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.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

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.     

Structural and Optical Properties of Tunable Warm‐White Light‐Emitting ZrO2:Dy3+–Eu3+ Nanocrystals

A series of Dy³⁺–Eu³⁺‐codoped ZrO₂ nanocrystals with tetragonal and cubic symmetry was synthesized via a wet chemical reaction. When the Eu³⁺‐doping content was fixed, the crystal structure could be stabilized from the mixed phase to single cubic phase by simply adjusting the content of Dy³⁺. The cubic ZrO₂:Dy³⁺–Eu³⁺ nanoparticles exhibited spherical and nonagglomerated morphology. The effective phonon energy of cubic ZrO₂:5%Dy³⁺–5%Eu³⁺ was calculated to be 445 cm^?1, which is lower than the previously reported results. Extensive luminescence studies of ZrO₂:Dy³⁺–Eu³⁺ as a function of Dy³⁺ content demonstrated that the dopant concentration and its site symmetry play an important role in the emissive properties. Under 352 nm excitation, the increment of Dy³⁺ concentration in ZrO₂:Dy³⁺–Eu³⁺ led to an increase in orange (590 nm) and red (610 nm) emissions of Eu³⁺ ions, which are attributed to the ⁵D₀→⁷F_J(J = 1, 2) transitions of Eu³⁺ ions. This increment is possibly due to the efficient energy transfer (ET) ⁴F_9/2:Dy³⁺→⁵D₀:Eu³⁺. The phosphors can generates light from yellow through near white and eventually to warm white by properly tuning the concentration of Dy³⁺ ions through the ET and change in site symmetry. These phosphors may be promising as warm‐white‐/yellow‐emitting phosphors.     

Warm white light emitting from single composition SrGa12O19:Dy3+ phosphors for AC-LED

Making illumination light sources become comfortable to the human eye is a long-term effort, which justifies the current research on warm white-light-emitting diodes (w-LEDs). In this work, a novel phosphor for w-LEDs, namely SrGa₁₂O₁₉: Dy³⁺(SGO: Dy³⁺), with a low-color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy³⁺ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off-time of a few seconds, which indicates that the SGO: Dy³⁺ phosphor has anti-flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC-LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy³⁺ phosphors with different Dy³⁺ concentrations are close with an optimal doping at 4.00 mol% Dy³⁺ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy³⁺ is a suitable candidate for illumination sources that are beneficial to human health.     

Study on the color tunability and energy transfer mechanism in Tm3+/Dy3+ co-doped LiLaSiO4 phosphors

Many color-tunable LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors were prepared using the traditional high-temperature solid-phase method. The phase composition, surface morphology, fluorescence spectrum, fluorescence lifetime, energy transfer mechanism, and color coordinates of the samples were analyzed using XRD, SEM, TEM and fluorescence spectrometer. The results show that LiLaSiO4: αTm3+ phosphor emits high intensity blue light at 460 nm and the concentration quenching point of Tm³⁺, α = 0.015 mol. In LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors, as the doped Dy³⁺ doping increases, the luminescence intensity of Tm³⁺ gradually decreases, the luminescence intensity of Dy³⁺ first increases and then decreases. The concentration quenching point of Dy³⁺, β = 0.015 mol. Adjustable light-emitting color can be obtained by changing the doping molar mass of Dy³⁺ or the wavelength of the excitation light. There is an effective energy transfer between Tm³⁺→Dy³⁺. The energy transfer mechanism is the electric dipole-electric dipole interaction, and the energy transfer efficiency reaches 90.11% when β = 0.06 mol. The quantum yield of LiLaSiO₄:0.015 Tm³⁺,0.015Dy³⁺ was 39.0%. The single-matrix white light LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors with excellent performance is a prospective material for of white LEDs.     

Near white light emission from K+ ion compensated CaSO4:Dy3+,Eu3+ phosphors

Dy³⁺:Eu³⁺ doped calcium sulfate (CaSO₄:Dy³⁺,Eu³⁺) phosphors co-doped with various K⁺ compensator concentrations were synthesized by recrystallization method. These orthorhombic phased phosphors showed intense multi-color near white light. The multi-color aspect ratios and the emission life times were strongly dependent on K⁺-concentration. These results suggest that the rare-earth (Re³⁺) ions are situated at the sites of Ca²⁺ and the site occupancy was being compensated by K⁺ ions. The near white light emission and large lifetimes suggest that present phosphor could be potentially applied as a blue excited white light-emitting phosphor for light emitting diodes.     

Tunable colors and applications of Dy3+/Eu3+ co-doped CaO-B2O3-SiO2 glasses

A series of Dy³⁺/Eu³⁺ single- and co-doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt-quenching method. A compact glass structure is obtained by the addition of Dy³⁺/Eu³⁺ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy³⁺/Eu³⁺ fill in the interspaces of glass network and contribute to the conversion of [BO₃] to [BO₄]. Dy³⁺/Eu³⁺ co-doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white-emitting glasses have proved the existence of energy transfer. The average lifetime of Dy³⁺ decreases from 0.251 to 0.165 ms with the increasing Eu³⁺ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy³⁺/Eu³⁺ co-doped glass shifts from cyan to white with increasing excitation wavelength. A white-light emission is obtained when the concentration of Dy³⁺ and Eu³⁺ equals to 4% and 2%, respectively. Moreover, the Dy³⁺/Eu³⁺ co-doped calcium borosilicate glass shows high-thermal stability and it may be applicable for high-quality white LEDs based on high power near ultraviolet (n-UV) LED chip in the future.     

Long Afterglow SrAl2O4:Eu2+,Dy3+ Phosphors as Luminescent Down‐Shifting Layer for Crystalline Silicon Solar Cells

SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors can convert near ultraviolet light with lower sensitivity to the solar cell to yellow‐green light at which the solar cell has higher sensitivity and exhibit the excellent luminescent property of long persistence. Therefore, in this study, the authors firstly synthesized the fine SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors and then produced SrAl₂O₄:Eu²⁺,Dy³⁺/SiO₂ composite films as spectral shifters to understand the effects of SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor on photoelectric conversion efficiencies of a crystalline silicon photovoltaic module. Under one sun illumination, the composite film containing an appropriate amount of SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor enhances the photoelectric conversion efficiency of the cell through spectral down‐shifting as compared to the bare glass substrate, and the maximum achieves 11.12%. In contrast, the commercial SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor composite film is not effective for improving the photoelectric conversion efficiency because of the relatively lower visible light transmittance of film caused by the large aggregates. After one sun illumination for 1 min, the light source was turned off, and the cell containing the synthesized SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor still shows an efficiency of 1.16% in the dark due to the irradiation by the long persistent light from SrAl₂O₄:Eu²⁺,Dy³⁺, which provides a possibility to fulfill the operation of solar cells even in the dark.     

Effects of Eu3+ doping on the luminescence properties of novel Sr2CaLa(VO4)3 from partial substitution of Sr2+ by Ca2+ in Sr3La(VO4)3

Eu³⁺-activated Sr_3−xCa_xLa(VO₄)₃ phosphors were fabricated via citric-acid-assisted sol combustion. Characterization of the Sr_3−xCa_xLa(VO₄)₃:Eu³⁺ samples with different concentrations of Ca²⁺ revealed a hexagonal crystal structure belonging to the R-3m space group. The amount of Ca²⁺ added (x) was controlled within 0 ≤ x ≤ 2 to yield high-purity phosphors. Scanning electron microscopy results showed that an increase in Ca²⁺ concentration resulted in a decrease in the particle size of Sr_3−xCa_xLa(VO₄)₃:Eu³⁺, with the shape gradually changing from nearly equiaxed to lath-shaped. The Sr₂CaLa(VO₄)₃:Eu³⁺ phosphor (denoted as SCLVO:Eu³⁺) exhibited the strongest photoluminescence (PL) intensity at 618 nm among the samples under excitation of 394-nm near-UV (NUV) light. The study of Eu³⁺ doping concentration confirmed that Eu³⁺ could enter the lattice of the SCLVO matrix without altering its crystal structure. SCLVO:Eu³⁺ was found to strongly absorb 394 nm NUV light and 464 nm blue light. The optimal concentration of the Eu³⁺ dopant in the SCLVO host was 0.11, which resulted in the phosphor achieving an excellent PL intensity and a color purity of 98.68%. Tunable luminescence from the orange area (0.5280, 0.4522) of Commission Internationale de l'éclairage (CIE) to the red area (0.6313, 0.3650) was achieved by adjusting the concentration of Eu³⁺. Under 394 nm excitation, SCLVO:0.11Eu³⁺ phosphor has a quantum yield (QY) of 28.2% and excellent thermal stability with 0.383 eV activation energy. Consequently, White-light-emitting diode (WLED) based on SCLVO:0.11Eu³⁺ phosphor yielded a high color rendering index (CRI), low correlated color temperature (CCT), and CIE coordinates of 91.8, 5196 K, and (0.3407, 0.3612), respectively, under the 20 mA driven current. These results indicated the tremendous potential of SCLVO:0.11Eu³⁺ phosphors for application in WLEDs excited by NUV or blue light.     

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.     

Strong f–f excitation in hafnium germanate: Near-UV LED and cathode beam–pumped red phosphor with thermal robustness

Developing narrowband red phosphors has always been a frontier topic in the phosphor community. In this study, a novel hafnium germanate red phosphor, BaHfGe₃O₉:Eu³⁺, was successfully synthesized by solid-state reaction method. The phase and crystal structure of BaHfGe₃O₉ were investigated by the Rietveld refinement of powder X-ray powder diffraction. The band structure was analyzed by density functional theory calculations. Most importantly, the luminescence behavior of phosphors under near-ultraviolet (n-UV) light and cathode rays sources was studied in detail to explore the possibility of their applications in white light-emitting diodes and field emission display. The BaHfGe₃O₉:Eu³⁺ phosphor exhibits strong f–f excitation and excellent thermal robustness due to Eu³⁺ localization in the rigid lattice and asymmetric Ba²⁺ sites. Under cathode rays and n-UV light excitation, BaHfGe₃O₉:Eu³⁺ exhibits narrowband red light emission peaked at 610 nm. Moreover, BaHfGe₃O₉:Eu³⁺ shows excellent saturation resistance and aging resistance. The performance of the LED lamp encapsulated by the BaHfGe₃O₉:Eu³⁺ phosphor was studied. The results show that BaHfGe₃O₉:Eu³⁺ is a potential red phosphor for multifunctional applications.     

Synthesis and photoluminescence of novel blue-emitting phosphor of Eu2+-activated fluoroborate BaGaBO3F2

Pure and Eu²⁺-activated fluoroborate BaGaBO₃F₂ was prepared using high-temperature solid-state reaction. BaGaBO₃F₂ is a wide band semiconductor with the indirect transition characteristic. The excitation and luminescence spectra of the phosphor were measured, and it was found that Eu²⁺-activated BaGaBO₃F₂ exhibits a bright blue color under ultraviolet (UV) light. The narrow emission band peaked at 425 nm is attributed to the transitions of 4f⁶5d→4f⁷(⁸S_7/2), and the Stokes shift estimated for this phosphor sample is 3140 cm⁻¹. The lifetime of the luminescence is also reported. The absolute quantum efficiency (QE) of the phosphor was evaluated, and it was found that the absolute QE decreases with increasing Eu²⁺ concentration. The phosphor shows an excellent quantum efficiency of 72.5% and a high thermal activation energy of 0.342 eV. The study concludes that Eu²⁺-doped BaGaBO₃F₂ phosphor has promising luminescence application abilities and can be used as a blue-emitting phosphor in a variety of applications.     

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

LaF₃:Eu nanophosphors were prepared by a traditional hydrothermal method with citric acid as a reducing agent. X-ray diffraction, scanning electronic microscopy, and luminescence spectroscopy were used to study the nanophosphors. The formation of three different luminescence centers of Eu²⁺ and two different luminescence centers of Eu³⁺ is attributed to the existence of abundant surface defects in this nanophosphor. Eu³⁺ is effectively excited by energy transfer from Eu²⁺ to Eu³⁺. The excitation wavelength of Eu³⁺ covers a broad spectral range from 250 to 480 nm. The nanophosphor shows a tunable luminescence color varying from blue to white and then to red, which is explained from three aspects of Eu concentration, energy transfer, and concentration quenching. Utilizing the surface defect of nanoparticles to control the reduction of Eu³⁺ is considered a promising strategy for exploring Eu²⁺ and Eu³⁺ codoped phosphor suitable for the lighting and display application.     

Synthesis,energy transfer mechanism,and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

Structure and Luminescence Characteristics of Eu3+‐Activated Trigonal Layered Perovskite Ba2La2ZnW2O12

Eu³⁺‐doped tungstate Ba₂La₂ZnW₂O₁₂ phosphors with perovskite‐structure were prepared by the high temperature solid‐state reaction. The X‐ray powder diffraction (XRD) patterns and structure refinements indicate that the phosphors crystalized in the trigonal layer‐perovskite. The luminescence properties of the phosphors were investigated such as photoluminescence (PL) excitation and emission spectra, decay lifetimes, and color coordinates. It was found that the pure host shows self‐activated emission excited by the UV light. Moreover, Ba₂La₂ZnW₂O₁₂ also shows scintillation characteristics under the X‐ray irradiation. The near‐UV and blue light can efficiently excite Eu³⁺‐doped Ba₂La₂ZnW₂O₁₂ phosphors inducing the strong orange–red luminescence. The optimal Eu³⁺ doping concentration in this host is 40 mol%. The luminescence spectra and the luminescence color of the phosphors strongly depend on the doping levels and excitation wavelength. The different luminescence features were discussed on the base of crystal structure. Eu³⁺ ions have two possible substitutions on A or B sites in this trigonal layered perovskite. The phosphor could act as a candidate for the potential application in near‐UV excited white‐LEDs lighting.     

Warm-white light performance of Dy3+, Eu3+: NaLa(WO4)2 phosphors excited with a 450-nm LED

Dy³⁺, Eu³⁺: NaLa(WO₄)₂ phosphors are successfully synthesized through the solid-state reaction technique. The phase-structure and morphology are measured via X-ray diffraction and energy dispersive spectrometry. The concentrations of Dy³⁺, Eu³⁺, La³⁺, and W⁶⁺ are measured via ICP. The absorption and excited spectra are presented, which indicate that a blue band ranging from 430 to 480 nm is suitable for excitation. Using a commercial blue LED with a wavelength of 450 nm as the excitation light source, emission spectra for samples with varying dopant concentration ratios of Dy³⁺ to Eu³⁺ are obtained, which show good tunable yellow and red emission. For the purpose of investigating white LED performance, CIE spectra and a white light photo are also presented. The results reveal that varying the dopant concentration ratio of Dy³⁺ to Eu³⁺ plays a key role in the warm-white performance. With increasing concentration of Eu³⁺, the correlated color temperature decreases from 4069 to 3172 K, which indicates good warm-white performance.     

Effects of adding B<Subscript>2</Subscript>O<Subscript>3</Subscript> as a flux on phosphorescent properties in synthesis of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: (Eu<Superscript>2+</Superscript>, DY<Superscript>3+</Superscript> phosphor

SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was prepared by solid state reaction. B₂O₅ as a flux was added in SrAl₂O₄:(Eu ²⁺, Dy³⁺) in order to accelerate a solid state reaction. In this paper, the effects of B₂O₃ on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B₂O₃ contents. The maximum afterglow intensity of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was obtained at the B₂O₃ content of 5%. Adding the B₂O₃ caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and Β angle of the SrAl₂O₄ crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation of Eu²⁺ ions. The afterglow characteristic of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was thus enhanced.     

Highly thermally stable and emission color tunable borate glass for white‐light‐emitting diodes with zero organic resin

White‐light‐emitting glass is a kind of potential bireplacement of both phosphors and epoxy resin in high‐power white‐light‐emitting diodes (WLEDs) because of its high thermal conductivity and excellent thermal stability in aspect of luminescence, CIE chromaticity, and transmittance. In this study, a series of tunable white‐light‐emitting strontium borate (SBO) glass SBO:Tb³⁺,Eu³⁺ were prepared by conventional melt quenching method, and their luminescence properties were systematically studied through their photoluminescence excitation and emission spectra, decay curves, and quantum efficiency. Intense white light emitting can be achieved by in situ mixing of yellowish green and reddish orange emissions from Tb³⁺ and Eu³⁺, respectively, in single glass component SBO, and mixed white emissions can be tuned by Tb³⁺→Eu³⁺ energy transfer with the increasing concentration of energy acceptor Eu³⁺. The quantum efficiency of optimal glass SBO:10%Tb³⁺,6%Eu³⁺ was measured as 36.78%. And the excellent thermal stability of this glass can remain its luminescence intensity above 80% at the temperatures below 523 K. Its chromaticity shift is less than 0.01 at the temperature below 548 K, which is far smaller than that of commercial DS‐200 and triple‐color white‐emitting phosphor mixture. Except all above, the transmittance of this glass hardly shows loss after thermal aging at 120°C for 240 hours, which is superior to the only remaining 58.8% transmittance of epoxy resin. The thermal conductivity of this glass is 0.65 W/mK much better than the 0.16 W/mK of epoxy resin. Based on above research results, SBO:Tb³⁺,Eu³⁺ glass is considered as a promising candidate for high‐power WLEDs, thus a SBO‐WLED is simply assembled by SBO:10%Tb³⁺,6%Eu³⁺ glass and 378 nm LED chip that can present excellent luminescence performance with V=10 V, I=600 mA.