Emission Phosphor Research Articles

New isomeric ancillary ligands and their EuIII complexes: a single component white light emissive phosphor and their applications in red/white smart LEDs, electronic noses, and temperature sensing

Dual emissive isomeric trivalent europium complexes were explored as single component white light emissive luminogens and further exploited as an electronic nose as well as a temperature sensor.

A non-rare earth ion doped broadband emission phosphor located in NIR-II for ethanol concentration detection.

In this work, a new NIR phosphor Ca2GeO4:xCr was developed, whose emission range (1000-1700 nm) is well within NIR-II, with a full width at half maximum (FWHM) of 215 nm. Interestingly, by sintering under an air atmosphere, the Cr3+ ions in the raw material are oxidized to Cr4+, and the near-infrared light emitted by the material is not the usual luminescence of Cr3+ ions located in NIR-I, which can be attributed to the dominant substitution of Cr4+ ions doped into the lattice sites. A pc-LED fabricated with this phosphor can detect different concentrations of ethanol, which demonstrates its good potential for non-destructive testing applications.

White-light emission lead-free perovskite phosphor Cs2ZrCl6:Sb3+

Obtaining phosphors with white-light emission is a promising and economical approach for phosphor-conversion light emitting diodes (pc-LEDs), but traditional single-phase white light emission phosphors are inefficient. Here a white-light-emission phosphor was prepared via a co-precipitation method by doping Sb 3+ into lead-free and vacancy-ordered double perovskite Cs 2 ZrCl 6 . X-ray diffraction, X-ray photoelectron spectroscopy, and formation energy calculations confirmed that Sb 3+ ions replaced the Zr 4+ sites in the [ZrCl 6 ] 2− octahedron. The optical properties of Cs 2 ZrCl 6 :Sb 3+ were investigated and compared with those of blank Cs 2 ZrCl 6 . The origination of the emission bands was determined according to their fluorescence spectra and decay-time at an approximate temperature of 4 K Sb 3+ -doped Cs 2 ZrCl 6 exhibited white-light emission with double emission bands at 495 and 622 nm due to the 1 P 1 → 1 S 0 and 3 P 2, 1, 0 → 1 S 0 transitions of Sb 3+ , respectively. The intensity ratios of cyan light (495 nm) and the red light emission bands (622 nm) were tunable by adjusting the Sb 3+ concentration. The red component increased with increasing Sb 3+ concentration in the present experimental range. Moreover, 10% Sb 3+ -doped Cs 2 ZrCl 6 showed the strongest emission with a photoluminescence quantum yield of approximately 78% under excitation of 333-nm light White LED devices with different correlated color temperatures were achieved by combining 1% or 10% Sb 3+ -doped Cs 2 ZrCl 6 with a 310-nm ultraviolet chip, suggesting that the synthesized samples have potential applications in white-illumination LEDs. Single-phased white emitting phosphor Cs 2 ZrCl 6 : Sb 3+ and corresponding LEDs.

Luminescence properties, energy transfer and thermal stability of white emitting phosphor Sr3(PO4)2:Ce3+/Tb3+/Mn2+ for white LEDs.

A series of Sr3(PO4)2:Ce3+/Mn2+/Tb3+ phosphors were synthesized by a high temperature solid phase method. After introducing Ce3+ as sensitizer in Sr3(PO4)2:Ce3+/Mn2+, the efficient energy transfer from Ce3+ to Mn2+ was observed and analyzed in detail, and Sr3(PO4)2:Ce3+/Mn2+ was demonstrated to be color tunable, changing from blue to orange red. In addition, Tb3+ ion, which mainly emits green light, was further added into the Sr3(PO4)2:Ce3+/Mn2+. Due to the addition of this green emission, the white emitting phosphors with good quality were obtained. At the same time, the energy transfer mechanisms among Ce3+, Tb3+ and Mn2+ ions were also analyzed in detail. The results show that Sr3(PO4)2:Ce3+/Mn2+/Tb3+ is a promising candidate for white light emitting diodes.

Novel Dual-Excitation and Dual-Emission Materials: Eu2+,Pb2+ Co-doped Core-Shell-Structured CaS@CaZnOS Phosphors and Their Application for Highly Efficient Photosynthesis of Plants.

Eu2+,Pb2+-doped core-shell-structured CaS@CaZnOS phosphors were synthesized by a two-step high-temperature solid-phase method. The as-synthesized CaS:Eu2+,Pb2+@CaZnOS:Pb2+ phosphors possess excellent dual-excitation and dual-emission (DE2) luminescent properties, which give rise to red emission peaking at 650 nm under green excitation, derived from the core CaS:Eu2+,Pb2+, and blue emission peaking at 424 nm, originating from the shell CaZnOS:Pb2+, under ultraviolet (UV) excitation. In addition, tunable red/blue emission can be achieved by changing the doping concentration of Pb2+ in the CaZnOS shell. The red/blue dual emission of core-shell DE2 phosphors under excitation of UV and green light significantly matches with the absorption spectrum of chlorophyll (a, b); hence, the as-prepared phosphors are excellent solar spectral conversion (SSC) auxiliaries of plastic films or laminated glass for greenhouses and provide ideas for creating more efficient and practically valuable SSC auxiliaries. The DE2 properties are described, and the energy transfer mechanism from Pb2+ to Eu2+ in the core is proposed and discussed in detail.

White light emission phosphor modulation, nitrobenzene sensing property and barcode anti-counterfeiting via lanthanides post-functionalized metal-organic frameworks

Three isostructural lanthanide metal-organic frameworks (Ln-MOFs) [Ln2(L)3(H2O)5]n (1-Ln, Ln ​= ​Eu, Tb, Dy and Eu/Tb), and a transition MOF {[Cd(L)(H2O)2]·H2O}n (1-Cd) based on 1-(4-carboxyphenyl)-1H-pyrazole-3-carboxylic acid (H2L) ligand were obtained by solvothermal method. The white-light-emitting (WLE) material Eu3+/Tb3+@1-Cd with the CIE coordinate (0.33, 0.34) was successfully modulated by introducing Eu3+ and Tb3+ into the blue-emitting 1-Cd. The post-synthetic doping provides a facile and practical strategy for the development of WLE materials. Besides, the luminescence sensing experiments showed that 1-Ln can be used as an excellent probe for nitrobenzene detecting. And the multi-color barcode of 1-Ln showed great potential in commodity anti-counterfeiting and information security.

Degradation dynamics of quantum dots in white LED applications

Quantum Dots (QDs) are being investigated in a hybrid white light LED structure which inculcates phosphor in the package with a blue LED chip as the light source recently. In this work, Zn doped CdS QD with ZnS shell together with green light emission phosphor is used. Upon prolonged operation, degradation of the LEDs due to the degradation of QDs is observed, which can limit its practical applications. The degradation includes intensity reduction as well as blue shift of the emitted wavelength from the white light. Three stages of degradation are observed, namely an enhancement state where light intensity is found to increase, followed by a rapid degradation stage where light intensity decreases rapidly, and finally a slower degradation stage where the degradation rate of light intensity slows down and continues till the end of the test. Through various detail material analysis, with confirmation from the density functional theory (DFT) calculations, we find that the degradation of the LEDs is due to the time evolving degradation of CdS core structure, beginning from the oxidation of sulfur vacancy of CdS QDs by the nearby oxygen atoms as a result of imperfection of the ZnS protective coating around the QDs in the presence of blue light. This oxidation renders a transformation of CdS into CdO at the initial stage. The final stage is the formation of CdSO4 via some intermediate processes.

Activation of bismuth aluminate for obtaining near infrared emission

New results on NIR emission in Bi2Al4O9 phosphors activated with Cr3+, Er3+or Nd3+ are presented. These phosphors were prepared by a simple two step method consisting of combustion followed by annealing at 800C. Annealing step was necessary to obtain powders with good crystallinity; as-combusted powders being amorphous. Host sensitization was observed in all the phosphors. An excitation band around 279 nm corresponds to bandgap excitation of the host1So→ 3P1 transition of the Bi3+ ion, while that at 360 nm to the defect absorption. Apart from the excitation in these host related bands, characteristic excitations also produced intense emission lines. It is suggested that these phosphors can be useful for making low cost NIR sources needed in various applications.

Excellent multi-color emission and multi-mode optical ratiometric thermometer in (Ca, Tb, Eu, Sm)Nb2O6 phosphors based on wide O2–→Nb5+ CTB

To meet the demand of ultra-sensitive and high accurate temperature measurements especially in the fields of medical treatment and diagnosis, multi-mode FIR-based optical thermometers as a novel strategy have been developed in recent years. In this work, two types of temperature probes, CaNb2O6 (CNO): Tb3+, Eu3+ and CNO: Tb3+, Sm3+, are firstly designed by high-temperature solid-state method. CNO possesses bright cyan emission excited at 267 nm, wide band gap and good temperature sensing property relative to BaNb2O6 (BNO) and SrNb2O6 (SNO) materials due to sandwich-type structure. Upon 267 nm excitation, Tb3+–Eu3+/Sm3+ doped CNO phosphors achieve multi-color tuning by host → Tb3+→Eu3+/Sm3+ ET channels. Furthermore, the characteristic emission intensity of Tb3+ decrease quickly than that of Eu3+ and Sm3+ due to the competition between thermal quenching and ET process as temperature rising. In the view of different temperature-dependent behaviors, multi-mode FIR (FIR1: ITb1/IEu1/Sm1, FIR2: ITb2/IEu2/Sm2, FIR3: ITb1/IEu2/Sm2 and FIR4: ITb2/IEu1/Sm1) show excellent temperature-sensing performance with the maximum Sa and Sr of 0.036 K−1/ 4.09 % K−1 at high temperature. This work provides a new luminescent material to gain excellent optical thermometer with low cost and high accuracy by multi-mode FIR collaboration.

AlN–Ce-doped yttrium aluminum garnet composite ceramic phosphor for high-power laser lighting

Ce-doped yttrium aluminum garnet (YAG:Ce) has been used as a phosphor emitting white light using a blue-light-emitting diode as a light source. Recently, studies on laser lighting as next-generation lighting have been carried out. However, because a high-power blue laser diode is used as the light source, the decrease in phosphor emission due to temperature increase (thermal quenching) has become a serious issue. Therefore, it is desirable to develop a method to suppress the temperature increase of the YAG:Ce phosphor. To increase the thermal conductivity of the YAG:Ce phosphor and suppress the temperature increase, we fabricated a composite ceramic of AlN (nonoxide), which has a high thermal conductivity, and YAG:Ce (oxide) using a modified vapor transport equilibration technique. The oxynitride was not completely removed, but we succeeded in adding up to 80 wt% AlN to YAG:Ce. The ceramic with 50% added AlN had a thermal conductivity up to 19.2 W m−1K−1 and emitted almost the same intensity as that of the nondoped YAG:Ce. This thermal conductivity exceeds the reported values of 12–13 W m−1K−1 for Al2O3–YAG:Ce composite ceramics. Moreover, the luminous efficacy exhibited by the ceramic with a 20 wt% AlN addition was 266.0 lmW−1, which is larger than the reported values obtained from composite ceramics.

Multi-responsive deep-ultraviolet emission in praseodymium-doped phosphors for microbial sterilization.

Perusing multimode luminescent materials capable of being activated by diverse excitation sources and realizing multi-responsive emission in a single system remains a challenge. Herein, we utilize a heterovalent substituting strategy to realize multimode deep-ultraviolet (UV) emission in the defect-rich host Li2CaGeO4 (LCGO). Specifically, the Pr3+ substitution in LCGO is beneficial to activating defect site reconstruction including the generation of cation defects and the decrease of oxygen vacancies. Regulation of different traps in LCGO:Pr3+ presents persistent luminescence and photo-stimulated luminescence in a synergetic fashion. Moreover, the up-conversion luminescence appears with the aid of the 4f discrete energy levels of Pr3+ ions, wherein incident visible light is partially converted into germicidal deep-UV radiation. The multi-responsive character enables LCGO:Pr3+ to response to convenient light sources including X-ray tube, standard UV lamps, blue and near-infrared lasers. Thus, a dual-mode optical conversion strategy for inactivating bacteria is fabricated, and this multi-responsive deep-UV emitter offers new insights into developing UV light sources for sterilization applications. Heterovalent substituting in trap-mediated host lattice also provides a methodological basis for the construction of multi-mode luminescent materials.

Phosphor-in-Glass for High Performance WLEDs by Reduction Phosphor Interaction and AR Coating

We demonstrate co-doped phosphor-in-glass (PiG) for high performance white light-emitting diodes (WLEDs) employing reduction of red/green phosphors interaction and antireflection coating (ARC). In this study, the novelties are a suitable selection of the 650-nm red and 540-nm green phosphor materials to reduce the mutual interaction between the emission of green phosphor and the absorption of red phosphor, evidenced by photoluminescence spectroscopy, and then an ARC on both sides of the PiG to reduce Fresnel reflection loss. Therefore, the PiG with high luminous efficiency of 63 lm/W, high color rendering index (CRI) of 96, and less amount of phosphor material are obtained. The overall luminous efficiency of the PiG-based WLED is improved by about 15% and the total amount of phosphors is reduced by about 58%. This proposed of co-doped PiG with excellent performance and less amount of phosphor material usage is essential to meet the economic requirement for high-quality WLEDs indoor lighting applications.

Tuning of Emission Wavelength of CaS:Eu by Addition of Oxygen Using Atomic Layer Deposition.

Atomic layer deposition (ALD) technology has unlocked new ways of manipulating the growth of inorganic materials. The fine control at the atomic level allowed by ALD technology creates the perfect conditions for the inclusion of new cationic or anionic elements of the already-known materials. Consequently, novel material characteristics may arise with new functions for applications. This is especially relevant for inorganic luminescent materials where slight changes in the vicinity of the luminescent centers may originate new emission properties. Here, we studied the luminescent properties of CaS:Eu by introducing europium with oxygen ions by ALD, resulting in a novel CaS:EuO thin film. We study structural and photoluminescent properties of two different ALD deposited Eu doped CaS thin films: Eu(thd)3 which reacted with H2S forming CaS:Eu phosphor, or with O3 originating a CaS:EuO phosphor. It was found that the emission wavelength of CaS:EuO was 625.8 nm whereas CaS:Eu was 647 nm. Thus, the inclusion of O2− ions by ALD in a CaS:Eu phosphor results in the blue-shift of 21.2 nm. Our results show that ALD can be an effective way to introduce additional elements (e.g., anionic elements) to engineer the physical properties (e.g., inorganic phosphor emissions) for photonics and optoelectronics.

Deep-red emissive colloidal lead-based triiodide perovskite/telluride nanoscale heterostructures with reduced surface defects and enhanced stability for indoor lighting applications

Integrating together the nanostructures of two dissimilar materials into a single architecture can usually gain superior physical properties owing to the strong interaction. Herein, we proposed an epitaxial growth strategy to synthesize lead-based triiodide perovskite/telluride colloidal nanoscale heterostructures (CsPbI3/PbTe CNHs) via a rapid hot-injection method. The as-obtained CNHs exhibited a longer fluorescence lifetime associated with the radiative recombination of charge carriers, compared with the pristine CsPbI3 colloidal nanocrystals (CNCs). This was mainly attributed to the passivation of surface defects achieved by the PbTe component, which could be evidenced by the time-resolved spectroscopic studies. The stability of the CNHs had been improved considerably in comparison with that of pristine CNCs. The theoretical calculations based on density function theory (DFT) further revealed that the strong interaction and high binding energy at the CsPbI3/PbTe interfaces were responsible for the enhancement of α-phase stability. Moreover, the as-prepared CNHs were used as a deep-red emissive phosphor for assembling light-emitting diode (LED) devices, which demonstrated good prospects for broad applications in the field of indoor lighting, such as full-visible-spectrum and plant growth LEDs.

A Highly Efficient Eu2+ Excited Phosphor with Luminescence Tunable in Visible Range and Its Applications for Plant Growth

AbstractA series of RbxK2−xCaPO4F:Eu2+ phosphors are synthesized using a high‐temperature solid‐phase method. An increase in the Rb+ concentration leads to the Eu2+‐excited phosphor emission spectra being shifted from red to cyan. Interestingly, the excitation spectrum does not exhibit any variations, which indicates the possibility of mixing the red (Rb0.2K1.8CaPO4F:Eu2+) and cyan (Rb2CaPO4F:Eu2+) phosphors for plant growth. This luminescence tuning is attributed to the substitution of K+ with Rb+, which produces an inferior crystal‐field splitting that increases the energy at the lowest 5d level, and enhances the rigidity of the crystal structure, which results in a gradual decrease in the Stokes shift and a consequent blue shift in the emission spectrum. Time‐resolved photoluminescence emission spectroscopy further confirms the occurrence of broadband emission owing to the occupation of multiple sites by Eu2+. Light‐emitting devices appropriate for plant growth are fabricated by mixing the two phosphors with a 380‐nm UV chip, and a light‐conversion film is prepared using the red phosphor and PDMS glue. The Chlorella‐based plant growth experiment reveals that the growth rate of Chlorella is 12.2% higher than that of the blank group, indicating the favorable effect of the light‐conversion film on plant growth.

Improvement of Photoluminescence of Perovskite CH3NH3PbI3 by Adding Additional CH3NH3I during GrindingSupported by the National Natural Science Foundation of China (Grant Nos. 11774187 and U1902218), the National Key R&D Program of China (Grant No. 2018YFE0203400), the Natural Science Foundation of Tianjin City (Grant No. 19JCYBJC17600), and the 111 Project (Grant No. B07013).

The organic-inorganic hybrid perovskite CH3NH3PbI3 has been a good candidate for many optoelectronic applications such as light-emitting diodes due to its unique properties. Optimizing the optical properties of the CH3NH3PbI3 material to improve the device performance is a hot topic. Herein, a new strategy is proposed to enhance the light emission of CH3NH3PbI3 phosphor effectively. By adding the reactant CH3NH3I powder in an appropriate proportion and simply grinding, the emission intensity of CH3NH3PbI3 is greatly improved. The advantages of the proposed method are swiftness, simplicity and reproducibility, and no requirement for a complex organic ligand. The mechanism of this phenomenon is revealed by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, photoluminescence, and temperature-dependent photoluminescence. This study offers a unique insight for optimizing the optical properties of halide perovskite materials.

Temperature-dependent x-ray fluorescent response from thermographic phosphors under x-ray excitation

Phosphor thermometry has been successfully applied within several challenging environments. Typically, the thermographic phosphors are excited by an ultraviolet light source, and the temperature-dependent spectral or temporal response is measured. However, this is challenging or impossible in optically thick environments. In addition, emission from other sources (e.g., a flame) may interfere with the optical phosphor emission. A temperature dependent x-ray excitation/emission could alleviate these issues as x-rays could penetrate obscurants with no interference from flame luminosity. In addition, x-ray emission could allow for thermometry within solids while simultaneously x-ray imaging the structural evolution. In this study, select thermographic phosphors were excited via x-ray radiation, and their x-ray emission characteristics were measured at various temperatures. Several of the phosphors showed varying levels of temperature dependence with the strongest sensitivity occurring for YAG:Dy and ZnGa2O4:Mn. This approach opens a path for less intrusive temperature measurements, particularly in optically opaque multiphase and solid phase combustion environments.

A near UV-excited abnormal broad yellow emission phosphor Ba2CaB2Si4O14:Eu2+ for white-light LEDs

Phosphor-converted white LEDs are realized by combining blue InGaN chips with yellow and red emitting materials. Due to the lack of efficient red phosphor materials, we can design a broadband yellow phosphor material containing as many red components as possible. We found an abnormal broadband yellow-emitting Ba2CaB2Si4O14:Eu2+ borosilicate phosphor inspired by natural minerals, which has been synthesized by traditional high temperature solid-state method. The structural information and photoluminescence characteristics of Ba2CaB2Si4O14:Eu2+ were characterized in detail, and applied to the fabrication of white LED devices. Excited by near ultraviolet light at 365 nm, it displays a wide emission band from 400 to 800 nm centered on the 595 nm peak. White LED devices were fabricated by physically mixing the yellow phosphor Ba2CaB2Si4O14:Eu2+ and synthesized blue phosphor BaMgAl10O17:Eu2+ with 365 nm UV chip as excitation. The correlation color temperature (CCT) value and the chromaticity coordinates of the fabricated WLED devices were found to be 5522 K and (0.3293, 0.3036) respectively. In conclusion, Ba2CaB2Si4O14:Eu2+ has great potential in the preparation of near UV excited white LEDs.

Li+ Ion Induced Full Visible Emission in Single Eu2+‐Doped White Emitting Phosphor: Eu2+ Site Preference Analysis, Luminescence Properties, and WLED Applications

AbstractA series of Eu2+ single doped Ca9Na1–xLixSc0.667(PO4)7 phosphors with full‐spectrum emission have been synthesized. Under the 385 nm excitation, the Eu2+ single doped Ca9NaSc0.667(PO4)7 without Li+ doping displays a broad cold white light emission with the peaks at about 480 and 610 nm. With the introduction of Li+ ions, the Eu2+ ions selectively occupy the Ca1, Ca2/Ca3, and Na sites. The variation of local environment of Eu2+ ions caused by Li+ ions enhances the luminous intensity, solves the problem of the lack of a red light component, and realizes the emission color tuning from cold white via warm white to orange. A special charge compensation method caused by Li+ migration avoids the generation of defects and is beneficial to the improvement of luminescence properties. Eventually, a warm white light‐emitting diode device is prepared by combining the white emitting Ca9Na0.8Li0.2Sc0.667(PO4)7:2%Eu2+ phosphors with 385 nm LED chip, which exhibits a high color‐rendering of 92.9, low correlated color temperatures of 4529 K, and excellent color stability under working temperature. The as‐reported warm white emitting Eu2+‐doped phosphors have potential applications in full‐spectrum solid‐state lighting. The site engineering strategy provides an extensive guide for optimizing and designing novel single‐composition white‐emitting phosphor materials.

Environmental impacts of a rice-beef-biogas integrated system in the Mekong Delta, Vietnam evaluated by life cycle assessment

It is essential to increase the production of foods to meet the increasing future food demand, but this should be done in an environmentally sustainable manner. Integrated crop-livestock systems have been suggested to balance the reduction of environmental impacts and the increase in food production. Here we assessed and compared the environmental impacts of specialized (SPC) and integrated (ITG) rice and beef production systems in the Mekong Delta, Vietnam, using a life-cycle assessment (LCA). The productions of rice and beef are separated in the SPC, whereas they are integrated in the ITG: cattle manure is treated by a biodigester for biogas production, its digestate is applied to rice paddy fields as fertilizer, and part of the rice straw is used as cattle feed. We developed an LCA model based on data collected by site investigations of rice and beef farms and the relevant literature and LCA databases. Our evaluation of the ITG and SPC rice-beef production systems using the LCA revealed that among the four environmental impact categories investigated herein, the ITG had less environmental impacts on climate change (22%), energy consumption (22%), and eutrophication (14%) compared to the SPC. With the ITG, the reduction of methane emissions from paddy fields, the avoided energy consumption by the biogas produced, and the lower ammonia, nitrate, and phosphorous emissions from cattle manure and no eutrophying pollutant emissions from grassland were the main contributors to the lower greenhouse gas emissions, energy consumption, and eutrophication potential of this system, respectively. A sensitivity analysis showed that the use of cover for digestate storage resulted in lower environmental impacts of the ITG system compared to SPC system in all of the impact categories investigated here. These results provide helpful information to develop a circular and resource-efficient rice and beef production system that balances increasing productivity with environmental sustainability in rice-producing countries, particularly in Asia.