Co-doped Glass Ceramics Research Articles

Enhanced upconverted emission in Yb3+/Er3+ co-doped GdPO4 transparent glass ceramics

Yb3+/Er3+ co-doped transparent glass ceramics (GC) containing GdPO4 nanocrystals have been successfully fabricated using a conventional melt-quenching method with subsequent heat treatment. The structural and the luminescence properties were investigated by X-ray diffraction, transmission electron microscopy, and upconverted emission spectra. Under the excitation of a 980nm diode laser, the total upconverted emission in GC as well as the Green/Red emission intensity ratio in the GC670 sample was enhanced compared to that in the precursor glass, indicating that Er3+ ions have entered into GdPO4 nanocrystals after crystallization. Our results also show that the Green/Red emission intensity ratio of GC is closely related to crystallinity of the samples. The outstanding properties of GdPO4-based transparent GC provide a promising candidate for wide application fields, such as in all-solid-state upconversion lasers and optical fibers.

Near-infrared down-conversion in Pr3+–Yb3+ co-doped transparent glass ceramic containing Ca5(PO4)3F nanocrystals

Pr3+–Yb3+ co-doped transparent oxyfluoride glass ceramics containing Ca5(PO4)3F nanocrystals were synthesized by a melting-quenching method. Spectral analyses demonstrate that Pr3+ and Yb3+ ions are both incorporated into the Ca5(PO4)3F nanocrystals. Near-infrared down-conversion around 1000nm was observed when the glass ceramics were excited at 435nm. The maximum actual down-conversion efficiency for 0.3mol% Pr3+–0.8mol% Yb3+ co-doped glass ceramic is about 125%.

Behavior of Yb3+ and Er3+ during Heat Treatment in Oxyfluoride Glass Ceramics

The effects of alumina content and heat treatment on upconversion properties of codoped (ErF3‐YbF3) oxyfluoride glass ceramics were investigated. Results showed that alumina content had an effect on phase separation and viscosity of the glass. Due to the high viscosity of low alumina content glass, the phase separated areas were smaller in these specimens. Increasing the heat treatment temperature led to the incorporation of Er3+ ions into CaF2 crystals and also increased the Yb3+ concentration in them. This increase improved the energy transfer and back transfer process between Er3+ and Yb3+ ions and as result upconversion intensity was increased.

Spectroscopic properties and mechanism of Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals

Transparent Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode (LD), compared with the glass before heat treatment, the Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark-split peaks; X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm3+, Er3+ and (or) Yb3+ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm3+, Er3+ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.

Upconversion in Nd–Tm–Yb triply doped oxyfluoride glass–ceramics containing CaF2 nanocrystals

Upconversion and energy transfer processes in Nd3+–Tm3+–Yb3+ triply doped oxyfluoride glass–ceramics containing CaF2 nanocrystals have been studied. Under 792nm excitation, we investigated the strong blue emission from Tm3+ ions in Tm3+–Yb3+, Tm3+–Nd3+, and Nd3+–Tm3+–Yb3+ doped glass–ceramics. The Nd3+–Tm3+–Yb3+ doped glass–ceramics has shown the strongest blue emission via a multiple-step energy transfer processes following the ground state absorption of Tm3+ and Nd3+ ions. In the Nd3+–Yb3+ doped glass–ceramic, much enhanced visible emission was observed due to the back transfer from Yb3+ ions. However, under 980nm excitation of Yb3+ ions, the triply doped glass–ceramics showed slightly weaker visible upconversion emission than the Tm3+–Yb3+ and Nd3+–Yb3+ co-doped glass–ceramics. Detailed upconversion mechanisms for observed emissions were suggested.

Optical Investigations in Er<sup>3+</sup>/Yb<sup>3+</sup> Co-Doped Nanostructured Phosphate Glass Ceramics

Er3+/Yb3+co-doped transparent phosphate glass ceramics were fabricated and characterized optically. The formation of nanocrystals is confirmed by x-ray diffraction. Stark split near infrared emission peaks of Er3+have been observed in the glass ceramics, and the effective bandwidth increases with increasing annealing temperature. Upconversion emissions of Er3+in the glass ceramics under 975nm wavelength excitation, especially in the green wavelength region, are enhanced. The results can be attributed to the enhancement of ligand field due to incorporation of Er3+ions into the crystal lattices.

Study of the focusing effect of silica microspheres on the upconversion of Er3+–Yb3+ codoped glass ceramics

• Silica microspheres have been located on the surface of glass and glass ceramics samples codoped with Er and Yb. • Microspheres act as microlens of the 950 nm excitation light resulting in focalized excited regions in the samples with sizes under the micron. • Intense red upconversion is achieved in the focalized areas. • Microspheres collect the upconversion emission light, scoping with the together microlensing properties an enhancement of the detected signal in a 3x factor. • Performed Finite-Difference Time-Domain simulations predict the size of the focalized regions in good agreement with the experimental measurements. The upconversion emission properties of Er 3+ –Yb 3+ codoped glass and glass ceramic samples with different Si/Al ratios and thermal treatments were analyzed by covering their surfaces with silica microspheres (3.8 μm diameter). A 950 nm laser beam is focused by the microspheres producing a set of photonic nanojets near the surface of the samples. After the upconversion processes of the Er 3+ ions located in each microsphere focus area, these ions emit light in the green and red regions. The red emission from each sample was measured, yielding an upconversion intensity in the focal areas three times higher than the emission from the bare substrate. To estimate the real size of the red emission area under a single microsphere, a deconvolution of the measured focal spots with the Point Spread Function of the experimental setup was performed, resulting in a Full Width at Half Maximum of 330 nm. The results obtained by Finite-Difference Time-Domain simulations are in good agreement with the experimental values.

Near-infrared quantum cutting in Pr3+-Yb3+ Co-doped oxyfluoride glass ceramics containing CaF2 nanocrystals

The Pr3+-Yb3+ co-doped oxyfluoride glass-ceramics containing CaF2 nanocrystals were obtained by thermal treatment on the as-made glasses. The structure of fluoride nanocrystals was investigated. The light-emitting mechanism of Pr3+-Yb3+ in the near infrared region was proposed and the fluorescence lifetime and quantum efficiency was calculated. The results indicate that the main phase in the oxyfluoride glassceramics is CaF2 nanocrystal sized at 30 nm. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) have proved the incorporation of Pr3+ and Yb3+ into CaF2 nanocrystal lattice. Near-infrared quantum cutting involving Yb3+ 980 nm and 1 015 nm (2F5/2→2 F 7/2) emission has been achieved upon the excitation of the 3 P 0 energy level of Pr3+ at 482 nm. The fluorescence lifetime decreases sharply and quantum efficiency increases with increasing Yb3+ concentration, and the optimal quantum efficiency reaches 191%.

Fabrication, photoluminescence, and potential application in white light emitting diode of Dy3+–Tm3+ doped transparent glass ceramics containing GdSr2F7 nanocrystals

Dy3+–Tm3+ doped transparent glass ceramics containing GdSr2F7 nanocrystals were fabricated successfully by a melt-quenching method and subsequent heating. X-ray diffraction and transmission electron microscopy analyses show that tetragonal GdSr2F7 nanocrystals are homogeneously precipitated among the borosilicate glass matrix. If excited with 354 nm UV light, the photoluminescence spectrum of Dy3+ single-doped transparent glass ceramics shows white-light emission. With doping of Tm3+, the overall emission color of Tm3+–Dy3+ co-doped transparent glass ceramics can be tuned from white to blue through energy transfer between Dy3+ and Tm3+. CIE chromaticity and color temperature measurements show that the resulting TGCS may be a candidate as a white LED material pumped by a UV InGaN chip.

Enhancement of infrared emission in Er3+ , Yb3+ co-doped sodium niobium tellurite nano glass-ceramics

In the present work, sodium niobium tellurite (SNT) glass-ceramics co-doped with Er2O3 and Yb2O3 were prepared and analyzed. Initially SNT glasses were prepared using high pure chemicals namely TeO2, Nb2O5, Na2CO3, B2O3, and SiO2. DTA analysis was performed to identify the glass transition (Tg) and crystallization (Tc) temperatures. Following the data of DTA, the initial host glass was annealed at different temperatures (450, 550, and 650 °C). From the XRD pattern, glass annealed at 650 °C is taken to be optimized temperature for the formation of glass-ceramics from the host glass. The glass-ceramics thus formed were found to be translucent rather transparent. Similar procedure is followed to form Er3+ single doped and Er3+, Yb3+ co-doped SNT glass-ceramics. It was found that the crystallite size in the glass-ceramics calculated from the Debye Scherrer's formula is around the nano scale. Optical absorption and Judd–Ofelt (J–O) calculations were done for the transparent glasses doped with the rare earths. Radiative properties were also estimated from the J–O parameters. NIR emission spectra specifically observing the 1.5 µm luminescence of Er3+ ion in the doped glasses and glass-ceramics were recorded. It was found that nano glass-ceramics co-doped with Er3+ and Yb3+ ions were of maximum efficiency compared to single Er3+ doped SNT glass which could be used for fiber amplifiers in the NIR region.

Up- and down-conversion in Yb3 +–Pr3 + co-doped fluoride glasses and glass ceramics

Pr3+–Yb3+ co-doped transparent ZrF4-based bulk and planar waveguide glass ceramics (GCs) have been fabricated using the physical vapor deposition. X-ray diffraction and transmission electron microscopy analysis have shown the presence of a single crystalline phase that belongs to the LaF3–ZrF4 system. Upon 980nm excitation, blue, orange and red emissions have been obtained both in bulk and waveguides. Intense luminescence of Yb3+ ions has been observed after excitation at 476nm and is ascribed by to energy transfer (ET) from Pr3+ to Yb3+. The ET efficiency was estimated to be 92% for 0.5mol% Pr3+–10mol% Yb3+ co-doping.

Enhanced green upconversion in Tb3+–Yb3+ co-doped oxyfluoride glass ceramics containing LaF3 nanocrystals

Tb3+–Yb3+ co-doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals were successfully fabricated by the melt-quenching technique in air atmosphere. The structural and luminescent properties were systemically investigated by X-ray diffraction, transmission electron microscopy and upconversion spectra. All samples exhibited intense characteristic emissions of Tb3+ (5D4→7FJ (J=3−6) and 5D3→7FJ (J=4−6)) under 980nm laser excitation. Besides, the upconversion intensity in glass ceramics was stronger than that in precursor glass and increased with crystallinity degree, which could be ascribed to the incorporation of Tb3+ and Yb3+ ions into LaF3 nanocrystals with low phonon energy. Laser power dependence of upconversion proved two-photon process was responsible for green emission.

Infrared to Visible Up‐Conversion Emission in Er3+/Yb3+ Codoped Fluoro–Phosphate Glass–Ceramics

Erbium Er3+ and ytterbium Yb3+ codoped fluoro‐phosphate glasses belonging to the system NaPO3–YF3–BaF2–CaF2 have been prepared by the classical melt‐quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV–visible and near‐infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X‐ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite‐type cubic crystals based during the devitrification process. Finally, infrared to visible up‐conversion emission upon excitation at 975 nm has been studied on the Er3+ and Yb3+ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up‐conversion emissions–about 150 times‐ has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare‐earth ions (REI) into the crystalline phase.

Enhanced ~ 2 μm and upconversion emission from Ho–Yb codoped oxyfluoride glass ceramics

Enhanced 2μm and upconversion emission from Ho3+–Yb3+ codoped oxyfluoride silicate glass ceramics containing nanocrystals Ba2YbF7 was demonstrated. Ho3+–Yb3+ codoped oxyfluoride silicate glass and glass ceramics containing nanocrystals Ba2YbF7 were fabricated. Fluoride nanocrystals Ba2YbF7 were successfully precipitated in glass matrix, which was confirmed by the X-ray diffraction (XRD), and transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) spectrometer results. 2μm and upconversion emissions were obtained from these glass examples under 980nm excitation. Compared with the precursor glass, enhanced 2μm and upconversion luminescence was measured in the glass ceramics, which were due to scattering by the formed nanocrystals, lower phonon energy obtained in the nanocrystals and efficient Yb3+–Ho3+ interionic interactions. Therefore, the material investigated in this study could find potential application in 2μm laser gain media or upconversion light material.

Color variety of up-conversion emission of Er3+/Yb3+ co-doped phosphate glass ceramics

The sample of Er3+/Yb3+ co-doped phosphate glass ceramic was prepared. At 975 nm laser diode (LD) excitation, the strong up-conversion (UC) emissions were observed, which were the UC green emission at 510–570 nm and the UC red emission at 636–692 nm, respectively. At low pump power (126 mW), the red emission is primary, and the color purity Rcp is 0.81. With the increasing of pump power, the emission color gradually varies from red to green. The intensity of the green emission is stronger compared to that of the red emission at high power (868 mW), and the color purity Rcp is 0.76. Thus, this material can be applied to fluorescence anti-counterfeiting by the color variety of UC emission under different pump power.

Mechanism of quantum cutting in Pr3+–Yb3+ codoped oxyfluoride glass ceramics

Quantum cutting of 0.44μm photon into 1.0μm and 1.3μm photons was demonstrated in Pr3+–Yb3+ codoped oxyfluoride glass ceramics by spectroscopic investigation from blue to near-infrared region. The Pr3+–Yb3+ codoped sample showed energy transfer (Pr3+:3P0→1G4)→(Yb3+:2F5/2←2F7/2). Both under 0.44μm and 0.94μm excitations, the codoped sample showed Pr3+:1G4→3H4 luminescence at 1.3μm, as well as Yb3+:2F5/2→2F7/2 luminescence at 1.0μm. The relative intensity of (Pr3+:1.3μm/Yb3+:1.0μm) by 0.44μm excitation was much higher than that by 0.94μm excitation. The mechanism of downconversion was proposed as a quantum cutting process by one-step energy transfer (Pr3+:3P0→1G4)→(Yb3+:2F5/2←2F7/2), which results in generation of two near-infrared photons via the Pr3+:1G4→3H5 and Yb3+:2F5/2→2F7/2 transitions.

Fabrication and luminescence behavior of phosphate glass ceramics co-doped with Er3+ and Yb3+

Transparent phosphate glass ceramics co-doped with Er3+ and Yb3+ in the system P2O5Li2OCaF2TiO2 were successfully synthesized by melt-quenching and subsequent heating. Formation of the nanocrystals was confirmed by X-ray powder diffraction. Judd–Ofelt analyses of Er3+ ions in the precursor glasses and glass ceramics were performed to evaluate the intensity parameters Ω2,4,6. Under 975nm excitation, intense upconversion (UC) and infrared emission (1545nm) were observed in the glass ceramics by efficient energy transfer from Yb3+ to Er3+. The luminescence processes were explained and the emission cross section was calculated by Fuchtbauer–Ladenburg (F–L) formula. The results confirm the potential applications of Er3+/Yb3+ co-doped glass ceramics as laser and fiber amplifier media.

Preparation and luminescence properties of Ce3+/Dy3+-codoped fluorosilicate glass ceramics

The Ce3+and Dy3+ co-doped fluorosilicate glass and glass ceramics containing SrF2 or CeF3 nanocrystals were prepared under reducing atmosphere. The precipitated nano-crystalline phase shifted from cubic SrF2 to hexagonal CeF3 gradually with the heat treatment temperature increasing from 620 to 680 °C. The glass and glass ceramics emitted white light, deriving from a combination of the Ce3+ blue and the Dy3+ yellow light. The CIE coordinates could be tuned by adjusting the ratio of Ce3+/Dy3+ concentration. The luminescence could be enhanced significantly by annealing the samples at the temperatures lower than 640 °C.

Optimizing Er/Yb ratio and content in Er–Yb co-doped glass-ceramics for enhancement of the up- and down-conversion luminescence

Er3+–Yb3+ co-doped transparent glass-ceramics with varying Er/Yb content and ratio have been prepared. High quantum yields for up- and down-conversion luminescence by energy transfer from Yb3+ to Er3+ and from Er3+ to Yb3+, respectively, have been detected and optimized with respect to the Er/Yb content and ratio, and proposed in particular for up- and down-conversion of solar spectrum for enhancement of the efficiency of solar cells. The rise and decay kinetics for the population of the excited levels of Er3+ and Yb3+ have been studied and fit. Based on these experimental data, the mechanisms for the energy transfers have been suggested with emphasis on the optimized Er/Yb content and ratio for enhancement of the efficiency of the Er3+↔Yb3+ energy transfers.

Effects of Annealing Temperature and SiO2 Matrix on the Structure and Optical Properties of Co-Doped ZnAl2O4/SiO2 Nanoglass–Ceramic Composites

Co-doped glass–ceramics containing spinel nanocrystals attach much attention as optical materials. The composition and preparation conditions of the material will influence its structure and optical properties. In this study, the samples (100–x)Co0.1Zn0.9Al2O4–xSiO2 (x = 0–95) were prepared by the sol–gel method and characterized by X-ray powder diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy were used to study the chemical environments of cations and oxygen in the nanocomposites as a function of annealing temperature and SiO2 concentration. The results show that all the samples are composed of a silica matrix and enclosed ZnAl2O4 nanocrystalline particles. Besides the tetrahedral, octahedral, and second octahedral coordination sites present in Co0.1Zn0.9Al2O4 nanocrystals, the five-coordinate sites of Al3+ ions are observed in the nanocomposites. The inversion parameter (two times the fraction of Al3+ ions in the tetrahedral sites) ...