Nanocrystals precipitation and up-conversion luminescence in Yb^(3+)-Tm^(3+) co-doped oxyfluoride glasses

Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·（4.8-x） GdFy0.1NdF3.xYbF3·0.1TmF3 （x=-0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8） in molar ratio was developed. When the oxyfluoride glasses were heat-treated at the first crystallization temperature, the glasses gave transparent glass-ceramics in which rare earth containing fluorite-type nanocrystals of about 17.2 nm in diameter uniformly precipitated in the glass matrix. Compared with the glasses before heat treatment, the glass-ceramics exhibited very strong blue up-conversion luminescence under 800 nm light excitation. Rare earth containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass, the size of precipitated nanocrystals could be controlled by laser power and scan speed. The intensity of the blue up-conversion luminescence was strongly dependent on the precipitation of β-PbF2 nanocrystal and the YbF3 concentration. The reasons for the highly efficient Tm^3＋ up-conversion luminescence after laser irradiation were discussed.

Research on Up-Conversion Mechanism in Er^(3+)/Yb^(3+)-Codoped Oxyfluoride Glass

Er3 +/Yb3 +-codoped oxyfluoride crystallite glass was prepared with melting technique. The compositions and the melting temperature and the annealing temperature of the rare earth-doped crystallite glass were studied in detail. The emission spectra of samples were measured with the Hitachi F-4500 fluorescent photometer pumped by 980 nm wavelength laser. The up-conversion luminescence mechanism was illuminated on the view of the photophysics. By measuring the relationship between luminescent intensity and pump power, it is confirmed that the emission peaks at 550 nm belong to two-photon process, while that at 665 nm belongs to three-photon process. Moreover, the distributions of crystalline were determined by SEM.

Spectroscopic Properties and Judd-Ofelt Theory Analysis of Er^(3+)-Doped Heavy Metal Oxyfluoride Silicate Glass

Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime of each energy levels for Er^(3+) were calculated by Judd-Ofelt theory, and stimulated emission cross-section of (()~4I_(13/2))→(()~4I_(15/2)) transition was calculated by McCumber theory. The results show that fluorescence full width at half maximum and stimulated emission cross-section of Er^(3+)-doped heavy metal oxyfluoride silicate glass are broad and large, respectively. Compared with other host glasses, the gain bandwidth property of Er^(3+)-doped heavy metal oxyfluoride silicate glass is close to those of tellurite and bismuth glasses, and has advantage over those of silicate, phosphate and germante glasses.

Upconversion luminescence of Tm^3＋/Yb^3＋ codoped oxyfluoride glasses

Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - （4.9 - x） AlF3（x=0, 0.5, 1.0, 1.5, 2.0） in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3＋： ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3＋ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3＋ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.

Evolution of Er^(3+) Distribution in the Oxyfluoride Glass Ceramics with Heating

The distribution characteristics of Er^3＋ ions doped in the oxyfluoride glass ceramics containing LaF3 nanocrystals heat-treated at 650 ℃ for different durations were investigated. The results of the integral absorption cross-section analysis demonstrated that the partition fraction of Er^3＋ in LaF3 nanocrystals increases with prolonging of heating time, The anomalous phenomena of Er^3＋ emissions in the up-and the down-conversion fluorescence spectra are well explained based on the calculated results.

Near-infrared Quantum Cutting in Pr^(3+)-Yb^(3+) Co-doped Oxyfluoride Glass Ceramics Containing CaF_2 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 glass- ceramics 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 tun （2F5/2→2F7/2） emission has been achieved upon the excitation of the 3P0 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%.

Study of Binary Rare－Earth Oxyfluoride for ODE Reaction and Their XRD ＆In－Situ Raman Characterization

A series of new binary rare earth oxyfluoride (Sm2O3-LaF3) catalysts have been developed for ODE reaction. High C2H4 selectivity(91.5%) with C2H6 conversion 21.7% was achieved on the catalyst Sm2O3/LaF3 with molar ratio 1/1 at 700℃. The addition of 16.7 mol% BaF2 into Sm2O3/LaF3(1/1 in mol) led to the increase of C2H6 conversion from 21.7% to 40.8%,however. the change of ethene seletivity was not apparent (from 91.5% to 88.0%).

Spectroscopic properties of Yb^(3+)-doped TeO_2–BaO–BaF_2–Nb_2O_5-based oxyfluoride tellurite glasses

A series of oxyfluoride glasses with the compositions of 75 mol% TeO2, 10 mol% Nb2O5, （15 mol%-x） BaO, x BaF2 （x =0 mol%, 5 mol%, 10 mol%, 15 mol%） doped with Yb2O3 were prepared by the melt-quenching method. Their emission cross-sections, fluorescence lifetimes, and gain properties were investigated by using the absorption spectra and the fluorescence decay curves. The results show that by substituting BaF2 for BaO, the emission cross-section decreases from 1.37 pm^2 to 1.21 pm^2, and the fluorescence lifetime increases from 0.71 ms to 0.96 ms. These properties indicate that this oxyfluoride tellurite glass may have potential uses as the Yb2O3-doped gain medium in a solid laser.

METHANE OXIDATIVE COUPLING OVER METAL OXYFLUORIDE CATALYSTS

The MOC reaction over ZrO_2/LaF_3, CeO_2/LaF_3 and ThO_2/LaF_3 catalysts indicated that these catalysts had high activity and high C_2 selectivity at low temperature. In the temperature range 480℃ to 650℃. The methane conversion was 24. 4% to 30. 8% and the C_2 selectivity was 40. 0% to 55. 4%. The XRD characterization of the catalysts indicated that O^2. and F exchang happened and LaOF was formed.

Synthesis,Crystal Structure,and Properties of Inorganic-organic Hybrid M(Ⅱ)-Nb(V) (M=Co,Cu) Oxyfluorides

Two isostructural inorganic-organic hybrid M（II）–Nb（V） oxyfluorides, namely, M（H2O）2（pyz）NbOF5 （M=Co 1, Cu 2; pyz=pyrazine） have been hydrothermally synthesized and structurally characterized. Both compounds possess two-dimensional layer structure constructed by neutral M（H2O）2NbOF5 chains inter-connected via bridging pyrazine ligands. The structure is further extended into three-dimensional supramolecular architecture through inter-layer H-bonding interactions between the coordinated water molecules and fluorine ions. The luminescent properties and thermal stability of both compounds have been investigated.

Upconversion Luminescence of Er^3＋ and Co-Doped Er^3＋/Yb^3＋ Novel Transparent Oxyfluoride Glasses and Glass Ceramics： Spectral and Structural Properties

Transparent oxyfluoride silicate precursor glasses and glass ceramics with the novel composition （1） SiO2-PbO-PbFE-Er2O3, （2） SiO2-GeOE-PbO-PbFE-Er2O3 （3） SiO2-Al2O3-Y2O3-Na2O-NaF-LiF-Er2O3-YbF3 doped with Er^3＋ and co-doped with Er^3＋/Yb^3＋ ions were synthesized. X-ray diffraction analysis （XRD） and Er3＋ absorption spectra revealed precipitation of PbF2 nanocrystals dispersed in the glassy matrix. Under 980 nm laser excitation, intense green, red and near IR bands of upconversion luminescence （UCL） were recorded both before and after heat treatment. In the glass ceramics the upconversion intensity increased significantly. To our knowledge, for the first time the composition of the glass ceramics characterized by the small-angle neutron scattering （SANS） showed the cluster organization of PbF2 nanocrystals.

Luminescent properties of Dy^3+/Eu^3+ doped fluorescent glass for white LED based on oxyfluoride matrix

Rare earth ion-doped fluorescent glass has become a hotspot due to its characteristics.This work shows that the prepared Dy^3+and Dy^3+/Eu^3+doped glasses have white light emission under ultraviolet excitation.There is a higher yellow light/blue light(Y/B)value,indicating an increase in the covalentity of Dy-O,and decrease in the symmetry with the increasing concentration of dopants(Dy^3+).The correlated color temperature(CCT)can be effectively reduced by the red light emission of Eu^3+,and the order of influence of excitation wavelength on CCT is 395 nm>382 nm>365 nm.The delay curve demonstrates the energy transfer from Dy^3+to Eu^3+.The glass has the characteristics of anti-blue light damage and wide tunable color temperature,which illustrates that it has potential application in the field of white LED.

Preparation and luminescence properties of Eu^(3+) doped oxyfluoride borosilicate glass ceramics

Oxyfluoride borosilicate glass with the molar composition of 60SiO2-15B2O3- 15Na2O-8CaF2-2NaF-0.25Eu2O3 was synthesized lay a traditional glass melting method. Glass ceramics containing CaF2 nanocrystals were prepared by heat treating the glass samples at a temperature in the range of 6204580 ℃. The results of X-ray diffraction （XRD） indicated that the average crystallite size and the lattice constant of CaF2 nanocrystals increased with the heat treatment temperature increasing. The luminescence spectra showed that the emission intensity of Eu3＋ doped glass ceramics was stronger than that of the glass matrix, and increased with the heat treatment temperature increasing. The left edge of excitation band shifted to shorter wavelength in the glass ceramics. The local environments of Eu3＋ ions in the glass and glass ceramics were different.

Luminescent properties of Ce^(3+)-doped transparent oxyfluoride glass ceramics containing BaGdF＿5 nanocrystals

The transparent oxyfluoride glass ceramics containing Ba Gd F5 nanocrystals were prepared with a composition of 42 Si O2-12Na2O-16Al2O3-24 Ba F2-4Gd2O3-2Ce F3（mol.%） by thermal treatment technology. The typical DSC curve, X-ray diffraction（XRD） and transmission electron microscopy（TEM） patterns were measured. The transmission spectra and luminescent properties were investigated. The decay times of the Gd^3＋ ions at 312 nm excited with 275 nm for the Ce^3＋ ions doped glass and glass ceramics specimens and the energy transfer process between Gd^3＋ ions and Ce^3＋ ions were also studied. The XRD analysis and the TEM images confirmed the generation of the spherical Ba Gd F5 nanocrystals. Compared with the PG specimen, the intensity of the luminescence spectra of the glass ceramics specimens was apparently enhanced with the heat treatment temperature increasing, and a blue shift in the excitation spectra and the emission spectra of glass ceramics specimens was obviously observed. In the fluorescence decay curves of the Gd^3＋ ions, it could be obviously observed that the fluorescent intensity decays in the Ce^3＋ ions doped glass and glass ceramics specimens decreased rapidly with the increase of the heat treatment temperature. In addition, the energy transfer efficiency from Gd3＋ions to Ce^3＋ ions was also calculated.

Ultraviolet and visible upconversion luminescence of Tm(0.1)Yb(5):FOV oxyfluoride nanophase vitroceramics

The ultraviolet upconversion luminescence of Tm3+ ions sensitized by Yb3+ ions in oxyfluoride nanophase vitroceramics when excited by a 975 nm diode laser was studied. An ultraviolet upconversion luminescence line positioned at 363.6 nm was found. It was attributed to the fluorescence transition of 1D2→3H6 of Tm3+ ion. Sev- eral visible upconversion luminescence lines at 450.7 nm, (477.0 nm, 462.5 nm), 648.5 nm, (680.5 nm, 699.5 nm) and (777.2 nm, 800.7 nm) were also found, which result respectively from the fluorescence transitions of 1D2→3F4, 1G4→3H6, 1G4→3F4, 3F3→3H6 and 3H4→3H6 of Tm3+ ion. The careful measurement and analysis of the variation of upconversion luminescence intensity F as a function of the 975 nm pumping laser power P prove that the upconversion luminescence of 1D2 state is partly a five-photon upconversion luminescence, and the upconversion lumines- cence of 1G4 state and 3H4 state are respectively the three-photon and two-photon upconversion luminescence. The theoretical analysis suggested that the upcon- version mechanism of the 363.6 nm 1D2→3H6 upconversion luminescence is partly the cross energy transfer of {3H4(Tm3+)→3F4(Tm3+), 1G4(Tm3+)→1D2(Tm3+)} and {1G4(Tm3+)→3F4(Tm3+), 3H4(Tm3+)→1D2(Tm3+)} between Tm3+ ions. In addition, the upconversion luminescence of 1G4 and 3H4 state results respectively from the se- quential energy transfer {2F5/2(Yb3+)→2F7/2(Yb3+), 3H4(Tm3+)→1G4(Tm3+)} and {2F5/2(Yb3+) →2F7/2(Yb3+), 3F4(Tm3+)→3F2(Tm3+)} from Yb3+ ions to Tm3+ ions.

Designing excellent mid-infrared nonlinear optical materials with fluorooxo-functional group of d^0 transition metal oxyfluorides

Exploration of new infrared(IR) nonlinear optical(NLO) materials is still in urgency owing to the indispensable roles in optoelectronic devices, resource exploration, and long-distance laser communication. The formidable challenge is to balance the contradiction between wide band gaps and large second harmonic generation(SHG) effects in IR NLO materials. In the present work, we proposed new kinds of NLO active units, d^0 transition metal fluorooxofunctional groups for designing mid-IR NLO materials. By studying a series of d^0 transition metal oxyfluorides(TMOFs),the influences of fluorooxo-functional groups with different d^0 configuration cations on the band gap and SHG responses were explored. The results reveal that the fluorooxo-functional groups with different d^0 configuration cations can enlarge band gaps in mid-IR NLO materials. The first-principles calculations demonstrate that the nine alkali/alkaline earth metals d^0 TMOFs exhibit wide band gaps(all the band gaps >3.0 e V), large birefringence Δn(> 0.07), and two W/Mo TMOFs also exhibit large SHG responses. Moreover, by comparing with other fluorooxo-functional groups, it is found that introducing fluorine into building units is an effective way to enhance optical performance. These d^0 TMOFs with superior fluorooxo-functional groups represent a new exploration family of the mid-IR region, which sheds light on the design of mid-IR NLO materials possessing large band gap.

Research on upconversion luminescence in new Er^(3+)/Yb^(3+) codoped oxyfluoride borosilicate glass ceramics

The upconversion luminescence of Er^3＋/Yb^3＋ ions is researched in a novel transparent oxyfluoride borosil- icate glass and glass ceramics under 980-nm excitation. Fluoride nanocrystals Ba2YF7 are successfully precipitated in glass matrix, which is affirmed by the X-ray diffraction results. Compared with the parent glasses, significant enhancement of upconversion luminescence is observed in the Er^3＋/Yb^3＋ codoped transparent glass-ceramics, which may be due to the variation of coordination environment around Er^3＋ and Yb^3＋ ions after crystallization. The possible upconversion mechanism is also discussed.

Intense upconversion luminescence of Er^(3+)/Yb^(3+) codoped oxyfluoride borosilicate glass ceramics containing Ba_2GdF_7 nanocrystals

Er3+/Yb3+-codoped transparent oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals were prepared and spectroscopic properties of rare earth ions were investigated. Fluoride nanocrystals Ba2GdF7 were successfully precipitated in glass matrix, which was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) results. In comparison with the as-made precursor, significant enhancement of upconversion luminescence was observed in the Er3+/Yb3+ codoped oxyfluoride glass ceramics, which may be due to the variation of coordination environment around Er3+ and Yb3+ ions after crystallization. The transition mechanisms of the green and red upconversion luminescence were ascribed to a two-photon process, and that of the blue upconversion luminescence was a three-photon process.

Spectroscopic investigations on Er^(3+)/Yb^(3+)-doped oxyfluoride glass ceramics containing YOF nanocrystals

Spectroscopic properties of Er3＋/Yb3＋-doped transparent oxyfluoride borosilicate glass ceramics containing YOF nanocrystals were systematically investigated. X-ray diffraction （XRD） confirmed the formation of YOF nanocrystals in the glassy matrix. Based on the Judd-Ofelt theory, the intensity parameters Ωi （i=2, 4, 6）, spontaneous emission probability, radiative lifetime, radiative quantum efficiency and the effective emission bandwidth were investigated. The upconversion luminescence intensity of Er3＋ ions in the glass ceramics increased significantly with the increasing crystallization temperature. The transition mechanisms of the green and red upconversion luminescence were ascribed to a two-photon process, and the blue upconversion luminescence was a three-photon absorption process.

Role of Heavy Metal Ions in the Formation of Oxyfluoride Glasses and Glass Ceramics

In order to investigate the influence of different heavy metal ions on the formation of the oxyfluoride glasses and glass ceramics, samples with different Pb F2/Cd F2 ratios have been prepared by the melting quenching and thermal treatment method. The different effects of Pb2 tand Cd2ton the glass network structure are investigated by FTIR and Raman spectra. During the formation of glass network structure, Pb2 tprefers to break the Sie Oe Si bond and subsequently bond to F for charge compensation, and Cd2 tprefers to break the SieO eA l bond and is surrounded by O2. Pb2 tand F gather together and form the fluoride nanocrystals,while Cd2 tremains in oxide matrix after thermal treatment. Introduction of proper Cd F2 is important to adjust and control the glass network structure and crystallization process in the fabrication of the transparent glass ceramics.