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.     

Tunable full color emission from single-phase LiSr3.99−xDy0.01(BO3)3:xEu3+ phosphors

Tunable full color emissive LiSr_3.99?xDy_0.01(BO₃)₃:xEu³⁺ (0≤x≤0.09) phosphors peaked at 481 nm (blue), 574 nm (yellow), 592 nm (orange), and 617 nm (red) were synthesized in air by high temperature solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), photoluminescence excitation (PLE) and photoluminescence (PL) spectra. The PLE spectra in the range from 200 to 500 nm include an Eu–O charge transfer band (CTB) and several 4f–4f transition peaks of Dy³⁺ and Eu³⁺, indicating its potential application in white light emitting diodes (LEDs). The effect of Eu³⁺ concentration on the emission intensity of LiSr_3.99?xDy_0.01(BO₃)₃:xEu³⁺ phosphors was investigated in detail and the optical concentration is found to be x=0.005. The CIE chromaticity coordinates for LiSr_3.99?xDy_0.01(BO₃)₃:xEu³⁺ phosphors are simulated. With an increase in Eu³⁺ ion concentration, the chromaticity color coordinates can be tuned efficiently from the border of greenish white region to its equal-energy white light point, and eventually to red region. All the results imply that the studied LiSr_3.99?xDy_0.01(BO₃)₃:xEu³⁺ phosphors could be potentially used as white LEDs.     

Crystal structure and luminescence properties of green-emitting Sr1−xAl12O19:xEu2+ phosphors

In this paper, a series of novel luminescent Sr_1−xAl₁₂O₁₉:xEu²⁺ phosphors were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the decay curves were investigated. The quenching concentration of Eu²⁺ in SrAl₁₂O₁₉ was about 0.15 (mol). Upon excitation at 378 nm, the composition-optimized Sr_0.85Al₁₂O₁₉:0.15Eu²⁺ exhibited strong broad-band green emission at 530 nm with the CIE chromaticity (0.2917, 0.5736). The results indicate that Sr_1−xAl₁₂O₁₉:xEu²⁺ phosphors have potential applications as green-emitting phosphors for UV-pumped white-light LEDs.     

Effect of Sr/Ca substitution on phase structure and photoluminescence properties of micro-SrxCa1−xAlSiN3: Eu2+ phosphor for high CRI white LEDs

Sr_xCa_1−xAlSiN₃: Eu²⁺ phosphors were prepared by using the high temperature solid state reaction in a 1.1 Mpa N₂ atmosphere. The phase structures, photoluminescence (PL) properties, and chromaticity properties of the phosphors affected by Sr/Ca Substitution have been investigated in detail. With increasing Sr content (x value), the crystal grain became bigger and the average grain size increased from 5 µm to 10 µm. PL emission bands of Sr_xCa_1−xAlSiN₃: Eu²⁺ showed a blue-shift from 660 (x=0) to 617 nm (x=0.8), the shoulder of the excitation spectra around 550 nm showed a slightly blue-shift and decay lifetime shortened from 776.96 (x=0.2) to 642.35 ns (x=0.8). Both the emission and excitation intensity of peak position increased with Sr content increased. The ideal white light with high CRI (Ra>88) can be obtained by mixing the Sr_xCa_1−xAlSiN₃: Eu²⁺ phosphors and commercial green phosphors with appropriate proportion of the components.     

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.     

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.     

Gel-combustion assisted synthesis of eulytite-type Sr3Y(PO4)3 as a single host for narrow-band Eu3+ and broad-band Eu2+ emissions

A series of eulytite-type Sr₃Y_1-x(PO₄)₃:xEu³⁺ (x = 0–0.13) and Sr_3-yY(PO₄)₃:yEu²⁺ (y = 0–0.10) phosphors were successfully synthesized via gel-combustion and subsequent calcination in O₂ and Ar/H₂ atmospheres at 1250 °C, respectively. Detailed crystal structure analysis via Rietveld refinement showed that the phosphors were crystallized in the cubic system (space group I-43d, No. 220), in which the Eu³⁺ and Eu²⁺ activators reside at the Y³⁺ and Sr²⁺ sites, respectively. The trivalent Eu³⁺ ions (CN = 6) exhibited typical narrow-band luminescence via intra-4f⁶ transitions, with the red emission at ~ 615 nm being dominant (⁵D₀ → ⁷F₂ transition, FWHM = 15.9 ± 0.2 nm). The divalent Eu²⁺ ions (CN = 6 and 9) showed broad-band luminescence ranging from light-blue to blue via 4f⁶5d¹ → 4f⁷ transitions (FWHM = 115 ± 2 nm). The optimal Eu³⁺ and Eu²⁺ concentrations were determined to be 10 at% (x = 0.10) and 7 at% (y = 0.07), respectively, and the mechanisms of concentration quenching were discussed. The excitation/emission properties, fluorescence decay kinetics, CIE chromaticity, and particularly the rarely addressed thermal stability of the phosphors were investigated in detail.     

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.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Defects characterization of Dy-doped BaTiO3 ceramics via electron paramagnetic resonance

The point defects and the structural and dielectric properties of Dy-doped BaTiO₃ ceramics prepared at 1400 °C were investigated. The solubility of Dy in the self-compensation mode was determined to be x = 0.07 for (Ba_1−xDy_x)(Ti_1−xDy_x)O₃, and no EPR signals associated with the Dy³⁺ Kramers ion or the Ba and Ti vacancies were detected using the electron paramagnetic resonance (EPR) technique. As x increases, the dielectric behavior changed from a first-order phase transition to a diffuse phase transition to a Y7R dielectric-temperature stability. A strong EPR signal at g = 1.974, which is rare among rare-earth-doped BaTiO₃ ceramics appeared unexpectedly in the single-phase (Ba_1−xDy_x)Ti_1−x/4O₃ ceramics with deliberately designed Ti vacancies. This signal was attributed to ionized Ba vacancy defects. A preference for the self-compensation mode of Dy³⁺ ions is responsible for the appearance of Ba vacancies. The real formula of the nominal (Ba_1−xDy_x)Ti_1−x/4O₃ is expressed as (Ba_1−xDy_3x/4)(Ti_1−x/4Dy_x/4)O₃. In addition, the defect chemistry is discussed.     

Crystal structure and luminescence properties of novel Sr10−x(SiO4)3(SO4)3O:xEu2+ phosphor with apatite structure

In this paper, a series of novel luminescent Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors with apatite structure were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the PL thermal stability were investigated. Sr_9.92(SiO₄)₃(SO₄)₃O:0.08Eu²⁺ phosphor exhibits better thermal quenching resistance, retaining the luminance of 66.55% at 150 °C compared with that at 25 °C. The quenching concentration of Eu²⁺ in Sr₁₀(SiO₄)₃(SO₄)₃O was about 0.08 (mol) with the dipole–quadrupole interaction. The Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors exhibited a broad-band green emission at 538 nm upon excitation at 396 nm. The results indicate that Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs.     

Molten salt synthesis and optical properties of Eu3+, Dy3+or Nd3+ doped NiNb2O6 columbite-type phosphors

Pure, Eu³⁺, Dy³⁺ or Nd³⁺-doped NiNb₂O₆ powders have been prepared by a molten salt synthesis method by using Li₂SO₄–Na₂SO₄ salt mixture as a flux at relatively low temperatures as compared to the solid state reaction method. X-ray diffraction patterns of pure NiNb₂O₆ samples indicated an orthorhombic single phase. For Eu³⁺-doped NiNb₂O₆ samples, the luminescence of Eu³⁺ was observed at 615 nm as red emission while Dy³⁺-doped NiNb₂O₆ showed yellow emission at 577 nm and Nd³⁺ doped sample exhibited a typical emission at 1064 nm varying with the Eu³⁺ or Nd³⁺ doping concentrations. These luminescence characteristics of the doped samples may be attributed to the energy transfer between rare earth ions and NiO₆ octahedral groups in the columbite structure.     

Li ion conduction of perovskite Li0.375Sr0.4375Ti0.25Ta0.75O3 and related compounds

In this work, perovskite-structured Li_0.375Sr_0.4375M_0.25N_0.75O₃ (M=Ti, Sn, N=Nb, Ta) solid electrolytes were synthesized by conventional solid state reaction method. Phase compositions, fractured morphologies and conductivities of these compounds were investigated by X-ray diffraction, scanning electron microscope and AC-impedance spectroscopy, respectively. X-ray diffraction analysis confirms that all of Li_0.375Sr_0.4375M_0.25N_0.75O₃ (M=Ti, Sn, N=Nb, Ta) ceramics present perovskite structure. Pure Li_0.375Sr_0.4375Ti_0.25Ta_0.75O₃ and Li_0.375Sr_0.4375Sn_0.25Ta_0.75O₃ perovskite ceramics were obtained. But impurities were detected in Li_0.375Sr_0.4375Ti_0.25Nb_0.75O₃ and Li_0.375Sr_0.4375Sn_0.25Nb_0.75O₃. Among all investigated compounds, Li_0.375Sr_0.4375Ti_0.25Ta_0.75O₃ shows the highest total ionic conductivity of 2.60 × 10^?4 S cm^?1 at room temperature and the lowest activation energy of 0.347 eV. Conductivities of Li_0.375Sr_0.4375Sn_0.25Ta_0.75O₃ and Li_0.375Sr_0.4375Sn_0.25Nb_0.75O₃ were 4.4 × 10^?5 S cm^?1 and 1.82 × 10^?6 S cm^?1, respectively. Their conductivities were much lower than Li_0.375Sr_0.4375Ti_0.25Ta_0.75O₃ and Li_0.375Sr_0.4375Ti_0.25Nb_0.75O₃.     

Sr3GdLi(PO4)3F:Eu2+, Mn2+: A tunable blue-white color emitting phosphor via energy transfer for near-UV white LEDs

A series of Eu²⁺ and Mn²⁺ co-doping Sr₃GdLi(PO₄)₃F phosphors have been synthesized through high temperature solid state reaction. Eu²⁺ single doped Sr₃GdLi(PO₄)₃F phosphors have an efficient excitation in the range of 230–430 nm, which is in good agreement with the commercial near-ultraviolet (n-UV) LED chips, and gives intense blue emission centering at 445 nm. The critical distance of the Eu²⁺ ions in Sr₃GdLi(PO₄)₃F is computed and demonstrated that the concentration quenching mechanism of Eu²⁺ is mostly caused by the dipole-dipole interaction. By co-doping Eu²⁺ and Mn²⁺ ions in the Sr₃GdLi(PO₄)₃F host, the energy transfer from Eu²⁺ to Mn²⁺ that can be discovered. With the increase of Mn²⁺ content, emission color can be adjusted from blue to white under excitation of 380 nm, corresponding to chromatic coordinates change from (0.189, 0.108) to (0.319, 0.277). The energy transfer from Eu²⁺ to Mn²⁺ ions is proven to be a dipole-dipole mechanism on the basis of the experimental results and analysis of photoluminescence spectra and decay curves. This study infers that the obtained Sr₃GdLi(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors may be a potential candidate for n-UV LEDs.     

Study of structure and conductivity of Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 solid electrolytes

Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized using the conventional solid-state reaction method. In order to increase the vacancy concentration, La³⁺ was doped on the Sr²⁺ site. Crystal structures of doped samples were characterized by X-ray diffraction. Except, perovskite-type Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15) samples were fabricated by heat treatment at 1250 °C, 1275 °C, 1275 °C and 1275 °C, respectively, for 15 h. Lattice sizes decreased with the increase of doping amounts because of the smaller ion radius of La³⁺ compared to that of Sr²⁺. Ionic conductivities of the samples were measured by AC impedance spectroscopy. The results showed that the ionic conductivity increases at first and then decreases with raising doping amounts and sintering temperatures. So the optimized composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) sintered at 1275 °C was selected with the highest total conductivity of 3.33 × 10^?5 S cm^?1at 30 °C and an activation energy of 0.27 eV. Additionally, potentiostatic polarization test was used to evaluate the electronic conductivity. The optimal composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) as a possible Li-ion conducting solid electrolyte has an electronic conductivity of only 8.39 × 10^?9 S cm^?1.     

The influence of Mo6+ doping on the luminescence properties of red-emitting phosphor Sr9Eu2W4−xMoxO24 (x = 0–4)

A series of red emitting phosphors Sr₉Eu₂W_4?xMo_xO₂₄ (x = 0–4) have been synthesized by solid-state reactions and their crystal structures, photoluminescence properties were studied. The excitation and emission spectra of Sr₉Eu₂W_4?xMo_xO₂₄ phosphors can be modified by Mo⁶⁺ doping. As the molybdate content increased, the Eu³⁺ emission intensity of Sr₉Eu₂W_4?xMo_xO₂₄ (x = 0–4) under 395 nm excitation was found to increase and reached a maximum at x = 2. The excitation spectra, the emission intensities and the chromaticity coordinates of Sr₉Eu₂W_4?xMo_xO₂₄ (x = 2) were compared to those of the conventional red phosphor Y₂O₂S: Eu³⁺. The intense red-emission under near-UV excitation suggests that Sr₉Eu₂W_4?xMo_xO₂₄ (x = 2) could be a potential candidate for white light generation by using near-UV LEDs. In this study, the effects of Mo⁶⁺ doping on the crystal structure and photoluminescence properties of Sr₉Eu₂W_4?xMo_xO₂₄ were discussed.     

Microstructure and thermoelectric properties of La0.1Dy0.1SrxTiO3 ceramics

La_0.1Dy_0.1Sr_xTiO₃ (x=0.80, 0.78, 0.75, 0.70) powders were synthesized via a sol-gel method, followed by sintering at 1550 °C in a reducing atmosphere of 5 vol% hydrogen in nitrogen. The microstructure and thermoelectric properties of the Sr-deficient La and Dy co-doped SrTiO₃ were investigated. The result of XRD revealed that La_0.1Dy_0.1Sr_xTiO₃ consisted of SrTiO₃ with a cubic crystal structure as the main phase and of a small amount of Dy₂Ti₂O₇ as the second phase. All the Sr-deficient samples exhibited a step-like microstructure. As the nominal Sr deficient content increased, the electrical conductivity of the Sr-deficient La_0.1Dy_0.1Sr_xTiO₃ ceramics enhanced due to the increasing Sr and oxygen vacancies, the absolute value of the Seebeck coefficient increased a little, and the thermal conductivity decreased to ~3.0 W m⁻¹ K⁻¹, leading to a high ZT value of 0.19 for La_0.1Dy_0.1Sr_0.75TiO₃ at 500 °C.     

Color tuning in (Ca1−xSrx)8MgLu(PO4)7:Eu2+,Mn2+ phosphor via host composition design and energy transfer

In this work, a series of Eu²⁺-doped (Ca_1−xSr_x)₈MgLu(PO₄)₇ and Eu²⁺/Mn²⁺-codoped Ca_6.5Sr_1.5MgLu(PO₄)₇ phosphors were prepared via the combustion-assisted solid-state reaction process. XRD patterns and Rietveld refinements were used to verify the incorporations of Sr into Ca₈MgLu(PO₄)₇:Eu²⁺. Upon the same excitation wavelength of 380 nm, the emission peaks of Eu²⁺-doped (Ca_1−xSr_x)₈MgLu(PO₄)₇ (0≤x≤1) phosphors red-shifted from 453 to 519 nm with increasing Sr/Ca ratio. The red-shift of the Eu²⁺ emission with increasing Sr/Ca ratio was ascribed to the change of Eu²⁺ emission at different lattice sites. With variation of the Mn²⁺ content, the emission color of Eu²⁺/Mn²⁺ codoped Ca_6.5Sr_1.5MgLu(PO₄)₇ phosphors exhibited the luminescence tunable from greenish blue to white and eventually to red. The energy transfer from Eu²⁺ to Mn²⁺ in Ca_6.5Sr_1.5MgLu(PO₄)₇ host matrix was demonstrated to be of a resonant type via a dipole- dipole mechanism with the critical distance of ∼16.7 Å. By the Sr substitution for Ca and properly tuning by the relative composition change of Eu²⁺/Mn²⁺, chromaticity coordinates of (0.329, 0.326) can be reached at near UV light excitation. The combination of host composition design and energy transfer may provide a novel strategy to obtain white light and tunable luminescence.     

Influence of Al3+ on the cross relaxation process and electrical properties of Dy3+ activated Gd2O3 phosphor for white LED application

Gd₂O₃:Dy³⁺ Al³⁺ phosphors is synthesised by a wet-chemical method for various concentrations of Al³⁺ ion. X-ray diffraction, photoluminescence and impedance spectroscopy are used to understand the physio-chemical properties of the phosphors. The emission spectra of Dy³⁺ ion exhibit transition peaks centred at 572 nm (yellow), 486 nm (blue) and 669 nm (red). Energy transfer from Gd³⁺ to Dy³⁺ is also verified by exciting the phosphors at 274 nm. Some of the Dy³⁺ ions occupy both C₂ and S₆ site of Gd³⁺ ion in Gd₂O₃ matrix. It is also revealed that the enhancement of Dy³⁺ emission is strongly correlated to the surface morphology of the phosphors. Introducing Al³⁺ ions in Gd₂O₃:Dy³⁺ phosphor affect the emission properties of Dy³⁺ ions and its influence is explored at various concentration of Al³⁺ ions. The energy level diagram is presented to explain the cross-relaxation process among Dy³⁺ ions and the energy transfer from Gd³⁺ to Dy³⁺ ion.     

Tunable single-phased white-emitting Sr3Y(PO4)3:Dy3+ phosphors for near-ultraviolet white light-emitting diodes

Single-component white-emitting Sr₃Y(PO₄)₃:Dy³⁺ phosphors were synthesized by a high-energy deformation process. X-ray diffraction patterns showed the resulting crystallized phase to be of cubic structure, space group I-43d (no. 220). The broad-band excitation spectra between 250 and 500 nm were observed by monitoring the emission wavelength at 576 nm, which matches well with commercial near-UV or blue LED chips. Under a 352 nm excitation, the emission peaks were observed at 483 nm (blue), 576 nm (yellow), and 666 nm (red), corresponding to the ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺ ions. The optimized doping concentration of Dy³⁺ ion was 8 mol%. By controlling the Dy³⁺ ion concentration, tunable colors from white to yellow were obtained in Sr₃Y(PO₄)₃:Dy³⁺ phosphors. These results reveal that studied materials may be a promising candidate for white LED applications.