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.     

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.     

Luminescence properties of Eu2+ and Mn2+ doped Sr1.7Mg0.3SiO4 phosphors

Eu²⁺, Mn²⁺ doped Sr_1.7Mg_0.3SiO₄ phosphors were prepared by high temperature solid-state reaction method. Their luminescence properties were studied. The emission spectra of Eu²⁺ singly doped Sr_1.7Mg_0.3SiO₄ consist of a blue band (455 nm) and a green band (550 nm). The relative intensities of two emissions varied with Eu²⁺ concentration. Eu²⁺ and Mn²⁺ co-doped Sr_1.7Mg_0.3SiO₄ phosphors emit three color lights and present whitish color. The blue (455 nm) and green (550 nm) emissions are attributed to the transitions of Eu²⁺, while the red (670 nm) emission is originated from the transition of Mn²⁺ ion. The results indicate the energy transfer from Eu²⁺ to Mn²⁺. The mechanism of the energy transfer is resonance-type energy transfer due to the spectral overlap between the emission of Eu²⁺and the absorption of Mn²⁺.     

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 single-phase white-light-emitting Ba2Mg(BO3)2:Ce3+, Na+, Tb3+, Eu2+ phosphor based on energy transfer

A series of white-light-emitting phosphors of single-phase Ba₂Mg(BO₃)₂:Ce³⁺, Na⁺, Tb³⁺, Eu²⁺ were synthesized by conventional solid-state reaction. The crystal structure of the host was characterized by X-ray diffraction and investigated by Rietveld refinement. Photoluminescence properties were studied in detail. The energy transfer from Ce³⁺ to Tb³⁺ in Ba₂Mg(BO₃)₂ host was investigated and demonstrated to be a resonant type via a quadrupole–quadrupole mechanism. White light with wavelength tunable was realized by coupling the emission bands peaking at 417, 543 and 626 nm attributed to Ce³⁺, Tb³⁺ and Eu²⁺, respectively. By properly tuning the relative composition of Ce³⁺(Na⁺)/Tb³⁺/Eu²⁺, optimized Commission Internationale de l׳Eclairage (CIE) chromaticity coordinates (0.363, 0.295), high color rendering index (CRI) 90 and low correlated color temperature (CCT) 3793 K were obtained from the phosphor of Ba_1.90Ce_0.04Na_0.04Eu_0.02Mg_0.94Tb_0.06(BO₃)₂ upon the excitation of 296 nm UV radiation. These results indicate that Ba₂Mg(BO₃)₂:Ce³⁺, Na⁺, Tb³⁺, Eu²⁺ phosphor has a potential application as an UV radiation down-converting phosphor 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.     

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

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

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.     

White emitting Dy3+ activated perovskite titanates and energy transfer by Eu3+ codoping

Perovskite type titanate phosphors Sr_0.97−xDy_0.03Li_xTi_1−xNb_xO₃, Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ and Sr_0.87−yDy_0.03Eu_yLi_0.1Ti_0.9Nb_0.1O₃ were prepared by conventional solid state method. Herein, white light emission from Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ phosphors and the lowering of its color temperature through codoping with Eu³⁺ ions are reported. Raman measurements have shown that the incorporation of dopants alters the vibrational properties of these phosphors significantly, indicating the reduction of the local symmetry in the crystal lattice. The addition of LiNbO₃ in SrTiO₃:Dy³⁺ phosphor enhances the luminescence intensity and the yellow to blue ratio resulting in emission of high quality white light with color coordinates corresponding to that of standard white. Life time measurements and data fits of Sr_0.9−xDy_xLi_0.1Ti_0.9Nb_0.1O₃ phosphors revealed the biexponential behaviour of luminescence decay profiles. From Judd-Ofelt analysis it is found that the intensity parameter Ω₂ increases with Dy³⁺ concentration and a quantum efficiency of 90.4% was obtained for optimum concentration. In the case of Dy³⁺ and Eu³⁺ codoped phosphors, the color coordinates are found to be sensitive to the Eu³⁺ concentration and the highest energy transfer efficiency of 92% was obtained for the phosphor doped with 10 mol% Eu³⁺. The emission color changes from cold white to reddish orange when the wavelength of excitation alters from 452 to 388 nm, since the energy transfer mechanism alone take place under 452 nm excitation and both direct absorption and the energy transfer mechanism occurs under 388 nm excitation.     

Warm white-light generation in Ca9MgNa(PO4)7:Sr2+, Mn2+, Ln (Ln=Eu2+, Yb3+, Er3+, Ho3+, and Tm3+) under near-ultraviolet and near-infrared excitation

To obtain warm white-light emission, a series of Ca₉MgNa(PO₄)₇:Sr²⁺, Mn²⁺, Ln (Ln=Eu²⁺, Yb³⁺, Er³⁺, Ho³⁺, and Tm³⁺) phosphors were designed and their photoluminescence properties under near-ultraviolet and near-infrared excitation were studied. For near-ultraviolet excitation, blue-white emission is produced initially in the Eu²⁺ single-doped Ca₉MgNa(PO₄)₇, whose excitation band can well match with the near ultraviolet LED chip. By introducing Sr²⁺ ions into Ca₉MgNa(PO₄)₇:Eu²⁺, the Eu²⁺ emission band beyond 500 nm is enhanced obviously. Correspondingly, the emitting light color is tuned to nearly white. To generate warm white light further, Mn²⁺ is doped into the Ca_8.055MgNa(PO₄)₇:0.045Eu²⁺, 0.9Sr²⁺ and the correlated color temperature is decreased largely. For near-infrared excitation, the green, red, and blue emissions have been obtained in the Yb³⁺-Er³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Er³⁺ co-doped Ca₉MgNa(PO₄)₇ phosphors, respectively. And warm white light is also produced in the Ca₉MgNa(PO₄)₇:Yb³⁺, Er³⁺, Ho³⁺, Tm³⁺ under 980 nm excitation.     

Luminescence and structural properties of Gd2SiO5:Eu3+ phosphors synthesized from the modified solid state method

This paper reports the preparation of Eu³⁺ doped Gadolinium oxyorthosilicate (Gd₂SiO₅:Eu³⁺) phosphor with different concentration of Eu³⁺(0.1–2.5 mol%) using the modified solid state reaction method. The synthesis procedure of the Gd₂SiO₅:Eu³⁺phosphor using inorganic materials such as Gd₂O₃, silicon dioxide (SiO₂), europium oxide (Eu₂O₃) and boric acid (H₃BO₃) as flux is discussed in detail. The prepared phosphor samples were characterized by using X-Ray Diffraction (XRD), Field Emission Gun Scanning Electron Microscopy (FEGSEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence (PL) and Thermoluminescence (TL). The Commission Internationale de l′Eclairage(CIE) coordinates were also calculated. The PL emission was observed in the 350–630 nm range for the Gd₂SiO₅:Eu³⁺ phosphor. PL excitation peaks were observed at 266, 275, 312 and 395 nm while the emission peaks were observed at 380, 416, 437, 545, 579, 589, 607, 615 and 628 nm. The emission peak at 615 nm was the most intense peak for all the different Eu³⁺ concentration samples. From the XRD data, using the Scherrer's formula, the average crystallite size of the Gd₂SiO₅:Eu³⁺ phosphor was calculated to be 33 nm. TL was carried out for the phosphor after both UV and gamma irradiation. The TL response of the Gd₂SiO₅:Eu³⁺ phosphor for the two different radiations was compared and studied in detail. It was found that the present phosphor can acts as a single host for red emission (1.5 mol%) for display devices and light emitting diode (LED) and white light emission for Eu³⁺(0.1 mol%) and it might be used as a TL dosimetric material for gamma dose detection.     

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.     

Improved photoluminescence,thermal stability and temperature sensing performances of K+ incorporated perovskite BaTiO3:Eu3+ red emitting phosphors

K⁺ ions incorporated perovskite Ba_(1−x)TiO₃:x Eu³⁺ red emitting phosphors synthesized via facile solid -state reaction method has been investigated in the current study. The photoluminescence and decay time behavior of Ba_(1−x−y)TiO₃:x Eu³⁺,yK⁺ phosphors are investigated as a function of Eu³⁺, K⁺ concentration and temperature. An intense and sharp emission peak at 615 nm was exhibited by the phosphors upon excitation at 397 nm (⁷F₀→⁵L₆). It can be credited to the hypersensitive electric dipole transition ⁵D₀→⁷F₂, which confirms that Eu³⁺ ions are located at non-centrosymmetric site of the host. The incorporation of K⁺ ions in optimized Ba_0.95TiO₃:0.05 Eu³⁺ phosphor resulted in a remarkable enhancement of photoluminescence intensity by 2.33 times as compared to bare one. The Ba_0.89TiO₃:0.05 Eu³⁺, 0.06 K⁺ phosphors were found to observe good temperature sensing along with adequate thermal stability even at 427 K. Furthermore, the photometric parameters have been also studied which are strongly facilitate the prepared ceramic samples as suitable for potential application in lighting.     

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.     

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.     

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.     

LiSr3SiO4Cl3—A novel host lattice for Eu2+-activated luminescent materials

Eu²⁺-activated LiSr₃SiO₄Cl₃ phosphors were successfully designed, and prepared at low calcination temperature (650 °C). The crystal structure, morphology, and photoluminescence properties have been investigated in detail. The LiSr₃SiO₄Cl₃ crystallizes in orthorhombic LiEu₃SiO₄Cl₃-type structure. Under 316 nm excitation, the phosphor exhibits an asymmetric emission band peaking at 495 nm, which is probably attributed to the 4f–5d transitions of Eu²⁺ in various crystallographic sites. Their luminescence properties are investigated as a function of activator concentration (Eu²⁺). The quenching concentration of Eu²⁺ in LiEu₃SiO₄Cl₃ is about 0.01 due to dipole–dipole interaction. The investigation indicates that Eu²⁺-activated LiEu₃SiO₄Cl₃ phosphor can be used as a green emitting phosphor for white LEDs.     

Tunable color emission in LaScO3:Bi3+,Tb3+,Eu3+ phosphor

LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ (x = 0 − 0.04, y = 0 − 0.05, z = 0 − 0.05) phosphors were prepared via high-temperature solid-state reaction. Phase identification and crystal structures of the LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors were investigated by X-ray diffraction (XRD). Crystal structure of phosphors was analyzed by Rietveld refinement and transmission electron microscopy (TEM). The luminescent performance of these trichromatic phosphors is investigated by diffuse reflection spectra and photoluminescence. The phenomenon of energy transfer from Bi³⁺ and Tb³⁺ to Eu³⁺ in LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors was investigated. By changing the ratio of x, y, and z, trichromatic can be obtained in the LaScO₃ host, including red, green, and blue emission with peak centered at 613, 544, and 428 nm, respectively. Therefore, two kinds of white light-emitting phosphors were obtained, LaScO₃:0.02Bi³⁺,0.05Tb³⁺,zEu³⁺ and LaScO₃:0.02Bi³⁺,0.03Eu³⁺,yTb³⁺. The energy transfer was characterized by decay times of the LaScO₃:xBi³⁺, yTb³⁺, zEu³⁺ phosphors. Moreover absolute internal QY and CIE chromatic coordinates are shown. The potential optical thermometry application of LaScO₃:Bi³⁺,Eu³⁺ was based on the temperature sensitivity of the fluorescence intensity ratio (FIR). The maximum S_a and S_r are 0.118 K⁻¹ (at 473.15 K) and 0.795% K⁻¹ (at 448.15 K), respectively. Hence, the LaScO₃:Bi³⁺,Eu³⁺ phosphor is a good material for optical temperature sensing.     

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).     

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

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