A novel pure red phosphor Ca8MgLu(PO4)7:Eu3+ for near ultraviolet white light-emitting diodes

A novel red-emitting phosphor Ca₈MgLu(PO₄)₇:Eu³⁺ was synthesized by a high-temperature solid-state reaction method. Its crystal structure, photoluminescence emission and excitation spectra, and decay time were investigated in detail. X-ray diffraction (XRD) results indicate that Ca₈MgLu(PO₄)₇ crystallizes in single-phase component with a whitlockite-like structure and the space group R3c of β-Ca₃(PO₄)₂. The emission spectrum shows a dominant peak at 612 nm due to the dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and the luminescence intensity keeps increasing with increasing the content of Eu³⁺ to 100%. The excitation spectrum is coupled well with the emission of near ultraviolet (NUV) LED (380–410 nm). The CIE coordinates of Ca₈MgLu(PO₄)₇:Eu³⁺ phosphor is (0.654, 0.346), being close to the standard value of National Television Standard Committee (NTSC) for red phosphor, (0.670, 0.330). The internal quantum efficiency of the phosphor is 69% under the excitation of 394 nm. The results show that Ca₈MgLu(PO₄)₇:Eu³⁺ is a very appropriate red-emitting phosphor with a high ratio of red and orange for NUV-based white LEDs.     

Color-tunable luminescence performance of single-component Na5Y(MoO4)4:Dy3+, Tm3+ white-emitting phosphor for white light-emitting diodes

The single-component Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ white-emitting phosphor was prepared by the sol-combustion method, and Tm³⁺ was codoped for color-tunable white emission. The XRD patterns confirm that the as-prepared samples have a Na₅Y(MoO₄)₄ structure and do not change with Dy³⁺/Tm³⁺ codoping. Under ultraviolet excitation at 352 nm, the Na₅Y(MoO₄)₄:Dy³⁺ phosphor shows a characteristic white emission consisting of a weak peak at 485 nm and a strong peak at 577 nm. By codoping a small amount of Tm³⁺, the blue emission of phosphor is enhanced, and the chromaticity coordinates can be adjusted between (0.3663, 0.416) and (0.319, 0.3407); thus, color-tunable white emission is achieved with the synergistic effect of Dy³⁺ and Tm³⁺. The luminescence intensity of Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ at 483 K still retains 72% of the initial intensity, showing excellent thermal stability. By combining Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ with a 365 nm chip, the fabricated w-LED device emits bright white light for illumination. Therefore, the as-prepared Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ has potential applications in the field of w-LEDs as white-emitting phosphors.     

White light emitting from YVO4/Y2O3:Eu3+,Bi3+ composite phosphors for UV light-emitting diodes

A series of (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 (0≤x≤0.54) composite phosphors was synthesized in one step by high temperature solid state reaction and the photoluminescence properties were investigated. By means of co-doping Eu³⁺ and Bi³⁺ ions into the composite matrices composed of YVO₄ and Y₂O₃ crystals, the YVO₄/Y₂O₃:Eu³⁺,Bi³⁺ phosphor exhibits simultaneously the blue (418 nm), green (540 nm) and orange-red (595, 620 nm) emissions. The broad blue and green emissions are attributed to the ³P₁–¹S₀ transitions of Bi³⁺ ion both in Y₂O₃ and in YVO₄ matrices. Moreover, the sharp orange-red emissions are attributed to the ⁵D₀–⁷F_1,2 transitions of Eu³⁺ ion in YVO₄ matrix. By tuning the mole ratio of YVO₄/Y₂O₃ matrices the white light-emitting could be obtained. The results indicated that when the mole ratio of Y₂O₃ (x) is at 0.11–0.54 mol, the (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 phosphors emit white light by combining the blue, green and orange-red emissions under the excitation of 360–370 nm wavelength which matches the emission of the commercial UV-LED diode. This implies that the phosphors may be the promising white light materials with broad absorption band for 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.     

Fluorescence properties with red-shift of Eu2+ emission in novel phosphor-silicate apatite Sr3LaNa(PO4)2SiO4 phosphors

A series of Eu²⁺-activated novel phosphor-silicate apatite Sr₃LaNa(PO₄)₂SiO₄ phosphors were synthesized by solid-state reaction. The X-ray diffraction (XRD) and Rietveld refinement, diffuse reflectance spectra, luminescent spectra, decay curves and thermal quenching properties were applied to characterize the obtained phosphors. The XRD result revealed that all the samples possessed only a single phase with hexagonal structure and the doping of Eu²⁺ ions were successfully incorporated into the crystal lattice. The reflectance spectra showed an obvious red-shift of the wavelength from 400 to 700 nm with increasing Eu²⁺ ion concentration. The three different crystallographic sites of Eu²⁺ ions had been confirmed by their lifetimes. All the samples exhibited broad absorption bands from 200 to 450 nm, revealing the phosphor-silicate phosphor interesting for application in the near-UV used phosphor-converted LED chips. These results suggested that the Eu²⁺-activated phosphor-silicate Sr₃LaNa(PO₄)₂SiO₄ phosphors have the potential for near-UV pumped white-light-emitting diodes (w-LEDs).     

Soluble silica assisted synthesis and luminescent characteristics of yellow emitting CaSrSiO4:Eu2+ phosphors for warm white light production

To meet the challenges and additional requirements towards the development of white LED׳s with utmost efficacy, a sol–gel approach is adopted wherein a water soluble silicon compound is used as a silica source. The phosphor material obtained is subjected to detailed structural, morphological and luminescent studies. The results obtained show that the XRD patterns of Eu²⁺ doped CaSrSiO₄ phosphors are in good agreement with the CaSrSiO₄ (ICSD no. 49660) whose structure is orthorhombic. The output of the luminescence studies clearly portrays a broad yellow emission between 450 and 750 nm with a peak at ~600 nm under the broad excitation range. This confirms its efficient emission towards the development of a warm white light using blue LEDs. A red shift in the peak emission wavelength was observed for the prepared samples. This longer shift in wavelength can be credited to the sol–gel method adopted and is not offered by the conventional solid state reaction method. A warm white emitting LED was fabricated by combining near ultraviolet LED (400 nm) chip with our sol–gel synthesized CaSrSiO₄:Eu²⁺ phosphor. The CIE chromaticity coordinates (0.44 and 0.41), color correlated temperature (CCT) <4000 K, color rendering index (CRI) >80 provide their emission potentiality in the warm white light region.     

Crystal structure,luminescent properties and white light emitting diode application of Ba3GdNa(PO4)3F:Eu2+ single-phase white light-emitting phosphor

A series of single-phase white-light-emitting phosphors, Eu²⁺-activated Ba₃GdNa(PO₄)₃F phosphors were synthesized by solid-state reactions. The crystal structure of Ba₃GdNa(PO₄)₃F was been identified by Rietveld refinement of X-ray diffraction pattern. The Eu²⁺-activated Ba₃GdNa(PO₄)₃F phosphors exhibit broad excitation spectra from 250 to 420 nm, which matched well with the n-UV LED chips. Under the excitation of 365 nm, the emission spectrum almost covered the entire visible region including two emission bands peaked at 472 nm and 640 nm. Three different Eu²⁺ emission centers in Ba₃GdNa(PO₄)₃F:Eu²⁺ phosphor were confirmed by their fluorescence decay lifetimes. The optimal concentration of Eu²⁺ in Ba₃GdNa(PO₄)₃F:xEu²⁺ was 3 mol% and the corresponding concentration quenching mechanism was verified to be exchange coupling interaction. Furthermore, the white light-emitting diode fabricated with Ba₃GdNa(PO₄)₃F:0.05Eu²⁺ phosphor and a 370 nm UV chip has a CIE of (0.3267, 0.2976) with a color-rendering index of 78.4 at the CCT of 5287 K.     

Synthesis and photoluminescence performance of single-component Ca3YAl3B4O15:Dy3+, Eu3+ white-emitting phosphor for white light-emitting diodes

A single-component Ca₃YAl₃B₄O₁₅ (CYAB):Dy³⁺, Eu³⁺ phosphor was synthesized by the traditional high temperature solid-phase method, Dy³⁺ and Eu³⁺ were codoped in the structure to obtain a warm white emission. The results of XRD and EDS revealed that all samples had the standard Ca₃YAl₃B₄O₁₅ structure, and no impurity phase appeared with codoping. The emission of Dy³⁺ in CYAB consisted of both main peaks at 476 nm and 570 nm, with which a white emission could be observed. Furthermore, a characteristic emission peak of Eu³⁺ appeared at 617 nm in Dy³⁺/Eu³⁺-codoped samples to supplement red component for the white emission of Dy³⁺, due to the energy transfer effect between Dy³⁺ and Eu³⁺. With the amount of Eu³⁺ raised, the correlated colour temperature of CYAB:Dy³⁺, Eu³⁺ phosphor obviously decreased, and a warm white light was successfully realized from the manufactured w-LEDs. Therefore, all results indicated that the single-component Dy³⁺/Eu³⁺ codoped CYAB white-emitting phosphor had a potential application in ultraviolet excited w-LEDs.     

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.     

Single-phased emission-tunable Ca3Si2O7:Ce,Eu phosphors for white light-emitting diodes

A series of single-phased emission-tunable Ca₃Si₂O₇:Ce³⁺, Eu²⁺ phosphors has been prepared by the solid-state reaction method. The phosphors show two intense emission bands at about 450 nm and 610 nm, which are attributed to the 5d→4f transitions of Ce³⁺ and Eu²⁺ ions, respectively. The emission colors of Ca₃Si₂O₇:Ce³⁺, Eu²⁺ phosphors vary from blue (0.148, 0.147) to white (0.309, 0.260), and eventually to orange (0.407, 0.319) by tuning the Eu²⁺/Ce³⁺ ratio. Energy transfer from Ce³⁺ to Eu²⁺ is studied by luminescence spectra and energy transfer efficiency. The results show an electric quadrupole–quadrupole interaction plays an important role in the process of energy transfer. The phosphors with tunable emission are suitable for application in white light-emitting diodes.     

Synthesis and photoluminescence properties of Sr3(PO4)2:Re3+, Li+ (Re = Eu,Sm) red phosphors for white light-emitting diodes

Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) red phosphors were prepared via a high temperature solid state reaction, and their structure and luminescence properties were investigated. X-ray diffraction patterns indicate that the phase of as-prepared samples is in good agreement with standard Sr₃(PO₄)₂ structure. Under 395 nm excitation, the emission of Sr₃(PO₄)₂:Eu³⁺ consists of a strong peak centered at 622 nm and two weak peaks centered at 598 nm and 660 nm, which correspond to ⁵D₀→⁷F₂, ⁵D₀→⁷F₁ and ⁵D₀→⁷F₃ transitions, respectively. Also, the emission spectrum of Sr₃(PO₄)₂:Sm³⁺ shows three main peaks at 568 nm, 603 nm and 651 nm, which are attributed to ⁴G_5/2→⁶H_I/2 (I = 5, 7, 9) transitions of Sm³⁺. Furthermore, luminescence properties of Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) samples are enhanced significantly by Li⁺ ions doping as charge compensator. Results indicate that as-prepared Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) could be the potential red phosphors used in white light-emitting diodes.     

Upconversion emission,cathodoluminescence and temperature sensing behaviors of Yb3+ ions sensitized NaY(WO4)2:Er3+ phosphors

A series of Yb³⁺ ions sensitized NaY(WO₄)₂:Er³⁺ phosphors were synthesized through a solid-sate reaction method. The X-ray diffraction (XRD), upconversion (UC) emission and cathodoluminescence (CL) measurments were applied to characterize the as-prepared samples. Under the excitation of 980 nm light, bright green UC emissions corresponding to (²H_11/2,⁴S_3/2)→⁴I_15/2 transitions of Er³⁺ ions were observed and the UC emission intensities showed an upward trend with increasing the Yb³⁺ ion concentration, achieving its optimum value at 25 mol%. Furthermore, the temperature sensing behavior based on the thermally coupled levels (²H_11/2,⁴S_3/2) of Er³⁺ ions was analyzed by a fluorescence intensity ratio technique. It was found that the obtained samples can be operated in a wide temperature range of 133–773 K with a maximum sensitivity of approximately 0.0112 K⁻¹ at 515 K. Ultimately, strong CL properties were observed in NaY(WO₄)₂:0.01Er³⁺/0.25Yb³⁺ phosphors and the CL emission intensity increased gradually with the increment of accelerating voltage and filament current.     

Synthesis,structure and luminescence of a high-purity and thermal-stable Sr9LiMg(PO4)7: Eu3+ red phosphor

Eu³⁺-activated Sr₉LiMg(PO₄)₇ phosphors, which presented bright red emissions mainly from the ⁵D₀→⁷F₂ transition of Eu³⁺ ions upon the near-ultraviolet excitation, were successfully synthesized in ambient atmosphere. The crystal structure, phase constitution, photoluminescent behaviors, decay time, internal quantum efficiency and thermal stability of the resultant phosphors were investigated in detail. Eu³⁺ ions are found to tend to occupy multiple Sr²⁺ sites, which are 7, 8 and 10-coordinated. The optimal doping concentration is 7 mol% and the electrical multipolar interaction contributed to the non-radiative energy transfer between Eu³⁺ ions in Sr₉LiMg(PO₄)₇ host lattices. Temperature-dependent PL spectra indicated Sr₉LiMg(PO₄)₇: Eu³⁺ possess excellent emission and color stability at elevated temperature. Fabricated single-chromatic LED prototype emit bright red light under 20 mA bias current, which demonstrates that Sr₉LiMg(PO₄)₇: Eu³⁺ phosphor is of great potential as converted phosphor in NUV LED application.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Abnormal thermal quenching behavior and optical properties of a novel apatite-type NaCa3Bi(PO4)3F:Sm3+ orange-red-emitting phosphor for w-LED applications

Novel apatite-type NaCa₃Bi(PO₄)₃F:xSm³⁺ (0.01 ≤ x ≤ 0.30) orange-red-light phosphors were synthesized through the solid-state method at high temperature. The crystal structure, energy band structure, density of state, phase purity, particle morphology, photoluminescence properties, thermostability, and luminescence decay of the phosphors were comprehensively characterized. When λ_ex = 404 nm, the optimal NaCa₃Bi(PO₄)₃F:0.05 S m³⁺ phosphor showed the orange-red emission (597 nm). The NaCa₃Bi(PO₄)₃F:Sm³⁺ phosphors exhibited abnormal thermal quenching properties as their emission intensity increased by about 2.57% from 300 to 380 K. Their intensity at 440 K was still 1.01-fold stronger than that at room temperature. The abnormal thermal quenching mechanisms were well explained via the coordinate configuration scheme. The thermal activation energy (E_a) was calculated to be 0.79 eV. The color purity of all the phosphors reached 99.9%. Ultimately, a white light-emitting diode (w-LED) was fabricated based on the tri-color RGB method. The color rendering index and the chromaticity coordinates of the fabricated w-LED were 89 and (0.310, 0.319), respectively. Thus, these high thermostability NaCa₃Bi(PO₄)₃F:Sm³⁺ orange-red phosphors can be potentially used in w-LED applications.     

Photoluminescence and energy transfer of efficient and thermally stable white-emitting Ca9La(PO4)7:Ce3+, Tb3+, Mn2+ phosphors

The development of novel single-component white-emitting phosphors with high thermal stability is essential for improving the illumination quality of white light-emitting diodes. In this work, we synthesized a series of Ce³⁺, Tb³⁺, Mn²⁺ single- and multiple-doped Ca₉La(PO₄)₇ (CLPO) phosphors with β-Ca₃(PO₄)₂-type structure by the simple high-temperature solid-state reaction. The crystallization behavior, crystal structure, surface morphology, photoluminescence performance, decay lifetime and thermal stability were systematically investigated. The PL spectra and decay curves have evidenced the efficient energy transfer from Ce³⁺ to Tb³⁺ and from Ce³⁺ to Mn²⁺ in the CLPO host, and corresponding energy transfer efficiency reaches 41.8% and 54.1%, respectively. The energy transfer process of Ce³⁺→Tb³⁺ and Ce³⁺→Mn²⁺ can be deduced to the resonant type via dipole-dipole and dipole-quadrupole interaction mechanism, and corresponding critical distance were determined to be 12.23 and 14.4 Å, respectively. Based on the efficient energy transfer, the white light emission can be successfully achieved in the single-component CLPO:0.15Ce³⁺, 0.10Tb³⁺, 0.04Mn²⁺ phosphor, which owns CIE chromaticity coordinates of (0.3245, 0.3347), CCT of 5878 K, internal and external quantum efficiency of 84.51% and 69.32%. Especially, compared with the emission intensity at 25 °C, it still remains 98.5% at 150 °C and 92.0% at 300 °C. Based on these results, the single-component white light emission phosphor CLPO:0.15Ce³⁺, 0.10Tb³⁺, 0.04Mn²⁺ is a potential candidate for UV-converted white LEDs.     

Tunable white light and energy transfer of Dy3+ and Eu3+ doped Y2Mo4O15 phosphors

A series of Dy³⁺ or/and Eu³⁺ doped Y₂Mo₄O₁₅ phosphors were successfully synthesized at a low temperature of 600 °C via solid state reaction. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL) excitation, emission spectra and PL decay curves. XRD results demonstrate that Y₂Mo₄O₁₅: Dy³⁺, Eu³⁺ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy³⁺ and Eu³⁺ ions activated Y₂Mo₄O₁₅ phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y₂Mo₄O₁₅: 0.08Dy³⁺, yEu³⁺ phosphors can be adjusted by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions and a white light is achieved when the doping concentration of Eu³⁺ is 5%. In addition, the energy transfer from Dy³⁺ to Eu³⁺ is also confirmed based on the luminescence spectra and decay curves.     

Cyan-emitting Ba0.45Ca2.5La6(SiO4)6: 0.05 Eu2+ and Ba1.45Ca1.5La6(SiO4)6:0.05 Eu2+ solid-solution phosphors for white light-emitting diodes

Two cyan-emitting phosphors with different bandwidths were successfully synthesized through the high-temperature solid-state method in a reducing atmosphere. The crystal structures, morphologies, and luminescence properties of the as-prepared phosphors were investigated. The Rietveld refinements of the powder X-ray diffraction (XRD) data demonstrated the single phase of the samples, and two crystallographic sites of La³⁺ were observed in the crystal structure. Under the excitation of UV light, both Ba_0.45Ca_2.5La₆(SiO₄)₆: 0.05 Eu²⁺ and Ba_1.45Ca_1.5La₆(SiO₄)₆: 0.05 Eu²⁺ phosphors emitted cyan light due to the 4f⁶5 d¹→4f⁷ transitions of the Eu²⁺ ion. The emission spectra could be well fitted by two component Gaussian peaks corresponding to two different coordination environments of the Eu²⁺ ions. The temperature-dependent photoluminescence spectra show a large difference on the thermal stability between the two phosphors. The two phosphors exhibit effective absorption of near-UV light and their internal quantum efficiencies (IQEs) were calculated as 31.5% and 42.4% under 295 nm UV-light excitation. The experimental results indicate that the novel cyan phosphors might have potential applications in white light-emitting diodes (LEDs) based on the near-UV LED chip.     

Tunable emission of single-phased NaY(WO4)2:Sm3+ phosphor based on energy transfer

A series of NaY(WO₄)₂:Sm³⁺ phosphors were prepared by high temperature solid state reaction. When excited by ultraviolet and blue light, their emission spectra cover entirely visible light region, due to intrinsic luminescence of WO₄^2- group as well as Sm³⁺ 4f-4f transitions. White light emission was obtained from NaY_0.99Sm_0.01(WO₄)₂ phosphor under radiation of 265 nm UV light, and intense yellow and red emission from ⁶H_{J(J=5/2, 7/2, 9/2)} transitions were observed when pumped Sm^{3+ 4}G_5/2 by 405 nm blue light. With incorporation of Sm³⁺ into NaY(WO₄)₂ host, higher-level emission from Sm³⁺ at 650 nm was generated by energy transfer from WO₄^2- to Sm³⁺ under excitation of 265 nm. The corresponding energy transfer mechanism was demonstrated to be a dipole-dipole interaction. In addition, tunable emission from blue to white and, finally, to red was realized by increasing Sm³⁺ doping concentration. The band gap of NaY(WO₄)₂ calculated from diffuse reflection spectra indicates a semiconducting character. All these results show that NaY_1−xSm_x(WO₄)₂ phosphor provides promising application for conversion of frequencies emitted by UV or blue LEDs.     

A novel single-phase Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphor for tunable and white light emission

A new type of Bi³⁺,Eu³⁺ single- and co-doped Na_3.6Y_1.8(PO₄)₃ phosphate phosphors were manufactured using conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. The crystal structure, luminescent properties, luminescent mechanism and quantum efficiency were thoroughly explored. Results show that there are two crystallization sites for Bi³⁺ and Eu³⁺ ions. Upon the excitation of 342 and 373 nm, Bi³⁺ single-doped phosphors exhibit green and blue emission, derived from the ³P₁ to ¹S₀ transition of Bi³⁺ located in different occupancy sites. Thanks to radiative energy transfer process from Bi³⁺ to Eu³⁺, adjustable emission could be acquired by altering Eu³⁺ content in co-doped phosphors. Pure white-light emission with quantum efficiency value of 22.9% can be realized in Na_3.6Y_1.8(PO₄)₃:0.01Bi³⁺,0.1Eu³⁺ sample and the integrated intensity of white light emission at 417 K remains 85% of that at room temperature. Our results indicate that Na_3.6Y_1.8(PO₄)₃:Bi³⁺,Eu³⁺ phosphors have feasible application in high-power ultraviolet driven solid-state lighting.