Color-tunable up-conversion emission from Yb3+/Er3+/Tm3+/Ho3+ codoped KY(MoO4)2 microcrystals based on energy transfer

Tunable up-conversion luminescent material KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) has been synthesized by a typical hydrothermal process. Under 980 nm laser diode (LD) excitation, the emission intensity and the corresponding luminescence colors of KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) have been investigated in detail. The energy transfer from the Yb³⁺ sensitizer to Ho³⁺, Er³⁺ and Tm³⁺ activators plays an important role in the development of color-tunable single- phased phosphors. The emission intensity keep balance through control of the Ho³⁺ co-doping concentrations, white light was experimentally shown at KY(MoO₄)₂: 20 mol% Yb³⁺, 0.8 mol% Er³⁺, 0.5 mol% Tm³⁺, 1.0 mol% Ho³⁺ phosphor with further calcination at 800 °C for 4 h under 980 nm laser excitation. The color tunability, high quality of white light and high intensity of the emitted signal make these up-conversion (UC) phosphors excellent candidates for applications in solid-state lighting.     

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.     

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

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

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.     

EDTA-assisted hydrothermal synthesis of KLa(MoO4)2:Eu3+ microcrystals and their luminescence properties

Monoclinic KLa(MoO₄)₂:Eu³⁺ microarchitectures with different morphologies were synthesized by an EDTA-assisted hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and photoluminescence (PL) spectrometer. It was found that the amounts of EDTA and the pH values of precursor solution have crucial influences on the structure, morphology and size of the obtained samples, respectively. Under 270 nm excitation, Eu³⁺ doped KLa(MoO₄)₂ samples showed red emission centered at 618 nm which attributed to ⁵D₀→⁷F₂ transition of Eu³⁺. The dependence of luminescence intensity on different morphologies were discussed in detailed. With further annealing treatment, the emission intensities of peanut-like samples increased amazingly. Moreover, the lifetime of the annealed samples were calculated. The significantly enhanced photoluminescence performances indicate that the as-annealed samples are promising phosphors which can be used for white light-emitting diodes (WLEDs).     

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 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.     

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.     

Photoluminescent properties and site occupation preference in Bi3+, Eu3+ doped CaY4(SiO4)3O phosphor

Bi³⁺, Eu³⁺ doped CaY₄(SiO₄)₃O phosphors were synthesized through high temperature solid state reaction. Their photoluminescent properties were investigated and site occupation preference of Bi³⁺ in cationic sites was analyzed. The structure of CaY₄(SiO₄)₃O is characterized by three non-equivalent cationic sites with different coordination and cation-oxygen distances. By means of dielectric theory of the chemical bond for complex crystals, several kinds of chemical bond parameters like fractional covalence of CaY₄(SiO₄)₃O were calculated and integrated to yield environmental factor h_e. According to quantitative equations between the transition energy of Bi³⁺ and environmental factor h_e, the excitation bands at 308 and 226 nm were assigned to ¹S₀→³P₁ transition of Bi³⁺ in Y(6h) and Y(4f) site, respectively. Another excitation band centered at 210 nm should be the overlap of Bi³⁺ A-band in Ca site and C-band in Y(6h) site. Optical band gap of pure CYSO was calculated using Kubelka–Munk method from diffuse reflectance spectra. Red emission can be realized in CaY₄(SiO₄)₃O:Bi³⁺, Eu³⁺ under UV light excitation because of efficient energy transfer from Bi³⁺ to Eu³⁺ and decay behaviors of Bi³⁺ and Eu³⁺ emission were investigated. Without optimization, the internal quantum efficiency of CYSO:2%Bi³⁺, 7%Eu³⁺ at 310 and 393 nm excitations were 31.563%, 74.252%, respectively.     

Photoluminescence and electron-beam excitation induced cathodoluminescence properties of novel green-emitting Ba4La6O(SiO4)6:Tb3+phosphors

Tb³⁺ions activated Ba₄La₆O(SiO₄)₆ (BLSO:Tb³⁺) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction pattern confirmed their oxyapatite structure. The field-emission scanning electron microscope image established that the BLSO:Tb³⁺phosphor particles were closely-packed and acquired irregular shapes. The photoluminescence (PL) excitation spectra of BLSO:Tb³⁺phosphors showed intense f–d transitions along with low intense peaks corresponding to the f–f transitions of Tb³⁺ions in the lower energy region. The PL emission spectra displayed the characteristic emission bands of Tb³⁺ions, and the optimized concentrations were found to be at 1 and 6 mol% for blue and green emission peaks, respectively. The cathodoluminescece (CL) spectra exhibited a similar behavior that was observed in the PL spectra except the intensity variations in the blue and green regions. The CL spectra of the BLSO:6 mol% Tb³⁺phosphor unveiled accelerating voltage induced luminescent properties.     

Synthesis,crystal structure and temperature dependent luminescence of Eu3+ doped SrGd2O4 host: An approach towards tunable red emissions for display applications

In the present paper, an investigation on the structural and photoluminescence (PL) properties of SrGd₂O₄:Eu³⁺ ceramic phosphors synthesized by homogeneous precipitation method followed by combustion process has been reported. The samples, annealed at 1200 °C, were crystallized into orthorhombic phase without any impurities. Microscopic studies revealed the irregular morphology of the obtained ceramic phosphor particles having sizes in the range of 0.3–3 µm. The characteristic photoluminescence properties and decay curves were studied in detail as a function of Eu³⁺ concentration and temperature. The Eu³⁺ doped ceramic samples illuminated with UV light revealed the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The concentration quenching phenomenon of Eu³⁺ ions in the present host, analyzed in the light of ion-ion interaction, indicated multipolar interaction between Eu³⁺ ions. Finally, the intensity parameters (Ω₂, Ω₄) and various radiative properties such as stimulated emission cross-section (σ_e), gain band-width (σ_e×Δλ_eff) and optical gain (σ_e×τ_exp) of Eu³⁺ in the SrGd₂O₄ ceramic phosphors have been calculated by using Judd-Ofelt theory. The present phosphor system exhibited efficient red emission with high red color purity (95%) and adequate thermal stability even at 200 °C. Present research broadly indicated the suitability of SrGd₂O₄:Eu³⁺ ceramic phosphor for display applications.     

Near-ultraviolet light–induced dazzling red emission in CaGd2(MoO4)4:2xSm3+ compounds for phosphor-converted WLEDs

The Sm³⁺-activated CaGd₂(MoO₄)₄ phosphors were prepared through a sol-gel reaction route. From the results of excitation spectrum, three-dimensional emission spectra and contour lines, it was confirmed that the near-ultraviolet (NUV) light was the proper excitation light source for the synthesized phosphors. Under 405 nm irradiation, the luminescent behaviors of the studied samples were revealed to be dependent on the Sm³⁺ ion concentration and its optimal value of 0.03 mol was obtained. Through theoretical analysis, it is evident that the dipole-dipole interaction can be responsible for the involved concentration quenching mechanism in the final products and the critical distance was 39.7 Å. Moreover, the temperature-dependent emission spectra demonstrated that the studied samples had admirable thermal stability and the activation energy was decided to be 0.21 eV. Furthermore, the internal quantum efficiency of the Sm³⁺-activated CaGd₂(MoO₄)₄ phosphors was found to be 21.6%. Finally, to explore the practical applications of obtained compounds for indoor illumination, a white light-emitting diode (WLED) device which contained a NUV chip, prepared phosphors, and commercial blue-emitting and green-emitting phosphors was packaged. The packaged WLEDs device can emit dazzling white light with satisfied color coordinate of (0.305, 0.318), proper color rendering index (82.6), and correlated color temperature (7069 K).     

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 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.     

Microwave Sol–Gel Synthesis of CaGd2(MoO4)4:Er3+/Yb3+ Phosphors and Their Upconversion Photoluminescence Properties

CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ phosphors with the doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2, and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by the microwave sol–gel method, and the crystal structure refinement and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after heat‐treatment at 900°C for 16 h, showed a well‐crystallized morphology. Under the excitation at 980 nm, CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited strong 525 and 550‐nm emission bands in the green region and a weak 655‐nm emission band in the red region. The Raman spectrum of undoped CaGd₂(MoO₄)₄ revealed about 15 narrow lines. The strongest band observed at 903 cm^?1 was assigned to the ν₁ symmetric stretching vibration of MoO₄ tetrahedrons. The spectra of the samples doped with Er and Yb obtained under 514.5 nm excitation were dominated by Er³⁺ luminescence preventing the recording Raman spectra of these samples. Concentration quenching of the erbium luminescence at ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions in the CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ crystal structure was established to be approximately at the 10 at.% doping level.     

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.     

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.     

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.     

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).     

Luminescent properties of Gd3+ sensitized low-phonon energy CaGd4O7:Tb3+ green emitting novel phosphors

The trivalent terbium (Tb³⁺) ions activated CaGd₄O₇ (CG) phosphors were synthesized by a sol–gel method. The characterizations were performed after the samples annealed at 1500 °C. The structural and morphological properties were analyzed from the X-ray diffraction patterns and scanning electron microscope images. The photoluminescence excitation spectra showed a broad-band between the wavelengths 250 and 300 nm, which were overlapped with the Gd³⁺ excitation bands. The photoluminescence spectra exhibited efficient green emission due to the sensitization effect of Gd³⁺ ions on the Tb³⁺ ions when exciting with the Gd³⁺ wavelength at 278 nm. In order to analyze the influence of Tb³⁺ concentration on the luminescence behavior of Tb³⁺ ions in the CG host lattice, the decay curves were measured. The temperature-dependent luminescence measurements were done to identify the thermal stability of CG:Tb³⁺ phosphors at elevated temperatures. The cathodoluminescent spectra also showed a similar behavior to that observed in PL spectra. The CIE chromaticity coordinates as a function of Tb³⁺ concentration were calculated and all the obtained chromaticity coordinates have been placed in the green spectral region.