LaF3 Nanocrystals Research Articles

Efficient Near-Infrared Down-Conversion in Pr3+–Yb3+ Codoped Glasses and Glass Ceramics Containing LaF3 Nanocrystals

The Pr3+–Yb3+ ion codoped 40SiO2–30Al2O3–18Na2O–12LaF3 glasses were synthesized by a conventional melting–quenching method. Near-infrared downconversion emission with 12% quantum yield has been realized. Transparent glass ceramics containing LaF3 nanocrystals were prepared by heat treatment. X-ray diffraction and scanning electron microscopy results show that fluorides favor the formation of small crystals. Comparing the absorption and emission spectra of the glasses with that of the glass ceramics indicates that the Pr3+ ions are incorporated in priority into the LaF3 crystals, due to the similar crystal lattice. Thus, energy transfer efficiency cannot be enhanced in the present glass by crystallization. It is suggested that fluorides from TbF3 to LuF3 (including YF3) having the orthorhombic structure in aluminosilicate glass are suitable for incorporating YbF3 during the crystallization process.

Increase in the Tb3+ green emission in SiO2–LaF3 nano-glass-ceramics by codoping with Dy3+ ions

95 SiO 2 – 5 LaF 3 sol-gel derived nano-glass-ceramics single doped with 0.1Dy3+ or 0.1Tb3+ mol % and codoped with 0.1Dy3+ and xTb3+ (x=0.1,0.3) mol % were successfully obtained. XRD and HRTEM measurements confirm the precipitation of LaF3 nanocrystals during the ceramming process, with mean size ranging from 10 to 20 nm and increasing with the thermal treatment temperature. About 75% of lanthanide ions are partitioned into LaF3 nanocrystals, as calculated from luminescence decays. The effect of increasing the Tb3+ concentration and also of codoping with Dy3+ in the Tb3+ green emission from the D54 level have been studied. The energy transfer mechanisms between Tb3+ ions and also between Tb3+–Dy3+ ions, which favor the green emission, have been analyzed.

Colour tuneability and white light generation in Yb3+–Ho3+–Tm3+ co-doped SiO2–LaF3 nano-glass-ceramics prepared by sol–gel method

Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 co-doped with 0.3Yb3+, 0.1Ho3+ and 0.1Tm3+ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron microscopy analysis point out the precipitation of hexagonal LaF3 nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power.

Luminescence behavior of Ce3+ and Dy3+ codoped oxyfluoride glasses and glass ceramics containing LaF3 nanocrystals

The Ce3+ and Dy3+ codoped oxyfluoride glasses and glass ceramics containing LaF3 nanocrystals have been prepared in the reducing atmosphere. The emission intensity and Commission International de I'Eclairage (CIE) chromaticity coordinates of the Ce3+ and Dy3+ codoped glasses significantly changed with concentration ratio of Ce3+ to Dy3+. The emission intensity of both Ce3+ ions and Dy3+ ions in the 3.0% Ce3+ and 3.0% Dy3+ codoped glass ceramics increased significantly in comparison with that in the glass. The glasses and glass ceramics could emit bright white light by adjusting the concentration ratio of Ce3+ to Dy3+.

Size-dependence of LaF3:Eu3+ nanocrystals on Eu3+ photo-luminescence intensity

Size-dependence of Eu3+-doped LaF3 nanocrystals on the 5D0-7FJ photoluminescence intensity was investigated, where LaF3:Eu3+ nanocrystals were prepared through a hydrothermal route with a cationic surfactant cetyltrimethylammonium bromide (CTAB) as size-controlled agent and by post-annealing at an appropriate temperature at N2 atmosphere. It was found that LaF3:Eu3+ obtained was in hexagonal structure with space group P3c1 and had good crystalinity. When LaF3:Eu3+ nanocrystals were synthesized with 0.006 mol/L CTAB the average particle size was maximized to be 25.4 nm and the luminescence intensity was 1.5 times higher than that prepared without CTAB or with more CTAB concentration. The mechanism of the particle growth was also discussed in this paper.

Tb-doped Aluminosilicate Oxyfluoride Scintillating Glass and Glass-ceramic

AbstractTwo aluminosilicate oxyfluoride glass systems, a lead-cadmium-aluminosilicate oxyfluoride and a lithium-lanthanum-aluminosilicate oxyfluoride, doped with different TbF3 concentrations, have been fabricated and investigated. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics (TGC) were obtained. The glass-ceramics contain Tb:Pb(Cd)F2 or Tb:LaF3 nano-crystals in the glass-matrix. Differential scanning calorimetry, Raman scattering, and luminescence under both UV and β-particle excitation have been investigated on as-prepared glasses and glass-ceramics. It has been found that the terbium-doped lithium-lanthanum-aluminosilicate oxyfluoride glass exhibits good UV excited luminescence and β-induced luminescence. The luminescence yield increases for glass-ceramic compared to that of the as-prepared glass. The including of LaF3 in the glass-matrix is beneficial for a higher Tb-doping concentration and a high light yield. The light yield of lithium-lanthanum-aluminosilicate oxyfluoride glass and glass-ceramic is comparable to that of Schott IQI-301 product. However, the terbium-doped lead-cadmium-aluminosilicate oxyfluoride glass and glass-ceramic have a detrimental luminescence performance. The lead cations in the glass-matrix may create non-bridging oxygen defects, which are a strong source of charge traps, and correlated to a strong Raman “Boson” peak.

Spectroscopic study of thulium doped transparent glass ceramics

A systematic investigation on fluorescence spectroscopy of trivalent thulium doped in oxyfluoride glass ceramics containing LaF3 nanocrystals has been carried out in a spectral range from 400 to 900 nm under the direct excitation of 1D2 level at a low temperature. Specific optical transitions related to the fluorescence emissions are studied based on experimental measurements in frequency and time domain. Fluorescence emissions from the ions in crystal phase are distinguished from what in glass phase and their spectroscopic properties are explored. The dynamical process shows that the temporal decay of fluorescence emission consists of two parts: a rapid decay from the ions in glass phase and a slower decay from the ions in crystal phase.

Infrared-to-visible and infrared-to-violet upconversion fluorescence of rare earth doped LaF3 nanocrystals

This paper reports that hexagonal-phase LaF3:Yb0.203+, Er0.023+ and LaF3:Yb0.203+, Tm0.023+ nanocrystals (NCs) were synthesized via a hydrothermal method. The transmission electron microscopy, selected area electron diffraction, powder x-ray diffraction, and thermogravimetric analysis are used to characterize the NCs. Under 980 nm excitation, the Yb3+/Er3+ and Yb3+/Tm3+ codoped NCs colloidal solutions present bright green and blue upconversion fluorescence, respectively. These NCs show efficient infrared-to-violet and infrared-to-visible upconversion. The upconversion fluorescence mechanisms of La F3:Yb0.023+ Er0.023+ and LaF3:Yb0.023+, Tm0.023+ NCs are investigated with a 980-nm diode laser as excitation source.

Synthesis of LaF3 nanocrystals by laser-induced Nd3+ atom heat processing in oxyfluoride glasses

Oxyfluoride glasses with the compositions of 33SiO2–21Al2O3–33NaF–9LaF3–4Nd2O3–xErF3 (mol%), x=0 and 0.5, are prepared using a conventional melt-quenching technique, and the laser-induced crystallization method using continuous-wave (cw) diode lasers with a wavelength of λ=795nm is applied to form LaF3 crystals on the glass surface. It is found from X-ray diffraction analyses and micro-photoluminescence spectra that Nd3+-, Er3+-doped LaF3 crystals with a diameter of ∼23nm are patterned by laser irradiations with a laser power of 1.8W and a laser scanning speed of 10μm/s. It is proposed that the lines patterned by laser irradiations are consisted of the composite of Nd3+-doped LaF3 nanocrystals and the SiO2-based oxide glassy phase. It is suggested that the combination of cw diode laser (λ=795nm) irradiations and the non-radiated relaxation process in the f–f transition level of 4F5/2→4I9/2 of Nd3+ ions is effective in the spatially selected local patterning of fluoride crystals in oxyfluoride glasses with Nd3+ ions.

Wide colour gamut generated in triply lanthanide doped sol–gel nano-glass–ceramics

The generation of a wide colour gamut, based on up-conversion of cheap near-infrared photons into the visible range, is of great importance for general lighting appliances and integrated optical devices. Here, we report for the first time on up-conversion luminescence under infrared excitation at 980 nm in Yb3+–Er3+–Tm3+ triply doped sol–gel derived SiO2–LaF3 based nano-glass–ceramics (SOL-YET), containing LaF3 nanocrystals with a size about 13 nm. Efficient simultaneous up-conversion emission of the three primary colours (blue, green and red) gives rise to a balanced white overall emission. The ratio between up-conversion emission bands can be varied by changing pump power intensity resulting in colour tuneable up-conversion phosphor.

Fluorescence characteristics of Tm3+ in different local environments

Fluorescence from ions in both the crystal and glass phases was investigated by selective excitation of Tm3+ doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals. The spectroscopic properties of ions in different local environments were studied. It was found that the glass phase favored blue up-conversion of Tm3+ when a pulsed red light was applied. The most efficient up-conversion was obtained when the excited state absorption was resonant with the excitation.

Ionic Liquid-Based “All-in-One” Synthesis and Photoluminescence Properties of Lanthanide Fluorides

A facile route to the synthesis of LnF3 nanocrystals has been accomplished in three ionic liquids (ILs) (OmimPF6, OmimBF4, and BmimPF6). The partial hydrolysis of PF6− and BF4− was utilized to introduce a new fluoride source. Uniform LnF3 (Ln = La, Ce, Pr, Nd, Sm, Eu, Er), Tb3+-doped CeF3, and Eu3+-doped LaF3 nanocrystals could be obtained in a large scale, and the products were up to 0.15 g per 10 mL solvents. In the “all-in-one” systems, the ILs acted as solvents, reaction agents, and templates. The effects of cosolvents, cationic and anionic parts of the ILs on the nanocrystals morphologies, and sizes were studied. The optical properties of the nanocrystals synthesized in different ILs were discussed. The simple and large-scale synthesis of these unique luminescent inorganic nanocrystals will find great potential applications in biolabels, light-emitting diodes (LEDs), and redox luminescent switches.

Up‐conversion in nanostructured Yb3+–Tm3+ co‐doped sol–gel derived SiO2–LaF3 transparent glass‐ceramics

AbstractNanostructured transparent glass‐ceramics with composition of 95SiO2–5LaF3 doped with 0.1 mol% of Tm3+ or co‐doped with 0.1 mol% of Tm3+ and 0.3 mol% of Yb3+ were synthesized by thermal treatment of precursor sol–gel derived glasses. A comparative luminescence analysis in terms of different temperatures of thermal treatments has been carried out. Segregation of LaF3 nanocrystals in the matrix was con‐ firmed by X‐ray diffraction. Blue and red efficient up‐conversion emissions were observed under 980 nm excitation at room temperature. These results indicate partition of a significant fraction of co‐dopants into the precipitated LaF3 nanocrystals. The mechanisms involved in the up‐conversion emissions have been analyzed and can be ascribed to processes with two, three and four photons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gain cross-section of 1.06 μm emission in Nd3+-doped SiO2–LaF3 glass–ceramics prepared by sol–gel method

The room temperature near-infrared emission at 1.06μm corresponding to the 4F3/2→4I11/2 laser transition in Nd3+-doped SiO2–LaF3 transparent glass–ceramics prepared by sol–gel method has been characterized in terms of the product of emission cross-section and fluorescence lifetime. Stimulated emission cross-sections have been calculated from experimental emission spectra using the Füchtbauer–Ladenburg equation. The precipitation of LaF3 nanocrystals after heat-treatment, confirmed by X-ray diffraction, induces a significant increment of the 1.06μm near-infrared emission compared with the as made sample. An enhancement of emission cross-section of about 10% has been achieved with increasing temperature of heat-treatment of the nano-ceramming process from 800 to 1000°C, which is related to the growth of LaF3 nanocrystals.

Labelling of silica microspheres with fluorescent lanthanide-dopedLaF3 nanocrystals

Fluorescent microspheres have been demonstrated to be useful in a variety of biologicalapplications. Fluorescent silica or polymer microspheres have been produced byincorporation of chromophores into the microspheres, which usually produces microsphereswith nonuniform sizes and reduced fluorescence. Here we present a simple andstraightforward method to produce silica microspheres with fluorescent lanthanide-dopedLaF3 nanocrystals grownon the surface. LaF3 nanocrystals are in situ grown on silica microspheres of different sizes to forma raspberry-like structure. The microspheres exhibit strong fluorescenceand the colour could be altered by changing the lanthanide ions doped inLaF3 nanocrystals.

Luminescence of Er3+-doped nanostructured SiO2–LaF3 glass-ceramics prepared by the sol–gel method

Transparent glass ceramics with composition of 95SiO2–5LaF3 doped with 0.1mol% of Er3+ were synthesized by thermal treatment of precursor sol–gel glasses. Segregated LaF3 nanocrystals in the glass were confirmed from a structural analysis performed by X-ray diffraction. Blue, green and red efficient up-conversion emissions were observed under 980nm excitation at room temperature. Under this excitation near infrared down-conversion at 1.55μm is also observed. These results could be attributed to the precipitation of LaF3 nanocrystals and the incorporation of most Er3+ ions in these nanocrystals. The mechanisms involved in the up-conversion emissions could be ascribed to two and three photon processes.

Luminescence and structural characterization of transparent nanostructured Eu3+-doped LaF3–SiO2 glass–ceramics prepared by sol–gel method

Glass–ceramics with composition of 89.9SiO2–10LaF3–0.1EuF3 (mol%) were prepared by sol–gel method. LaF3 nanocrystals, precipitated by heat-treatments, were identified by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Besides the well-known red emission of Eu3+ ions, higher energy emissions coming from upper-lying levels 5D1 and 5D2 can be observed at room temperature due to the very low phonon energies of the LaF3 matrix. Moreover, from site selective excitation and emission spectra in the temperature range from 13 to 300K, it is concluded that the fraction of Eu3+ ions partitioned into LaF3 nanocrystals, substituting La3+ ions, is comparable to the one staying in the SiO2 glassy phase.

Facile synthesis of water-soluble LaF3∶ Ln3+ nanocrystals

Water-soluble lanthanide-doped LaF3 nanocrystals were synthesized using a simple method carried out in aqueous solution at low temperature. The nanocrystals have a nearly spherical shape and an average size of below 30 nm. They consisted of well crystallized hexagonal phases. The luminescence quantum efficiency was about 16% in aqueous solution. LaF3 nanocrystals doped with different lanthanide ions (Eu3+, Ce3+, Tb3+, and Nd3+) were synthesized, which showed strong luminescence in the visible (VIS) and near-infrared (NIR) spectral regions.

Judd–Ofelt analysis and upconversion emission of Er3+–Yb3+ co-doped oxyfluoride glass ceramics containing LaF3 nanocrystals

Er3+–Yb3+ co-doped glasses and glass ceramics containing LaF3 nanocrystals were prepared and their absorption spectra obtained. The Judd–Ofelt parameters Ω t (t = 2, 4, 6) for f–f transition of Er3+, as well as spontaneous emission probabilities, branching ratios and radiative lifetimes for stimulated emission of each band were determined. Addition of Er3+ and Yb3+ ions into low-phonon energy LaF3 nanocrystals makes the upconversion emission of Er3+–Yb3+ co-doped glass ceramic much stronger than that of Er3+–Yb3+ co-doped glass.

Spectroscopy of different sites in Pr3+-doped oxyfluoride glass ceramics

Praseodymium doped oxyfluoride glass has been treated at 725 °C for 4 h to form LaF3 nanocrystals in the amorphous matrices. Absorption, emission, and excitation spectra of the glass ceramics are presented at different concentrations of Pr3+ (0.01–1at.%) and at different temperatures. Spectral and dynamical properties of Pr3+ in nanocrystals and glass have been investigated through selective excitation. Temperature and concentration effects have also been discussed.