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.     

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.     

Dy and Eu activated Ca3B2O6 phosphors for near ultraviolet‐based light‐emitting diodes

The Dy‐ and Eu‐activated Ca₃B₂O₆ phosphors were synthesized by a high‐temperature solid‐state reaction technique and their structural and luminescent properties were investigated. The phosphors are characterized by X‐ray diffraction, photoluminescence spectra, and Commission International de I'Eclairage (CIE) chromaticity coordinates. It is found that the charge compensator Na⁺ plays an important role in modifying the emission spectral profiles of Dy and Eu ions in the phosphors. The ratio of the emission located at the yellow wavelength portion to that located at the blue wavelength region of the Dy³⁺ ions can be apparently tuned by changing the Na⁺ content. The luminescence intensity of the phosphors can be enhanced with introducing Na⁺ ions as well. The emission colors of Dy/Eu codoped phosphors change from blue to white and successfully acquire the superior white light emission (x = 0.330, y = 0.329) by appropriately tuning the Na⁺/Dy³⁺ content and the excitation wavelength. The energy transfer process from Eu²⁺ to Dy³⁺ and Eu³⁺ occurs in the Dy/Eu codoped phosphors, providing a further approach to modify the emission spectral profile of the examined phosphors. The phosphors presented here have promising applications in the fields of 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.     

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

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

White light emission from novel host-sensitized single-phase Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) phosphors

A series of Eu³⁺- or Dy³⁺-doped and Eu³⁺/Dy³⁺ co-doped Y₂WO₆ in pure phase was synthesized via high-temperature solid-state reaction. X-ray diffraction, diffuse reflection spectra, photoluminescence excitation and emission spectra, the CIE chromaticity coordinates and temperature-dependent emission spectra were exploited to investigate the phosphors. Upon UV excitation at 310 nm, efficient energy transfer from the host Y₂WO₆ to dopant ions in Eu³⁺ or Dy³⁺ single-doped samples was demonstrated and those phosphors were suitable for the UV LED excitation. The intense red emission was observed in Y₂WO₆: Eu³⁺, and blue and yellow ones were observed in Y₂WO₆: Dy³⁺. Concentration quenching in Y₂WO₆: Dy³⁺ phosphors could be attributed to the electric dipole-dipole interaction. In Eu³⁺/Dy³⁺ co-doped Y₂WO₆ phosphors energy transfer process only took place from the host to Eu³⁺/Dy³⁺ ions and warm white-light emission can be obtained by adjusting the dopant concentrations. The temperature-dependent luminescence indicated Eu³⁺/Dy³⁺ co-doped Y₂WO₆ was thermally stable. Our overall results suggested that Y₂WO₆: Ln³⁺ (Ln³⁺=Eu³⁺, Dy³⁺) as warm white-light emitting host-sensitized phosphor might be potentially applied in WLEDs.     

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.     

Tuning of emission by effect of local symmetry in BaLaLiWO6:Dy3+/Eu3+ for WLEDs

The luminescence center energy transfer, crystal field strength, and covalency are limited by the crystal structure of the host and subsequently affect the luminescence efficiency, color, and intensity. Here, we report an excellent red phosphor BaLaLiWO₆:0.40Eu³⁺ and the dependence between symmetry and luminous performance. A model for changing symmetry is drawn by analyzing the Coulomb potential and structure for the application of a double-perovskite phosphor BLLWO: Dy³⁺, Eu³⁺ in white light LEDs. The addition of Dy³⁺/Eu³⁺ makes the W-O bond formed by the B-site and oxygen ion longer and the Li-O bond shorter, and the difference between the eight octahedral around the A-site is reduced, increasing the symmetry of the A-site. Local symmetry was successfully modulated by changing the Eu³⁺ concentration to control the Y/B ratio of Dy³⁺ and the R/O ratio of Eu³⁺ and smoothly achieved (0.382, 0.373) warm white light color coordinate. The phosphor has excellent thermal stability and still has 92.3% intensity at 475 K. The above results show that the wavelength composition of the luminescence is tunable by changing the symmetry of the environment in which the doped ions are located. It applies to single hosts for the regulation of white light emission.     

A novel scheelite-type LiCaGd(WO4)3:Eu3+ red phosphors with prominent thermal stability and high quantum efficiency

A series of LiCaGd(WO4)3 : xEu³⁺ (0 ≤ x ≤ 1.0) red phosphors with tetragonal scheelite structure were synthesized via the conventional solid-state reaction. Their crystal structure, photoluminescence excitation (PLE), and photoluminescence (PL) spectra, thermal stability and quantum efficiency were investigated. The phosphors exhibit a typical red light upon 395 nm near ultraviolet excitation, and the strongest emission peak at 617 nm is dominated by the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The PL intensity of the phosphors gradually increases with the increase of Eu³⁺ doping concentration, and the concentration quenching phenomenon is hardly observed. The quantum efficiency and the color purity of the phosphor reach maximum values of about 94.2 and 96.6% at x = 1.0, respectively. More importantly, LiCaGd(WO₄)₃:xEu³⁺ phosphors have prominent thermal stability. The temperature-dependent PL intensity of the phosphors at 423 K is only reduced to 89.1% of the PL intensity at 303 K, which is superior to that of commercial red phosphors Y₂O₃:Eu³⁺. Finally, LiCaGd(WO₄)₃:Eu³⁺ phosphor is packaged with near ultraviolet InGaN chips to fabricate white light emitting diodes, which has a low color temperature (CCT = 4622 K) and a high color rendering index (CRI= 89.6).     

Eu3+-activated double perovskite Sr3MoO6 phosphors with excellent color purity for high CRI WLEDs and flexible display film

A red-emitting Eu³⁺-activated double perovskite Sr₃MoO₆ phosphor material was successfully synthesized by a high-temperature solid-state reaction. Upon 353 and 467 nm excitations, the prepared phosphors exhibited the feature emission properties of Eu³⁺ ions with the corresponding characteristic electronic transitions. The concentration quenching of Eu³⁺ ions was found at 30 mol% and the quadrupole-quadrupole interaction was dominant in quenching process. The chromaticity coordinates for the optimal doping concentration of Eu³⁺ ions under the 353 and 467 nm excitations were in the pure red region, while the color purity was calculated to be about 94.536 and 94.780%, respectively. The superior luminescence properties of the red-emitting Sr₃MoO₆:0.3Eu³⁺ phosphor were achieved and with further blending with commercial phosphors, the white light-emitting diode (WLED) devices were fabricated for practical application. The fabricated WLED device based on 385 nm near-ultraviolet (NUV) chip revealed the color-rendering index and color temperature values of 90.96 and 6381 K, respectively. And the soft polydimethylsiloxane film emitted the pure red region under NUV light. These results suggest that this kind of material could be a promising red-emitting phosphor for WLEDs and flexible display film.     

High luminescent brightness and thermal stability of red emitting Li3Ba2Y3(WO4)8:Eu3+ phosphor

A series of Li₃Ba₂Y_3−x(WO₄)₈:xEu³⁺ (x=0.1, 1, 1.5, 2 and 2.8) phosphors were synthesized by a high temperature solid-state reaction method. Under the excitation of near ultraviolet (NUV) light, the as-prepared phosphor exhibits intense red luminescence originating from the characteristic transitions of Eu³⁺ ions, which is 1.8 times as strong as the commercial Y₂O₂S:Eu³⁺ phosphor. The optimal doping concentration of Eu³⁺ ions here is confirmed as x=1.5. The electric dipole-quadrupole (D-Q) interaction is deduced to be responsible for concentration quenching of Eu³⁺ ions in the Li₃Ba₂Y₃(WO₄)₈ phosphor. The analysis of optical transition and Huang-Rhys factor reveals a weak electron-phonon coupling interaction. The temperature-dependent emission spectra also indicate that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor has better thermal stability than that of the commercial Y₂O₂S:Eu³⁺ phosphor. Therefore, our results show that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor is a promising candidate as red emitting component for white light emitting diodes (LEDs).     

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.     

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.     

X-ray photoelectron spectroscopy and optical analysis of pure white light emitting Dy3+ and Mn2+ codoped Na3Y(PO4)2 phosphors for solid-state lighting

A single-phase and optimized pure white light emitting Dy³⁺-doped and Dy³⁺/Mn²⁺ codoped Na₃Y(PO₄)₂ phosphors (NYPO) were synthesized by traditional solid state reaction process. The as-synthesized phosphors were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectra and photoluminescence studies. The results suggested that the NYPO: Dy, Mn phosphors were crystallized in orthorhombic structures. The presence of dopants Dy and Mn was quantified by XPS analysis. All of the phosphors were effectively excited using a light of wavelength 351?nm and emissions in two regions, blue (~482?nm, ⁴F_9/2→⁶H_15/2) and yellow (~573?nm, ⁴F_9/2→⁶H_13/2), were obtained due to the f-f transitions of Dy³⁺ ions. The maximum intensities of Dy and Mn obtained were 0.07 and 0.05 for NYPO:Dy and NYPO:0.07Dy, Mn, respectively. The chromaticity coordinates, color temperatures, and color rendering indices of NYPO: 0.07Dy ((0.32, 0.33), 6194?K, and 48) and NYPO:0.07Dy, 0.05Mn phosphors ((0.33, 0.33), 5688?K, and 62) were determined. The energy transfer mechanism and oxygen vacancies that arise due to the introduction of Mn²⁺ ions in the NYPO:Dy phosphors, are responsible for the tuning of cool white light to pure day white light. The introduction of Mn in the Dy doped NYPO phosphor enhances the emission intensity in the phosphor.     

Photoluminescence properties of NUV light excited Ba(Mg1/3Nb2/3)O3:Eu3+ red phosphor with high color purity

In this work, a new red phosphor with high color purity, Eu³⁺ ions doped Ba(Mg_1/3Nb_2/3)O₃ phosphor has been prepared by wet chemical method. The structure analysis suggests BMN:x%Eu phosphors have a hexagonal phase and Ba²⁺ ions are replaced by Eu³⁺ ions in BMN. Upon excitation of NUV light, the BMN:x%Eu phosphors emit strong red light around 615?nm, derived from the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The relationship between luminescent properties and structure of BMN:x%Eu was discussed. The Judd-Ofelt intensity parameters (Ω₂, Ω₄) were calculated to analyze the asymmetry of the Eu³⁺ ions site occupancy further, and the quantum efficiency of BMN:3%Eu was found to be 77.26%. In addition, the decay curve indicates the decay time(τ) of BMN:3%Eu is determined to be 1.34?ms and Eu³⁺ ions occupy only one type of site. The CIE chromaticity coordinate (0.656,0.344) of BMN:3%Eu is quite close to the red phosphors standard value (0.670, 0.330), which indicates BMN:x%Eu can be a suitable red phosphor used in NUV-based white LEDs.     

New apatite-type phosphor Ca9La(PO4)5(SiO4)F2:Tb3+,Dy3+ with improved color rendering index

Ca₉La(PO₄)₅(SiO₄)F₂:Tb³⁺,Dy³⁺ (CLPSF:Tb³⁺,Dy³⁺) phosphors were successfully prepared using the traditional solid-state technique. The crystal structure was refined and the luminescence properties have been examined in detail. The band gap and electronic structure of Ca₉La(PO₄)₅(SiO₄)F₂ were performed by the periodic density functional theory (DFT) calculation. The spectral and fluorescence decay dynamics of CLPSF:Tb³⁺,Dy³⁺ show that the energy transfer behavior between Tb³⁺ and Dy³⁺ ions is observed. The CLPSF:Tb³⁺,Dy³⁺ phosphors can be efficiently excitable at the wavelengths range from 300 to 500 nm. The emission spectrum covers the whole visible part of the spectra with the sharp emission bands in red, green, and blue regions. The correlated color temperature (CCT) and color rendering index (CRI) of white light emission could be improved by the fine-tuning of the Tb³⁺ and Dy³⁺ ions ration in accordance with the energy transfer behavior. Thus, the CLPSF:Tb³⁺,Dy³⁺ phosphor could be used as a material for the near-ultraviolet (n-UV) and white light-emitting diodes (w-LEDs).     

Electronic Structure and Luminescence Properties of Phosphor Li8Bi2(MoO4)7: Dy3+

Dy³⁺‐doped Li₈Bi₂(MoO₄)₇ (LBM: Dy³⁺) white‐emitting phosphors have been prepared by sol‐gel method at about 400~550°C low temperature. The electronic structure of Li₈Bi₂(MoO₄)₇ is also calculated using density functional theory. The calculation results show that Li₈Bi₂(MoO₄)₇ has a direct band gap with 2.63 eV, the top of the valence band and the bottom of the conduction band are dominated by O 2p and Mo 4d, respectively. The effect from Bi³⁺ ions is so weak that it could be neglected, which is also be proved by the experimental results. The crystal structure and luminescent properties of the obtained phosphors are characterized by powder X‐ray diffraction and photoluminescence spectrum, respectively. Photoluminescence results showed that the obtained phosphors can be excited efficiently by near‐UV 387 nm and generated white light emission. The yellow/blue ratio and Commission International de I'Eclairage color coordinates could be tuned by adjusting the concentration of Dy³⁺. Results demonstrated that Li₈Bi₂(MoO₄)₇: Dy³⁺ was a potential white light‐emitting phosphor candidate for NUV‐based w‐LEDs.     

Preparation and luminescent modulation of KGaSiO4:Eu3+ phosphors using for multiple anti-counterfeiting

Anti-counterfeiting technology is of great significance to information security. To obtain high-quality anti-counterfeiting materials, the developments of inorganic materials are crucial. In this paper, a series KGaSiO₄:xEu³⁺ phosphors with persistent luminescence, photoluminescence, and thermochromic have been successfully prepared and the application of quadruple anti-counterfeiting is realized. The X-ray diffraction and Rietveld refinement indicate that the phosphors are pure phase. With Eu³⁺ ions doping, the structure change, site occupancies, and color-tunable phenomenon are carefully investigated. Different from another Eu³⁺ doping phosphor, the emission of KGaSiO₄:0.2% Eu³⁺ phosphor changes with the excitation light in the region of 240 nm–306 nm. The emission color can be modulated with the surrounding temperature. Surprisingly, this phosphor can emit green afterglow light, which is attributed to the different luminescent properties of the matrix and doping of Eu³⁺ ions. The series of phosphors exhibit abundant luminescent properties. Based on their wavelength dependence, concentration quenching, long afterglow, and thermochromic properties, the KGaSiO₄:xEu³⁺ phosphors can be effective materials for quadruple-modal anti-counterfeiting devices.     

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.     

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.