Comparison of YAG: Eu phosphor synthesized by supercritical water and solid-state methods in a batch reactor

Phosphor yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) doped with Eu (10 at%) was synthesized by supercritical water (SCW) and solid-state methods in a batch reactor. The crystals, morphologies and luminescent properties of the phosphors obtained from different pH conditions in the SCW were studied. Pure YAG phase was successfully synthesized at the alkaline condition in the SCW without formation of intermediate phases, while the size and luminescent property of YAG: Eu were strongly affected by pH condition. The luminescent intensity of YAG: Eu by the SCW method without further thermal treatment is stronger than that by the solid-state method with thermal treatment.     

Comparison of YAG: Eu phosphors synthesized by supercritical water in batch and continuous reactors

Luminescent yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) nanoparticles doped with Eu (10 at%) were synthesized in batch-type and continuous-type supercritical water (SCW) reactors. In the case of the continuous-type SCW method, the particles of YAG: Eu phosphors were much smaller and demonstrated a uniform spherical-like shape. Inversely, in the case of the batch-type SCW method, a needle-like or elliptical-like shape was formed because a finite amount of time was required to reach SCW conditions from ambient conditions. However, the emission intensity of YAG: Eu phosphors synthesized by using the batch-type SCW method was stronger. Therefore, it is concluded that the continuous-type SCW method is superior to the batch-type SCW method from the viewpoint of the particle size and shape, but the luminescence property of phosphors in the continuous-type SCW method needs to be improved. In addition, a calcination process slightly improved the luminescence intensities of YAG: Eu phosphors generated by using either the batch-type or continuous-type SCW methods.     

Sol–gel pyrolysis and photoluminescent characteristics of europium-ion doped yttrium aluminum garnet nanophosphors

Europium-ion doped Y₃Al₅O₁₂ garnet nanophosphors (YAG:Eu³⁺) with wide ranging size tunability (40–150 nm) have been prepared via a sol–gel pyrolysis method employing a fuel system that combined urea and polyvinyl alcohol (PVA). Well dispersed nanoparticles were prepared at 1000 °C. This temperature is lower than that required for synthesizing YAG:Eu³⁺ via the solid-state reaction route. The particle size and morphology of the synthesized powders are found to have critical dependence on the oxidizer (metallic nitrates) to fuel ratio. The importance of using an organic polymeric dispersion matrix to obtain well dispersed YAG:Eu³⁺ nanoparticles has been demonstrated. The photoluminescene properties of the prepared YAG:Eu³⁺ phosphors are profoundly dependent on the preparation conditions. The emission intensity of well dispersed YAG:Eu³⁺ nanoparticles is found to be much stronger than that of the bulk sample. The excitation spectrum of well dispersed nanoparticles shows an extension of the excitation peak in the high-energy region. These unique properties of YAG:Eu³⁺ nanoparticles can be rationalized by considering numerous surface states due to the large surface area to volume ratio of the nanoparticles. In addition, using the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ as a local probe, the role of surface states that modify the optical properties of YAG:Eu³⁺ nanophosphors has also been illustrated.     

Controllable hydrothermal synthesis and photoluminescence properties of CaGd2(WO4)4:Eu3+ red-emitting phosphor

CaGd₂(WO₄)₄:Eu³⁺ phosphors with controllable morphology were synthesized via the hydrothermal method. The influences of pH value, reaction time and Eu³⁺ concentration on the crystal structure, morphology, and photoluminescence properties of CaGd₂(WO₄)₄:Eu³⁺ were studied. The pure tetragonal structure CaGd₂(WO₄)₄ is obtained when the pH value is 8 and 9. Furthermore, by altering the pH value of the reaction solution, the morphologies of the CaGd₂(WO₄)₄:Eu³⁺ phosphors evolve from spindle-shaped grains to tetragonal plate-like grains and finally to aggregated bulk particles. Under the 394 nm excitation, the phosphors display a bright red emission corresponding to the characteristic 4f-4f transitions of Eu³⁺, and the intensity of emission peaks depends mainly on the pH value, the reaction time, and the Eu³⁺ concentration. The optimum photoluminescence performance is achieved for CaGd_2-x(WO₄)₄:xEu³⁺ (x = 1) phosphor synthesized at pH = 8 under the reaction time of 16 h. Finally, the thermal stability of the phosphors is analyzed at different ambient temperatures.     

Synthesis and optical characterization of novel Sr3Ga2O6:Eu phosphor

Alkaline earth metal gallets have been identified as an important ceramic material. The crystal chemistry of many of these gallets is well explored; however, very rare studies regarding optical properties of rare earth (RE) ions doped in such gallets, particularly in Sr₃Ga₂O₆ host, have been carried out. The present study reports on synthesis and characterization of novel Sr₃Ga₂O₆:Eu³⁺ phosphors. The phosphors have been synthesized using a conventional solid state reaction method. Crystal structure, morphology and luminescence properties (excitation, emission and CIE coordinate) of these phosphors have been studied as a function of sintering temperature and Eu³⁺ concentration. X-ray diffraction study reveals that the phosphor sintered at low temperature (900 °C) contains an impurity phase which is removed at higher sintering temperatures and results into cubic crystalline phase of Sr₃Ga₂O₆. Particle size of the phosphor increases with an increase in sintering temperature which results to a red shift in the peak position of excitation band lying in a broad range from 250 to 370 nm. Optimum emission intensity is attained for 0.12 mol% concentration of Eu³⁺ ions; above this concentration, a quenching in emission intensity is observed.     

Synthesis and photoluminescence properties of MgAl(PO4)O:Eu red phosphor for white LEDs

Eu³⁺-activated MgAl(PO₄)O:phosphor has been synthesized by a high temperature solid state reaction and efficient red emission under near-ultraviolet excitation is observed. The emission spectrum shows a dominant peak at 594 nm due to the ⁵D₀→⁷F₁ transition of Eu³⁺. The excitation spectrum is coupled well with the emission of UV LED (350–410 nm). The effect of Eu³⁺ concentration on the luminescent properties of MgAl(PO₄)O:Eu³⁺ and the mechanism of concentration quenching of Eu³⁺ are studied. The results show that MgAl(PO₄)O:Eu³⁺ is a promising red-emitting phosphor for white LEDs.     

Microwave-assisted solvothermal preparation and photoluminescence properties of Y2O3:Eu phosphors

Europium doped yttrium oxide phosphors were synthesized by a rapid microwave-assisted solvothermal method. The microwave processing time for synthesizing the precursors of Y₂O₃:Eu³⁺ powders was as short as 5 min. After calcination at 600 °C, a well-crystallized pure phase of Y₂O₃:Eu³⁺ was obtained. The morphology of the precipitated powders was spherical and composed of nano-sized grains. As the microwave irradiation time was increased, the average particle size of the spherical powders increased, and the crystallinity of heat-treated powders was also enhanced. The synthesized powders retained the spherical morphology after heating treatments. An intense red emission at 611 nm was assigned to the ⁵D₀-⁷F₂ transition of Eu³⁺.     

A novel red-emitting Na5W3O9F5:Eu3+ phosphor with high color purity for blue-based WLEDs

Red phosphor plays a key role in improving the lighting and display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). Meanwhile, developing new luminescent matrix materials can positively contribute to the acquisition of ideal and efficient phosphors. In this work, we propose a novel red-emitting Na₅W₃O₉F₅:Eu³⁺ (NWOF:Eu³⁺) phosphor. The phase composition, morphology, electronic structure and photoluminescence properties of the NWOF:Eu³⁺ phosphor were systematically investigated. The EXAFS results prove that the Eu³⁺ dopants occupy the Na2 and Na3 sites in the NWOF host. Under 466 nm blue light excitation, NWOF:xEu³⁺ (0.05 ≤ x ≤ 0.25) phosphors display a dominant red emission at 607 nm and achieves a high color purity (97.44%) due to the dominant electric dipole transition (⁵D₀→⁷F₂) of Eu³⁺ ions. Impressively, this red-emitting NWOF:0.25Eu³⁺ phosphor exhibits relatively superior thermal stability (450 K, >50%) and excellent chromaticity stability (2.32 × 10^?4 ≤ ΔE ≤ 6.23 × 10^?3) from 298 K to 498 K. The activation energy for thermal quenching effect is determined to be 0.22 eV. Moreover, the pc-WLED was fabricated by coupling a 460 nm blue chip with the as-synthesized NWOF:0.25Eu³⁺ red phosphor and commercial YAG:Ce³⁺ phosphor. The optical parameters of the as-fabricated pc-WLED are also measured, and the CIE coordinates remain almost constant as the drive current increases from 20 mA to 120 mA. These results indicate that the NWOF:0.25Eu³⁺ red phosphors should be a suitable candidate as a red component for the preparation of pc-WLEDs.     

Crystalline morphology and photoluminescent properties of YInGe2O7:Eu phosphors prepared from microwave and conventional sintering

This paper describes an investigation of the crystalline morphology and photoluminescent properties of YInGe₂O₇:Eu³⁺ powders using microwave assisted sintering. For comparison, the properties of YInGe₂O₇:Eu³⁺ powders sintered at 1200 °C in conventional furnace for 10 h were also investigated. X-ray powder diffraction analysis confirmed the formation of monoclinic YInGe₂O₇ without second phase or phases of starting materials as YInGe₂O₇:50 mol% Eu powders sintered at 1200 °C in microwave furnace for 1 h. Scanning electron microscopy showed smaller particle size and more uniform grain size distributions are obtained by microwave assisted sintering. In the PL studies, both microwave sintered and conventionally sintered powders emitted a maximum luminescence centered at 620 nm under excitation of 393 nm with similar luminescent intensity. The results show that microwave processing has the potential to reduce the time and required energy input for the production of YInGe₂O₇:Eu³⁺ phosphors without sacrificing the photoluminescence.     

A highly intense double perovskite BaSrYZrO5.5: Eu3+ phosphor for latent fingerprint and security ink applications

A novel double perovskite BaSrYZrO_5.5:Eu³⁺ red-emitting phosphor was synthesized and characterized by XRD, SEM and PL analyses. The structure of the prepared phosphor was confirmed through JCPDS as well as Rietveld refinement analysis. The present phosphor shows an intense red emission at 613 nm when excited by 394 nm. The CIE colour coordinates value of BaSrYZrO_5.5:Eu³⁺ (9 mol%) phosphor is found to be (0.6181, 0.3783) and it has high colour purity of 99.1%. The 613 nm transition integrated intensity of the present phosphor is 4.44 times higher compared to the commercial red phosphor. The thermal stability and Quantum yield of optimized BSYZ:Eu³⁺ (9 mol%) phosphor were also calculated. The BSYZ:Eu³⁺ phosphor results can be employed as an efficient red component in latent fingerprint detection and anti-counterfeiting applications.     

Synthesis and luminescence of Y2O3:Eu inorganic–organic hybrid nanostructures with thenoyltrifluoroacetone

Cubic Y₂O₃:Eu³⁺ nanoparticles with a size about 32 nm were synthesized using a facile hydrothermal method followed by an annealing process. As expected, the Y₂O₃:Eu³⁺ nanoparticles had a broad Eu–O excitation band ranging from 200 nm to 285 nm peaking at about 260 nm. The Y₂O₃:Eu³⁺ nanoparticles were then used to fabricate the inorganic–organic hybrid nanostructures with thenoyltrifluoroacetone (TTA). The Y₂O₃:Eu³⁺–TTA hybrid nanostructures exhibited a new strong excitation band ranging from 280 nm to 390 nm peaking at about 368 nm. This new excitation band was attributed to the energy transfer mechanism of the Y₂O₃:Eu³⁺–TTA hybrid system. It is interesting to note that this energy transfer mechanism had a close interaction with the Eu–O excitation of Y₂O₃:Eu³⁺ nanoparticles. The phase structures, chemical bonding information, microstructural characteristics and luminescence properties were investigated.     

Ultraviolet radiation excited strong red-emitting LaAlO3:Eu3+ nanophosphors: Synthesis and luminescent properties

We synthesized the trivalent europium ions (Eu³⁺) doped lanthanum aluminate (LaAlO₃, LAO) nanophosphors by a solvothermal method. Their structural, morphological, and luminescent properties were systematically investigated. The obtained nanoparticles possessed single nanocrystallinity with a rhombohedral structure. For the excitation originating from the charge transfer band (O^2- to Eu³⁺ ions) under 320 nm illumination, the featured emissions of Eu³⁺ ions were detected in all the compounds. The optimum doping concentration of Eu³⁺ ions in LAO was about 9 mol% and the concentration quenching was dominated by dipole-dipole interaction. Furthermore, the Judd-Ofelt (J-O) theory was used to estimate the J-O intensity parameters. Based on the temperature-dependent PL emission spectra, the thermal stability was analyzed and the activation energy was obtained to be 0.234 eV. Meanwhile, the decay time, color coordinate/purity, and cathodoluminescence behaviors of the synthesized nanophosphors were also studied. These characteristics make the Eu³⁺-doped LAO nanoparticles a promising red-emitting phosphor for both ultraviolet-based white light-emitting diodes and field-emission displays.     

Experimental evaluation of the luminescence performance of fired clay brick coated with SrAl2O4:Eu/Dy phosphor

This study evaluates the luminescence performance of fired clay bricks coated with SrAl₂O₄:Eu/Dy phosphor. To do so, SrAl₂O₄:Eu/Dy phosphor was first produced using the traditional solid-state reaction synthesis technique. The prepared phosphor was then used for coating fired clay bricks to analyze the luminescence performance via spectral analysis, decay characteristics, and microstructure of the bricks. The results reveal that excitation and emission spectra of the phosphor coated bricks range from 200 to 480 nm and 455 to 650 nm, respectively, suggesting that the phosphor coated bricks have the capacity of absorbing light with a wide range of wavelengths. The peak wavelength projected at 511 nm in the emission spectrum is achieved, which indicates 4f⁶5 d¹-4f⁷ transition of Europium (Eu²⁺). The repeated excitation and deexcitation of Eu²⁺ by using hole traps and trap levels offered by Dysprosium (Dy³⁺), exist between the ground and the excited state of Eu²⁺ leads to luminescent phenomenon. Moreover, the decay characteristics has revealed that phosphor coated bricks can emit light for a considerable amount of time (>8.5 min) upon the removal of the excitation source. The results reveal that phosphor coated bricks has the potential of increasing energy efficiency of residential and commercial buildings.     

Combustion Synthesis of Ca2Si5N8: Eu2+ Phosphors and their Luminescent properties

A combustion synthesis method has been developed for synthesis of Eu²⁺‐doped Ca₂Si₅N₈ phosphor and its photoluminescence properties were investigated. Ca, Si, and Eu₂O₃ powders were used as the Ca, Si, and Eu sources. NaN₃ and NH₄Cl were found necessary to be added for the formation of the product phase and addition of Si₃N₄ was found to enhance the product yield. These powders were mixed and pressed into a compact, which was then wrapped up with an igniting agent (Mg + Fe₃O₄). The reactant compact was ignited by electrical heating under a N₂ pressure of 0.7 MPa. Effects of these experimental parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized Ca₂Si₅N₈: Eu²⁺ phosphor absorbs light in the region of 300–520 nm and shows a broad band emission in the region of 500–670 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺. Eu₂O₃ was found partially unreacted and a certain amount of oxygen is believed to be incorporated into the lattice of the product phase. The peak emission intensity (~93% of a commercially available phosphor, YAG:Ce³⁺v) and the peak emission wavelength (571–581 nm) were found to be lower and shorter, respectively, than that reported in the literature. These are considered to be mainly due to oxygen incorporation, which not only reduces nephelauxetic effect and crystal field splitting but also causes a lowering of internal quantum efficiency.     

Solvothermal synthesis of red and green emitting Ca1.65Sr0.35SiO4:Eu and Ca1.65Sr0.35SiO4:Eu phosphors for solid-state lighting applications

A novel and facile synthetic approach has been trialed, and attempted with success in the preparation of two phosphors namely, a red emitting CaSrSiO₄:Eu³⁺ and a green emitting CaSrSiO₄:Eu²⁺. These phosphors were successfully synthesized using a simple co-precipitating solvo-thermal strategy wherein tetraethyl orthosilicate (TEOS) as silica source and the acetate precursors of strontium (Sr²⁺), calcium (Ca²⁺) and europium (Eu³⁺) are utilized. The material so obtained is subjected to an extensive photoluminescence behavior study. The concentration of the dopant (Eu³⁺and Eu²⁺) plays a significant role in the determination of photoluminescence behavior and hence a systematic and in-depth experimental studies were done and the results are synchronized. On interpretation of the output, it came to light that an intense emission signals sparked in the red region (590 and 615 nm) in the case of phosphor doped with Eu³⁺, which is excited under near ultra violet (395 nm) and blue (466 nm) region. In case of the CaSrSiO₄ sample doped with Eu²⁺_, an intense broad green signal (~510 nm) is obtained under the excitation range of 350–430 nm. The results obtained are quite encouraging and made a strong confirmation as, the solvo-thermally synthesized CaSrSiO₄, which is activated by the dopants namely Eu³⁺ and Eu²⁺ possesses an immense potential and it is exactly tapped by the adopted methodology. Despite its strong impact, it will also assure a strong revolution in the fabrication and thus the commercialization of white LEDs as both the red and green emitting phosphor.     

A single-phase white-emitting La10(SiO4)6O3：Eu2+/Eu3+ phosphor for near-UV LED-based application

A novel single-phase white-emitting phosphor La₁₀(SiO₄)₆O₃ (LSO): xEu has been synthesized by high-temperature solid-state reaction. Its crystal structure, luminescence properties, fluorescence decay time and oxygen vacancies have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. XRD result shows a typical oxyapatite structure with the space group of P6₃/m. Characteristic excitation and emission peaks of Eu²⁺ and Eu³⁺ were observed from PL studies. The optimum doping concentration of Eu was found to be 7.5 mol% (x = 0.075). In this work, the lifetimes of Eu³⁺ and Eu²⁺ were considerably longer than those from some references. Under the excitation of different near ultraviolet (n-UV) longer wavelengths (λex = 360, 370, and 380 nm), the white light emission can be realized with the CIE chromaticity coordinates (0.3907, 0.3595), (0.3472, 0.3282), and (0.3504, 0.3062) for the phosphor LSO: 0.075Eu. The chromaticity coordinates of the phosphor were all located in the white region. Therefore, it is suggested that the explored LSO: 0.075Eu phosphor can be a good candidate for white light-emitting diodes (W-LEDs) application.     

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

LaF₃:Eu nanophosphors were prepared by a traditional hydrothermal method with citric acid as a reducing agent. X-ray diffraction, scanning electronic microscopy, and luminescence spectroscopy were used to study the nanophosphors. The formation of three different luminescence centers of Eu²⁺ and two different luminescence centers of Eu³⁺ is attributed to the existence of abundant surface defects in this nanophosphor. Eu³⁺ is effectively excited by energy transfer from Eu²⁺ to Eu³⁺. The excitation wavelength of Eu³⁺ covers a broad spectral range from 250 to 480 nm. The nanophosphor shows a tunable luminescence color varying from blue to white and then to red, which is explained from three aspects of Eu concentration, energy transfer, and concentration quenching. Utilizing the surface defect of nanoparticles to control the reduction of Eu³⁺ is considered a promising strategy for exploring Eu²⁺ and Eu³⁺ codoped phosphor suitable for the lighting and display application.     

Synthesis of blue-emitting AlN:Eu2+ spherical phosphors by carbothermal reduction nitridation method

In this study, blue-emitting AlN:Eu²⁺ spherical phosphors were successfully synthesized for the first time by the carbothermal reduction nitridation (CRN) method, assisted with high nitrogen pressure, appropriate synthesis temperature, and the addition of CaF₂. The influence of typical experimental parameters, such as N₂ pressure, heating temperature, CaF₂ content and Eu²⁺ concentration on the morphologies and luminescence properties of AlN phosphors were comprehensively investigated. The formation mechanism of spherical morphology were significantly proffered, indicating that sufficient liquid Ca-aluminates during the AlN growth stage were essential for the spheroidization process under the action of surface tension. The synthesized AlN:Eu²⁺ spherical phosphors presented an intense blue emission band centered in the range of 427- 476 nm relative to the reaction temperature. The lifetime of AlN:Eu²⁺ phosphor was calculated to be around 1.89 μs. The temperature-dependent PL spectra suggested that the emission band did not shift until 225°C. In addition, the spectral analysis strongly suggested that the luminescence property of AlN:Eu²⁺ phosphors was significantly enhanced by the large particle size, spherical morphology, reduced impurity content, and appropriate Eu²⁺ concentration.     

Ca5Ga6O14:Eu3+: A novel phosphor with outstanding heat resistance for white light-emitting diodes

A novel red-emitting phosphor Ca₅Ga₆O₁₄:Eu³⁺ has been synthesized using solid-state method. The excitation and emission spectra show that the phosphor can emit the red light with the main peak at 611 nm under excitation of the 280 and 393 nm UV chip and the optimal Eu³⁺ concentration is determined to be x = 0.07. Analysis of emission spectrum shows that Eu³⁺ occupy the center of noninversion symmetry. With the increase of Eu³⁺ doping concentration, the decay time is prolonged due to deeper energy trap arising from nonequivalent substitution. Additionally, the measured thermal stability with 0.539 eV activation energy and calculated 90.5% color purity of optimal phosphor indicate that the phosphor has an enormous application potential in w-LEDs industry.     

Ternary type BaY2ZnO5: Eu3+ deep-red phosphor for possible latent fingerprint,security ink and WLED applications

Pc-WLEDs are considered to play a spectacular role in future generation light sources in view of their outstanding energy efficiency. In this regard, Eu³⁺ activated BaY₂ZnO₅ phosphor was prepared and investigated by XRD, PL and SEM analyses. Rietveld refinement analysis was carried out to confirm the structure of the synthesized phosphor. The prepared phosphor shows an intense red emission around 627 nm under excitation by near UV light. The ⁵D₀-⁷F₂ transition intensity of the prepared phosphor is three times higher compared to the commercial (Y,Gd)BO₃:Eu³⁺ red phosphor. The CIE colour coordinates of BaY₂ZnO₅:Eu³⁺ (9mol%) phosphor corresponds to be (0.6169, 0.3742) and it has a high 97.9 % colour purity. The obtained results reveal the utility of BaY₂ZnO₅:Eu³⁺ phosphor as an efficient red component in WLEDs, anti-counterfeiting and fingerprint detection applications.