Single-phase White-emitting Phosphor Research Articles

Optical tuning and energy transfer of single-phase white-emitting Y3TaO7:Bi3+, Eu3+ for ultraviolet converted pc-WLED with high chromatic stability

Reabsorption and color drift at high temperature hinder the high-quality application of the phosphor-converted white light-emitting diodes (pc-WLEDs) devices, thus it is urgent to develop the single-phase white-emitting phosphors with good chromatic stability. In this work, a series of color-tunable Y3TaO7:Bi3+, Eu3+ phosphors are designed by co-doping Bi3+ and Eu3+ based on the crystal structure information and energy transfer principle between Bi3+ and Eu3+, which can be adjusted to achieve single-phase white emission. By increasing the temperature to a high value of 473 K, the emission peak of Bi3+ ions still present at 470 nm in Y3TaO7:Bi3+ phosphors even when the concentration of Bi3+ ions changes, and the characteristic emission peaks of Bi3+ and Eu3+ basically maintain unchanged throughout in Y3TaO7:Bi3+, Eu3+ phosphors. Finally, the single-phased Y3TaO7:0.025Bi3+, 0.06Eu3+ phosphor was employed with ultraviolet chip to produce a warm WLED device with color rendering index of 81.5, correlated color temperature of 4165 K and the Commission International de I′Eclairage chromaticity coordinates of (0.3645, 0.3347). The results indicate that Y3TaO7:Bi3+, Eu3+ phosphors with high chromaticity stability have great application potential in full-spectrum WLEDs.

Color-tunable blue-emitting Na2MgSiO4:Ce3+ phosphors for white light-emitting diodes

Phosphor-converted white light-emitting diodes (pc-wLEDs) based on near-UV LED chip demand efficient blue-emitting phosphors, because the pc-wLED uses either multi phosphors or single-phase white-emitting phosphor both needs blue-emitting component. When using Ce3+ as the activator, the host structure usually has rare earth ions or alkaline earth ion such as Ca2+ for Ce3+ to occupy, due to similar ionic radius and charge. This work is going to report a blue-emitting phosphor Na2MgSiO4:Ce3+, where Ce3+ occupies the Na+ sites. The phosphor exhibits characteristic of tunable emission color upon increasing Ce3+ content or introducing Li+ as charge compensator. The relationship between the crystal structure and the luminescent properties was studied in detail based on structural refinement and in-depth luminescent studies. The phosphor with a proper Ce3+ content showed a high absolute quantum efficiency of 86.0% and acceptable thermal stability. The pc-wLED made of 365 nm UV chip, the as-prepared Na2MgSiO4:Ce3+,Li+, and commercial green and red phosphors showed good performance with color rendering index of 93.3.

A single-phase white-emitting La(BO3,PO4):Dy3+ phosphor with high thermostability

Developing single-phase white-emitting phosphor has increasingly become an effective strategy to solve the emerging challenges of multiple phosphors-converted white light-emitting diodes such as unavoidable reabsorption, high production cost, and low thermostability. In this work, a single-phase white-emitting La(BO3,PO4):Dy3+ phosphor was synthesized. The photoluminescence performance characterizes the two strong visible emissions of Dy3+: blue (470–500 nm, 4F9/2 → 6H15/2) and yellow lights (570–600 nm, 4F9/2 → 6H13/2). The content quenching of Dy3+ presents at x = 0.03 mol, which is controlled by the dipole–dipole interaction. The optimized product La0.97Dy0.03(BO3,PO4) has a high thermostability. It has also the comparable color coordinates with the ideal white light due to the proper yellow-blue intensity ratio. The above studies confirm that the Dy3+-activated La(BO3,PO4) phosphor could be a prospective white-emitting candidate in lighting application.

Bi4BPO10:Dy3+: a single-phase white-emitting phosphor for light-emitting diodes

We reported a single-phase white-emitting phosphor Bi4BPO10 (BBP):Dy3+ developed via a solid-state reaction route. Dy3+ activator is introduced into the BBP host by replacing Bi3+ ion with optimal content of 7 mol%. Under 390 nm excitation, due to the suitable combination of characteristic yellow and blue-emitting from Dy3+, the phosphor generates white light. The working temperature-dependent photoluminescence data confirms that it owns a satisfactory thermostability. Finally, the representative BBP:0.07Dy3+ phosphor-converted WLED device is pumped by a n-NV chip to display white light with a CCT of 3731 K. The report indicates that the studied phosphor could be potentially employed for solid-state white lighting source.

Luminescence and energy transfer of single-phase white-emitting phosphor Ba2Mg(PO4)2:Ce3+, Eu2+ for white LEDs.

A series of Ba2Mg(PO4)2:Ce3+, Eu2+ phosphors were synthesized by the traditional high temperature solid-state method, and the crystal structures and luminescence properties of the samples were discussed systematically. The energy transfer from Ce3+ to Eu2+ in Ba2Mg(PO4)2 was proved to be of resonant type via a dipole-dipole interaction mechanism. With a precisely controlled relative proportion of Ce3+/Eu2+, the emission color of the samples can vary from blue (0.157, 0.071) to white (0.352, 0.332) and ultimately to yellow (0.452, 0.466) under the 323 nm ultraviolet light radiation excitation. The result reveals that the Ba2Mg(PO4)2:Ce3+, Eu2+ phosphor may have potential application as a single-phased white-emitting phosphor for light emitting diodes.

Highly thermostable white-emitting Ca9ZnK(PO4)7:Ce3+,Dy3+ single-phase phosphor with tunable photoluminescence and energy transfer.

White light-emitting diodes (WLEDs) fabricated with single-phase white phosphor are currently widely used in lighting and displays. Herein, we describe the development of a single-component white-emitting micro-sized powder Ca9ZnK(PO4)7 (CZKP):Ce3+,Dy3+ with high thermal stability. Theoretical and experimental investigations confirmed that the phosphate CZKP with a whitlockite-like structure was suitable as a phosphor host. The photoluminescence of cerium/dysprosium single- and co-doped samples was comprehensively studied. Dipole-dipole interaction resulted in the Ce3+ → Dy3+ energy transfer, which contributed to the spectral regulation for acquiring the white-emitting performance. Moreover, the superior thermal stability of the representative CZKP:0.10Ce3+,0.15Dy3+ phosphor was revealed. Finally, we explored the working performance of single-phase white phosphor-converted WLEDs. The corresponding work shows a successful design for achieving a single-component white phosphor via the Ce3+ → Dy3+ energy transfer approach.

Synthesis and Luminescence Properties of a Single-Phase White-Emitting and Tunable Color Phosphor Na3Sc2(PO4)3∶Tm3+,Dy3+

Synthesis and Luminescence Properties of a Single-Phase White-Emitting and Tunable Color Phosphor Na3Sc2(PO4)3∶Tm3+,Dy3+

Single-phase white-emitting phosphors Ba3Bi(PO4)3:Dy3+, Eu3+ with tunable correlated color temperature and high thermal stability towards light emitting applications

Single-phase white-emitting phosphors Ba3Bi(PO4)3:Dy3+, Eu3+ with tunable correlated color temperature and high thermal stability towards light emitting applications

Single-phase white-emitting and tunable color phosphor Na3Sc2(PO4)3:Eu2+,Dy3+: Synthesis, luminescence and energy transfer

A series of Eu2+/Dy3+ single doped and co-doped Na3Sc2(PO4)3 phosphors were synthesized by the high-temperature solid-state method, and their phase, morphology, and luminescence properties were characterized. Under the excitation of 370 nm, the Na3Sc2(PO4)3:Eu2+,Dy3+ phosphor can emit white light whose spectrum is composed of a broad emission band centered at 460 nm and the other three peaks at 483, 577, and 672 nm, respectively. There is energy transfer from Eu2+ to Dy3+ ion in Na3Sc2(PO4)3:Eu2+,Dy3+ phosphor due to the good overlap between the emission spectrum of Na3Sc2(PO4)3:Eu2+ and the excitation spectrum of Na3Sc2(PO4)3:Dy3+, which is further confirmed by the fluorescence lifetime decrease of Eu2+ ion with the increase of Dy3+ concentration. The process of energy transfer is via dipole–quadruple interaction which is confirmed by applying Dexter's theory. By increasing the Dy3+ concentration, the color coordinates of the Na3Sc2(PO4)3:0.01Eu2+,xDy3+ phosphors can be adjusted from blue to white, and then to yellow. The optimized concentration of Dy3+ ions is 4.0 mol%, beyond which the concentration quenching will take place. The Na3Sc2(PO4)3:Eu2+,Dy3+ phosphor shows fairly good resistance to thermal quenching behavior, of which the emission intensity at 423 K can maintain 90.3% of the initial value (298 K). These results suggest that the Na3Sc2(PO4)3:0.01Eu2+,xDy3+ phosphors have potential applications as the color-tunable or a single-phase white emitting phosphor in white LEDs.

Tb3+/Eu3+/Tm3+ co-doped single-phase phosphors emitting close to standard white light

A sequence of Tb3+/Eu3+/Tm3+ co-doped LaAl2.03(B4O10)O0.54 single-phase phosphor samples have been produced using a sol-gel reaction. A number of properties such as phase composition, crystal structure, luminescence performance and lifetime decay curves were tested and discussed. The energy transfer process in Tb3+/Eu3+ co-doped LaAl2.03(B4O10)O0.54 phosphors was testified by luminescence spectra and lifetime decay curves. The transfer mechanism is determined to be a dipole-dipole interaction, and the energy transfer efficiency can reach 74.03%. By adjusting the doping ratio of the three ions of Tb3+, Tm3+ and Eu3+, the light emitting region of the phosphor can be adjusted to white light region. When the composition is LaAl2.03(B4O10)O0.54:0.1 Tb3+,0.06Tm3+,0.04Eu3+, the color coordinate is (0.334, 0.331), which is very close to the standard white light (0.33, 0.33). These results make clearly that Tb3+/Eu3+/Tm3+ co-doped LaAl2.03(B4O10)O0.54 phosphors have potential application value in the field of single-phase white-emitting phosphors.

Color tuning of the Ba1.96Mg(PO4)2:0.04Eu2+ phosphor induced by the chemical unit co-substitution of the (BO3)3− anion group

Replacing the tricolor blend of phosphors by a single-phase white-emitting phosphor has emerged as a new technology for devising white-light-emitting diodes (WLEDs). Modification of the local structure in the crystal plays the key role in obtaining a single-phased, high CRI white-emitting phosphor. This process can also be employed to tune the color emission of the phosphor, especially those doped with Eu2+ ions. In this context, the selection of an appropriate host and the substituting chemical unit plays a vital role, as the crystal environment of the host greatly influences the photoluminescence (PL) emission of the Eu2+ ions. Herein, the color tuning of a new single-phase solid-solution Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ (x = 0.2, 0.5, 0.7, 1, 1.2 and 1.5) phosphor synthesized by the sol-gel/Pechini method is demonstrated. The structural variation induced by the varying composition of the borate (BO3)3− unit was analyzed by X-ray diffraction and Rietveld refinement studies. Fourier transform infrared spectroscopy revealed the presence of the vibrations corresponding to both the BO3 and PO4 chemical groups in the Ba1.96Mg(PO4)2−x(BO3)x:0.04Eu2+ phosphor. Morphological variations were also observed with the chemical co-unit substitution, which was analyzed with Scanning Electron Microscopy (SEM). PL studies indicated that the color tuning from blue-white-orange light, under near UV excitation, was achieved by varying the composition of the (BO3)3− group. The co-existence of the PO4 and BO3 groups gave rise to a higher-energy emission (420 nm) and a lower-energy emission (585 nm), respectively. The PL decay curves were analyzed to estimate the energy transfer efficiency between the higher-energy and lower-energy emission sites of the phosphor. This work presents a new strategy to tune the color emission of a singly-doped phosphor by modifying the structure of the host lattice.

Eu3+ co-doped Sr3Gd(PO4)3:Dy3+ phosphors: luminescence properties and color-tunable white-light emission for NUV-WLEDs

A series of Dy3+ and Eu3+ co-doped Sr3Gd(PO4)3 phosphors were synthesized by a high-temperature solid-state method. The crystal structure, optical band gap energy, luminescence properties, concentration quenching, energy transfer process and thermal stability were investigated. All the phosphors are pure eulytite-type Sr3Gd(PO4)3 in structure. Under different wavelengths’ excitation, the Sr3Gd(PO4)3:Dy3+, Eu3+ phosphors exhibit different emission intensities for Eu3+ and Dy3+. The color and correlated color temperature (CCT) can be tuned from cool white to warm white by adjusting excitation wavelengths and the doping concentration of Eu3+. Under the 351-nm excitation, the optimal Sr3Gd(PO4)3:0.03Dy3+, 0.085Eu3+ phosphor displays a warm white emission with CIE coordinate of (0.3987, 0.3613), CCT of 3409 K, internal quantum efficiency of 44.8% and activation energy of 0.1883 eV. These results suggest that single-phased white-emitting phosphors Sr3Gd(PO4)3:Dy3+, Eu3+ can be used in the near-ultraviolet light-emitting diodes.

Fast synthesis of Dy3+ and Tm3+ co-doped double perovskite NaLaMgWO6: a thermally stable single-phase white-emitting phosphor for WLEDs

Single-phase double perovskite phosphor NaLaMgWO6 was successfully synthesized via a rapid microwave irradiation method.

Fast synthesis and energy transfer of the tunable single-phase white-emitting phosphor Li2Gd4(WO4)7:Dy3+, Tm3+ for WLEDs

A series of Dy3+ and Tm3+ co-doped Li2Gd4(WO4)7 (LGW) single-phase white phosphors were fast synthesized by microwave assisted solid-state reaction method. Single-ion doped LGW:Dy3+ and LGW:Tm3+ phosphors were synthesized to obtain quenching concentrations. The ideal white light (0.33, 0.33) locates on the straight line that connects the Commission Internationale de L'Eclairage (CIE) coordinates of LGW:Dy3+ and LGW:Tm3+. Therefore, Dy3+ and Tm3+ were selected to co-dope LGW to realize white light emission. By changing Dy3+ concentration, white light was obtained under the excitation wavelengths of 356 nm and 363 nm. Luminescence decay curves and the emission spectra of the co-doped phosphors were characterized to verify the existence of energy transfer between Tm3+ and Dy3+ in this single-phase phosphor. Energy transfer efficiency and energy transfer mechanism were investigated in detail. This fast synthesized single-phase white phosphor LGW:Dy3+, Tm3+ is a good candidate for the white light emitting diodes.

Synthesis, structure, and color-tunable luminescence properties of lanthanide activator ions doped bismuth silicate as single-phase white light emitting phosphors

A series of lanthanide activator ions (Ln3+) doped bismuth silicate Bi4Si3O12 phosphors have been fabricated via the Pechini sol−gel route. The as-synthesized eulytite structured Bi4Si3O12 sample which exhibits intense green-blue emission is beneficial for host materials of lanthanide activator ions. When the Ln3+ ions (Sm3+, Dy3+, or Eu3+) are doped into the Bi4Si3O12 host, an insufficient energy transfer occurs from the host matrix to Ln3+ ions, which can be confirmed by the photoluminescence spectra and decay lifetimes of the Ln3+ doped samples. The as-synthesized Bi4Si3O12:Ln3+ phosphors show both the intrinsic broad band luminescence of Bi4Si3O12 host and the characteristic sharp peak emissions of Ln3+ ions, which can generate the tunable multicolor emissions in a single-phase phosphor by adjusting the Ln3+ doping concentrations. More importantly, three kinds of Ln3+-doped single-phase white light emitting phosphors with excellent chromaticity coordinate (x, y) and CCT in the warm white region [Sm3+: (0.336, 0.330), 5315 K; Dy3+: (0.330, 0.370), 5614 K; Eu3+: (0.340, 0.307), 5034 K] can be obtained when the doping concentrations of Sm3+, Dy3+, and Eu3+ are fixed at 0.5, 5, and 1 mol%, which are quite close to the daily use of pure white light. By integrating the Bi4Si3O12:Ln3+ phosphors into a 280 nm UV LED chip, all the fabricated WLED devices can exhibit bright white light emission, which provides direct evidence that the as-synthesized BSO:Ln3+ (Ln = Sm, Dy, and Eu) single-phase white-emitting phosphors have great potential for WLEDs and optoelectronic devices.

Optimization of LaPO4:Bi3+ Single-Phased White-Emitting Phosphor Luminescence Properties by Li+/Na+ Doping

LaPO4:Bi3+ single-phased white-emitting phosphors doped with both Li+/Na+ ions were successfully prepared by a conventional solid-state reaction technique. Microstructures were analyzed by both X-ray diffraction and high-resolution scanning electron microscopy experiments. Under the excitation of 335 nm, the La0.97PO4:Bi3+0.03 phosphor showed four emission bands with maxima at 460 nm, 487 nm (blue), 530 nm (yellow), and 637 nm (red); these can be successfully combined to form pure white light in a single host lattice only by simple activator Bi3+ ion. It was found that changing the concentration of dopant (Li+, Na+ ions) did not produce a change in shape or location of the emission peaks, but the value of the emission intensity increased; this was particularly evident in the red emission, which could optimize the white light emitting performance of the phosphors. When the Na+ doping concentration was 0.02, the CIE chromaticity coordinate of phosphor La0.95PO4:Bi3+0.03, Na+0.02 was (0.3008, 0.3203), close to that of the standard white light.

Tunable color of Tb3+/Eu3+/Tm3+-coactivated K3La(PO4)2 via energy transfer: A single-phase white-emitting phosphor

A series of Tm3+, Tb3+, Eu3+ coped K3La(PO4)2 phosphors was synthesized via solid-state reaction. The compounds were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra as well as fluorescent decay curves. The energy transfers from Tb3+ to Eu3+ in the K3La(PO4)2 host were investigated according to the Inokuti–Hirayama theoretical model which suggests they are of the resonant type via a dipole–dipole mechanism. By adjusting the doping concentrations of Tb3+, Tm3+ and Eu3+, a white emission can be reached in the K3La(PO4)2 host. The energy transfer efficiency and the CIE coordinates of K3La(PO4)2:RE3+ (RE = Tm, Tb, Eu) phosphors were calculated. In addition, the temperature-dependent emission showed good thermal stability of as-prepared phosphors. The obtained properties indicated that prepared compounds can be used as a single-component white emitting phosphor in WLEDs structures.

Photoluminescence enhancement of Ca3Sr3(PO4)4:Dy3+ white-emitting phosphors by Li+ and Na+ charge compensation

A series of Ca3Sr3(PO4)4:Dy3+, M+ (M = Li and Na) white-emitting phosphors was prepared via a high-temperature solid-state reaction, where M+ was co-doped in Ca3Sr3(PO4)4:Dy3+ as charge compensators for enhancing its luminescence. Effects of synthesis temperature and charge compensator M+ on the structure and luminescence properties of as-prepared phosphors were studied in detail. The results of X-ray diffraction indicate that the structures of Ca3Sr3(PO4)4:Dy3+, M+ samples were in agreement with the standard Ca2Sr(PO4)2 phase. Under excitation of 352 nm, there are two apparent peaks at 484 nm (blue) and 577 nm (yellow) in the emission spectra of Ca3Sr3(PO4)4:Dy3+, M+ samples, which corresponding to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 electron transitions of Dy3+ ions, respectively. Luminescence intensity and lifetime of Ca3Sr3(PO4)4:Dy3+ can be significantly enhanced through adding a charge compensator M+, which suggest that Ca3Sr3(PO4)4:Dy3+, M+ can be used as a single-phase white-emitting phosphor in the applications of white light-emitting diodes.

Photoluminescence and tunable emissions of La2(GeO4)O:Bi3+, Eu3+ phosphor for ultraviolet converted light emitting diodes

In the past decades, a great variety of single-phase white-emitting phosphors have been developed, however most them can't satisfy us due to their low quantum efficiency and poor thermal stability. Herein, we reported a promising candidate of a white-emitting La2(GeO4)O:Bi3+/Eu3+ phosphor, exhibiting an efficient energy transfer, good thermal stability and high quantum efficiency. Rietveld structure refinement of La2(GeO4)O:Bi3+ was performed to confirm Bi3+ occupation of La sites in La2(GeO4)O. An analysis on the red-shift of both excitation and emission spectra of La2(GeO4)O:Bi3+ was made by combining the crystal structure and their spectroscopy. Thermal quenching temperature (T50%) of La2(GeO4)O:Bi3+ was approximately 532 K which is higher than that (473 K) of the LED chips under high power current driving and La2(GeO4)O:Bi3+ presented a spectral blue-shift as an increase in temperature. Furthermore, thermal quenching of La2(GeO4)O:Bi3+ was explained in detail by the configurational coordinate. More importantly, single Bi3+ doped La2(GeO4)O presented a blue-greenish broad band at 480 nm with a high quantum efficiency (48%) and excellent thermal stability (ΔE = 0.353 eV). Energy transfer from Bi3+ to Eu3+ in La2(GeO4)O efficiently occurred and energy transfer mechanism of Bi3+→Eu3+ was demonstrated to be dipole-quadrupole interaction. By codoping Eu3+ in La2(GeO4)O:Bi3+, La2(GeO4)O:Bi3+, Eu3+ phosphor exhibited the blue-green and red dual emissions. Fortunately, a single-phase white-emitting phosphor La1.94(GeO4)O:0.03Bi3+, 0.03Eu3+ was obtained with excellent resistance against thermal quenching and a quantum efficiency of 37%.

M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) Single-Phase Full-Color Phosphor with High Thermal Emission Stability.

Two series of phosphors of Ca8MgSc(PO4)7:Dy3+ and Sr8MgSc(PO4)7:Dy3+ single-phase white-emitting phosphors with high thermal emission stability are synthesized by the high-temperature solid-state reaction. The crystal structure, photoluminescence (PL), PL excitation (PLE), and thermal PL quenching spectra of Ca8MgSc(PO4)7:xDy3+ and Sr8MgSc(PO4)7:xDy3+ were investigated and compared in detail. Upon excitation at 387 nm, M8MgSc(PO4)7:xDy3+ (M = Ca/Sr) showed white emission centered at 480, 571, 660, and 754 nm. The white-emitting Dy-phosphor Ca8MgSc(PO4)7:Dy3+ (CMSP:Dy) had good terminal stability. The emission intensity of Ca8MgSc(PO4)7:Dy3+ still remained 95.2% of that at room temperature at 160 °C, and remained 77.3% at 300 °C under 387 nm excitation.