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In this work, the fabrication of glass-ceramic materials containing MF3:Eu3+ (M = La, Gd) nanocrystals dispersed in silica sol-gel hosts has been presented. The transformation from liquid sols towards bulk samples was also examined based on IR measurements. The crystallization temperatures and formation of MF3 phases were verified based on TG/DSC analysis and XRD measurements. The optical properties of prepared Eu3+-doped samples were evaluated based on PLE and PL as well as luminescence decay analysis of the 5D0 excited state. Obtained samples exhibit a series of the 5D0 7FJ (J = 1-4) emission bands, which were recorded within the reddish-orange spectral area under near-UV illumination (λexc = 393 nm). Recorded luminescence spectra and double-exponential character of decay curves for prepared glass-ceramic samples indicated the successful migration of Eu3+ dopant ions from amorphous silica framework to low-phonon energy MF3 nanocrystal phases. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of multicolor light-emitting nanomaterials based on rare earths (RE 3+ ) are of great importance due to their possible use in optoelectronic devices, such as LEDs or displays. In the present work, oxyfluoride glass-ceramics containing BaF 2 nanocrystals co-doped with Tb 3+ , Eu 3+ ions were fabricated from amorphous xerogels at 350 °C. The analysis of the thermal behavior of fabricated xerogels was performed using TG/DSC measurements (thermogravimetry (TG), differential scanning calorimetry (DSC)). The crystallization of BaF 2 phase at the nanoscale was confirmed by X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM), and the changes in silicate sol-gel host were determined by attenuated total reflectance infrared (ATR-IR) spectroscopy. The luminescent characterization of prepared sol-gel materials was carried out by excitation and emission spectra along with decay analysis from the 5 D 4 level of Tb 3+ . As a result, the visible light according to the electronic transitions of Tb 3+ ( 5 D 4 → 7 F J (J = 6-3)) and Eu 3+ ( 5 D 0 → 7 F J (J = 0-4)) was recorded. It was also observed that co-doping with Eu 3+ caused the shortening in decay times of the 5 D 4 state from 1.11 ms to 0.88 ms (for xerogels) and from 6.56 ms to 4.06 ms (for glass-ceramics). Thus, based on lifetime values, the Tb 3+ /Eu 3+ energy transfer (ET) efficiencies were estimated to be almost 21% for xerogels and 38% for nano-glass-ceramics. Therefore, such materials could be successfully predisposed for laser technologies, spectral converters, and three-dimensional displays.

In this work, the series of Tb 3+ /Eu 3+ co-doped xerogels and derivative glass-ceramics containing CaF 2 nanocrystals were prepared and characterized. The in situ formation of fluoride crystals was verified by an X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). The studies of the Tb 3+ /Eu 3+ energy transfer (ET) process were performed based on excitation and emission spectra along with luminescence decay analysis. According to emission spectra recorded under near-ultraviolet (NUV) excitation (351 nm, 7 F 6 → 5 L 9 transition of Tb 3+ ), the mutual coexistence of the 5 D 4 → 7 F J (J = 6-3) (Tb 3+ ) and the 5 D 0 → 7 F J (J = 0-4) (Eu 3+ ) luminescence bands was clearly observed. The co-doping also resulted in gradual shortening of a lifetime from the 5 D 4 state of Tb 3+ ions, and the ET efficiencies were varied from η ET = 11.9% (Tb 3+ :Eu 3+ = 1:0.5) to η ET = 22.9% (Tb 3+ :Eu 3+ = 1:2) for xerogels, and from η ET = 25.7% (Tb 3+ :Eu 3+ = 1:0.5) up to η ET = 67.4% (Tb 3+ :Eu 3+ = 1:2) for glass-ceramics. Performed decay analysis from the 5 D 0 (Eu 3+ ) and the 5 D 4 (Tb 3+ ) state revealed a correlation with the change in Tb 3+ -Eu 3+ and Eu 3+ -Eu 3+ interionic distances resulting from both the variable Tb 3+ :Eu 3+ molar ratio and their partial segregation in CaF 2 nanophase.

In this work, we performed a systematic analysis of the impact of selected chemical reagents used in sol-gel synthesis (i.e., N,N-dimethylformamide) and different catalyst agents (i.e., CH 3 COOH, HNO 3 ) on the formation and luminescence of Eu 3+ -doped SiO 2 -LaF 3 nano-glass-ceramics. Due to the characteristic nature of intra-configurational electronic transitions of Eu 3+ ions within the 4f 6 manifold ( 5 D 0 → 7 F J , J = 0-4), they are frequently used as a spectral probe. Thus, the changes in the photoluminescence profile of Eu 3+ ions could identify the general tendency of rare earth materials to segregate inside low-phonon energy fluoride nanocrystals, which allows us to assess their application potential in optoelectronics. Fabricated sol-gel materials, from sols to gels and xerogels to nano-glass-ceramics, were examined using several experimental techniques: X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR), and luminescence measurements. It was found that the distribution of Eu 3+ ions between the amorphous silicate sol-gel host and LaF 3 nanocrystals is strictly dependent on the initial composition of the obtained sols, and the lack of N,N-dimethylformamide significantly promotes the segregation of Eu 3+ ions inside LaF 3 nanocrystals. As a result, we detected long-lived luminescence from the 5 D 0 excited state equal to 6.21 ms, which predisposes the obtained glass-ceramic material for use as an optical element in reddish-orange emitting devices.

In the present work, the Tb 3+ /Eu 3+ co-activated sol-gel glass-ceramic materials (GCs) containing MF 3 (M = Y, La) nanocrystals were fabricated during controlled heat-treatment of silicate xerogels at 350 °C. The studies of Tb 3+ → Eu 3+ energy transfer process (ET) were performed by excitation and emission spectra along with luminescence decay analysis. The co-activated xerogels and GCs exhibit multicolor emission originated from 4f n -4f n optical transitions of Tb 3+ ( 5 D 4 → 7 F J , J = 6-3) as well as Eu 3+ ions ( 5 D 0 → 7 F J , J = 0-4). Based on recorded decay curves, it was found that there is a significant prolongation in luminescence lifetimes of the 5 D 4 (Tb 3+ ) and the 5 D 0 (Eu 3+ ) levels after the controlled heat-treatment of xerogels. Moreover, for both types of prepared GCs, an increase in ET efficiency was also observed (from η ET ≈ 16% for xerogels up to η ET = 37.3% for SiO 2 -YF 3 GCs and η ET = 60.8% for SiO 2 -LaF 3 GCs). The changes in photoluminescence behavior of rare-earth (RE 3+ ) dopants clearly evidenced their partial segregation inside low-phonon energy fluoride environment. The obtained results suggest that prepared SiO 2 -MF 3 :Tb 3+ , Eu 3+ GC materials could be considered for use as optical elements in RGB-lighting optoelectronic devices operating under near-ultraviolet (NUV) excitation.

Nanocrystalline transparent BaF 2 :Eu 3+ glass-ceramic materials emitting reddish-orange light were fabricated using a low-temperature sol-gel method. Several experimental techniques were used to verify structural transformation from precursor xerogels to sol-gel glass-ceramic materials containing fluoride nanocrystals. Thermal degradation of xerogels was analyzed by thermogravimetric analysis (TG) and differential scanning calorimetry method (DSC). The presence of BaF 2 nanocrystals dispersed in sol-gel materials was confirmed by the X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). In order to detect structural changes in silica network during annealing process, the infrared spectroscopy (IR-ATR) was carried out. In particular, luminescence spectra of Eu 3+ and their decays were examined in detail. Some spectroscopic parameters of Eu 3+ ions in glass-ceramics containing BaF 2 nanocrystals were determined and compared to the values obtained for precursor xerogels. It was observed, that the intensities of two main red and orange emission bands corresponding to the 5 D 0 → 7 F 2 electric-dipole transition (ED) and the 5 D 0 → 7 F 1 magnetic-dipole (MD) transition are changed significantly during transformation from xerogels to nanocrystalline BaF 2 :Eu 3+ glass-ceramic materials. The luminescence decay analysis clearly indicates that the measured lifetime 5 D 0 (Eu 3+ ) considerably enhanced in nanocrystalline BaF 2 :Eu 3+ glass-ceramic materials compared to precursor xerogels. The evident changes in luminescence spectra and their decays suggest the successful migration of Eu 3+ ions from amorphous silica network to low-phonon BaF 2 nanocrystals.

GdF3 nanocrystals doped with Eu3+ ions in oxyfluoride glass ceramics were prepared by a solgel method. The structural properties were examined by x-ray diffraction measurements. The effects of gadolinium codoping on europium emission in the prepared solgel glasses and glass ceramics have been studied. The emission bands originating from the 5D0 state of Eu3+ ions are enhanced under excitation of Gd3+ ions by 273 nm line. The electric dipole 5D0→7F2 transitions were dominant in the samples before heat treatment, whereas magnetic dipole 5D0→7F1 transitions had a higher probability in the samples after annealing. The luminescence lifetime for the 5D0 level of Eu3+ ions in the samples after excitation at 273 nm is long lived in comparison to excitation at 393 nm and increased to 190%. Energy transfer from Gd3+ to Eu3+ was observed.