Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even ...fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.
The Cu-doped mesoporous silica-based particles (Cu-BMS) were prepared using an evaporation-induced self-assembly sol-gel procedure as a heterogeneous catalyst for the activation of peroxydisulfate ...(PDS). The formation of well-organized mesoporous structures with amorphous nature and high surface area of 286 m2/g was demonstrated. The catalytic activity of Cu-BMS in the degradation of Methylene Blue (MB) and the effects of operating parameters, including Cu-BMS dosage, initial PDS amount, initial MB concentration, temperature and initial pH, were investigated in details. The Cu-BMS demonstrated a remarkable catalytic activity (93.5% degradation efficiency within 60 min) and good stability.
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•Cu-BMS achieves 93.5% MB degradation within 60 min.•Enhancement of the catalytic activity of Cu(II) by immobilization on BMS.•Acidic pH enhanced the Cu-BMS catalytic performance.•SO4•− radicals play the main role in degradation of MB in the Cu-BMS/PDS system.•The Cu-BMS catalyst showed good activity over 12 continuous cycles.
Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly ...disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected.
Yttrium aluminate glasses (76.8 mol% of Al
2
O
3
, 23.2 mol% of Y
2
O
3
) doped with Er
3+
and Nd
3+
ions at different concentration levels (0.25 mol%, 0.5 mol% and 0.75 mol% Er
2
O
3
/Nd
2
O
3
) ...were prepared by flame synthesis in the form of glass microspheres. The prepared samples were XRD amorphous, without presence of any crystalline phases in measured patterns. The two exothermic effects (~ 940, ~ 1010 °C), which can be assigned to the two steps of YAG crystallization, were observed in the DSC records of all prepared samples. The high temperature XRD measurements showed YAG (900–1200 °C) and α-Al
2
O
3
(1300–1450 °C) phase crystallization. The emission spectra were measured in the VIS and NIR regions for Er-doped samples and in the NIR region for Nd-doped samples. All measured emission spectra contain of characteristic bands due to the typical 4
f
–4
f
transitions within the Er
3+
and Nd
3+
ions. Comparison of the measured intensities of Er-doped samples made it evident that the highest intensities were obtained for the 0.5 mol% Er
2
O
3
-doped sample (in both the NIR and VIS spectral regions). The maximum intensity for Nd-doped samples was found when the sample was doped with 0.75 mol% of Nd
2
O
3
. The slowly increasing of emission intensities in samples after 20 min annealing at 1000 °C and Stark splitting of emission bands in samples after 40 and 60 min annealing at 1000 °C and after 20, 40 and 60 min annealing at 1500 °C was observed.
The glass of gehlenite composition was prepared by flame synthesis in the form of microspheres. The powder precursor was synthesised by standard solid-state reaction method using SiO
2
, Al
2
O
3
and ...CaCO
3
. The prepared glasses were characterized from the point of view of surface morphology, phase composition and thermal properties by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The prepared samples contained only completely re-melted spherical particles. SEM did not reveal any features indicating the presence of crystalline phases. However, traces of crystalline gehlenite were detected by XRD. The high-temperature XRD measurements (HT XRD) were carried out to identify the phase evolution during glass crystallization. In the studied temperature range, gehlenite phase was identified as the main crystalline phase. Non-isothermal DSC analysis of prepared glass microspheres was carried out from room temperature up to 1200 °C at five different heating rates: 2, 4, 6, 8 and 10 °C/min to determine the thermal properties of microspheres. In order to study the crystallization kinetics, the DSC curves were transformed into dependence of fractional extent of crystallization (
α
) on temperature. The Johnson–Mehl–Avrami–Kolmogorov model was found to be suitable for description of crystallization kinetics. Frequency factor
A
= 5.56 × 10
29
± 1.73 × 10
29
min
−1
, apparent activation energy
E
app
= 722 ± 3 kJ mol
−1
and the Avrami coefficient
m
= 2 were determined. In the studied system, the linear temperature dependence of nucleation rate, diffusion controlled crystal growth interface and a 2D crystal growth were confirmed.
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•Fabrication of novel GeSbNaB:Eu3+ lasing material by melt-quenching Technique.•Structural disorder of the glasses is detected with the incorporation of Eu3+ ions.•The trend ...Ω2 > Ω4 > Ω6 confirmed the covalent nature the as developed glasses.•PL, quantum efficiency and fluorescence intensity ratio (R) are highest for1.0 Eu glass.•GeSbNaB:Eu3+stands out as a solid state active laser medium for intense red emission.
Glasses activated with europium show promising potential for use in applications relating to photonics, in particular solid-state laser generation. In the current work, Eu2O3 incorporated gemanium borate glasses were developed and explored their potentiality towards lasing active medium by probing physical, structural, optical and lasing properties in detail. The physical and structural features of each glass indicated the presence of non-bridging oxygens (NBOs) and an enhancement in network stability on account of the inclusion of europium ions into the GeO2 glass network. Optical energy band gaps, Ed, Eo, no, So, and λo values were obtained by absorption spectra and found to be increased with europium content. The sequence of Judd-Ofelt (JO) intensity parameters (Ω2, Ω4, and Ω6) exhibited the trend Ω2 > Ω4 > Ω6, and it confirmed the covalent nature of the as-developed glasses. 1 mol% Eu2O3 doped glasses exhibited the highest photoluminescence, quantum efficiency and fluorescence intensity ratio (R). The decay profiles showed single exponential nature for 5D0 state of Eu3+ ions and their lifetime values were calculated. The results amply demonstrated the viability of the manufactured glasses as a potential solid-state active laser medium, with the CIE diagram confirming the intense red color emission as seen from the PL spectra.
The ytterbium aluminum garnet composition YbAG (62.5 mol.% Al
2
O
3
, 37.5 mol.% Yb
2
O
3
) was prepared in the form of glass microspheres by flame synthesis. Precursor powder for flame synthesis ...with high homogeneity was prepared by modified sol–gel Pechini method. XRD pattern of prepared glass microspheres indicated predominantly amorphous nature of the sample. Detailed study of morphology of the microspheres by scanning electron microscopy revealed the presence of a small fraction of partially or fully crystallized microspheres. The high-temperature X-ray powder diffraction analysis (HT XRD) was carried out in the temperature interval 750–1450 °C: The temperature dependence of phase composition was determined. Crystallization of Yb
3
Al
5
O
12
—ytterbium aluminum garnet phase—was observed in the temperature range 900–1200 °C. The DSC analysis with heating rates 2, 4, 6, 8, 10 °C min
−1
in temperature interval 25–1200 °C was performed in N
2
atmosphere to study thermal behavior and crystallization kinetics of prepared glass microspheres. The two exothermic effects at 918 and 939 °C were observed, which were attributed to Yb
3
Al
5
O
12
crystallization. The crystallization kinetics of prepared sample was examined with the use of JMAK model, and the kinetic triplet—frequency factor
A
= (1.8 ± 2.2) 10
+28
min
−1
(for the first peak),
A
= (1.2 ± 1.6) 10
+55
min
−1
(for the second peak), apparent activation energy
E
app
= (6.4 ± 0.1) 10
+02
kJ mol
−1
(for the first peak),
E
app
= (1.3 ± 0.1) 10
+03
kJ mol
−1
(for the second peak) and the Avrami coefficient
m
= 3 (for the first peak) and
m
= 2 (for the second peak)—was determined using RSS,
R
adj
2
, AIC and
W
AIC
criteria.
Cerium doped yttrium oxide nanoparticles with various Ce3+ concentrations between 0.001 and 0.010 at% have been synthesised by precipitation method using ammonium hydroxide as a precipitation agent. ...The synthesised powders are characterised by a mean particle size of ca. 55 nm. Highly dense specimens, with a relative density> 98.8%, were obtained by sintering the green compacts shaped by pressure filtration, at 1550 °C for 3 h in air. The sintering behaviour of Ce3+ doped Y2O3 was studied by constructing Master Sintering Curves (MSC); the results showed that the apparent activation energy of sintering for Ce3+ doped Y2O3 increases with the increase of cerium concentration. The segregation of larger Ce3+ cations in the grain boundaries is likely to be responsible for the increase in the sintering activation energy.
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The ALaE glass with eutectic composition (76.2 mol% Al2O3, 23.8 mol% La2O3) and the ALaP glass with LaAlO3 (lanthanum-aluminium perovskite) composition (50 mol% Al2O3, 50 mol% La2O3) were prepared by ...combination of sol-gel Pechini method and flame synthesis in the form of glass microspheres (diameter ≈ 10 μm). The prepared glasses were characterized by OM, SEM, XRD and DSC. The prepared samples contained only completely re-melted spherical particles. However, more detailed study by SEM revealed small fraction of crystalline microspheres. Traces of crystalline LaAlO3 were detected in X-ray powder diffraction patterns of both glasses. DSC analysis in the temperature range 35–1200 °C with heating rates 2, 4, 6, 8 and 10 °C/min was performed in nitrogen atmosphere to study the thermal behaviour and crystallization kinetics of prepared glasses. In the DSC curve of the eutectic ALaE glass recorded at 10 °C/min two exothermic effects were observed at 920 and 936°. Only one exothermic effect at 868 °C was present in the DSC curve of the ALaP sample with perovskite composition. The high-temperature X-ray powder diffraction analysis was carried out in the temperature interval 25–1200 °C. For both compositions formation of LaAlO3 as the main crystalline phase was observed in the whole measured temperature range. In order to study the crystallization kinetics, the DSC curves were transformed into dependence of fractional extent of crystallization, α on temperature. The JMAK model was found suitable for description of crystallization kinetics of both studied systems. The kinetic parameters (A, Eapp and m) were calculated for this model and crystallization mechanisms have been proposed.
The influence of Al2O3 addition on the precipitation of NaYF4 crystals in oxyfluoride glasses has been investigated through the thermal, structural, and optical characterization of the parent glasses ...and corresponding glass–ceramics (GCs). The high‐resolution transmission electron microscopy analysis of the GC with 5 mol% of Al2O3 shows the presence of phase‐separated droplets about 69 nm in size containing several NaYF4 nanocrystals with the diameter of about 10–15 nm. Raman and magic angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy were used to examine the structural changes attributed to the addition of Al2O3. The 19F MAS‐NMR analysis indicated that fluorine atoms are present in different chemical environments (Na–F, Na–Si–F, Na–Al–F, and NaYF4). The increasing amount of Al2O3 reduces the crystallization of NaYF4 phase due to the increased fraction of fluorine bound in Na–Al–F environments. The visible luminescence investigation of the glasses and GCs demonstrated that the intensity of Er3+ ions emission transitions in the GCs was higher than that of the parent glass. This difference was attributed to the presence of Er3+ ions bound in NaYF4 crystalline phase. Further evidence that the Er3+ ions were present in NaYF4 phase was provided by the fact that the excited level Er3+:4S3/2 lifetime was increased in GCs as compared to parent glass.
