Emission Phosphor Research Articles

Efficient solution-processed yellow/orange phosphorescent OLEDs based on heteroleptic Ir(Ⅲ) complexes with 2-(9,9-diethylfluorene-2-yl)pyridine main ligand and various ancillary ligands

Abstract Efficient solution-processible yellow/orange emissive phosphors are highly required in solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs). With respect to phenyl pyridine (ppy)-type Ir(III) complexes, 2-(9,9-diethylfluoren-2-yl)pyridine (Flpy)-type Ir(III) complexes have huge potential in yellow/orange s-PhOLEDs due to their extended conjugation and excellent solubility in common organic solvents. Herein, a new series of phosphorescent Ir(III) complexes, i.e. Ir(Flpy)2pic-N O, Ir(Flpy-CF3)2pic-N O, Ir(Flpy-CF3)2dbm and Ir(Flpy-CF3)2acac, based on Flpy main ligand and picolinic N-oxide (pic-N O), acetylacetone (acac), and dibenzoyl methane (dbm) ancillary ligands are synthesized. The photophysical, electrochemical, and electroluminescent (EL) properties of these phosphorescent Ir(III) complexes are investigated in details. By introducing the CF3 group in Flpy ligand and varying the ancillary ligands, the emission spectra of these phosphorescent complexes are tuned in a large range with EL emission peaks from 544 nm to 588 nm. The s-PhOLEDs employing these phosphors show promising EL performance with maximum external quantum efficiency (EQE) from 15.4% to 23.7% and high power efficiency from 61.9 l m W−1 to 80.4 l m W−1. These highly efficient phosphorescent Ir(III) complexes may serve as ideal chromaticity components in solution-processed full-color displays and lighting devices.

Bluish-White Luminescence in Rare-Earth-Free Vanadate Garnet Phosphors: Structural Characterization of LiCa3MV3O12 (M = Zn and Mg).

Extensive attention has been focused toward studies on inexpensive and rare-earth-free garnet-structure vanadate phosphors, which do not have a low optical absorption due to the luminescence color being easily controlled by its high composition flexibility. However, bluish emission phosphors with a high quantum efficiency have not been found until now. In this study, we successfully discovered bluish-white emitting, garnet structure-based LiCa3MV3O12 (M = Zn and Mg) phosphors with a high quantum efficiency, and the detailed crystal structure was refined by the Rietveld analysis technique. These phosphors exhibit a broad-band emission spectra peak at 481 nm under near UV-light excitation at 341 nm, indicating no clear difference in the emission and excitation spectra. A very compact tetrahedral [VO4] unit is observed in the LiCa3MV3O12 (M = Zn and Mg) phosphors, which is not seen in other conventional garnet compounds, and generates a bluish-white emission. In addition, these phosphors exhibit high quantum efficiencies of 40.1% (M = Zn) and 44.0% (M = Mg), respectively. Therefore, these vanadate garnet phosphors can provide a new blue color source for LED devices.

Single Source Precursor Chemical Vapor Decomposition Method to Fabricate Stable, Bright Emissive Aluminum Hydroxide Phosphors for UV‐Pumped White Light‐Emitting Devices

AbstractAluminum hydroxides are considered to be a potential abundant, low‐cost blue emissive material to construct UV‐pumped white light‐emitting diodes (WLEDs). In this work, a single‐source precursor chemical vapor decomposition method is adapted to fabricate stable, strongly emissive aluminum hydroxide phosphors with photoluminescence quantum yield of up to 69% in solid state by thermal decomposing aluminum diacetate hydroxide (Al(OH)(Ac)2) at temperatures (260–360 °C) in N2 atmosphere. It exhibits layered, amorphous structure and its emission of aluminum hydroxide is enhanced by electron‐donating surface hydroxyl groups and originates from F+ centers and carbon‐related defects contributing to UV (388 nm) and blue (450–520 nm) spectral regions, respectively. Employing the as‐fabricated aluminum hydroxides as blue phosphor and CuInS2 nanocrystals as red phosphor, high color rendering and high‐efficiency WLEDs with luminous efficiencies up to 37 lm W−1 and high color rendering index of 91 are fabricated. This is the best performance reported so far for aluminum hydroxide based LEDs.

Novel Red-Orange Phosphors Na2BaMg(PO4)2:Pr3+: Synthesis, Crystal Structure and Photoluminescence Performance

Abstract A series of new red-orange emission phosphors Na2BaMg(PO4)2:Pr3+ were synthesised by a high-temperature solid-state reaction. The crystal structure and photoluminescence properties of these samples were characterised by X-ray diffraction and spectroscopic measurements. This compound holds P3̅m1 space group of the trigonal system with the lattice parameters of hexagonal cell a=0.5304(3) nm and c=0.6989(3) nm. The phosphor emits the strongest peak at 606 nm when excited by 449 nm. The average Commission Internationale de l’Eclairage chromaticity coordinates calculated for the phosphors are (0.52, 0.46). The results demonstrate the potential application of these phosphors in solid-state lighting and other fields.

Dual role of Y1.86WO6(Eu0.14)3+ phosphor compound to improve the efficiency of dye-sensitized solar cells

Rare earth doped metal tungstate (Y1.86WO6: (Eu0.14)3+) of submicron sized particles were prepared via low-temperature combustion method. This was later used as down converter and light scattering material in dye-sensitized solar cells (DSSCs). Morphological, compositional and optical properties were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV-Visible diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) spectroscopy. These particles were added with other constituents in the process of fabricating N719 or N749 stained photoanode for DSSCs. Devices fabricated using 2 wt% phosphor constituent showed an appreciable enhancement in short-circuit current density (Jsc) as well as higher power conversion efficiency (PCE) compared to devices without phosphor content. The observed enhancement in efficiency is due to downconversion luminescence and light scattering effects arising from these phosphors particles. Further compared with the N719 based device, the enhancement in PCE for N749 based device is 59%. The significant enhancement in PCE is mainly attributed to the optical wavelength matching between the emission of phosphor and the absorbance of the N749 sensitizer. Thus our work demonstrates how the phosphor material dually improves the DSSC efficiencies.

Employing one crystalline phase to gain different phosphor emissions for distinctive applications: Preparation, crystallization and luminescence of SrAl2B2O7 with different additions via glass ceramic technique

SrAl2B2O7 phosphor was crystallized via glass-ceramic technique. The effect of adding TiO2, Eu2O3, Dy2O3 and CeO2 on both crystallization process and luminescent properties were studied using differential thermal analysis (DTA), X-Ray diffraction analysis (XRD), scanning electron microscope (SEM), Fourier-Transform infrared absorption spectra (FT-IR), optical ultra violet (UV) -visible near infrared (NIR) absorption and fluorescence spectrophotometer. The batches were melted around 1450°C. New method to revealed reducing atmosphere was applied. DTA results show broad exothermic peak revealing surface crystallization. The XRD patterns depict crystallization of pure SrAl2B2O7 in hexagonal form. Presence of CeO2 enhances the crystallization of SrAl2B2O7 phase while TiO2 inhibit it. Increasing the time or temperature of heat treatment didn’t affect the nature of the crystalline phase. Optical UV–visible NIR absorption and luminescent properties clarified the presence of titanium and cerium ions as Ti4+ and Ce3+ form, while europium present in both Eu2+ and Eu3+. The resulting phosphor revealed different colors depending on the excited wavelength used and heat treatment applied.

Crystal structure and characteristic luminescence properties investigation of novel red-emitting phosphor Na3MgZr(PO4)3:Eu3+ for white light-emitting diodes

A series of novel red emission phosphors Na3MgZr(PO4)3:Eu3+ was synthesized by solid state reaction. The phase purity, crystal structure of Na3MgZr(PO4)3 host and the site occupancy behaviour of Eu3+ were investigated through X-ray diffraction refinement and series X-ray diffraction patterns analysis. The structure and temperature related luminescence properties were studied in detail by photoluminescence excitation, emission spectra and decay times. Upon 393 nm excitation, Na3MgZr(PO4)3:Eu3+ phosphor can exhibit strong red emission dominated at 611 nm (5D0–7F2 transitions) with excellent thermal stability. The thermal stability property and the quenching mechanism were investigated. The observed abnormal transitions from 5D1 energy level were discussed. The results indicated that Na3MgZr(PO4)3:Eu3+ could be a suitable red-emitting phosphor candidate for white light emitting diodes.

Enhancing Photovoltaic Performance Using Broadband Luminescent Down-Shifting by Combining Multiple Species of Eu-Doped Silicate Phosphors.

This paper demonstrates the application of a broadband luminescent downshifting (LDS) layer with multiple species of europium (Eu)-doped silicate phosphors using spin-on film technique to enhance the photovoltaic efficiency of crystalline silicon solar cells. The surface morphology of the deposited layer was examined using a scanning electron microscope (SEM). The chemical composition of the Eu-doped silicate phosphors was analyzed using energy-dispersive X-ray spectroscopy (EDS). The fluorescence emission of the Eu-doped silicate phosphors was characterized using photoluminescence (PL) measurements at room temperature. We also compared the optical reflectance and external quantum efficiency (EQE) response of cells with combinations of various Eu-doped phosphors species. The cell coated with two species of Eu-doped phosphors achieved a conversion efficiency enhancement (∆η) of 19.39%, far exceeding the ∆η = 15.08% of the cell with one species of Eu-doped phosphors and the ∆η = 8.51% of the reference cell with the same silicate layer without Eu-doped phosphors.

Critical Review—Narrow-Band Emission of Nitride Phosphors for Light-Emitting Diodes: Perspectives and Opportunities

Searching for narrow-band red-emitting and thermally stable phosphors is the ultimate strategy toward enhanced performance of phosphor converted light emitting diodes (pc-LED). The red emission is assured by the nitride host because of its relatively more covalent character than oxides and sulfides; however, the narrow emission is attributed to crystallographic, morphological, and electronic considerations. The symmetric coordination site ensures equal ligand effect in all direction fits well with the configuration of Eu2+ f orbitals in the excited state, as observed in cuboid nitrides. Further, thermal stability is ascribed not only to suitable bandgap but more specifically, a relatively distant location of the lowest 5d level from the bottom of the conduction band (CB) that consequently entails high energy to quench excited electrons by exciting them further up to the CB. Modes toward the development of new nitride hosts with potentially narrow-band emission have been identified. A viewpoint on light-emitting diode (LED), backlighting, and laser lighting, which remains the most economically-rewarding phosphors application, is presented. Other exciting frontiers, such as agricultural illumination and persistent luminescence, maximize nitride systems that have other properties other than the stringent narrow-band red emission and excellent thermal stability required for the desired improvement of the mainstream LED application.

Synthesis and photoluminescence of amorphous AlBCO phosphors

Amorphous and nitrogen-free AlBCO phosphors were synthesized by a sol-gel method. The phase evolution, microstructure and photoluminescent properties of the AlBCO phosphors were discussed. The as-prepared phosphors exhibited a broad emission band in the blue–green region under the excitation of violet irradiation with a wavelength of 370 nm. The sample synthesized at 650 °C for 1 h exhibited the highest photoluminescence intensity and quantum yield. The emission band of the sample prepared with the optimum process can be well fitted with three peaks centered at 412, 450 and 516 nm. The preparation process had great effects on the photoluminescent properties of AlBCO phosphors. The intense emission of AlBCO phosphors was assigned to the photoluminescence of both the BO centers coordinated with the Al–O group and the defect levels of C-doped amorphous Al2O3.

A remote phosphor film of silicate-poly(styrene-co-glycidyl methacrylate) composites for NUV chip-based white LED

Herein we adopt a simple route to prepare silicate phosphor-containing transparent composite film which is able to emit white light on the base of a blue emitting co-polymer matrix poly(styrene-co-glycidyl methacrylate) under excitation of 365 nm. SEM micrographs indicate that the surface treated silicate phosphor particles modified by silane coupling agent and embedded in co-polymer matrix separate from each other with a certain spacing and without agglomeration. More importantly, mutual enhancement in characteristic emission peak of two ingredients is observed. By varying the weigh percentage of silicate phosphor, yellow-to-white photoluminescent color-tuning could be readily accomplished depending on the variation of the intensity ratios between the characteristic yellow emission of silicate phosphor and the blue luminescence of the polymer matrix. And white emission [CIE: (0.354,0.322)] could be obtained from the simultaneous blue and yellow emission (intensity ratios value is 0.93). Simple NUV-based WLEDs were fabricated using prepared silicate phosphor doped composite material, showing Tc of 5917 K, CRI of 84.6. When a larger size composite film was simply assembled with COB, large area white lighting device with a certain color reduction came into being. All the results indicate that the of silicate phosphor-containing transparent composite film has practical significance for the packaging of remote phosphor converted white LEDs.

(Invited) Narrow Band Emission of Nitrides Phosphors and All Inorganic Perovskite Quantum Dots for the Application in Light Emitting Diodes

A narrow band emission nitride SrLiAl3N4:Eu2+ (SLA) red phosphor prepared through a high-pressure solid state reaction was coated with organosilica layers in 400 ~ 600 nm thickness to improve its waterproof property. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70% of its initial EQE after being aged for 5 days in harsh conditions. White light-emitting diodes (LEDs) of SLA red-phosphors and commercial Y3Al5O12:Ce3+ (YAG:Ce) yellow-phosphor on a blue-InGaN chip were shown high color rendition (CRI = 89, R9 = 69) and low correlated color temperature of 2406 K. All-inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots (PQDs) with narrow emission bad were synthesized by hot injection methods. We propose an efficient and simple method to prevent the anion-exchange effect. We mixed green CsPbBr3 PQDs with purchased mesoporous silica. We applied the new PQD-based LEDs for backlight displays. Our white LED device for backlight display passed through a color filter with an NTSC value of 113% and Rec. 2020 of 85%. For lighting application, we used red perovskite quantum dots assisted by a yellow YAG:Ce phosphor were integrated on a blue chip. This warm white light with CCT (3328K), high color rendering index (CRI = 84.7) and a super high value of saturated red color component R9 as 96. Nitrides phosphors and all inorganic quantum dots were a good candidate for the application of white light LEDs with narrow emission band.

Photoluminescence Characteristics of Yag:Ce, Gd Based Phosphors with Different Prehistories

Luminescence characteristics of yttrium-aluminum garnet based phosphor samples differed by their elemental composition and prehistory of synthesis are studied. The morphology, structure, and elemental composition of phosphor samples, their excitation and emission spectra, efficiency of phosphor conversion of chip emission, and kinetics of luminescence decay are measured. The emission characteristics of phosphors are compared with their structural properties and elemental composition.

Luminescence Properties of an Orange-Reddish Emitting Phosphor KCaBi(PO4)2:Sm3+ with Excellent Thermal Stability

Luminescence Properties of an Orange-Reddish Emitting Phosphor KCaBi(PO₄)₂:Sm³⁺ with Excellent Thermal Stability

Color - Tunable Phosphors in Weberite Type System, La3 SbO7 :Bi3+ , Eu3+ for Near-UV LED Applications

A new series of color tunable from yellow to near white emitting phosphors, La3SbO7:xBi3+, yEu3+ were prepared using a conventional solid state method and its structural, morphological, absorbance and photoluminescence properties and lifetime measurements were carried out to analyze the phosphor characteristics. The La3SbO7:Bi3+ phosphors crystallize into a phase pure weberite type structure with good particle morphology. Upon UV light excitation at 315 nm, these phosphors show broad band emission in the blue green region centered near 517 nm owing to the 3P1-1S0 transitions of the Bi3+ activator. Critical emission quenching of La3SbO7:xBi3+ samples was observed at x = 0.04. Eu3+ is co-doped with La3SbO7:0.04Bi3+ blue green phosphor to incorporate the red component to make a full color emission phosphor. The effective energy transfer from Bi3+ to Eu3+ ions has been assessed using Dexter's theory indicating resonance type through dipole-quadrupole interaction. Further the decreasing trends in lifetime measurements confirm the existence of energy transfer process from Bi3+ to Eu3+. The near white light emitting phosphor La3SbO7:xBi3+, yEu3+ can be realized by adjusting the concentrations of the Bi3+ and Eu3+ with chromaticity coordinates: (0.30,0.48). The above results suggest that the developed phosphor could be potential to be used as a single phase white emission phosphor for n-UV LED applications.

Effects of chemical bonds on luminescence properties of BCNO phosphors with yellow and orange emission

We prepared BCNO phosphors with yellow and orange emission and investigated the effects of chemical bonds on luminescence and absorption properties for BCNO phosphors in solid phase, water, acid and alkaline solutions. The BCNO phosphors are mainly consisted of B‒N, C‒N, B‒O, C˭C, C‒H and N‒H chemical bonds, and the intensity and content of chemical bonds are related to the ratio of boric acid to glycine. The emission peaks of BCNO phosphors are red shifted from 559nm to 605nm with increasing ratio of boric acid to glycine (1:1 to 1:10). The range of excitation and absorption spectra are broadened with increased ratio of boric acid to glycine. In addition, the acid and alkaline solutions have different effects on excitation, emission and absorption spectra of BCNO phosphors. The changes of luminescence and absorption properties of BCNO phosphors are related to the regulation of surface states and chemical binding status of BCNO phosphors, which is originated from the variety of relative energy band structure.

Enhancing identified circular economic benefits related to the deployment of the Solrød biogas plant

This paper investigates how experiences from the deployment of the Solrod biogas plant in Denmark - a large scale centralized biogas plant - can assist future biogas technologies in achieving circular economic benefits. Departing from a theoretical understanding of a circular economy provided by the Ellen MacArthur Foundation, the paper analyzes three areas: 1) biogas production, 2) nitrogen, phosphorous & green house gas (GHG) emissions, and 3) re-cycle/cascade materials. It consequently elaborates on the environmental benefits obtained, in terms of CO 2 emission from biogas production substituted for fossil fuels, improved water quality and hence reduced GHG emissions due to lower nitrogen effluents, and re-cycling of nutrients on farmland thereby recovering finite resources and improving crop yield. Economic spin-off effects are presented, including new jobs created in the local community. Learning from Solrod Biogas, this paper further proposes to include the following activities when planning for future biogas plants: waste-stream identification and coupling in the local community, measuring the value of digestate as a fertilizer, short distance to farmers delivering manure, and plant design adapted to the local energy market. Finally, the paper suggests how to qualify the circular economic concept based on the findings from the Solrod biogas plant. It is here concluded, that emphasis should be on cascading energy from biogas production by means of combined heat and power (CHP), district heating or process heat to industry. Besides this, cascades in the manufacturing chain must also be intensified, allowing a more efficient materials and energy utilization and re-cycling in this part of the production chain. This will consequently reduce the total quantity of waste being generated by manufacturing industries, and thus benefit re-cycling strategies that only capture and seek to re-use a limited fraction of the waste being generated from industry.

Tuning of the Emission Color of Ba1−xGa2S4:xEu2+ Phosphors for Use in Three‐Band White LEDs

Ba1‐xGa2S4:xEu2+ (x = 0.10, 0.25, 0.50, 0.75, 1.0) phosphors were prepared by performing a solid‐state reaction. The PL spectra of the Ba1−xGa2S4:xEu2+ phosphors were recorded. Very broad excitation bands are located in the range 300–480 nm, which suggests that the Ba1−xGa2S4:xEu2+ can be used as color emission phosphors when pumped with an excitation of 465 nm, which is the wavelength of a commercial blue‐emitting diode. The emission wavelength at the maximum PL intensity (λmax) for the Ba1−xGa2S4:xEu2+ phosphors increases gradually from 504 to 548 nm as the mole fraction of europium ions (x) in the phosphors increases. The variation in λmax for the Ba1−xGa2S4:xEu2+ phosphors with the mole fraction of europium ions can be interpreted in terms of the crystal structures of the Ba1−xGa2S4:xEu2+ phosphors. A three‐band white emission was obtained by coating a mixture of Ba0.5Ga2S4:0.5Eu2+ and CaS:Eu2+ phosphors onto the surface of a blue‐emitting diode.

Metaheuristics-Assisted Combinatorial Screening of Eu2+-Doped Ca-Sr-Ba-Li-Mg-Al-Si-Ge-N Compositional Space in Search of a Narrow-Band Green Emitting Phosphor and Density Functional Theory Calculations.

A metaheuristics-based design would be of great help in relieving the enormous experimental burdens faced during the combinatorial screening of a huge, multidimensional search space, while providing the same effect as total enumeration. In order to tackle the high-throughput powder processing complications and to secure practical phosphors, metaheuristics, an elitism-reinforced nondominated sorting genetic algorithm (NSGA-II), was employed in this study. The NSGA-II iteration targeted two objective functions. The first was to search for a higher emission efficacy. The second was to search for narrow-band green color emissions. The NSGA-II iteration finally converged on BaLi2Al2Si2N6:Eu2+ phosphors in the Eu2+-doped Ca-Sr-Ba-Li-Mg-Al-Si-Ge-N compositional search space. The BaLi2Al2Si2N6:Eu2+ phosphor, which was synthesized with no human intervention via the assistance of NSGA-II, was a clear single phase and gave an acceptable luminescence. The BaLi2Al2Si2N6:Eu2+ phosphor as well as all other phosphors that appeared during the NSGA-II iterations were examined in detail by employing powder X-ray diffraction-based Rietveld refinement, X-ray absorption near edge structure, density functional theory calculation, and time-resolved photoluminescence. The thermodynamic stability and the band structure plausibility were confirmed, and more importantly a novel approach to the energy transfer analysis was also introduced for BaLi2Al2Si2N6:Eu2+ phosphors.

Electronic structure and photoluminescence property of a novel white emission phosphor Na3MgZr(PO4)3:Dy3+ for warm white light emitting diodes**Project supported by the Doctoral Research Fund of Liaoning Province, China (Grant No. 201601351), the National Natural Science Foundation of China (Grant No. 51502142), and the General Program of Natural Science Foundation of the Jiangsu Provincial Higher Education Institutions, China (Grant No. 15KJB430021).

To explore suitable single-phase white emission phosphors for warm white light emitting diodes, a series of novel phosphors Na3MgZr(PO4)3:xDy3+ (0 ≤ x ≤ 0.03) is prepared, and their phase purities as well as photoluminescence properties are discussed in depth via x-ray diffraction structure refinement and photoluminescence spectrum measurement. The electronic structure properties of the Na3MgZr(PO4)3 host are calculated. The results reveal that Na3MgZr(PO4)3 possesses a direct band gap with a band gap value of 4.917 eV. The obtained Na3MgZr(PO4)3:Dy3+ phosphors are all well crystallized in trigonal structure with space group , which has strong absorption around 365 nm and can generate warm white light emissions peaking at 487, 576, and 673 nm upon ultraviolet excitation, which are attributed to the transitions from 4F9/2 to 6H15/2, 6H13/2, and 6H11/2 of Dy3+ ions, respectively. The optimal doping content, critical distance, decay time, and Commission International de L’Eclairage (CIE) chromaticity coordinates are investigated in Dy3+ ion-doped Na3MgZr(PO4)3. The thermal quenching analysis shows that Na3MgZr(PO4)3:Dy3+ has a good thermal stability, and the thermal activation energy is calculated. The performances of Na3MgZr(PO4)3:Dy3+ make it a potential single-phase white emission phosphor for warm white light emitting diode.