Elaboration,Structure, and Luminescence of Eu3+‐Doped BaLuF5‐Based Transparent Glass‐Ceramics

Novel Eu³⁺‐doped transparent oxyfluoride glass‐ceramics containing BaLuF₅ nanocrystals were successfully fabricated by melt‐quenching technique for the first time. Analyses of XRD patterns prove that the new precipitated glass‐ceramics are crystallized in cubic BaLuF₅ based on isostructural BaGdF₅. Intense red emissions observed in glass ceramics are attributed to the enrichment of Eu³⁺ ions into BaLuF₅ nanocrystals. Besides, obvious stark splitting emissions, low forced electric dipole ⁵D₀→⁷F₂ transition, and long decay lifetimes of Eu³⁺ ions also evidence the partition of Eu³⁺ ions into BaLuF₅ nanocrystals with low phonon energy. Such transparent material may find applications in photonics.     

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.     

Energy transfer,tunable emission and optical thermometry in Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramics

Tb³⁺/Eu³⁺ co-doped glass ceramics containing NaCaPO₄ nanocrystals were successfully synthesized via traditional melt-quenching route with further heat-treatment and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy. The energy transfer process of Tb³⁺→Eu³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results indicated that the efficient emission of Eu³⁺ was sensitized by Tb³⁺ under the excitation of 378 nm, realizing tunable emission in the transparent bulk glass ceramics containing NaCaPO₄ nanocrystals. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺:⁵D₄→⁷F₅ (~542 nm) and Eu³⁺:⁵D₀→⁷F₂ (~612 nm). The maximum absolute sensitivity of 4.55% K⁻¹ at 293 K and the maximal relative sensitivity of 0.66% K⁻¹ at T=573 K for Tb³⁺/Eu³⁺ co-doped transparent NaCaPO₄ glass ceramic are obtained. It is expected that the investigated transparent NaCaPO₄ glass ceramics doped with Tb³⁺/Eu³⁺ have prospective applications in display technology and optical thermometry.     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

Er3+ Ions‐Doped Germano‐Gallate Oxyfluoride Glass‐Ceramics Containing BaF2 Nanocrystals

Er³⁺ ions‐doped germano‐gallate oxyfluoride glass‐ceramic containing BaF₂ nanocrystals was prepared through conventional melt quenching and subsequent thermal treatment method. X‐ray diffraction patterns and transmission electron microscope images confirmed the formation of BaF₂ nanocrystals in glass‐ceramics. Preferential incorporation of Er³⁺ ions into the BaF₂ nanocrystals were confirmed by the absorption spectra and emission spectra, and enhanced upconversion emission and infrared emission were observed. Relatively high transmittance in the mid‐infrared region indicated great potential of this germano‐gallate oxyfluoride glass‐ceramics as host materials for the efficient mid‐infrared emission from rare‐earth ions.     

Investigation of optical properties: Eu with Al codoping in aluminum silicate glasses and glass‐ceramics

Eu‐doped transparent oxyfluoride aluminosilicate glass was prepared by controlling with Al codoping of melt‐quenched glass fabricated under air atmosphere. In the presence of Al input, the photoluminescence emission spectra under 393 nm excitation shows a blue shift by adjusting the ratio of Eu³⁺ and Eu²⁺. After heat treatment of glass, the ratio of Eu³⁺ and Eu²⁺ of luminescence emission were changed by controlling treatment temperature. The PL intensity of Eu³⁺ and Eu²⁺ ions in the glass‐ceramics (GC) was much stronger than in the precursor glass (PG). The possible mechanism responsible for color tuneability of the ratio of Eu³⁺ and Eu²⁺ doped was discussed.     

Novel Upconversion Behavior in Ho3+‐Doped Transparent Oxyfluoride Glass‐Ceramics Containing NaYbF4 Nanocrystals

Novel Ho³⁺ doped highly transparent NaYbF₄ glass‐ceramics were successfully fabricated by melt‐quenching technique. Their structural and luminescent properties were systemically investigated by XRD, TEM, absorption spectra, upconversion spectra, and lifetime measurements. Excited by 980‐nm laser, samples exhibit characteristic emissions of Ho³⁺. Impressively, the luminescent color can be tuned easily from red for precursor glass to green for glass‐ceramics. Such novel phenomenon was elaborately investigated and is owing to the reduced multiphonon nonradiative relaxation and enhanced cross‐relaxation of Ho³⁺ in NaYbF₄ nanocrystals after crystallization. Our results indicate that NaYbF₄ transparent glass‐ceramics is an excellent host for upconversion.     

Enhanced and Long‐Lived Near‐Infrared Luminescence of Er3+ Ions in Lead Borate Glass‐Ceramics Containing PbWO4 Nanocrystals

Lead tungstate PbWO₄ nanocrystals in transparent lead borate glass‐ceramics containing Er³⁺ ions were fabricated. Luminescence spectra at about 1530 nm due to main ⁴I_13/2–⁴I_15/2 laser transition of Er³⁺ ions were examined for glass samples before and after heat treatment. Near‐infrared luminescence of Er³⁺ ions in glass‐ceramics is enhanced and long‐lived in comparison to precursor glasses. It suggests that the Er³⁺ ions are partially incorporated into PbWO₄ crystalline phase.     

Microstructure of Eu3+‐Doped Perovskites‐Type Niobate Ceramic La3Mg2NbO9

Eu³⁺‐doped red‐emitting ceramics of Eu³⁺‐doped La₃Mg₂NbO₉ were prepared via typical solid state. X‐ray diffraction and scanning electron microscope were utilized to characterize the ceramics. The photoluminescence excitation and emission spectra, the fluorescence decay curves, and color coordinates were investigated. The concentration quenching of the samples were discussed as well. The microstructures of the ceramics were discussed according to the spectral properties of probe ions of Eu³⁺, for example, substitution sites for Eu³⁺, inhomogeneous broadening and splitting of the emission bands, nonexponential decay, ⁵D₀→⁷F₀ emission transition, distorted symmetry sites, etc. The crystal structure of La₃Mg₂NbO₉ is heavily distorted due to the mixed occupation of Mg and Nb on B sites. Eu³⁺ ions only substitute La³⁺ sites and Eu³⁺ ions (or rare‐earth ions) are arranged in the heavily disordered environments over the whole structure in La₃Mg₂NbO₉.     

Evolution of Strong Red Upconversion Luminescence in Er3+‐Containing Oxy‐Fluoride Glass and Glass‐Ceramics

The Er³⁺ concentration dependencies of upconversion luminescence in oxy‐fluoride glass and glass‐ceramics containing PbF₂ nanocrystals were investigated. Strong red emission from the ⁴F_9/2 → ⁴I_15/2 transition was observed with the addition of ~0.8 mol% Er³⁺ ions, whereas ~10 mol% of Er³⁺ is required to achieve such emission in several other crystalline hosts. Intensities of red emission further increased with the formation of nanocrystals through heat treatment. The Er³⁺ ions enriched in glass and segregated preferentially inside the PbF₂ nanocrystals that decreased the distance among Er³⁺ ions and thereby facilitated energy transfer.     

Wavelength Tailorability of Broadband Near‐Infrared Luminescence in Cr4+‐Activated Transparent Glass‐Ceramics

Four Cr⁴⁺‐activated transparent glass‐ceramics containing different species of silicate nano‐crystals (Zn₂SiO₄, Mg₂SiO₄, Li₂ZnSiO₄, and Li₂MgSiO₄) were successfully prepared. Absorption spectra, photoluminescence spectra, lifetime decay curves, and quantum yield of these transparent glass‐ceramics were measured. According to the crystal field strength of Cr⁴⁺‐incorporated tetrahedral sites, the broadband near‐infrared (NIR) luminescence of Cr⁴⁺ can be tailored from 1130 to 1350 nm and the lifetime of Cr⁴⁺ luminescence can be prolonged from 6 to 100 μs. Quantum yield in the transparent glass‐ceramics containing Li₂ZnSiO₄ nano‐crystals reached at 17%, which is the highest value of NIR luminescence in transition‐metal‐activated glass materials.     

Elaboration,Structure, and Intense Upconversion in Transparent KYb2F7:Ho3+ Glass‐Ceramics

Novel transparent oxyfluoride glass‐ceramics containing KYb₂F₇:Ho³⁺ nanocrystals were successfully elaborated by melt‐quenching technique with further thermal treatment for the first time. Their structural and luminescent properties were investigated systemically by XRD, HRTEM, absorption spectra, upconversion spectra, and lifetime measurements. Under 980 nm laser excitation, all samples exhibited characteristic emissions of Ho³⁺. Attractively, the upconversion emissions of Ho³⁺, especially green and near‐infrared emissions, were enormously enhanced 190 times after crystallization. The incorporation of Ho³⁺ into KYb₂F₇ nanocrystals with lower phonon energy was responsible for this phenomenon. Our research may enrich the understanding of fluoride‐nanocrystals‐based transparent oxyfluoride glass‐ceramics.     

Structural and luminescence properties of silica powders and transparent glass‐ceramics containing LaF3:Eu3+ nanocrystals

In this work, silica powders and transparent glass‐ceramic materials containing LaF₃:Eu³⁺ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu³⁺‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λ_em = 611 nm) and emission (PL: λ_exc = 393 nm, λ_exc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f⁶‐4f⁶ transitions originated from Eu³⁺ optically active ions (⁵D₀ → ⁷F_J, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu³⁺ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ₁(⁵D₀) = 2.07 ms, τ₂(⁵D₀) = 8.07 ms and τ₁(⁵D₀) = 0.79 ms, τ₂(⁵D₀) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu³⁺ ions from amorphous silica framework to low phonon energy LaF₃ nanocrystal phase.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

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.     

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.     

Eu2+‐Doped Yellow‐Emitting CsBaB3O6 Glass‐Ceramic Prepared by Melt Quenching and Re‐Crystallization Method

Eu³⁺‐doped cesium barium borate glass with the composition of Cs₂O·2BaO·3B₂O₃ was prepared by the conventional melt quenching method. The glass‐ceramic sample was obtained from the re‐crystallization of the as‐made glass to change the amorphous glass into a crystalline host. This reduces the Eu³⁺ in glass to Eu²⁺ ions resulting in a yellow‐emitting phosphor of Eu²⁺‐activated CsBaB₃O₆. The samples were investigated by the XRD patterns and SEM micrograph, the optical absorption, the photoluminescence spectra, and decay curves. The as‐made glass has only Eu³⁺ centers. Under the excitation of blue or near‐UV light, Eu²⁺‐doped CsBaB₃O₆ presents yellow‐emitting color from the allowed inter‐configurational 4f–5d transition in the Eu²⁺ ions. The maximum absolute luminescence quantum efficiencies of Eu²⁺‐doped CsBaB₃O₆ phosphor was measured to be 47% excited at 430 nm light at 300 K. By taking into account the efficient excitation in blue wavelength region, this new phosphor could be a potential yellow‐emitting phosphor for an application in white light‐emitting diodes fabricated with blue chips.     

Fabrication and Characterization of Transparent (Y0.98−xTb0.02Eux)2O3 Ceramics with Color‐Tailorable Emission

Transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ (x = 0–0.04) ceramics with color‐tailorable emission have been successfully fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h. These ceramics have the in‐line transmittances of ~73%–76% at 613 nm, the wavelength of Eu³⁺ emission (the ⁵D₀→⁷F₂ transition). Thermodynamic calculation indicates that the Tb⁴⁺ ions in the starting oxide powder can essentially be reduced to Tb³⁺ under ~10^?3 Pa (the pressure for vacuum sintering) when the temperature is above ~394°C. The photoluminescence excitation (PLE) spectra of the transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics exhibit one spin‐forbidden (high‐spin, HS) band at ~323 nm and two spin‐allowed (low‐spin, LS) bands at ~303 and 281 nm. Improved emissions were observed for both Eu³⁺ and Tb³⁺ by varying the excitation wavelength from 270 to 323 nm, without notably changing the color coordinates of the whole emission. The transparent (Y_0.98Tb_0.02)₂O₃ ceramic exhibits the typical green emission of Tb³⁺ at 544 nm (the ⁵D₄→⁷F₅ transition). With increasing Eu³⁺ incorporation, the emission color of the (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics can be precisely tailored from yellowish‐green to reddish‐orange via the effective energy transfer from Tb³⁺ to Eu³⁺ under the excitation with the peak wavelength of the HS band. At the maximum Eu³⁺ emission intensity (x = 0.02), the ceramic shows a high energy‐transfer efficiency of ~85.3%. The fluorescence lifetimes of both the 544 nm Tb³⁺ and 613 nm Eu³⁺ emissions were found to decrease with increasing Eu³⁺ concentration.     

Influence of LaF3 on the crystallization and luminescence of Eu-doped oxyfluoride glass ceramics

The influence of LaF₃ on the crystallization behavior and luminescence of Eu³⁺ ions in the oxyfluoride borosilicate glass ceramics was investigated in details. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) results indicated that the addition of LaF₃ decreased the glass transition temperature and promoted the crystallization of BaF₂ nanocrystals, which distributed homogeneously in the glassy matrix. A reduction of the lattice parameters of BaF₂ nanocrystals, the obvious Stark splitting of emission peaks and long fluorescence lifetime evidenced the incorporation of Eu³⁺ and La³⁺ into the BaF₂ lattice. Furthermore, experimental results indicated the distribution of Eu³⁺ ions in the oxyfluoride glass ceramics may be modified by the addition of LaF₃ content.     

Enhanced Sunlight Excited 1‐μm Emission in Cr3+–Yb3+ Codoped Transparent Glass‐Ceramics Containing Y3Al5O12 Nanocrystals

Cr³⁺–Yb³⁺ codoped transparent glass‐ceramics containing Y₃Al₅O₁₂ nanocrystals were prepared by heat treatment of as‐prepared glass sample and characterized by X‐ray diffraction and transmission electron microscopy. The efficient energy transfer from Cr³⁺ to Yb³⁺ ions through multi‐phonon‐assisted process was confirmed by the luminescence spectrum and fluorescent lifetime measurements. When excited by the lights from a solar simulator in the wavelength region of 400–800 nm, greatly enhanced near‐infrared emission around 1 μm was achieved from Cr³⁺–Yb³⁺ codoped glass ceramic compared with that from as‐prepared glass and Ce³⁺–Yb³⁺ codoped glass ceramic. These results demonstrate that the Cr³⁺–Yb³⁺ codoped glass ceramic is a promising material for enhancement of the efficiency of solar energy utilization.