Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

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.     

Enhanced Light Storage of SrAl2O4 Glass‐Ceramics Controlled by Selective Europium Reduction

A luminescent Eu, Dy: SrAl₂O₄ glass‐ceramics with high transparency in the visible region was successfully synthesized using the frozen sorbet technique with the control of O₂ partial pressure () for the oxidation of Eu²⁺ ions. The glass‐ceramics include Eu²⁺, Eu³⁺, and Dy³⁺ ions, and thus exhibits three characteristic types of emission bands, 4f–5d at around 520 nm (Eu²⁺ ions), 4f–4f at 610 nm (Eu³⁺ ions), and 480 nm (Dy³⁺ ions). The Eu, Dy: SrAl₂O₄ glass‐ceramics provide remarkable long‐persistent luminescence under dark condition. The glass‐ceramics also exhibits color‐changing luminescence in the visible region based on their remarkable light storage properties. The luminescent Eu, Dy: SrAl₂O₄ glass‐ceramics using the frozen sorbet technique with control of are promising materials for application in novel photonic and light storage materials.     

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.     

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.     

Luminescence Properties and Energy‐Transfer Behavior of a Novel and Color‐Tunable LaMgAl11O19:Tm3+, Dy3+ Phosphor for White Light‐Emitting Diodes

Novel LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphors were prepared utilizing a high‐temperature solid‐state reaction method. The phase formation, luminescence properties, energy‐transfer mechanism from the Tm³⁺ to the Dy³⁺ ions, the thermal stability, and CIE coordinates were investigated. When excited at 359 nm, the LaMgAl₁₁O₁₉: xTm³⁺ phosphors exhibit strong blue emission bands at 455 nm. After codoping with Dy³⁺ and excitation at 359 nm, the LaMgAl₁₁O₁₉:0.03Tm³⁺, yDy³⁺ phosphors emitted white light consisting of the characteristic emission peaks of Tm³⁺ and Dy³⁺. The Dy³⁺ emission intensity increased with the Dy³⁺ concentration due to the energy transfer from Tm³⁺ to Dy³⁺, and concentration quenching due to the high Dy³⁺ doping concentration (y = 0.1 mol) did not occur. The calculation of the CIE coordinates of the LaMgAl₁₁O₁₉:Tm³⁺, yDy³⁺ phosphors revealed the tunability of the emission color from blue to bluish‐white and to white by changing the excitation wavelength and the doping concentration. An energy transfer from Tm³⁺ to Dy³⁺ by dipole–dipole interaction was confirmed by the decay curve, lifetime, and energy‐transfer efficiency measurements. When excited at 359 nm, the LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphor also showed good thermal stability, suggesting that it can be used in white LEDs excited by a GaN‐based ultraviolet LED.     

Eu‐Doped β‐SiAlON Phosphors: Template‐Assistant Low Temperature Synthesis,Dual Band Emission,and High‐Thermal Stability

A hard template route has been successfully developed for synthesis of β‐SiAlON:Eu phosphors at low temperatures. The synthesis utilizes mesoporous silica (SBA‐15) skeleton as an active Si source, combined with the carbothermal reduction and nitridation method. It has been shown that the additional driving force from high surface area and porosity of SBA‐15 enables β‐SiAlON:Eu (with compositions of Si_6?zAl_z?xO_z+xN_8?z?x: xEu, x = 0.010–0.200 and z = 1.000) phosphors to be formed as a dominant phase at low temperature of 1400°C. The resultant β‐SiAlON:Eu phosphor powders exhibit a typical rod‐like morphology and a well dispersed state. By tailoring the Eu²⁺ concentration in the phosphors, a continuous change in emission band can be realized, that is a blue emission dominated for low Eu²⁺ concentrations and a green emission dominated for high Eu²⁺ doping concentrations. Furthermore, the resultant phosphors exhibit a small thermal quenching up to high temperature of 250°C. Therefore, the developed method is beneficial to synthesize LED phosphors of oxynitride systems at lower temperatures.     

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.     

Effect of Tm3+ Ions on the White Light Emission of Dy3+–Tm3+ Codoped SrMg2La2W2O12 Phosphors

Dy³⁺–Tm³⁺ ions codoped SrMg₂La₂W₂O₁₂ (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high‐temperature solid‐state reaction method. X‐ray analysis of the end products revealed the well‐crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand‐to‐metal charge‐transfer state (LMCT) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg₂La₂W₂O₁₂:Dy phosphors exhibited single exponential, where as the codoped SrMg₂La₂W₂O₁₂:DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage (CIE) coordinates using the photoluminescence data. The color of singly doped SrMg₂La₂W₂O₁₂:Dy phosphor has been tuned by codoping with Tm³⁺ ions. It has been noticed that the CIE chromaticity coordinates (x,y) determined from the luminescence spectrum of singly Dy³⁺ doped SrMg₂La₂W₂O₁₂ phosphor shifted toward the white light region, when codoped with Tm³⁺ ions. The increase in correlated color temperatures (T_cct) has been noticed with the increase of Tm³⁺ ions concentration in SrMg₂La₂W₂O₁₂:DyTm phosphors.     

The tri-emitting phosphate phosphors SrIn2(P2O7)2: Tm,Dy, Eu for ratiometric optical thermometer

Developing new phosphors used for ratiometric optical thermometers has attracted broad attention recently. According to the recent research, the phosphate SrIn₂(P₂O₇)₂ with regard to the structural rigidity has been adopted as the host of Tm and Dy activators behaving the super-stable white emission. Herein, Tm, Dy, Eu tri-doped phosphors were prepared to investigate the interaction of three different activators and their coupling sensitivity to temperature. Based on concentration control and energy transfer among three activators, the tunable emission, including the idea warm white, has been obtained. In the case of increasing temperature, the emission intensities of Dy³⁺ and Eu³⁺ partially decrease, whereas the Tm³⁺ fluorescence extremely keeps increasing to 155.4% of 473 K compared with that of room temperature. This phenomenon can be defined the negative thermal-quenching. It is believed that the back energy transfer (BET) from Dy³⁺ and that from Eu³⁺ to Tm³⁺ help the negative thermal-quenching of Tm³⁺ to a certain extent. Both cation occupation and structural rigidity obviously affect the BET efficiency. In the new phosphors, the fluorescence intensity ratios of Tm³⁺ and Eu³⁺ (blue/red) and (blue/orange) of Tm³⁺/Dy³⁺ are closely related to temperature and vary linearly over a wide temperature range, which can be regarded as an important index of temperature sensor. The SI_1.92P: T_0.01D_0.01E_0.06 shows excellent temperature sensitivity and recyclability. The current results show that SrIn₂(P₂O₇)₂: Tm, Dy, Eu phosphors can be regarded as candidate materials for optical thermometry.     

A novel dazzling Eu3+‐doped whitlockite‐type phosphate red‐emitting phosphor for white light‐emitting diodes

A series of novel red‐emitting Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors were successfully synthesized using the high‐temperature solid‐state reaction method. The crystal structure, photoluminescence spectra, thermal stability, and quantum efficiency of the phosphors were investigated as a function of Eu³⁺ concentration. Detailed analysis of their structural properties revealed that all the phosphors could be assigned as whitlockite‐type β‐Ca₃(PO₄)₂ structures. Both the PL emission spectra and decay curves suggest that emission intensity is largely dependent on Eu³⁺ concentration, with no quenching as the Eu³⁺ concentration approaches 100%. A dominant red emission band centered at 611 nm indicates that Eu³⁺ occupies a low symmetry sites within the Ca₈ZnLa(PO₄)₇ host lattice, which was confirm by Judd‐Ofelt theory. Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors exhibited good color coordinates (0.6516, 0.3480), high color purity (~96.3%), and high quantum efficiency (~78%). Temperature‐dependent emission spectra showed that the phosphors possessed good thermal stability. A white light‐emitting diode (LED) device were fabricated by integrating a mixture of obtained phosphors, commercial green‐emitting and blue‐emitting phosphors into a near‐ultraviolet LED chip. The fabricated white LED device emits glaring white light with high color rendering index (83.9) and proper correlated color temperature (5570 K). These results demonstrate that the Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors are a promising candidate for solid‐state lighting.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>,<Emphasis Type="Italic">RE</Emphasis><Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and Dy³⁺ codoped strontium aluminates SrAl₂O₄: Eu²⁺,Dy³⁺ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu²⁺ ion doped in SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy³⁺ ion introduced into SrAl₂O₄: Eu²⁺ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy³⁺ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE ³⁺ ions have a different effect on persistent luminescence. Only the RE ³⁺ ions (for example, Dy³⁺ and Nd³⁺), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl₂O₄: Eu²⁺. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated. The text was submitted by the authors in English.     

Dy3+/Ce3+ Codoped YAG Transparent Ceramics for Single‐Composition Tunable White‐Light Phosphor

Superior optical, thermal, and mechanical properties of transparent ceramics are very important in the applications of solid lasers, solid‐state lighting, and transparent armors. Herein, a series of (Dy_0.03Ce_xY_0.97?x)₃Al₅O₁₂ transparent ceramics were fabricated using vacuum reactive sintering method. Importantly, these Dy³⁺/Ce³⁺ codoped yttrium aluminum garnet (YAG) transparent ceramics served as single‐composition tunable white‐light phosphors for UV‐LEDs is developed for the first time. By combining with commercially available UV‐LEDs directly, the optimal chromaticity coordinates and correlated color temperature (CCT) are (x = 0.33, y = 0.35) and 5609 K, respectively. Notably, the codoping of Ce³⁺ enhances the luminescent intensity of Dy³⁺ ions while excited at 327 nm. The emission color of YAG transparent ceramics can be tuned from white to yellow through energy transfer between Dy³⁺ and Ce³⁺. These new phosphors, possessing of pure CIE chromaticity and environmentally friendly nature, are promising for applications in white UV‐LEDs.     

Structure and Luminescence of New Red‐Emitting Materials‐Eu3+‐Doped Triple Orthovanadates NaALa(VO4)2 (A = Ca,Sr, Ba)

The new red‐emitting phosphors of Eu³⁺‐doped triple orthovanadates NaALa(VO₄)₂ (A = Ca, Sr, Ba) were prepared by the high‐temperature solid‐state reaction. The formation of single phase compound with isostructural structure of Ba₃(VO₄)₂ was verified through X‐ray diffraction (XRD) studies. The photoluminescence excitation and emission spectra, the fluorescence decay curves and the dependence of luminescence intensity on doping level were investigated. The phosphor can be efficiently excited by near UV and blue light to realize an intense red luminescence (613 nm) corresponding to the electric dipole transition ⁵D₀→⁷F₂ of Eu³⁺ ions. Their potential applications as red‐emitting phosphors for solid‐state lighting were evaluated in comparison with the Eu³⁺‐doped lanthanum orthovanadate LaVO₄ and other reported references. The luminescence was discussed in detail on the base of the crystal structures. The luminescence thermal stability on temperature was investigated and the thermal activated energy was calculated. The phosphors can be suggested to be a potential red‐emitting phosphor for the application on white LEDs under irradiation of near‐UV or blue chips.     

Effect of Al/Sr ratio on the luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

Recent studies have brought out many phosphors like Eu²⁺, Dy³⁺-doped alkaline earth aluminates. The trivalent Dy³⁺ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission.In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu²⁺ and Dy³⁺ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis.A variety of strontium aluminates, such as SrAl₂O₄, Sr₄Al₂O₇, Sr₃Al₂O₆, Sr₃Al₂(Eu, Dy, Y)O_7.5, Al₅(Eu, Dy, Y)O₁₂, Sr₄Al₁₄O₂₅, SrAl₁₂O₁₉ and (Eu, Dy, Y)AlO₃ have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl₄O₇ phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl₂O₄ phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition.     

Improved Blue‐Emitting AlN:Eu2+ Phosphors by Alloying with GaN

A method is designed to improve the luminescence of AlN‐based phosphors by tuning the band structure and crystal structure due to alloying with GaN. The pure (Al,Ga)N:Eu phosphors were initially prepared by gas‐phase reaction in an NH₃ atmosphere. GaN alloying was used to expand the crystal lattice of AlN due to Ga³⁺ substituting for smaller Al³⁺ ions, making dissolution of Eu²⁺ easier. The dissolution of Ga in the AlN lattice was proven by the result of the Rietveld refinement and the increase in lattice parameters with increasing Ga content. To introduce other energy states mixing with the 5d states of Eu²⁺, Ga doping was also used to tune the band structure of AlN by acting on Eu²⁺ ions. The theoretical result was analyzed using the Cambridge Sequential Total Energy Package (CASTEP). According to the calculated total and atom resolved partial density of states, it was observed that the Ga 5p states contribute a large portion to the corresponding Eu²⁺ absorption band in (Al,Ga)N:Eu phosphors. As a consequence, an enhanced emission intensity at 470 nm and a high quantum efficiency for excitation at 330 nm was obtained despite of stronger thermal quenching of the (Al,Ga)N:Eu phosphors compared with AlN:Eu.     

Ce3+‐ and Dy3+‐Doped Oxyfluoride Borosilicate Glasses with Near White Luminescence

A series of Ce³⁺/Dy³⁺‐doped oxyfluoride borosilicate glasses prepared by melt‐quenching method are investigated for light‐emitting diodes applications. These glasses are studied via X‐ray diffraction (XRD), optical absorption, photoluminescence (PL), color coordinate, and Fourier transform infrared (FT‐IR) spectra. We find that the absorption and emission bands of Ce³⁺ ions move to the longer wavelengths with increasing Ce³⁺ concentrations and decreasing B₂O₃ and Al₂O₃ contents in the glass compositions. We also discover the emission behavior of Ce³⁺ ions is dependent on the excitation wavelengths. The glass structure variations with changing glass compositions are examined using the FT‐IR spectra. The influence of glass network structure on the luminescence of Ce³⁺/Dy³⁺ codoped glasses is studied. Furthermore, the near‐ideal white light emission (color coordinate x = 0.32, y = 0.32) from the Ce³⁺/Dy³⁺ codoped glasses excited at 350 nm UV light is realized.     

White light emission from Eu co-activated Ca2Gd8Si6O26:Dy nanophosphors by solvothermalsynthesis

Ca₂Gd₈(SiO₄)₆O₂ (CGS) nanophosphors with different concentrations of single-doped Dy³⁺ ions and co-doped Dy³⁺/Eu³⁺ ions were prepared by a solvothermal synthesis. Very fine particles in the nanometer range could be achieved by this method, as evidenced by transmission electron microscope measurements. The hexagonal phase of the oxyapatite structure was confirmed by X-ray diffraction patterns. The energy transfer between Eu³⁺ and Dy³⁺ ions was investigated by photoluminescence excitation and emission properties. These phosphors had absorption bands in the UV and NUV region, which are suitable for the emission wavelength of UV or NUV light-emitting diodes (LEDs). With increasing the Eu³⁺ ion concentration, the emission peak intensity corresponding to the ⁵D₀→⁷F₂ transition increased and the yellow (⁴F_9/2→⁶H_13/2) emission intensity also increased compared to the blue (⁴F_9/2→⁶H_15/2) emission intensity due to the increased energy transfer between Dy³⁺ to Eu³⁺ ions. Thus, the Eu³⁺ ions compensated the red emission component of the Dy³⁺ doped CGS nanophosphors. Such phosphors are expected to have potential applications for NUV based white LEDs.     

Synthesis,Structure, and Thermally Stable Luminescence of Dy3+‐Doped Na3YSi2O7 Host Compound

Dy³⁺‐activated Na₃YSi₂O₇ phosphors have been prepared via a solid‐state reaction technique and may be used as a component of white light‐emitting diodes. X‐ray diffraction analysis demonstrates the single‐phase formation and the substitution of activator ions for Na₃YSi₂O₇:Dy³⁺ materials. The emission of Dy³⁺ in different Y³⁺ lattice sites exhibits blue (⁴F_9/2→⁶H_15/2) and yellow (⁴F_9/2→⁶H_13/2) lights, which function together to generate white light. The optimum doping concentration is 3 mol% and energy transfer between Dy³⁺ ions has been validated to be a resonant type via an electric dipole–dipole mechanism. The temperature‐dependent luminescent properties from 25°C to 400°C are studied, and the blue emission increases as a function of the temperature. This interesting phenomenon is proposed to be the result of the model in the configurational coordination diagram. The present investigation reveals the potential application for Na₃YSi₂O₇:Dy³⁺ system in solid‐state lighting.     

Preparation,luminescence properties and energy transfer of Ca9Y(PO4)7: Eu2+‐Tb3+ phosphors

Tb³⁺‐doped and Eu²⁺, Tb³⁺ co‐doped Ca₉Y(PO₄)₇ phosphors were synthesized by conventional solid‐state method. Additionally, the luminescence properties, decay behavior and energy transfer mechanism have already been investigated in detail. The green emission intensity of Tb³⁺ ions under NUV excitation is weak due to its spin‐forbidden f‐f transition. While Eu²⁺ can efficiently absorb NUV light and yield broad blue emission, most of which can be absorbed by Tb³⁺ ions. Thus, the emission color can be easily tuned from cyan to green through the energy transfer of Eu²⁺→Tb³⁺ in Ca₉Y(PO₄)₇:Eu²⁺,Tb³⁺ phosphor. In this work, the phenomenon of cross‐relaxation between ⁵D₃ and ⁵D₄ are also mentioned. The energy transfer is confirmed to be resulted from a quadrupole‐quadrupole mechanism.