Co-doped Transparent Glass Ceramics Research Articles

Luminescence and energy transfer studies of Eu3+-Tb3+ co-doped transparent glass ceramics containing BaMoO4 crystallites

The Tb3+ mono-doped and Eu3+-Tb3+ co-doped transparent glass-ceramics (GCs) were fabricated via melt-quenching technique and subsequent heating. The crystal structural and luminescence properties of the samples were systematically investigated via X-ray diffraction (XRD), scanning electron microscope (SEM), transmittance, excitation and emission spectra, and fluorescence lifetime, respectively. The emission spectra of Tb3+ mono-doped GCs are composed of several sharp emission lines about at 410 nm, 436 nm, 488 nm, 545 nm, 587 nm and 622 nm, respectively. Among them, when the Tb3+ mono-doped concentration is 0.7mol%, the brightest green light is generating at 545 nm due to 5D4→7F5 transition of Tb3+ ions. The effective energy transfer from Tb3+ to Eu3+ was observed by fluorescence spectra and fluorescence lifetimes of Eu3+-Tb3+ co-doped GCs. In addition, the emission of Eu3+-Tb3+ co-doped GCs from light green-white-yellow can be achieved by adjusting the doping concentration of Eu3+ and Tb3+. These results indicate that Eu3+-Tb3+ co-doped GCs have potential applications in the field of white light emitting diodes (w-LEDs).

Preparation and Characterization of Tb<sup>3+</sup>/Eu<sup>3+</sup> Co-Doped Na<sub>2</sub>O-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Glass Ceramics

Tb3+/Eu3+co-doped sodium nepheline transparent glass ceramics with the weight percentage composition of 27Na2O-19Al2O3-23SiO2-13H3BO3-6TiO2-6ZrO2-3Tb4O7-3Eu2O3were prepared by melting crystallization method. The heat treatment system, crystal phase, micromorphology, transmittance and luminescent properties of the samples were tested and characterized by DSC, XRD, SEM, UV-Vis-NIR and fluorescence spectrometer, respectively. The results show that the optimum heat treatment condition of glass at 480°C nucleated 1h and 580°C grew 1h., the crystal phase was NaAlSiO4(35-0424), and the incorporation of rare earth ions did not affect the crystal phase. The transmittance of glass ceramics in the visible area can reach 78%. The effect of different Tb3+/Eu3+doping concentration on the luminescent properties of glass ceramic samples was discussed. It was found that there was a phenomenon of Tb3+to Eu3+energy transfer, and the luminescence effect was best when the percentage of mass of Tb3+/Eu3+was 1:1.

Gd3+ doping induced enhanced upconversion luminescence in Er3+/Yb3+ co-doped transparent oxyfluoride glass ceramics containing NaYF4 nanocrystals

In this article, transparent oxyfluoride glass ceramics containing β-NaYF4 nanocrystals were successfully prepared via Gd3+ doping. Compared to conventional non-doped glasses, the thermal treatment temperature required for the precipitation of β-NaYF4 nanocrystals can be lowered with the doping of Gd3+. Furthermore, under the same thermal treatment condition, more β-NaYF4 nanocrystals were precipitated in Gd3+ doped ones, which greatly improves the luminescence efficiency of rare earth doped glass ceramics. Possible mechanism for the Gd3+ doping induced enhanced upconversion luminescence phenomenon was proposed, based on thorough structural and optical characterizations. The results revealed that the doping of Gd3+ ions could decrease the crystallization activation energy and promote the formation of Y-F-Na bonding, which helps the precipitation of β-NaYF4 nanocrystals. Consequently, a large enhancement in upconversion luminescence was achieved. Moreover, the strategy can be successfully applied to the development of other glass ceramic systems for various optoelectronic applications.

Enhanced up-conversion luminescence and optical thermometry characteristics of Er3+/Yb3+ co-doped transparent phosphate glass-ceramics

Novel Er3+/Yb3+ co-doped transparent glass-ceramics (GCs) containing orthorhombic NaZnPO4 nanocrystals (NCs) were successfully prepared for the first time by a conventional melt-quenching and subsequent heating. Under 980nm laser prompting, the GC samples produced intense red and green up-conversion emissions. The emission intensities varied with Yb3+ concentration and heat treatment conditions. Optimum emission intensities were obtained for the sample with 2mol% of Yb3+ heat treated at 580°C for 4h. Furthermore, the temperature dependent fluorescence intensity ratio (FIR) of thermally coupled emitting states (4S3/2, 2H11/2) in Er3+/Yb3+ co-doped GCs was evaluated under 980nm. A high relative temperature sensitivity of 1.329% K−1 was obtained at 303K and the maximal absolute temperature sensitivity at 612K was evaluated to be 5.732 × 10−3K−1. It is expected that the as-fabricated GCs containing NaZnPO4 NCs are an efficient up-conversion material with potential application in optical temperature sensor.

Efficient near-infrared down conversion in Nd3+-Yb3+ co-doped transparent nanostructured glass ceramics for photovoltaic application

Down conversion involving emission of two near-infrared photons for one ultraviolet photon absorbed was achieved in Nd3+ and Yb3+ co-doped transparent YAG glass ceramics. Upon excitation of Nd3+ ions with an ultraviolet photon at 355nm, Yb3+ ions emitted two near-infrared photons at 980nm through an efficient two-step energy transfer process from Nd3+ to Yb3+. The mechanisms of the two-step energy transfer were verified by spectra and lifetime measurements, and the optimal quantum efficiency achieved was as high as 185.0%, which was close to the theoretical value of 200%. Therefore, the Yb3+ emission centered at 980nm was efficiently enhanced and responded to the strongest absorption of crystalline silicon solar cells. The development of near-infrared down conversion transparent glass ceramics would allow an increase of the energy efficiency of the silicon solar cells.

Effects of crystal structure transformation on cooperative up-conversion luminescence in the Tb3+-Yb3+ co-doped oxyfluoride glass-ceramics

In this study, Tb3+-Yb3+ co-doped transparent oxyfluoride glass-ceramics were prepared respectively from melt-quenched glass samples with the molar compositions of 45SiO2-15Al2O3-12Na2CO3-21BaF2-(7-x)LaF3-xYF3 (x = 0, 1, 3, 6 and 7). It was found that the crystal structure of the annealed glass-ceramics strongly depended on the ratio of YF3/LaF3. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystal structure transformed from cubic Ba2LaF7 phase to cubic intermediate phase and finally to cubic BaYF5 phase, the BaYF5 nanocrystal was determined as cubic structure instead of the reported tetragonal structure for the first time via a Rietveld refinement method with TOPAS. In the process of crystal structure transformation, the local symmetry around Tb3+ ions was infected by different types of irregularly arranged interstitial F- ions, which further affected the effective phonon energy around Tb3+ ions. The high effective phonon energy around Tb3+ ions in the intermediate phase could strongly enhance the up-conversion (UC) luminescence intensity, and thus improved the UC luminescence efficiency.

Up-conversion luminescent properties of Er3+/Yb3+ co-doped transparent glass ceramics containing Na3.6Y1.8(PO4)3 crystals

Er3+/Yb3+ co-doped transparent glass ceramics containing Na3.6Y1.8(PO4)3 crystals were prepared by high-temperature melting and subsequent heat treatment the precursor glass, and their up-conversion luminescent properties were investigated. The optimum heat treatment condition of glass at 630 °C for 2 h were determined by a series of experimental results, and confirmed the existence of Na3.6Y1.8(PO4)3 crystals in glass ceramics. The up-conversion luminescence spectra of the glass ceramic samples under pulsed excitation at 980 nm revealed luminescence bands corresponding to Er3+ ion transitions in the green (4F7/2-4I15/2, 2H12/2-4I15/2,4S3/2-4I15/2) and red (4F9/2 - 4I15/2) spectral regions. The fluorescence spectra reaches a maximum when the molar ratio of Er2O3 to Yb2O3 is 1:7. Luminescence quantum yield of the samples was measured by using an integrating sphere. The transmission spectra proved that the glass ceramics sample still maintained a high transparency up to 83% in the visible region.

Super broadband near-infrared luminescence in Ni2 +-Er3 + co-doped transparent glass ceramics

Ni2+-Er3+ co-doped glass ceramics containing ZnGa2O4 nanocrystals were fabricated by in situ controlled crystallization method. The adverse energy transfer between Ni2+ and Er3+ could be suppressed in the ZnGa2O4 glass ceramics. And the super-broadband infrared luminescence with full width at half maximum (FWHM) of about 400nm covering 1.1–1.7μm wavelength region was observed in Ni2+-Er3+ co-doped glass ceramics. The two lifetimes of 1NE-GC950 revealed that two luminescence mechanism involved in the luminescence process, Ni2+: 3T2g (3F)→3A2g (3F) and Er3+: 4I13/2→4I15/2 respectively. Compared to that in the Ni2+/Er3+ co-doped glass ceramic containing γ-Ga2O3 and LaF3 nanocrystals, the nanocrystals in the present paper is just only one, ZnGa2O4 nanocrystals, and it could also present super-broadband luminescence.

Optical thermometry based on up-conversion luminescence of Tm3+ doped transparent Sr2YF7 glass ceramics

Tm3+/Yb3+ co-doped transparent glass ceramics (GC) containing Sr2YF7 nanocrystals were successfully manufactured by traditional melt-quenching technique. Their structural and up-conversion luminescent properties were systemically investigated through X-ray diffraction (XRD), transmission electron microscope (TEM) and a series of spectroscopy methods. Tremendously enhanced up-conversion emissions with obvious Stark splitting and prolonged luminescence lifetime were observed after crystallization. These optical spectroscopy results manifest that Tm3+ ions have incorporated into the Sr2YF7 crystalline lattice with low phonon energy (~ 400cm−1) after heat-treatment. The 3F2,3 and 3H4 levels of Tm3+ can be explored as thermally coupled energy levels (TCEL) for temperature sensing because of their befitting energy gap (~ 2000cm−1). At the same time, the population of 1G4 state of Tm3+ is indirectly originated from 3H4 one. Therefore the temperature sensing performances of Tm3+ doped Sr2YF7 GC were investigated by fluorescence intensity ratio (FIR) between 3F2,3 → 3H6 and 1G4 → 3F4 up-conversion emissions of Tm3+. Results show that the theoretical maximum value of relative sensitivity SR-max is 1.16%K−1 at 428 K, and absolute sensitivity SA keeps increasing with temperature. Such Tm3+/Yb3+ co-doped Sr2YF7 GC may be excellent candidate for optical temperature sensors.

Structural characterization and temperature-dependent luminescence of CaF2:Tb3+/Eu3+ glass ceramics

Tb3+/Eu3+ co-doped transparent glass ceramics containing CaF2 nanocrystals were successfully synthesized by high temperature melt-quenching method and subsequent heating. The structure and morphology of the samples were investigated by X-ray diffraction (XRD), transmittance electron microscopy (TEM), high resolution TEM (HRTEM) and selected area electron diffraction (SAED). The photoluminescence properties and energy transfer process from Tb3+ to Eu3+ of CaF2:Tb3+,Eu3+ phosphors were also investigated through excitation spectra and decay curves. In addition, the emission spectra of the glass ceramics in a wide temperature range from 21 to 320 K were recorded under the excitation of 485 nm. It was found that the fluorescence intensity ratios of Tb3+ at 545 nm (5D4→7F5) to Eu3+ at 615 nm (5D0→7F2) was highly temperature-dependent with an approximate linear relationship, and the temperature sensitivity was about 0.4%/K. It is expected that the investigated Tb3+/Eu3+ co-doped CaF2 glass ceramics may have prospective application in optical thermometry.

Effects of Li+ ions on the enhancement of up-conversion emission in Ho3+-Yb3+ co-doped transparent glass–ceramics containing Ba2LaF7 nanocrystals

The up-conversion (UC) emission of Ho3+-Yb3+ and Li+ co-doped transparent glass ceramics 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-0.2HoF3-1YbF3-xLi2CO3 (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba2LaF7 nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass ceramics sample without Li+, the UC emission intensity of glass ceramics samples with Li+ were enhanced. It can be proved that the Li+ can affect the enhancement up-conversion (UC) emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the concentration of Li+ increasing up to 4 mol%. Through the comparison and analysis of the energy graph, it was shown that the 5F4/5S2→5I8 transition of Ho3+ ion obtained the green (546 nm) light. There are two weak fluorescences in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the 5F4/5S2→5I7 and 5F5→5I8 transition of Ho3+. Therefore, the emission results showed that the incorporation of Li+ ions into the Ba2LaF7:Eu3+ lattice could induce a remarkable change of the emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that the symmetry of the lattice was destroyed by Li+ in glass ceramics. The possible mechanism responsible for the enhancement of UC emission in Ho-Yb co-doped was discussed.

Luminescence and energy transfer in Dy3+/Tb3+ co-doped transparent oxyfluorosilicate glass-ceramics for green emitting applications

Transparent oxyfluorosilicate glass-ceramics containing cubic SrF2 nanocrystals doped with Dy3+, Tb3+, and Dy3+/Tb3+ were successfully synthesized by melt quenching followed by heat treatment process. The crystalline phase of SrF2 nanocrystals during heat treatment was confirmed by X-ray diffraction. The emission intensity of glass-ceramics is much stronger than that of their parent glasses, on the one hand due to progressive incorporation of Dy3+ and Tb3+ ions within the SrF2 nanocrystals, on the other hand due to an efficient energy transfer from Dy3+ to Tb3+. Luminescence quantum efficiency of the samples was measured by using an integrating sphere. Luminescence decay curves of the 4F9/2 level were fitted to Inokuti-Hirayama (IH) model for analyzing the energy transfer rates between Dy3+ and Tb3+ ions. The chromaticity coordinates were determined from the measured emission spectra and they are located at the green and white light regions.

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 378nm, 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 (~542nm) and Eu3+:5D0→7F2 (~612nm). The maximum absolute sensitivity of 4.55% K−1 at 293K and the maximal relative sensitivity of 0.66% K−1 at T=573K 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.

Luminescent properties of Ce3+/Tb3+co-doped glass ceramics containing YPO4 nanocrystals for W-LEDs

Ce3+/Tb3+ co-doped transparent glass ceramics containing YPO4 nanocrystals were prepared using high temperature melting method, and their structural and luminous properties were investigated. XRD analysis and TEM images confirmed the existence of YPO4 nanocrystals in glass ceramics. The transmission spectra proved that the glass ceramics specimens still maintained a high transparency. Then the excitation and emission spectra of the Ce3+ and Tb3+ single-doped and co-doped glass and glass ceramics were discussed, which proved that the glass ceramics had better luminescent properties. Under the near ultraviolet (331 nm) excitation, the broadband emission located at 385 nm was observed which was ascribed to 5d→2F5/2 and 2F7/2 transition of Ce3+ ions. Several characteristic sharp peaks centered at 489, 543, 578 and 620 nm originated from the 5D4 to 7FJ (J=6, 5, 4, 3) of Tb3+ ions. The decay time of Tb3+ ions at 543 nm and the relevant energy levels of Ce3+ ions and Tb3+ ions illustrated the transfer process from Ce3+ ions to Tb3+ ions. The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as (x=0.3201, y=0.3749), which was close to the NTSC standard values for white (x=0.333, y=0.333). All the results suggested that the YPO4-based Ce3+/Tb3+ co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.

Near-infrared down-conversion in Er3+–Yb3+ co-doped transparent nanostructured glass ceramics for crystalline silicon solar cells

A two-step energy transfer was achieved in Er3+–Yb3+ co-doped transparent glass ceramics containing CaF2 nanocrystals, which involved down-conversion of an absorbed visible photon to two emitted near-infrared photons.

Optical thermometry based on luminescence behavior of Dy3+-doped transparent LaF3 glass ceramics

Dy3+-doped transparent LaF3 glass ceramics were fabricated, and its structures of resulting glass ceramics are studied by the X-ray diffraction and transmission electron microscopy. Optical temperature sensing of the resulting glass ceramics in the temperature range from 298 to 523 K is studied based on the down-conversion luminescence of Dy3+ ion. By using fluorescence intensity ratio method, the 4I15/2 and 4F9/2 of Dy3+ ions are verified as thermally coupled levels. A minimum SR = 1.16 × 10−4 K−1 is obtained at T = 294 K. By doping Eu3+ ion, the overall emission color of Eu3+–Dy3+ co-doped transparent glass ceramics can be tuned from white to yellow with the temperature increase through energy transfer between Eu3+ and Dy3+. Additionally, the thermal stability of the Dy3+ single-doped transparent glass ceramics becomes higher after doping Eu3+ ion.

Tb3+/Eu3+: YF3 nanophase embedded glass ceramics: Structural characterization, tunable luminescence and temperature sensing behavior

Tb3+/Eu3+ co-doped transparent bulk glass ceramics containing orthorhombic β-YF3 nanocrystals were successfully synthesized by melt-quenching and subsequent heating. The partition of the active centers into the YF3 crystalline lattice was confirmed by elemental mapping in the scanning transmission electron microscope, emission spectra and decay curves. As a consequence, Tb3+ → Eu3+ energy transfer was demonstrated to be more efficient in the glass ceramic than in the precursor glass, which resulted in color tunable luminescence by simply modifying Eu3+ content and induced the linearly temperature-dependent fluorescence intensity ratio between the Tb3+: 5D4 → 7F5 transition and the Eu3+: 5D0 → 7F4 one in the Tb3+/Eu3+ co-doped glass ceramic. It is expected that the investigated glass ceramic might be a promising candidate for solid-state lighting as well as optical temperature sensor.

Optimizing Nd/Er ratio for enhancement of broadband near-infrared emission and energy transfer in the Er3 +–Nd3 + co-doped transparent silicate glass-ceramics

The optimizing Nd/Er ratio for enhancement of broadband near-infrared (NIR) emissions in the Er3+–Nd3+ co-doped SiO2–AlF3–BaF2–TiO2–CaCO3 (SABTC) transparent silicate glass-ceramics containing BaF2 nanocrystals under 808nm excitation was investigated. The broadband NIR emission bands from 850 to 1700nm, which covered the whole O, E, S, C, L and U bands were observed in the Er3+–Nd3+ co-doped glass-ceramics samples, as a result of the overlap of Nd3+-doped emission band centered at 1342nm and the emission from 4I13/2→4I15/2 transition of Er3+ band centered at 1546nm. The NIR emission intensity of Er3+–Nd3+ co-doped bands centered at 895, 1065, 1342 and 1546nm, becomes stronger with varied depending on the mixing ratio of Nd3+ and Er3+ ions, and the full width at half-maximum (FWHM) extending from 1250 to 1700nm could be 340nm. Most NIR emission bands at 1065 and 1546nm are observed for the SABTC-1.0N0.4E glass-ceramics sample, corresponding to Nd/Er ratio of 2.5. At the same time, the energy transfer processes between the Nd3+ and Er3+ ions were also discussed.

Color-tunable luminescence in Eu3+/Tb3+ co-doped oxyfluoride glass and transparent glass–ceramics

The β-PbF2 nanocrystals containing SiO2–AlF3–BaF2–PbF2–GdF3 transparent glass–ceramics were fabricated by high temperature melting–quenched technique, and their luminescence properties were investigated. Transparent glass–ceramics were obtained after heat treatment at their first crystallization temperature. Compared with the glass samples before heat treatment, high efficiency luminescence of Eu3+/Tb3+ co-doped was observed in the glass–ceramics under excitation 377nm, and the emission intensity of Eu3+-doped showed different tendency to that emission intensity of Tb3+-doped after nanocrystals precipitate, resulting in color tunable luminescence. In addition, the energy transfer between the Eu3+ and Tb3+ ions are also investigated. The results suggest that the Eu3+/Tb3+ co-doped transparent glass–ceramics could be potentially applicable in the solid-state color displays.

Ultraviolet Light Induced White Emission of Eu3+ and Dy3+ Co-Doped Oxyfluoride Glass-Ceramics Containing LaF3 Nanocrystals

Dy3+ single doped and Dy3+-Eu3+ co-doped transparent glass-ceramics (GC) containing hexagonal LaF3 nanocrystals were fabricated by melt-quenching method and subsequent heating. XRD, TEM, absorption and emission spectra were used to investigate the structural and luminescent properties of resulting GC. Excited by 390 nm, the Dy3+-Eu3+ co-doped GC exhibited bright white emission with CIE coordinates 0.345, 0.333. Judd-Ofelt intensity parameters, radiative probability, luminescence branching ratio, cross-sections and effective bandwidth were calculated. The Judd-Ofelt parameters (Ω2, Ω4 and Ω6) have indicated that GC has a high asymmetrical and covalent feature. The resulting GC may be used in the white light emitting diode fields.