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.     

Photoluminescence Properties of Heavily Eu3+‐Doped BaCa2In6O12 Phosphor for White‐Light‐Emitting Diodes

Heavily Eu³⁺‐doped BaCa₂In₆O₁₂ phosphors were prepared by conventional solid‐state reaction, and its structural properties were investigated by means of Rietveld refinement method using an X‐ray source. XRD patterns confirm the hexagonal phase of BaCa₂In₆O₁₂: Eu³⁺ phosphors. The obtained spectrum data indicate that the emission spectra of Ba_1?xEu_xCa₂In₆O₁₂ samples excited at 393 nm exhibit a series of shaped peaks assigned to the ⁵D_0,1,2,3 →⁷F_J (J = 0,1,2,3,4) transitions. Luminescence from the higher excited states, such as ⁵D₁, ⁵D₂, and ⁵D₃, were also observed even though the Eu³⁺ concentration was up to x = 0.4. More importantly, the Ba_1?xEu_xCa₂In₆O₁₂ phosphor still emits white luminescence, when the Eu³⁺ ion concentration is up to x = 0.07 before concentration quenching is observed, which shows that the phosphor is a promising single‐phase phosphor for near ultraviolet (NUV) light‐emitting diodes (LED). Furthermore, the temperature's impact on white luminescent properties was studied. Finally, a white‐light‐emitting diodes (W‐LEDs) fabricated with the Ba_0.95Eu_0.05Ca₂In₆O₁₂ phosphor incorporated with an encapsulant in ultraviolet LEDs (λ_max = 395 nm) is discussed.     

Bright White‐Emitting Phosphors Ba2Gd(BO3)2Cl: Dy3+/Dy3+‐Tm3+ for Hg‐Free Lamps and White LEDs Applications

Spectroscopic properties of Ba₂Gd(BO₃)₂Cl: Dy³⁺ and Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ under vacuum ultraviolet (VUV) and ultraviolet (UV) light excitations were investigated. Dy³⁺ single‐doped Ba₂Gd(BO₃)₂Cl showed broad absorption band in the VUV region, and bright warm white light with chromaticity coordinates (CIE) of (0.340, 0.381) upon VUV excitation at 172 nm, demonstrating this phosphor's applicability in mercury free lamps. Upon direct excitation Tm³⁺ from its ⁶F₆ level to ¹D₂ level, the decrease of emission intensity and lifetime of Tm^{3+ 1}D₂–³F₄ emission with increasing concentration of Dy³⁺ in Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ confirmed the occurrence of energy transfer from Tm³⁺ to Dy³⁺. In addition, Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm³⁺. When 1% Tm³⁺ and 5% Dy³⁺ were codoped in the Ba₂Gd(BO₃)₂Cl, intensive white‐emitting light with CIE of (0.352, 0.328) and correlated color temperature of 4589 K was achieved upon 358 nm excitation, revealing the potential application of Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ for white light‐emitting diodes (LEDs).     

Yellow‐Emitting Y3Si6N11: Ce3+ Phosphors for White Light–Emitting Diodes (LEDs)

A novel Y_3?xSi₆N₁₁: xCe³⁺ yellow phosphor was synthesized using the carbothermal reduction and nitridition method at 1550°C for 16 h in this letter. Photoluminescence spectra indicated that the phosphor showed broad excitation spectrum and had strong absorption in range of 350–450 nm. It also gave a broad emission band (Full width at half maximum = 153 nm) centered at 575 nm under 425‐nm excitation. With increasing Ce³⁺ concentration, the strongest emission intensity was obtained at 5 mol% Ce³⁺ doping amount and a systematic redshift was observed as the Ce³⁺ concentration increased. The results indicate that this novel yellow phosphor is a promising candidate for using in blue‐chip‐excited white light–emitting diodes (LEDs).     

Optical Property of Dy3+‐and Ce3+‐Doped Si–B–Na–Sr Glasses

Novel Dy³⁺ and Ce³⁺ doped Si–B–Na–Sr (SBNS) glasses were synthesized by melt‐quenching technique. Excited by 327 nm, the 0.5Dy³⁺‐and 0.5Ce³⁺‐doped SBNS exhibits white emission with Commission Internationale de L'Eclairage coordinates of (0.308, 0.280). Basic optical characterizations have been performed by measuring the absorption and emission spectra and calculating Judd–Ofelt intensity parameters, radiative probability, luminescence branching ratio, cross sections, and effective bandwidth. The Judd–Ofelt parameters Ω₂, Ω₄, and Ω₆ indicate a high asymmetrical environment and covalent environment in the optical glass. The emission color of Ce³⁺ and Dy³⁺ codoped transparent glass can be tuned from blue to white through energy transfer from Ce³⁺ to Dy³⁺ ions. The resulting glass may have potential application in white‐light‐emitting source.     

Layered Ceramic Phosphors Based on CaAlSiN3:Eu and YAG:Ce for White Light‐Emitting Diodes

To develop warm‐white light‐emitting diodes via conversion phosphors, blue light‐emitting diodes are generally combined with mixtures of green and red‐emitting phosphor powders. Generally, the phosphors are provided by resin embedded particle dispersions. Such resin‐based solutions cause several drawbacks with respect to LED lifetime and quality. Therefore, it has been investigated whether the red‐emitting nitride phosphor CaAlSiN₃:Eu and the green‐emitting oxidic phosphor YAG:Ce can be cofired to layered ceramic composites. The shrinkage behavior and the composition of the interface in dependence of sintering temperature and the effect of interdiffusion processes at the interface on the luminescence properties were investigated. The formation of secondary phases at the interface in the cofired structures was found to limit the phosphor functionality for the nitride‐based CaAlSiN₃:Eu in such composite ceramics. To counteract this, sacrificial interlayers were introduced to produce multilayered ceramics comprising CaAlSiN₃:Eu and YAG:Ce for LED lighting applications. It is shown for the first time, that it is possible to sinter layered CaAlSiN₃:Eu and YAG:Ce composite ceramics in a pressureless process at moderate sintering temperatures if one uses thin‐film passivated interfaces to reduce luminescence‐disturbing diffusion phenomena. These results demonstrate that diffusion barriers can be suitable means to obtain layered ceramic composites comprising CaAlSiN₃:Eu and YAG:Ce in a pressureless sintering process with good optical properties.     

Far‐Red‐Emitting BiOCl:Eu3+ Phosphor with Excellent Broadband NUV‐Excitation for White‐Light‐Emitting Diodes

Rare‐earth ion‐doped semiconducting phosphor has attracted extensive attention due to the ability to achieve efficient luminescence through the host sensitization. Here, we present a new type red‐emitting Eu³⁺ ‐doped BiOCl phosphors possessing a broad excitation band in the near‐ultraviolet (NUV) region. Experimental measurements and theoretical calculations confirm that Eu³⁺ ion dopants result in forming impurity energy level near valence band, and the excellent broadband NUV‐exciting ability of Eu³⁺ ion is due to the electronic transitions of BiOCl band gap. Moreover, the highest emission intensity of the phosphors is from the ⁵D₀ → ⁷F₄ transition of Eu³⁺ around 699 nm (far‐red) through whether host excitation or direct Eu³⁺ ions excitation, which lie in the particular structure of BiOCl crystals. Our results indicate that the Eu³⁺ ‐doped BiOCl crystals show great potential as red phosphors for white‐light‐emitting diodes.     

Fabrication and Luminescence Properties of Transparent Glass‐Ceramics Containing Eu3+‐Doped TbPO4 Nanocrystals

Eu³⁺‐doped transparent phosphate precursor glasses and glass‐ceramics containing TbPO₄ nanocrystals were successfully fabricated by a conventional high‐temperature melt‐quenching technique for the first time. The formation of TbPO₄ nanocrystals was identified through X‐ray diffraction, transmission electron microscopy, high‐resolution transmission electron microscopy, selected‐area electron diffraction, and photoluminescence emission spectra. The obvious Stark splitting of ⁵D₀‐⁷F_J (J = 1, 2, 4) transitions of Eu³⁺and the increase of internal quantum efficiency indicate the incorporation of Eu³⁺ into TbPO₄ nanocrystals. Energy transfer from Tb³⁺ ions to Eu³⁺ ions was investigated using excitation and emission spectra at room temperature. The glass‐ceramics obtained have more efficient Tb³⁺ to Eu³⁺ energy transfer than the glass, and so serve as good hosts for luminescent materials.     

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.     

Cathodoluminescence Properties of Blue Emitting Eu2+‐Doped AlN‐Polytypoids for Field‐Emission Displays

Eu²⁺‐doped AlN‐polytypoids (8H, 15R, 12H, and 21R) were successfully synthesized by nitrogen‐gas‐pressure sintering. The phosphors show intense blue emissions under the electron beam excitation. All the polytypoid phosphors exhibit relatively a smaller degradation in luminance and a higher thermal stability in comparison to the oxide counterparts. Among the polytypoids, 12H has no luminance saturation, and shows a brightness of 40 cd/m² at 3 kV and 100 μA. These results indicate that Eu²⁺‐doped AlN‐polytypoids could also be used as blue phosphors for FEDs.     

Thermal,Structural, and Enhanced Photoluminescence Properties of Eu3+‐doped Transparent Willemite Glass–Ceramic Nanocomposites

The precursor glass in the ZnO–Al₂O₃–B₂O₃–SiO₂ (ZABS) system doped with Eu₂O₃ was prepared by the melt‐quench technique. The transparent willemite, Zn₂SiO₄ (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat‐treatment time was examined by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat‐treatment time which is caused by the partial replacement of ZnO₄ units of ZS nanocrystals by AlO₄ units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass‐ceramics compared with its precursor glass. The photoluminescence spectra of Eu³⁺ ions exhibit emission transitions of ⁵D₀→⁷F_j (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17‐fold with the process of heat treatment. This enhancement is caused by partitioning of Eu³⁺ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid‐state red lasers, phosphors, and optical display systems.     

Structural insights in Dy3+‐doped β‐Tricalcium phosphate and its multimodal imaging characteristics

A series of Dysprosium (Dy³⁺) doped β‐Tricalcium phosphate [β‐TCP, β‐Ca₃(PO₄)₂] were developed for applications in magnetic resonance imaging (MRI) and computed tomography (CT). Characterization studies confirmed the Dy³⁺ occupancy at Ca²⁺(1), Ca²⁺(2), and Ca²⁺(3) lattice sites of β‐Ca₃(PO₄)₂ and its substitution limit was determined as 4.35 mol%. The transitions from the ⁶H_15/2 ground state to various excited energy levels is validated by the characteristic absorption peaks of Dy³⁺. Luminescence studies inferred two intense bands at 480 and 572 nm due to ⁴F_9/2→⁶H_15/2 (blue) and ⁴F_9/2→⁶H_13/2 (yellow) transitions of Dy³⁺. The paramagnetic and nontoxic behavior of Dy³⁺‐doped β‐Ca₃(PO₄)₂ were confirmed from magnetic and MTT tests, respectively. Dy³⁺ in the host induces a high X‐ray absorption ability for X‐ray computed tomography (CT) and showed efficient contrast T₂‐enhancing modality. Thus the proposed system could be used as a promising probe for multimodality with optical imaging, computed tomography and magnetic resonance imaging.     

Phase Transformation in Ca3(PO4)2:Eu2+ via the Controlled Quenching and Increased Eu2+ Content: Identification of New Cyan‐Emitting α‐Ca3(PO4)2:Eu2+ Phosphor

A case of phosphor is reported where the cooling rate parameter significantly influences the luminescence property. By quenching the sample after the high‐temperature solid‐state reaction at 1250°C, we successfully prepared the Eu²⁺‐doped α form Ca₃(PO₄)₂ (α‐TCP:Eu²⁺) as a new kind of bright cyan‐emitting phosphor. The unusual emission color variation (from cyan to blue) depends on the cooling rate after sintering and Eu²⁺ doping level as it was observed in the TCP‐based phosphors. By the Rietveld analysis, it is revealed that the cyan‐ and blue‐emitting phosphors are two different TCP forms crystallizing in the monoclinic (space group P2₁/a, α‐TCP) and the rhombohedral structure (space group R3c, β‐TCP), respectively. Upon 365 nm UV light excitation, α‐TCP:Eu²⁺ exhibits an asymmetric broad‐band cyan emission peaking at 480 nm, while β‐TCP:Eu²⁺ displays a relatively narrow‐band blue emission peaking at 416 nm. The Eu²⁺‐doping in Ca₃(PO₄)₂ shifts the upper temperature limit of the stable structural range of β form from 1125°C to ≥1250°C. Moreover, the crystal structures of α/β‐TCP:Eu²⁺ were compared in the aspects of compactness and cation site sets. The emission thermal stability of α/β‐TCP:Eu²⁺ was comparatively characterized and the difference was related to the specific host structural features.     

Photoluminescence of Sr2P2O7:Sm3+ Phosphor as Reddish Orange Emission for White Light‐Emitting Diodes

A reddish orange emission Sr₂P₂O₇:Sm³⁺ phosphor is prepared by the solid‐state reaction method in air, and the crystal structure and luminescence properties of phosphors are investigated. Sr₂P₂O₇:Sm³⁺ phosphor shows Commission International de I'Eclairage (CIE) chromaticity coordinates (x = 0.5753, y = 0.4147). White light‐emitting diodes (W‐LEDs) fabricated using Sr₂P₂O₇:Sm³⁺ phosphor etc. show CIE chromaticity coordinates (x = 0.3471, y = 0.3124). These results indicate that Sr₂P₂O₇:Sm³⁺ phosphor could be a potential suitable reddish orange emitting phosphor candidate for W‐LEDs with excitation of a ~400 nm n‐UV LED chip.     

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.     

ZrO2/Dy2O3 Solid Solution Nano‐Materials: Tunable Composition,Visible light–Responsive Photocatalytic Activities and Reaction Mechanism

A series of ZrO₂/Dy₂O₃ solid solution nano‐materials with tunable compositions were successfully synthesized by the molten salt–assisted method. Structural characterization results show the positions, intensity, and width of the X‐ray diffraction peaks of products show a regular variation with increasing Dy³⁺ content which implies the gradually changes of crystal spacing and product size. In addition, all the products are single phase without the coexistence of zirconia and Dy₂O₃ further demonstrating the perfect formation of targeted solid solutions. Photocatalytic experiments reveal that Zr_0.8Dy_0.2O_2?δ nano‐crystals have pretty photocatalytic degradation activities on Rhodamine B and Methylene blue under visible light irradiations. Reaction mechanism indicates that the excellent photocatalytic activities of Zr_0.8Dy_0.2O_2?δ nano‐crystals result from the special defect structure, smaller size, and larger specific surface area. It follows that Zr_0.8Dy_0.2O_2?δ nano‐crystals are promising visible light–responsive photocatalysts with better prospect in environmental protection and dye wastewater treatment. Moreover, the present molten salt–assisted route might be generalized to synthesize other solid solution nano‐crystals with more complicated structures.     

Influence of the Eu2+ on the Silver Aggregates Formation in Ag+–Na+ Ion‐Exchanged Eu3+‐Doped Sodium–Aluminosilicate Glasses

Europium‐doping sodium–aluminosilicate glasses are prepared by melt‐quenching method, in which europium ions were spontaneously reduced from their trivalent to divalent state. The silver was introduced into glasses by Ag⁺–Na⁺ ion exchange and the interactions between europium ions and silver species were investigated. Owing to energy transfer (ET) from Ag⁺/silver aggregates to Eu³⁺, significant enhancements of Eu³⁺ emission were observed for 285/350‐nm excitation, respectively. The divalent europium ions promote the formation of silver aggregates in the process of ion exchange.     

Luminescent properties of long‐lasting BaAlxOy:Eu2+,Dy3+ nanocomposites

BaAl_xO_y:Eu²⁺,Dy³⁺ blue‐green phosphor samples were synthesized by a combustion method at the low temperature of 500°C. Phosphor nanocrystallites with high brightness were obtained without significantly changing the crystalline structure of the host. The crystallite sizes determined from the Scherrer equation ranged between 34 and 41 nm. Different volume fractions of the BaAl_xO_y:Eu²⁺,Dy³⁺ powder were then introduced in LDPE polymer. The resulting composites were similarly analyzed and also thermally characterized by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). PL results indicate that the LDPE‐phosphor interface, which is considered to have an influence on the composite behavior, did not significantly change the spectral positions of the phosphor materials, whose major emission peaks occurred at about 505 nm. The improved afterglow results for the composites may have been caused by morphological changes due to increased surface area and defects. Thermal results indicate that the BaAl_xO_y:Eu²⁺,Dy³⁺ particles acted as nucleating centers and enhanced the overall crystallinity in the LDPE nanocomposite while preventing lamellar growth, hence reducing the crystallite sizes in LDPE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dy3+‐Doped Selenide Chalcogenide Glasses: Influence of Dy3+ Dopant‐Additive and Containment

This work reports on process‐induced impurities in rare‐earth ion: Dy³⁺‐doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid‐infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat‐treating Dy‐foil‐only, and DyCl₃‐only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare‐earth additives. The presence of [Ga₂Se₃] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy³⁺‐doped Ge_16.5As₉Ga₁₀Se_64.5 glasses show that Dy‐foil is better than DyCl₃ as the Dy³⁺ additive in Ge‐As‐Ga‐Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy‐foil‐doped chalcogenide glasses, as found for DyCl₃‐doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy₂O₃ and/or [≡Si‐O‐Dy=]‐containing particles during chalcogenide glass melting, which are potential light‐scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α‐Ga₂Se₃ crystals.     

Synthesis and Luminescence Properties of Blue‐Emitting Phosphor Eu2+‐Doped Zinc Fluoro‐Phosphate Zn2[PO4]F

Eu²⁺‐doped zinc fluoro‐phosphate Zn₂[PO₄]F was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction measurements and the structure refinement. The photoluminescence excitation and emission spectra, and the decay curves were measured. The natures of the Eu²⁺ emission in inorganic hosts, e.g., the emission and excitation properties, the chromaticity coordinates, the Stokes shifts, the absolute quantum efficiency, and the luminescence thermal stability were reported. Under the excitation of near‐UV light, Eu²⁺‐doped Zn₂[PO₄]F presents a narrow blue‐emitting band centered at 423 nm. The thermal stability of the blue luminescence was evaluated by the luminescence intensities as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects.