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.     

Energy transfer to Eu(III) in the solid‐state low‐density polyethylene–poly(acrylic acid) and low‐density polyethylene–Fe2O3–poly(acrylic acid) matrices

Ion exchange between H⁺ and Eu³⁺ and/or Tb³⁺ was studied in the material modified by in situ sorption and thermal polymerization of acrylic acid in low‐density polyethylene (LDPE–PAA) and in the composite system LDPE–Fe₂O₃–PAA. Fluorescence spectroscopy showed evidence of Eu³⁺ and/or Tb³⁺ ion exchanges in these materials. The matrix LDPE–PAA after Eu(III) ion exchange presented luminescence (excitation 265 nm). This was explained by an energy‐transfer process from the matrix LDPE–PAA to Eu³⁺ ions. The LDPE–PAA matrix after simultaneous Eu³⁺/Tb³⁺ ion exchange exhibited Eu³⁺ and Tb³⁺ ion luminescence (excitation 265 nm), confirming an energy‐transfer process from LDPE–PAA to Eu³⁺ ions in LDPE–PAA–Eu³⁺–Tb³⁺ matrix. Fe₂O₃ in LDPE–Fe₂O₃–PAA quenched the matrix for excitation at 265 nm and no emission at the region 400 nm was observed. The luminescence of Tb³⁺ ions in the matrix LDPE–Fe₂O₃–PAA–Tb³⁺ (excitation 265 nm) was partially quenched by Fe₂O₃. However, a weak emission of Eu³⁺ ions was observed (excitation 265 nm) in the matrix LDPE–Fe₂O₃–PAA after simultaneous Eu³⁺ and Tb³⁺ ion exchanges, suggesting an energy transfer from Tb³⁺ to Eu³⁺ ions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 919–931, 2000     

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.     

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.     

Eu3+‐Activated Borogermanate Scintillating Glass with a High Gd2O3 Content

Eu³⁺‐activated borogermanate scintillating glasses with compositions of 25B₂O₃–40GeO₂–25Gd₂O₃–(10?x)La₂O₃–xEu₂O₃ were prepared by melt‐quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X‐ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd₂O₃ is of significance for designing dense glass. Furthermore, energy‐transfer efficiency from Gd³⁺ to Eu³⁺ ions can be near 100% when the content of Eu₂O₃ exceeds x = 4, the corresponding critical distance for Gd³⁺–Eu³⁺ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu³⁺ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu₂O₃. The degree of Eu–O covalency and the local environment of Eu³⁺ ions are evaluated by the value of Ω_t parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu–O bond increases with the increasing concentration of Eu³⁺ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X‐ray excitation is found to be in the case of 6 mol% Eu₂O₃, which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X‐ray energy.     

Enhanced visible emissions of Pr3+-doped oxyfluoride transparent glass-ceramics containing SrF2 nanocrystals

The Pr³⁺-doped oxyfluoride transparent glass and glass-ceramic (GC) with the composition of 41SiO₂ + 10Al₂O₃ + 25.5LiF + 23SrF₂ + 0.5Pr₂O₃ were prepared and investigated their optical and luminescence properties. The formation of SrF₂ nanocrystals in GC has been confirmed by X-ray diffraction (XRD) and transmission electron micrographs (TEM). The Fourier transform infrared spectroscopy (FT-IR) studies were used to examine the network structure characteristics of silicates in the glass matrices. The XRD and TEM results suggest that the Pr³⁺ ions are progressively incorporated into the SrF₂ nanocrystals in the GC with increase in time of thermal treatment at 650 °C, corresponding to the first crystallization temperature of the glass. The obtained visible emissions of Pr³⁺-doped GC are several times enhanced than that in the glass and the lifetime of the ³P₀ level of the Pr³⁺ ions in glass and GC are found to be 7 and 12 μs, respectively. Therefore, the enhanced visible emission and lifetimes in GC are due to the incorporation of Pr³⁺ ions into the lower phonon energy of SrF₂ nanocrystals in the GCs. Moreover, the smaller difference in ionic radius between the added trivalent ions (Pr³⁺) and Sr²⁺ induces the larger enhancement of luminescence intensity in the GC. Hence, these enhanced visible luminescence properties indicate that the present glass and GC could be useful for photonic device applications.     

Luminescent properties of MgAl2O4 ceramics doped with rare earth ions fabricated by spark plasma sintering technique

MgAl₂O₄ ceramics doped with rare earth ions (Eu²⁺ and Ce³⁺ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λ_em =?475?nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d–4f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700?nm centered around 500?nm, which can be ascribed to the allowed 4f⁶5d¹→4f⁷ (5d–4f) transition of Eu²⁺. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82?eV caused by F-type centers. It was demonstrated that the Eu²⁺ and Ce³⁺ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail.     

Enhancement of photoluminescence intensity of sintered CaAlSiN3:Eu2+ red phosphor-bismuthate glass composites

Wavelength converters in white light-emitting diodes are usually made by sintering of phosphor-glass powder compacts. An issue is that the sintering process usually results in the reduction of phosphor amount. In the present study, composites containing CaAlSiN₃:Eu²⁺ red phosphor and Bi₂O₃-B₂O₃-ZnO-Sb₂O₅ glass were fabricated by sintering method. Influences of CaAlSiN₃:Eu²⁺ phosphor content (10 vol%–30 vol%) and sintering temperature (410–430°C) on the residual amount of the phosphor phase and the resulting luminescence intensity of the composites were investigated. The change of CaAlSiN₃:Eu²⁺ content due to sintering was analyzed by X-ray diffraction. The interdiffusion between the CaAlSiN₃:Eu²⁺ and glass matrix was examine by scanning electron microscope equipped with energy dispersive X-ray spectrometry. This paper focuses on the change of luminescence intensity after sintering. It was found that although the content of phosphor CaAlSiN₃:Eu²⁺ reduces after sintering; the luminescent intensity of the composites anomalously increases. The optimum luminescence intensity is 14% higher than that of the as-mixed, unfired powder. It is proposed that the incorporation of Bi³⁺ ions from the glass matrix into the phosphor CaAlSiN₃:Eu²⁺ during sintering improves the luminescence ability of the phosphor particles.     

Highly efficient photostimulated luminescence of Pb2+ doped SrAl2O4:Eu2+, Dy3+ borate glass for long-term stable optical information storage

Despite the transformative role in society, information storage materials remain vulnerable to the corrosion by water, oxygen and heat, while topological engineering of glass provides an attractive solution to this tricky problem. Here, a considerable discovery is reported that the doping of Pb²⁺ ions could greatly affect the luminescence behavior of SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass, resulting in a controllable property between long persistent luminescence and photostimulated luminescence. Specifically, high concentration Pb doped samples featuring the deeper continuously distributed trap levels with 0.97–1.47 eV performed highly efficient photostimulated luminescence. In other words, the ultraviolet-visible photons could be “written” in the deeper traps and then “read out” under the stimulation of a 980 nm near-infrared laser. From the combined structural and luminescence characterizations, it was speculated that the deeper trap originated from the increase of oxygen vacancies at defect levels. The practical anti-counterfeiting application was successfully realized based on this material with superior photostimulated luminescence phenomenon, which rendered the SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass shine in a new field such as anti-counterfeiting, yet as a promising candidate for information storage application.     

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.     

Synthesis and Characterization of Eu3+‐Doped Transparent Glass–ceramics Containing Nanocrystalline SrIINbIVO3

The glass–ceramics containing a rarely achievable nanocrystalline Sr^IINb^IVO₃ phase in the 53.75SiO₂–18.25K₂O–9Bi₂O₃–9SrO–9Nb₂O₅–0.5CeO₂–0.5Eu₂O₃ (mol%) glass system were prepared by the melt‐quench technique followed by a two‐stage controlled heat treatment. The unusual oxidation state of Nb in Sr^IINb^IVO₃ crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of Sr^IINb^IVO₃ in the glass–ceramics. The microstructure of the glass–ceramics was studied using TEM and FESEM. The TEM images advocate 10–40 nm crystallite size of Sr^IINb^IVO₃. FTIR study confirms that all the samples consist of SiO₄, BiO₃, BiO₆, and NbO₆ structural units. The refractive index at different wavelengths was found to vary in the range 1.7105–1.7905 and increase with increase in heat‐treatment time. The luminescence spectra of Eu³⁺‐doped glass and glass–ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat‐treatment time due to increase in crystallinity. The high intensity ratio of ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ indicates that the Eu³⁺‐doped nanocrystalline Sr^IINb^IVO₃ glass–ceramics are promising candidate materials as red‐light source.     

Structure and luminescent properties of oxyfluoride glass-ceramics with YF3:Eu3+ nanocrystals derived by sol-gel method

In this paper, the transparent oxyfluoride glass-ceramic materials containing YF₃:Eu³⁺ nanocrystals were fabricated via controlled ceramization of precursor xerogels at relatively low temperature T = 350 °C. The formation of YF₃ nanocrystalline phase from Y(CF₃COO)₃ was verified based on X-ray diffraction (XRD) measurements as well as high-resolution transmittance electron microscopy (HR-TEM). Based on IR-ATR spectroscopy the functional groups inside sol-gel structures were identified. The optical properties of Eu³⁺ ions in fabricated sol-gel samples were investigated based on photoluminescence excitation and emission spectra as well as luminescence decay analysis of the ⁵D₀ excited level. Upon excitation at near-UV illumination, λ_exc = 393 nm, the series of 4f⁶-4f⁶ photoluminescence bands of Eu³⁺ ions in reddish-orange light area were recorded. The Stark splitting of photoluminescence bands, double-exponential character of decay curves and long-lived emission for fabricated glass-ceramic samples clearly evidenced the partial substitution of Y³⁺ by optically active Eu³⁺ ions in precipitated YF₃ nanocrystals. Indeed, it was identified that applied annealing conditions resulted in significant, almost 34-fold prolongation of luminescence lifetime from 0.24 ms (Eu³⁺ ions in xerogel host) up to 8.14 ms (Eu³⁺ ions incorporated into YF₃ nanocrystals). It was also observed a clear correlation between identified phonon energies from IR measurements and luminescence behavior of Eu³⁺ ions.     

Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB₂O₄, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB₂O₄ host lattice are studied for various beta doses ranging from 0.1 to 10?Gy. The high-temperature peak of Eu activated sample located at 192?°C exhibited a linear dose response in the range of 0.1–10?Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB₂O₄ were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu³⁺ ions located at 576–710?nm assigned to the ⁵D₀→⁷F_J (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ was reached Eu³⁺ concentration of 5?mol%; quenching occurred at higher concentrations. Strong emission peak for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ is observed. The CL experimental data indicate that ZnB₂O₄:Eu³⁺ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.     

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.     

Y2O3:Eu3+@SiO2 nanocomposites as a convertor for a broadband solar-blind UV photodetector

Core–shell nanocomposites have attracted extensive attention in the photoelectric field because of their improved material properties and the combination of multiple functions. Particularly, these nanocomposites exhibit tunable structure and excellent optical properties. Inspired by these unique features, a novel optically active nanocomposites, Y₂O₃:Eu³⁺@SiO₂ with a core–shell structure, is designed and fabricated by a hydrothermal method and electrophoretic deposition. In addition, the Y₂O₃:Eu³⁺@SiO₂ composite film is also successfully developed and applied as a spectral down-converter in the solar-blind ultraviolet (UV) waveband region of 200–280 nm. Moreover, a broadband solar-blind UV photodetector device is elaborated and a notable enhancement in the UV sensitivity is achieved. The findings not only provide a new idea for the development of broadband solar-blind UV photodetector but also extended the application range of core–shell nanocomposites in photonics.     

Improving white light emission and quantum yield of Ce@Eu co-doped silicate glass by reducing Eu3+ to Eu2+ with Si3N4

Rare-earth-doped transparent glass shows great potential in white light-emitting diodes (wLEDs) application due to its excellent optical and luminous properties. Currently reported commercial wLEDs have a drawback in red emission missing, which leads to a relatively low color rendering index (CRI) and a relatively high correlated color temperature (CCT). In this work, Ce@Eu Sr–Si–O glass is fabricated using a high-temperature quenching method. The white light is available when the ratio of Ce³⁺/Eu³⁺ equals 1, and the emitting color can be adjusted from blue to red by controlling the ratio of Ce³⁺/Eu³⁺. To further optimize the white light, Eu³⁺ ions can be reduced to Eu²⁺ according to the reaction of 6Eu³⁺ + 2N³⁻ → 6Eu²⁺ + N₂↑ by introducing Si₃N₄. As a result, the standard white light emission can be achieved in the Ce@Eu silicate glass contributed by the blue light from Ce³⁺, red light from Eu³⁺, and yellow–green light from Eu²⁺ (two elements, three emission). This glass shows excellent luminous properties, such as a color coordinate is (0.3651, 0.3269) in CIE 1931 color coordinate diagram, a CRI is over 70, a high quantum yield of 36.02%, and a CCT of 4117 K.     

Eu2+-activated blue-emitting glass phosphor derived from Eu3+ exchanged USY zeolites by thermal treatment in reducing atmosphere

In this work, we report a facile method to prepare Eu²⁺ activated blue-emitting glass phosphor via loading Eu³⁺ into USY (Na₂₈Si₁₆₈Al₂₈O₃₈₄·240H₂O, Si/Al ratio=6) zeolites’ cavities followed by thermal treatment in reducing atmosphere. The zeolites powders containing Eu³⁺ were treated at different temperatures from 800?°C to 1200?°C in flowing 5%H₂ +?95%N₂ ambient. The photoluminescence properties were investigated on aspects of the emission and excitation spectra, internal quantum efficiency (IQE), thermal stability and the fluorescence lifetime. The XRD patterns showed that the sample calcined at 950?°C was of pure glassy state. Under the broad 200–430?nm excitation, a strong blue emission band peaked at 451?nm with a full width of half maximum (FWHM) value of 74?nm was observed for this sample. Under the 365?nm excitation, the samples treated at different temperatures showed monotone red shift in the emission peak wavelengths with the thermal treatment temperature increasing. Transparent glass sheets were obtained from the glass phosphor powders by spark plasma sintering (SPS) at 1200?°C, 1250?°C and 1300?°C. The optical transmittance and thermal conductivity of transparent glass sheets were measured. The results indicated that this glass phosphor may be a potential candidate material for white LEDs.     

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.     

Synthesis and Structural Probing of Eu3+ Doped BaYF5 Nano-Crystals in Transparent Oxyfluoride Glass-Ceramics

Transparent oxyfluoride glass-ceramics containing Eu: BaYF₅ nano-crystals in the newly developed SiO₂–K₂CO₃–BaF₂–YF₃–Sb₂O₃ glass system are synthesized by melt quenching method followed by optimized ceramization process. The X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy confirmed the precipitation of tetragonal BaYF₅ nano-crystals in glass matrix. The coexistence of Eu²⁺ and Eu³⁺ ions in both glass and glass-ceramics are ascertained from their emission and excitation spectra. The in situ formation of divalent europium (Eu²⁺) along with Eu³⁺ during high temperature synthesis under ambient atmosphere is explained through optical basicity model. The Eu³⁺ emission from upper excitation states (⁵D₃₋₁) and reduced asymmetry ratio (R = I_ED/I_MD) in glass-ceramics have established the dopant ion incorporation into fluoride nano-crystalline environment. The observed luminescence properties of Eu:BaYF₅ are compared with that of Eu:BaYF₅ nanocrystals containing transparent glass-ceramics and their marked differences are discussed.     

Processing and Properties of Eu3+‐Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass–Ceramic Nanocomposites

Precursor glasses for the ferroelectric barium bismuth titanate (BaBi₄Ti₄O₁₅) (BBiT) have been prepared by the melt‐quench technique in the SiO₂–K₂O–BaO–Bi₂O₃–TiO₂ (SKBBT) glass system with and without Eu₂O₃ doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X‐ray diffraction (XRD), electron microscopy (FE‐SEM, TEM), and FT‐IR reflectance spectroscopy. FE‐SEM images show the formation of randomly oriented hexagonal rod‐shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT‐IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm^?1. The activation energy of crystallization (E_c) varies from 295 to 307 kJ/mol. The dielectric constants (ε_r) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat‐treated GCs show higher ε_r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the ⁵D₀ → ⁷F₂ transition. An intense 466 nm excitation band corresponding to the ⁷F₀ → ⁵D₂ transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat‐treatment times led to a 15‐fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu³⁺ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam^0.5) values obtained in the GCs are high and suitable for structural applications.