applications in plant cultivation.

Rare-Metal-Free Ultrabroadband Near-Infrared Phosphors.

Trivalent chromium (Cr3+) is an attractive near-infrared (NIR) emitter, but its ultrabroadband NIR emission is limited to host crystals containing large amounts of rare-metal elements and usually suffers from low internal quantum efficiency (IQE) and poor thermal stability. Here, a class of high-performance, rare-metal-free ultrabroadband NIR phosphors, are reported by revealing that weak-field Cr3+ centers featuring broadband NIR emission with near-unity IQEs are intrinsic, though in trace quantities, to Cr3+ doped MgAl2O4 spinel (MAS) and its derivatives well-known for their narrowband far-red emission. It is shown that such weak-field Cr3+ centers stem from cation inversion ubiquitous in spinel compounds, and their quantity can be increased simply by superstoichiometric Al2O3/Ga2O3. Then SiO2 is introduced into Al2O3-excess MAS to break the inversion symmetry of Cr3+ centers for greatly improving the probabilities of their otherwise parity-forbidden 3d-3d transitions. The as-fabricated phosphor-converted light-emitting diodes are capable of emitting ultrabroadband NIR light with high photoelectric efficiency (16.0%) and optical power (180.8mW), and excellent spectral stability, which apparently outperforms existing state-of-the-art devices.

(Luminescence and Display Materials Division Outstanding Achievement Award) Fiat Lux [1], or the Lighting Story of the Transition Metal and Rare Earth Ions

Nowadays getting artificial light is of paramount importance in all domains of human life. The story of the artificial light sources began with the invention of the incandescent lamps in the second half of the XIX century, followed by the fluorescent lamps and, finally, by discovery and development of the light emitting diodes (LED) in the end of the XX century. Modern LEDs have numerous advantages over their lighting predecessors: considerably longer life time, brightness, lower energy consumption, miniature size, flexibility etc. The lighting industry now is a very important sector of the world economy with huge ever-growing market. The main goal of the LED producers is to make the light sources that are able to produce light as close to the natural Sun light as possible.The transition metal and rare earth ions with unfilled 3d and 4f electron shells, respectively, are vital components of the phosphor materials that have to be used in lighting devices for getting emission of different colors. Modern white LEDs are the phosphor-converted LEDs, based on the combination of the GaN (or GaInN) blue LED and one or two phosphor materials, that partially absorb blue light and convert it into emission of other colors (usually yellow and red), to make together white light.In this presentation different theoretical models that are used to describe the electronic and optical properties of those 3d and 4f ions in optical materials will be discussed, with an emphasis on the transition metal ions with the 3d3 electron configuration (Cr3+ and Mn4+, in particular). Complicated interplay of electronic properties of impurity ions and host materials will be considered; the “structure-optical property” relationships will be considered. Some useful suggestions for tuning the optical properties of these ions in solids will be outlined.[1] Let there be light (Latin)

Replication of Leaf Surface Structures on Flat Phosphor-Converted LEDs for Enhanced Angular Color Uniformity.

We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired the design of artificial microstructures that can improve light extraction, scattering, and overall optical performance in LED applications. The effects of these leaf surface microstructures on the phosphor layer of flat pcLEDs were evaluated. An imprinting technique was employed to directly replicate the surface morphology structures from fresh plant leaves. The results indicated that this method provided excellent scattering capability and reduced the disparity in light output between blue and yellow light emissions from flat pcLEDs at various angles. Subsequently, uniform correlated color temperature in the flat pcLEDs was achieved, reducing the yellow ring effect. Furthermore, the availability of diverse wrinkle and surface patterns from a wide range of natural prototypes could reduce design costs compared with traditional mold fabrication, making the method suitable for application in mass production.

Unveiling Suppressed Concentration Quenching Enhanced Broadband Near-Infrared Emitters.

Transition metal ions are exceptional emitters of broadband near-infrared (near-IR) luminescence, enabling various applications in photonics and optics; however, their weak absorption and excitation bands often limit conversion performance. Among potential sensitizers, Cr3+ stands out, allowing the excitation of Ni2+ with broadband visible-near-IR light while preserving luminescence properties. Nevertheless, concentration-induced quenching in doped luminescent solids fundamentally undermines brightness due to a trade-off between internal quantum efficiency and excitation energy dynamics. In this study, we demonstrate unprecedented brightness in the broadband near-IR photoluminescence (PL) of the Cr3+-Ni2+ system, where single, heavily doped Cr3+ exhibits minimal PL, and tuning Ni2+ concentration offsets the competitive relationship between the light emitter and quencher. By coupling InGaN light-emitting diodes (LEDs) with an ultrabroadband near-IR PL phosphor, we achieve phosphor-converted LEDs with a record output power of 41.5 mW at 100 mA and a photoelectric efficiency of 19.53% at 20 mA, nearly doubling previous reports. Our findings unveil intrinsic suppression of concentration quenching and eliminate competing energy sinks by emphasizing the dominant role of emitters in downshifting excitation energies, thus opening new avenues for the design of bright, sensitized luminescent materials.

Antithermal-Quenching Near-Infrared Emitting Lu2SrAl4SiO12:Cr3+ Garnet-Type Phosphor for High-Resolution Nonvisual Imaging.

Near-infrared (NIR) light allows fast and nondestructive detection with deep penetration into biological tissues and is widely used in food inspection, biomedical imaging, night vision security, and other fields. Cr3+-doped NIR first region (NIR-I) phosphors have many interesting features that have attracted a lot of attention recently. However, practical issues, such as low photoluminescence quantum efficiency and poor thermal stability, need to be addressed. We synthesized Cr3+-doped Lu2SrAl4SiO12 garnet-type phosphors using a high-temperature solid-state reaction method. Under blue-light (@ 430 nm) excitation, the phosphors exhibited broadband NIR-I emission in the range of 600-1000 nm, with an emission peak at 710 nm. This system is unique, as the emission had multipeak sharp-line superposition and the Cr3+ ions were situated in a relatively strong crystal field environment, as opposed to a weak crystal field environment for other matrix. The optimal doping content of Cr3+ ions was 2 mol %, and its internal quantum efficiency was ∼76.8%. Surprisingly, this NIR phosphor showed an antithermal quenching effect, and the integrated luminescence intensity of NIR-I emission measured at 573 K was 206.3% of that measured at 303 K. We found that the antithermal quenching of NIR-I luminescence was caused by the extremely low thermal expansion coefficient and rigid structure of the Lu2SrAl4SiO12 matrix in the temperature range, as well as the weakening of electron-phonon coupling with increasing temperature. The optimized phosphor was packaged with a blue chip into a NIR phosphor-converted light-emitting diode device. The light source device showed an output power of 119.02 mW and an electro-optical conversion efficiency of 11.02% under a driving current of 300 mA. The application potential of this NIR phosphor was demonstrated in the field of high-resolution nondestructive imaging.

Enhancement strategy of thermal stability and photoluminescent intensity of Cr3+ doped Li3+xZn2–2xGaxSbO6 phosphor in a strong crystal field

Near-infrared phosphor-converted light-emitting diodes (pc-LEDs) have shown enormous influence in various applications such as night vision, non-destructive detection，especially in the realm of plant cultivation. However, the role of phosphors presently employed in plant cultivation is typically limited, serving primarily for the purpose of illumination. In this work, a series of near-infrared phosphors Li3+xZn2–2xGaxSbO6: 0.02Cr3+(LZGS: 0.02Cr3+) under 450 nm excitation was successfully synthesized by high-temperature solid-state method. Through precise modulation of Ga3+ ions, a blue shift in the emission spectrum was observed, demonstrating excellent overlap with the absorption spectrum of Phytochrome. To explain two phenomena of spectral blue shift and the enhancement in luminescence intensity, density functional theory calculations have been performed. Additionally, a crystal field strength Dq/B of 3.48 was achieved, which represents the highest value currently reported for Cr3+-doped phosphors. The results offer potential applications of LZGS: 0.02Cr3+ in temperature sensing, enabling precise detection of the environmental temperature for plant growth. Finally, pc-LED devices were made by combining LZGS: 0.02Cr3+ with 450 nm blue light chips and applied to plant lighting, temperature measurement, and anti-counterfeiting, demonstrating the potential of LZGS: 0.02Cr3+ in multifaceted applications.

Ammonothermal Synthesis of Luminescent Imidonitridophosphate Ba4P4N8(NH)2:Eu2.

The structural variability of a compound class is an important criterion for the research into phosphor host lattices for phosphor-converted light-emitting diodes (pc-LEDs). Especially, nitridophosphates and the related class of imidonitridophosphates are promising candidates. Recently, the ammonothermal approach has opened a systematic access to this substance class with larger sample quantities. We present the successful ammonothermal synthesis of the imidonitridophosphate Ba4P4N8(NH)2:Eu2+. Its crystal structure is solved by X-ray diffraction and it crystallizes in space group Cc (no. 9) with lattice parameters a=12.5250(3), b=12.5566(4), c=7.3882(2) Å and β=102.9793(10)°. For the first time, adamantane-type (imido)nitridophosphate anions [P4N8(NH)2]8- are observed next to metal ions other than alkali metals in a compound. The presence of imide groups in the structure and the identification of preferred positions for the hydrogen atoms are performed using a combination of quantum chemical calculations, Fourier-transform infrared, and solid-state NMR spectroscopy. Eu2+ doped samples exhibit cyan emission (λmax=498 nm, fwhm=50 nm/1981 cm-1) when excited with ultraviolet light with an impressive internal quantum efficiency (IQE) of 41 %, which represents the first benchmark for imidonitridophosphates and is promising for potential industrial application of this compound class.

Red-shifting and boosting the emission of NaScP2O7:Cr3+ via efficient energy transfer for information encryption and anti-counterfeiting

Highly-efficient near-infrared (NIR) phosphors with long-wavelength emission (>900 nm) are crucial to broaden the potential applications of NIR phosphor-converted light-emitting diodes (pc-LEDs) in practical scenarios. In this study, we synthesized an NIR phosphor, Cr3+-activated NaScP2O7 with emission centered at 920 nm and a full width at half maximum (FWHM) of 208 nm. Nevertheless, the phosphor yields an internal quantum efficiency (IQE) of 9.8 %, owing to severe non-radiative relaxation. By introducing Yb3+ co-dopant into NaScP2O7:Cr3+, the role of Cr3+ changes from an activator to a sensitizer, enabling efficient Cr3+-Yb3+ energy transfer (ET). The resulting NaScP2O7:Cr3+,Yb3+ exhibits a characteristic Yb3+ emission peaking at 1005 nm. Notably, the IQE of the co-doped phosphor is significantly enhanced to 58.9 %, attributed to the suppression of Cr3+ non-radiative relaxation and the efficient sensitization of Yb3+ emission through ET. Benefiting from the intensive short-wavelength infrared emission (SWIR), the phosphor demonstrates versatile applications in anti-counterfeiting and information encryption.

Broadband near-infrared emission of Cr3+ doped Zn7Sb2O12 phosphors for night vision imaging system sources

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are highly promising for various applications, including food analysis, night vision, and biological detection. In this work, we report a Cr3+-doped Zn7Sb2O12 phosphor, which was prepared through a high-temperature solid-phase method. Under excitation at 400 nm, the phosphor reveals an emission spectrum that extends from 700 to 1400 nm, peaking at 950 nm with a full width at half maximum (FWHM) of 179 nm. In addition, the internal quantum efficiency (IQE) of the Zn7Sb2O12: 0.01Cr3+ phosphor is recorded at 33.13%. When encapsulated in pc-LEDs, the phosphor achieves a near-infrared (NIR) output power of 18.90 mW at 160 mA, along with a photoelectric conversion efficiency (PCE) of 15.45% at 20 mA. The developed pc-LED shows promise in non-destructive testing and night vision technologies.

Calcium vacancy enhanced self-reduction of Ce4+ for single-phase full-spectrum lighting and information encryption

Due to the wide and adjustable emission range, Ce3+ is an indispensable luminous center for full spectrum lighting. However, it needs to be sintered at high temperature in a reducing atmosphere, resulting in difficulty to coexisting with other multivalent activated ions (such as Eu3+, Tm3+), which greatly hinders the formation of full spectrum. In this study, a calcium vacancy enhanced self-reduction of Ce4+ is realized in CaNaSb2O6F (CNSOF) host under air atmosphere sintering, through which Ce3+, Tm3+ and Eu3+ coexisting in a single-phase full spectrum phosphor was prepared. Notably, the artificial introduction of a calcium vacancy was designed to verify this self-reduction mechanism. Moreover, the energy transfer kinetics among Tm3+, Ce3+ and Eu3+ were explored. Finally, combined with a 340 nm UV chip, a full spectrum phosphor-converted light-emitting diode (pc-LED) was fabricated, showing a broad emission range from 400 to 750 nm, Commission Internationale de I’Eclairage (CIE) of (0.3485, 0.3673), Ra of 92 and correlated color temperature (CCT) of 4933 K. Utilizing the variation in emission colors of this phosphor under different UV wavelengths, a dual encryption method combining point character code and fluorescent encryption technique is proposed. This work provides an effective path for Ce4+ self-reduction to apply in full spectrum pc-LED and information encryption.