Energy transfer and color-tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

Single-composition Ba₂Y₂Si₄O₁₃:Bi³⁺,Eu³⁺ (BYSO:Bi³⁺,Eu³⁺) phosphors with color-tunable and white emission were prepared by conventional high temperature solid-state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X-ray diffraction, photoluminescence, and decay curves. BYSO:Bi³⁺ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi³⁺ in BYSO. The energy transfer from Bi³⁺ to Eu³⁺ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange-red light (0.644, 0.341) can be generated by adjusting the content of Eu³⁺. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi³⁺,20%Eu³⁺ phosphor. Besides, BYSO:Bi³⁺,Eu³⁺ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi³⁺,Eu³⁺ may be applied as conversion phosphors for n-UV-based W-LEDs.     

Eu2+ activated novel eulytite Na3Bi5(PO4)6: Eu3+ phosphors: Enhanced luminescence and thermal stability for photonics application

For the first time, novel eulytite-like Eu²⁺/Eu³⁺: Na₃Bi₅(PO₄)₆ phosphor was synthesized via high temperature solid-state reaction method in reduction environment, and the structure, luminescence performances and thermal stability were investigated and discussed using various techniques. X-ray refinement diffraction and Raman spectra revealed the around 200 nm well-crystallized eulytite-type (I43d space group) phosphors were synthesized, and a diagram of crystal structure of Na₃Bi₅(PO₄)₆ was proposed. X-ray photoelectron spectroscopy analysis confirmed the co-existence of Eu²⁺ and Eu³⁺ ions which exhibited characteristic 4f⁶5d→⁸S_7/2 transition of Eu²⁺ and ⁷F₀→⁵D_0,1,2,3,4 transitions of Eu³⁺ ions. On the other hand, due to the activation of Eu²⁺, samples displayed good tunability on excited and emission behaviors under different excited laser. The JO parameters, emission cross-section, branching ratio and asymmetric ratio indicated that the Eu doping increased the covalency and asymmetry of host. Thermal quenching was studied and the reasons were discussed. Through the comparison of phosphors prepared in different conditions, the thermal stability& repeatability, radiative lifetime, color purity and activation energy were remarkably superior due to the Eu doping and in particularly Eu²⁺ activation. Finally, the energy level and CIE chromaticity diagrams were plotted to explain the mechanism of Eu²⁺ activation and energy transfer between Eu²⁺ and Eu³⁺ ions. The 0.5%Eu doped Na₃Bi₅(PO₄)₆ exhibited promising tunable red-emission performance with quantum efficiency of 92%, activation energy of 0.24 eV, red color purity of 93.74% and very low non-radiative transfer ratio 44.20 s^?1 with smaller CCT (<2200 K).     

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Energy transfer and multicolor tunable emission in single-phase Tb3+, Eu3+ co-doped Sr3La(PO4)3 phosphors

A series of green-to-red color-tunable Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb³⁺ and a red emission from Eu³⁺ with considerable intensity under ultraviolet (UV) excitation (~377 nm). The emission colors of the phosphors can be tuned from green (0.304, 0.589) through yellow (0.401, 0.505) and eventually to red (0.557, 0.392) due to efficient Tb³⁺-Eu³⁺ energy transfer (ET). The Tb³⁺→Eu³⁺ energy transfer process was demonstrated to be quadrupole-quadrupole mechanism by Inokuti-Hirayama model, with maximum ET efficiency of 86.3%. The results indicate that the Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors might find potential applications in the field of lighting and displays.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Y(PO4)3 red phosphors

A series of red-emitting phosphors Eu³⁺-doped Sr₃Y(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Y(PO₄)₃:Eu³⁺ phosphors exhibit peaks associated with the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The integral intensity of the emission spectra of Sr₃Y_0.94(PO₄)₃:0.06Eu³⁺ phosphors excited at 392 nm is about 3.4 times higher than that of Y₂O₃:Eu³⁺ commercial red phosphor. The Commission Internationale de l’Eclairage chromaticity coordinates, the quantum efficiencies and decay times of the phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Y(PO₄)₃ phosphors are promising red-emitting phosphors pumped by near-UV light.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

White light emission from novel host-sensitized single-phase Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) phosphors

A series of Eu³⁺- or Dy³⁺-doped and Eu³⁺/Dy³⁺ co-doped Y₂WO₆ in pure phase was synthesized via high-temperature solid-state reaction. X-ray diffraction, diffuse reflection spectra, photoluminescence excitation and emission spectra, the CIE chromaticity coordinates and temperature-dependent emission spectra were exploited to investigate the phosphors. Upon UV excitation at 310 nm, efficient energy transfer from the host Y₂WO₆ to dopant ions in Eu³⁺ or Dy³⁺ single-doped samples was demonstrated and those phosphors were suitable for the UV LED excitation. The intense red emission was observed in Y₂WO₆: Eu³⁺, and blue and yellow ones were observed in Y₂WO₆: Dy³⁺. Concentration quenching in Y₂WO₆: Dy³⁺ phosphors could be attributed to the electric dipole-dipole interaction. In Eu³⁺/Dy³⁺ co-doped Y₂WO₆ phosphors energy transfer process only took place from the host to Eu³⁺/Dy³⁺ ions and warm white-light emission can be obtained by adjusting the dopant concentrations. The temperature-dependent luminescence indicated Eu³⁺/Dy³⁺ co-doped Y₂WO₆ was thermally stable. Our overall results suggested that Y₂WO₆: Ln³⁺ (Ln³⁺=Eu³⁺, Dy³⁺) as warm white-light emitting host-sensitized phosphor might be potentially applied in WLEDs.     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

A novel dazzling Eu3+‐doped whitlockite‐type phosphate red‐emitting phosphor for white light‐emitting diodes

A series of novel red‐emitting Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors were successfully synthesized using the high‐temperature solid‐state reaction method. The crystal structure, photoluminescence spectra, thermal stability, and quantum efficiency of the phosphors were investigated as a function of Eu³⁺ concentration. Detailed analysis of their structural properties revealed that all the phosphors could be assigned as whitlockite‐type β‐Ca₃(PO₄)₂ structures. Both the PL emission spectra and decay curves suggest that emission intensity is largely dependent on Eu³⁺ concentration, with no quenching as the Eu³⁺ concentration approaches 100%. A dominant red emission band centered at 611 nm indicates that Eu³⁺ occupies a low symmetry sites within the Ca₈ZnLa(PO₄)₇ host lattice, which was confirm by Judd‐Ofelt theory. Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors exhibited good color coordinates (0.6516, 0.3480), high color purity (~96.3%), and high quantum efficiency (~78%). Temperature‐dependent emission spectra showed that the phosphors possessed good thermal stability. A white light‐emitting diode (LED) device were fabricated by integrating a mixture of obtained phosphors, commercial green‐emitting and blue‐emitting phosphors into a near‐ultraviolet LED chip. The fabricated white LED device emits glaring white light with high color rendering index (83.9) and proper correlated color temperature (5570 K). These results demonstrate that the Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors are a promising candidate for solid‐state lighting.     

Synthesis,energy transfer mechanism,and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

Effect of A+ (A = Li,Na and K) co-doping on enhancing the luminescence of Ca5(PO4)2SiO4:Eu3+ red-emitting phosphors as charge compensator

A series of Ca_5-x(PO₄)₂SiO₄:xEu³⁺ red-emitting phosphors were synthesized through solid-state reaction, and alkali metal ions A⁺ (A = Li, Na and K) were co-doped in Ca₅(PO₄)₂SiO₄:Eu³⁺ to improve its luminescence property. The impacts of synthesis temperature, luminescence center Eu³⁺ concentration and charge compensator A⁺ on the structure and luminescence property of samples were studied in detail. X-ray diffraction results indicated that prepared Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ had a standard Ca₅(PO₄)₂SiO₄ structure with space group P6₃/m. Under the excitation of 392 nm, Ca₅(PO₄)₂SiO₄:Eu³⁺ phosphors showed a red emission consisting of several emission peaks at 593 nm, 616 nm and 656 nm, relevant to ⁵D₀→⁷F₁, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ electron transitions of Eu³⁺ ions, respectively. Luminescence intensity and lifetime of Ca₅(PO₄)₂SiO₄:Eu³⁺ can be significantly enhanced through co-doping alkali metal ion A⁺, which play an important role as charge compensator. The results suggest that Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ red phosphors with excellent luminescence property are expectantly served as red component for white light-emitting diodes excited by near-ultraviolet.     

Luminescent properties of Na2GdMg2(VO4)3:Eu3+ red phosphors for NUV excited pc-WLEDs

Herein, a series of novel Na₂GdMg₂(VO₄)₃:Eu³⁺ (NGMVO:Eu³⁺) red phosphors were elaborated by conventional solid-state reaction process. Their structural features, luminescent properties, energy transfer were researched at length. XRD patterns indicate that NGMVO:Eu³⁺ crystallized in single cubic garnet structure. Under the excitation of near ultraviolet light at 356 nm, the emission spectra of NGMVO host could be divided in two parts that resulted from ³T₂ → ¹A₁ and ³T₁ → ¹A₁ transitions of VO₄^3?. While NGMVO:Eu³⁺ phosphors show intense sharp red emission peaks including 590, 610, 652 and 706 nm that originated from ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺, respectively. The optimal concentration of Eu³⁺ is 0.7. Importantly, NGMVO:0.7Eu³⁺ sample presents high energy transfer efficiency (89 %) and high external quantum efficiency (48.3 %). Besides, its emission intensity remains 79 % at 420 K compared with that at 300 K, proving the good thermal stability of phosphors. All above results suggest that NGMVO:Eu³⁺ red phosphors have latent applications in white light emitting diodes.     

Synthesis and luminescence enhancement of red-emitting Sr9Y(PO4)7:Eu3+ phosphor through Gd3+ co-doping for white light-emitting diodes

A series of Sr₉Y(PO₄)₇:Eu³⁺ and Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphors were prepared via a high-temperature solid-state method, Gd³⁺ ion was co-doped in Sr₉Y(PO₄)₇:Eu³⁺ as sensitizer to enhance the luminescence property. The X-ray diffraction results verify that the structure of the as-prepared samples is consistent with the standard Sr₉Y(PO₄)₇ phase. All the Sr₉Y(PO₄)₇:Eu³⁺ samples show both characteristic emission peaks at 594 nm and 614 nm under near-ultraviolet excitation of 394 nm. The co-doping of Gd³⁺ significantly improves the luminescence intensity of the Sr₉Y(PO₄)₇:Eu³⁺ phosphors due to the crystal field environment effect and energy transfer of Gd³⁺→Eu³⁺ caused by the introduction of Gd³⁺, especially Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺, which emission intensity is higher than that of Sr₉Y(PO₄)₇:0.11Eu³⁺ by 1.21 times. The color purity and lifetime of Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺ phosphor are 88.26% and 3.7615 ms, respectively. A w-LED device was packaged via coating the as-prepared phosphor on n-UV chip of 395 nm with commercial phosphors. These results exhibit that the Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphor can be used as a red component in the w-LEDs application.     

Novel color tunable LaCaGaO4:Bi3+,Eu3+ phosphors for high color rendering warm white LEDs

A series of LaCaGaO₄:xBi³⁺,yEu³⁺ (x = 0.002–0.04, y = 0.02–0.45) phosphors with adjustable emission colors were synthesized by high-temperature solid-state reaction. The samples were identified as pure phases by X-ray diffraction and Rietveld refinement, and the crystal structures were analyzed in detail. The LaCaGaO₄:xBi³⁺ phosphor shows an intense blue emission under near-ultraviolet excitation, originating from the ³P₁ → ¹S₀ transition. The spectrum analysis reveals that the Bi³⁺ ions occupy two luminescence centers in the LaCaGaO₄ host and that energy transfer can occur. A model of the energy transfer between the Bi³⁺ and Eu³⁺ ions was also created and studied in detail. As the Eu³⁺-concentration increased, the emission color of the LaCaGaO₄:0.005Bi³⁺,yEu³⁺ phosphor changed from blue to pink to red. In addition, the fluorescence lifetime, quantum yield, thermal stability, and other properties of the phosphors were characterized and analyzed. Finally, two white light-emitting diode devices with R_a values of 96.6 and 95 and correlated color temperatures of 4578 and 3324 K were fabricated, indicating the potential of phosphors for warm white lighting applications.     

Enhanced red emission and improved thermal quenching of CaAlSiN3:Eu2+ phosphors via boron doping

The development of high-performance phosphors is required for phosphor-converted white light-emitting diodes. However, most approaches are unable to achieve optimum emission intensity and thermal quenching simultaneously. Here, a series of CaAlSiN₃:Eu²⁺ (CASN:Eu²⁺) red-emitting phosphors doped with B were synthesized using field-assisted sintering technology. Compared with CASN:Eu²⁺, the B-doped phosphor exhibited high external quantum efficiency (EQE) and good thermal quenching performance. With boron doping, the EQE of CaAlSiN₃:Eu²⁺ shows an obvious growth, increasing from 48.83% to 70.68%. Meanwhile, thermal quenching performance has also been greatly improved, which is strongly associated with the band structure of Eu²⁺ and the crystal structure of CASN. The location of B in the crystal lattice was studied and the mechanism of improving thermal quenching via B doping was discussed in detail. Finally, a white LED fabricated by the combination of a GaN blue chip (450 nm) with the as-synthesized red phosphors and Y₃(Al, Ga)₅O₁₂:Ce³⁺ green phosphors (531 nm), shows a high color rendering index (Ra =91.6). This study offers a novel method to improve luminescence properties of CASN:Eu²⁺ red-emitting phosphors, which may broaden their application in solid-state lighting devices.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

Effect of singly,doubly and triply ionized ions on downconversion photoluminescence in Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor: A comparative study

We report a change in the red photoluminescence of the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor via doping of singly, doubly and triply ionized ions. The synthesized phosphors show good crystalline nature. The EDS analysis confirms the presence of desired elements in the phosphor samples. The vibrational feature of the phosphor was confirmed by FTIR analysis. The photoluminescence excitation spectra of the phosphor show three peaks at 317, 395 and 467 nm. The Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor emits intense red color on excitations with 395 and 467 nm wavelengths. However, the photoluminescence intensity of the phosphor is larger for 395 nm excitation. When the singly, doubly and triply ionized ions are co-doped in the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor (i.e. F⁻, WO₄²⁻, MoO₄²⁻, VO₄³⁻, La³⁺, and Y³⁺) the photoluminescence intensity of the phosphor is decreased significantly. The decrease in photoluminescence intensity is due to change in local crystal structure created by these ions. Interestingly, the photoluminescence intensity of phosphor increases many times when the (Y³⁺) ion incorporated phosphor is excited with 317 nm wavelength. The CIE diagram shows color emitted in the red region of visible spectrum and the color purity is larger for triply ionized (Y³⁺) ion. Thus, the singly, doubly and triply ionized ions activated Na₂Sr₂Al₂PO₄Cl₉: Eu³⁺ phosphor may be used in displays devices, photonic devices, solid state lighting and white LEDs.     

The composition engineering of red-emitting Eu3+-doped Ca10.5(PO4)7-type solid solution phosphors and application in LED

In this work, using Ca_10.5(PO₄)₇ as the structural model, a number of Eu³⁺-doped [Ca₉Na_3xY_1-x(PO₄)₇ (CNYP-I, 0 ≤ x ≤ 1/2) ← Ca_10.5(PO₄)₇ → Ca_9+yNa_3/2-y/2Y_(1-y)/2(PO₄)₇ (CNYP-II, 0 ≤ y ≤ 1)] phosphors were designed and synthesized through the heterovalent substitution of Y³⁺ and Na⁺ to Ca²⁺. The substitution mechanism, composition structure, luminescence performance, and thermal stability of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) as well as the solid solutions of CNYP-II (0 ≤ y ≤ 1), were discussed in detail. The morphology and element composition of CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) solid solutions were analyzed by SEM and EDS. The PL spectra of the specimens were containing the predominant red peak of emission at 612 nm caused via the transition of ⁵D₀-⁷F₂, indicating that Eu³⁺ occupies the low-symmetry center. Moreover, the site symmetry Eu³⁺ occupied changed with the x/y value. The luminous intensity of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) phosphors at 150°C maintained about 60% of room temperature. The representative compound CNYP-I (x = 1/3) was used as the red phosphor to prepare a near-UV based white LEDs along with Ra of 80.9 and CCT of 4100 K.     

Site-selective occupation and luminescence property investigation of Ca18Na3Y(PO4)14:Eu2+ phosphor for full-spectrum LED

Cyan-emitting phosphors have attracted widespread attention as an integral part to realize full-spectrum lighting. Understanding the site occupation of luminescence centers is of great importance to design and clarify the luminescent mechanism for new cyan-emitting phosphors. Here, we report a cyan-emitting phosphor Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ synthesized by the high-temperature solid-state method. The crystal structure is characterized by X-ray diffraction and refined by the Rietveld method. The diffuse reflectance spectra, excitation/emission spectra, fluorescence decay curves, thermal stability, and related mechanism are systematically studied. The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ crystallizes in a trigonal crystal system with space group R3c. Under excitation at 350 nm, a broadband cyan emission can be obtained at 500 nm with a half-width of about 120 nm, which is caused by Eu²⁺ occupying five different sites in host, namely, Na2O₁₂ (450 nm), (Ca3/Na1)O₈ (485 nm), Ca2O₈ (515 nm), Ca1O₇ (565 nm), and (Ca4/Y)O₆ (640 nm), respectively. Moreover, crystal structure, room and low temperature spectroscopy, and luminescence decay time are used to skillfully verify the site-selective occupation of Eu²⁺. Finally, a full-spectrum light-emitting diode (LED) lamp is fabricated with an improved color rendering index (∼90.3), CCT (∼5492 K), and CIE coordinates (0.332, 0.318). The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ has the potential to act as a cyan emission phosphor for full-spectrum white LEDs.