Co-doped Oxyfluoride Glass Research Articles

Comparative Investigation of Optical Properties in Tm<sup>3</sup><sup>+</sup>/Er<sup>3</sup><sup>+</sup>/Yb<sup>3</sup><sup>+</sup> Co-Doped Oxyfluoride Tellurite and Germanate Glasses

Tm3+/Er3+/Yb3+co-doped oxyfluoride tellurite and germanate glasses have been synthesized by conventional melting method. Intense up-conversion (UC) luminescence emissions were simultaneously observed under 980 nm excitation at room temperature in two glasses. The possible UC mechanisms are discussed and estimated. However, in the studied Tm3+/Er3+/Yb3+co-doped oxyfluoride glasses, tellurite glass showed weaker UC emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between oxyfluoride tellurite and germanate glasses. Absorption spectrum and Raman spectroscopy were employed to investigate the origin of the difference in UC luminescence in two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is another important factor in determining the UC efficiency.

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.

Highly sensitive optical thermometry through thermally enhanced near infrared emissions from Nd3+/Yb3+ codoped oxyfluoride glass ceramic

Under 980nm diode laser excitation, the near infrared (NIR) emissions originated from the 4F7/2/4S3/2→4I9/2 (∼750nm), 4F5/2/2H9/2→4I9/2 (∼803nm), and 4F3/2→4I9/2 (∼863nm) transitions of Nd3+ ions in Nd3+/Yb3+ codoped oxyfluoride glass ceramic were obtained and studied as a function of temperature in the range of 303–623K. It was observed that these NIR emissions were greatly enhanced with the increase of temperature. An explanation based on the luminescence decay curves was given, and it was found that the thermally enhanced phonon-assisted energy transfer (ET) from Yb3+ to Nd3+ played an important role in such phenomenon. In addition, by using the fluorescence intensity ratio technique, the optical thermometry behavior based on the NIR emissions of Nd3+ ions was investigated. Using the 750 and 863nm emissions from the Nd3+/Yb3+ codoped glass ceramic, higher sensitivity for temperature measurement can be achieved compared to the previous reported rare earth ions fluorescence based optical temperature sensors. Due to its thermally enhanced NIR emissions, the Nd3+/Yb3+ codoped oxyfluoride glass ceramic is a promising candidate for optical temperature sensors with high sensitivity and good accuracy.

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.

An optical temperature sensor based on the upconversion luminescence from Tm3+/Yb3+ codoped oxyfluoride glass ceramic

Abstract An optical temperature sensor based on the upconversion luminescence of Tm3+ has been developed. Under a 980 nm diode laser excitation, the fluorescence intensity ratio (FIR) between 700 (Tm3+:3F2,3 → 3H6) and 800 nm (Tm3+:3H4 → 3H6) upconversion emissions from Tm3+/Yb3+ codoped oxyfluoride glass ceramic was studied as a function of temperature in the range of 293–703 K. The 3F2,3 and 3H4 states of Tm3+ are verified to be thermally coupled levels. By using FIR technique, the sensitivity for detecting temperature variations achieved here is better than previous reported rare earth ions fluorescence based temperature sensors. With the advantages of intense upconversion luminescence and absolutely separated 700 and 800 nm emission bands, the Tm3+/Yb3+ codoped oxyfluoride glass ceramic is a very promising candidate for accurate optical temperature sensors with much higher sensitivity and resolution.

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.

Visible to near-infrared down-conversion luminescence in Tb3 + and Yb3 + co-doped lithium–lanthanum–aluminosilicate oxyfluoride glass and glass-ceramics

Tb3+ and Yb3+ co-doped oxyfluoride glasses were fabricated in a lithium–lanthanum–aluminosilicate matrix (LLAS) by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion luminescence was studied for glass and glass-ceramic samples with different Yb3+ concentrations. It has been found that the luminescence intensity at 940–1020nm from Yb3+ ions increases while the emission lifetime of Tb3+ ions decreases in the glass-ceramic compared to that in the as-prepared glass, which indicates that the energy transfer efficiency increases in the glass-ceramics compared to that in the as-prepared glass. The down-conversion luminescence also increased for increasing Yb3+ concentration from 1mol% to 2mol%, but decreased for the sample with a high Yb3+ co-doping concentration of 8mol%, which is attributed to the concentration quenching.

A discussion on spectral modification from visible to near-infrared based on energy transfer for silicon solar cells

We report on spectral modification from visible to near-infrared (NIR) in Pr3+ and Yb3+ codoped oxyfluoride glass for c-Si solar cell. The excitation and emission spectra indicate the energy transfer from Pr3+ to Yb3+. The theoretical quantum efficiency is calculated based on the fluorescent lifetime and has reached more than 150%. However, the external quantum efficiency (EQE) of the Pr3+ and Yb3+ codoped glass covered on silicon solar cell is decreased compared to that of the host glass. The reasons of the negative effect of spectral modification on EQE are discussed and analyzed.

The Preparation and Photoluminescence Properties of Fluorosilicate Glass Ceramics Containing CeF3:Dy3+ Nanocrystals

Ce3+ and Dy3+ co-doped oxyfluoride glasses and glass ceramics containing CeF3 nanocrystals are prepared in a reducing atmosphere. XRD measurements and the calculated lattice parameters suggest that Dy3+ ions are incorporated with precipitated CeF3 nanocrystals along with a rise in the Dy3+ concentration or an increase in the annealing temperature. The glass ceramics emit white light close to the CIE coordinates of (0.3,0.3), derived from a combination of Ce3+ and Dy3+ emission. The CIE chromaticity coordinates of the Ce3+ and Dy3+ co-doped glass ceramics can be tuned by varying the ratio of Ce3+/Dy3+, while the luminescence intensity can be enhanced by heat treatment above 620°C.

Enhanced visible to near-infrared quantum cutting in Tb and Yb co-doped oxyfluoride glass-ceramic

ABSTRACTTb and Yb co-doped oxyfluoride glasses were fabricated in a lithium-lanthanum-aluminosilicate matrix by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion quantum cutting was studied for samples with different thermal annealing temperatures and time. Laser light at 488 nm was used to excite Tb3+ ions while Yb3+ ions were excited by energy transfer from the excited Tb3+ ions. Near-infrared emission at 940 – 1020 nm was observed. It has been found that the emission at 940 – 1020 nm increased significantly from the glass-ceramic compared to that of the as-prepared glass. This result suggests that the energy-transfer efficiency increases in glass-ceramics compared to that in glass. A significant portion of rare-earth ions may be incorporated inside LaF3 nanoparticles (NPs) in the glass-ceramic. Because the Yb3+ emission at 940 – 1020 nm is matched well with the band gap of crystalline Si, the quantum cutting effect may have its potential application in silicon-based solar cells.

Tm3+，Yb3+共掺微晶玻璃蓝色上转换荧光的温度特性

Tm³⁺，Yb³⁺共掺微晶玻璃蓝色上转换荧光的温度特性

White light generation of glass ceramics containing Ba2LaF7:Eu2+, Tb3+ and Sm3+ nanocrystals

The Eu2+/Tb3+/Sm3+ co-doped oxyfluoride glass ceramics containing Ba2LaF7 nanocrystals are prepared in the reducing atmosphere. The X-ray diffraction results show that Eu2+, Tb3+ and Sm3+ ions are enriched into the precipitated Ba2LaF7 nanophase after the annealing process. It deduces efficient energy transfers from Eu2+ to Tb3+ and Sm3+ and intenses warm white luminescence of the glass ceramics. Comparing with the glass, the luminescence quantum yield of the glass ceramics is also enlarged by about 3 times. This demonstrates the potential white light-emitting diode application of the glass ceramics produced in this letter.

Quantum cutting mechanism in Tb3+-Yb3+ co-doped oxyfluoride glass

Rate equations were created to describe cooperative quantum cutting phenomena, which incorporated the interactions between donor Tb3+ and acceptor Yb3+ ions. Two judgment criteria were developed for the excitation power dependence and time-resolved luminescence spectra of donor and acceptor ions, which can be used to verify the proposed mechanism. Under the excitation of a 473 nm continuous wave laser, the emission intensities of Tb3+ and Yb3+ increased linearly with the excitation power. The decay curve of Yb3+ indicated two distinct contributions: the fast decay time of its own lifetime, and the slow decay time representing the lifetime of the 5D4 energy level of Tb3+. The experimental results meet the two judgment criteria, which confirmed the proposed cooperative quantum cutting mechanism in Tb3+-Yb3+ co-doped oxyfluoride glass.

Preparation and photoluminescence properties of fluorosilicate glass ceramics containing CeOF: Dy 3+ nanocrystals

The Ce 3+ and Dy 3+ co-doped oxyfluoride glasses and glass ceramics containing CeOF or CeF 3 nanocrystals have been prepared in the reducing atmosphere. The crystallinity increased significantly with the Ce 3+ concentration, while the crystal size of nanocrystals is mainly influenced by the annealing temperatures. The glasses and glass ceramics emitted white light, deriving from a combination of the Ce 3+ blue and the Dy 3+ yellow light. The emission intensity and CIE chromaticity coordinates of the Ce 3+ and Dy 3+ co-doped glasses can be tuned by adjusting the ratio of Ce 3+/Dy 3+ concentration or the annealing temperature.

Efficient down- and up-conversion of Pr 3+–Yb 3+ co-doped transparent oxyfluoride glass ceramics

Pr 3+ and/or Yb 3+ doped transparent oxyfluoride glass ceramics (GCs) containing CaF 2 nanocrystals were fabricated and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Judd–Ofelt (J–O) intensity parameters, radiative transition probability, radiative lifetimes, and branching ratios of Pr 3+ have been calculated from the absorption spectra. Upon 470 nm excitation, Pr 3+ doped GCs yield intense visible-near infrared (NIR) luminescence corresponding to the 3P 0 → 3H 6, 3P 0 → 3F 2,3,4, 3P 1 → 1G 4, 1D 2 → 3H 5, and 1D 2 → 3F 4 transitions, respectively. With the addition of Yb 3+ ions, NIR down-conversion (DC) emissions at 976 nm ( 2F 5/2 → 2F 7/2) were achieved, due to efficient energy transfer (ET) from Pr 3+ to Yb 3+. Underlying mechanism for the NIR-DC is analyzed in terms of static and dynamic photoemission and monitored excitation spectra. The maximum quantum efficiency from Pr 3+: 3P 0 to Yb 3+: 2F 5/2 is calculated to be 153%. In comparison, intense up-conversion emissions at 489, 545, 606, and 651 nm have been obtained in Pr 3+–Yb 3+ codoped glass and GCs under 980 nm excitation, which is ascribed to be two-photon involved ET from Yb 3+ to Pr 3+.

Structure and luminescence properties of Eu/Tb codoped oxyfluoride glass ceramics containing Sr 2GdF 7 nanocrystals

Eu/Tb codoped transparent oxyfluoride borosilicate glass ceramics containing Sr 2GdF 7 nanocrystals were fabricated under a reductive atmosphere and the conversion of Eu 3+ ions to Eu 2+ ions was observed. The Sr 2GdF 7 nanocrystals with an average size of 32 nm were homogeneously precipitated in the oxyfluoride borosilicate glass matrix, which could be evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy. The enhancement of photoluminescence emission intensity, reduction of the relative emission intensities between 5D 0 → 7F 2 and 5D 0 → 7F 1, and long fluorescence lifetimes of Eu 2+, Eu 3+, and Tb 3+ ions revealed that more rare earth ions were partitioned into the low phonon energy environment Sr 2GdF 7 nanocrystals. Under ultraviolet excitation, pure and bright white light emission was obtained in the oxyfluoride borosilicate glass ceramic, which may be a potential blue, green and red-emitting phosphor for white LEDs.

The microstructure of erbium–ytterbium co-doped oxyfluoride glass–ceramic optical fibers

Oxyfluoride transparent glass–ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass–ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO2–11Al2O3–7Na2CO3–10CaO–10PbO–11PbF2–3ErF3 and 48SiO2–11Al2O3–7Na2CO3–10CaO–10PbO–10PbF2–3YbF3–1ErF3 (in molar%) were fabricated from high purity commercial chemicals (Sigma–Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er3+ doped and Er3+/Yb3+ co-doped oxyfluoride glass–ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass–ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous–crystalline microstructure with nano-crystals of size even below 10nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er3FO10Si3 (monoclinic; ICSD 92512), Pb5Al3F19 (triclinic; ICSD 91325) and Er4F2O11Si3 (triclinic; ICSD 51510) against to initially expected PbF2 crystals.

Er-doped and Er, Yb co-doped oxyfluoride glasses and glass–ceramics, structural and optical properties

The selected glasses and glass–ceramics pertinent to following chemical composition in mol%:48%SiO 2–11%Al 2O 3–7%Na 2O–10%CaO–10%PbO–11%PbF 2–3%ErF 3 and 48%SiO 2–11%Al 2O 3–7%Na 2O–10%CaO–10%PbO–10%PbF 2–1%ErF 3–3%YbF 3 have been manufactured from high purity components (Aldrich) at 1450 °C in normal atmosphere. Glass optical fibers were successfully drawn. Subsequently they were subject to the heat-treatment at 700 °C in various time periods. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. It has been observed that the controlled heat-treatment of oxyfluoride glass fibers results in the creation of Pb 5Al 3F 19, Er 4F 2O 11Si 3 and Er 3FO 10Si 3 crystalline phases. The identified phases were characterized by X-ray powder diffraction (XRD) and confirmed by selected area electron diffraction (SAED). The fibers consist of mixed amorphous–crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. Their morphology was investigated applying high-resolution transmission electron microscopy. Optical properties and excited state relaxation dynamics of optically active ions (Er 3+, Yb 3+) in glass and glass–ceramics have been studied. Based on absorption spectra the Judd–Ofelt analysis was carried out. The main attention was directed to NIR luminescence at. 1.6 μm related to 4I 13/2 → 4I 15/2 Er 3+ and less effective emission associated with 4I 11/2 → 4I 15/2 Er 3+ and 2F 5/2 → 2F 7/2 Yb 3+ transitions. The dissimilar spectroscopic properties have been revealed for glasses and glass–ceramic samples, respectively. The reduction of emission linewidth at 1.6 and 1.0 μm combined with substantial increase of 4I 13/2 lifetimes of erbium in glass–ceramics appear to be evidences that Er 3+ ions are accommodated in crystalline phases. The structural and optical characteristics of oxyfluoride glass–ceramic fibers indicate that these optical systems may be considered as promising materials for Er-doped optical amplifiers operating within third telecommunication window.

Origin of White Luminescence in Ag-Eu Co-doped Oxyfluoride Glasses

A combination of red, green and blue emissions has emerged to achieve pure white emission (X = 0.323, Y = 0.320) in Ag-Eu co-doped oxyfluoride glasses. The type of luminescent species, the origin of white emission and the enhancement mechanism for red and blue emissions were investigated by means of absorption, emission and excitation spectra, decay lifetime measurements, as well as time-resolved spectroscopy. Results prove that white emission is originated from f-f transitions of Eu3+ (red), ML-Ag (very small molecule-like, non-plasmonic Ag particles, green) and 5d-4f transition of Eu2+ (blue). Our researches show that Ag-Eu co-doped glasses may provide a new platform to design and fabricate novel phosphors for ultraviolet light-emitting diode (LED) chips.

Cooperative Quantum Cutting in Er3+/Yb3+ Codoped Oxyfluoride Glass Ceramics

Oxyfluoride glass ceramics doped with Er3+/Yb3+ was synthesized. Rare earth ions are doped into fluoride nanocrystals according to x-ray diffractive patterns. The enhanced red emission of Er3+/Yb3+ in the fluoride nanocrystals, excited by xenon lamp at 449 nm, is investigated and analyzed by cooperative quantum cutting mode. The cross relaxation appears from 4F5/2 → 4F9/2 to 4I15/2→4I13/2 because of the nearer distance of rare earth ions and the larger absorption section of 4I15/2→4I13/2 in the quantum cutting. It results in two emissions of 4F9/2→4I15/2 and 4I13/2→4I15/2. This implies that a 449 nm photon could dissolve into two photons with wavelength 665 nm and 1530 nm. This could be an effective way to obtain 1530 nm emission for optical communication.