Melt-quenching Process Research Articles

Ab Initio Molecular Dynamics Study of Trivalent Rare Earth Rich Borate Glasses: Structural Insights and Formation Mechanisms.

In this work, trivalent rare earth (RE)-rich borate glasses (30 La2O3-70 B2O3, 50 La2O3-50 B2O3, 60 La2O3-40 B2O3, and 50 Y2O3-50 B2O3) were modeled using ab initio molecular dynamics (AIMD) simulations through the melt-quenching route. It was found that the AIMD-derived structures reproduced the experimental structure factors and 11B solid-state nuclear magnetic resonance data. Isolated borate units (monomers, dimers, and trimers) terminated with nonbridging oxygen were found in the structures. Polymer units containing four or more boron atoms were identified with and without three-membered boron rings (3-rings). Increasing the proportion of La2O3 in La2O3-B2O3 glasses resulted in an increased number of isolated units, indicating that La3+ acts as a network modifier, breaking the borate glass network. The formation of these units via the melt-quenching process was detected by labeling boron species at each AIMD step from 1500 to 300 K. Representation with transition matrices clarified the specific reaction routes, leading to the formation of isolated boron units in solid glass. A key finding is the stabilization of polymer units involving 3-ring formation. The formation of isolated units is achieved through the reaction of polymers without 3-rings. The RE coordination structure was thoroughly analyzed from the perspective of shape and symmetry. Reference structures derived from the solution of the Thomson problem were compared to the AIMD-derived coordination structures and crystalline LaBO3 and YBO3. The results highlight the specificity of the Y coordination structure with 3-rings in YBO3, which is not observed in RE borate glasses. The analytical approaches and interpretations used in this study provide insights into the diverse coordination structures of glasses containing heavy elements other than REs.

Effect of Li2O on physical, structural, thermal, optical, and electrical properties of mixed alkali borate glasses containing silver nanoparticles

In this work, mixed alkali borate glasses doped with Li2O were prepared with a molar composition of (75-x) B2O3-15Na2O-8CaO-1V2O5-1AgCl-xLi2O; x = 0, 5, 10, 15, and 20 mol% by using traditional melt-quenching process. X-ray diffraction studies confirmed the amorphous nature of the samples. Upon Li2O doping the glass density, measured at ambient temperature, increases from 2.336to 2.518 g/cm3, while molar volume decreases from 29.637 to 24.337 cm3/mol. The direct and indirect band gap energies determined using UV–Visible absorption analysis was in the range 3.000 –3.285 eV and 2.910–3.218 eV respectively. The DTA measurements indicated that with Li2O addition the thermal stability of the glasses has improved. FTIR study revealed the vibrational modes corresponding to the functional groups present in the glasses. The DC conductivity of the samples (measured at 588 K) was found to increase from 2.394 x 10-4 to 3.987 x 10-4 Ω-1m-1with Li2O content. The temperature dependency of DC conductivity followed Mott’s Small Polaron Hopping (SPH) model at high temperature and Variable Range Hopping (VRH) model at low temperatures. The linear fit of the data to the SPH model yielded the activation energy (W) values in the range 0.152 to 0.693 eV, whereas the density of states at Fermi level evaluated by the VRH model was in the order of 1030 eV-1m-3. The improved electrical conductivity of the prepared Li doped glasses together with their good thermal stability and transparency render them as potential candidates for optoelectronics device applications.

Optical properties and energy transfer of Tm3+ single-doped and Tm3+-Tb3+ co-doped transparent glass-ceramics containing NaGd(MoO4)2 single phase

Tm3+ single-doped and Tm3+-Tb3+ co-doped SiO2–B2O3–Na2O–ZnO–MoO3-Gd2O3 glasses were successfully prepared by the melt-quenching process. X-ray diffraction and transmittance measurements were used to determine that the optimal heat treatment regime consisted of crystallization at 620 °C for 5 h and transparent glass-ceramics containing the NaGd(MoO4)2 single phase were obtained. The characterization results by SEM confirmed that the size of the crystals precipitated in the glass matrix was on the nanometer level. The effects of different contents of Tm2O3 on the luminescent properties of glass-ceramics in this system were explored. The results showed that the emission peak at 453 nm (1D2→3F4) had the highest intensity when Tm2O3 was doped with 0.5 mol% under the wavelength at 359 nm excitation. In addition, with the gradual increase of Tb2O3 contents, the luminescence colour of the Tm2O3–Tb2O3 co-doped glass-ceramics gradually shifted from blue to green. This indicates its potential application in blue-green light display technologies and various other areas. The experimental results of the water resistance stability of the samples show that the co-doped glass-ceramic still has good luminescence stability after being immersed in water, which provides further favourable support for its application.

High transparency Ce3+-doped oxyfluoride glass scintillator for X-ray imaging and γ-ray detection

High transparency Ce3+-doped dense gadolinium aluminum borosilicate (GSx) glass scintillator was synthesized in reducing atmosphere by melt-quenching process. The transmittance of the glasses exceeds 80%, and the light attenuation length is between 5-20 cm within the range of 400–600 nm. GSx glass shows an photoluminescence (PL) in range of 350–550 nm, with the strongest emission peak around 420 nm. The PL decay time of GSx glasses is around 37 ns, with a maximum PL quantum yield of 44.05%. The integrated X-ray excited luminescence (XEL) intensity of GSS glass is 52.5% compared with BGO crystal. For X-ray imaging, GSL glass based imaging system shows a high spatial resolution of 9 lp/mm, which is comparable to CsI:Tl X-ray detectors. Under γ-ray, the highest light yield of GSS glass is 1235 ph/MeV with an energy resolution of 24.0% at 662 keV, close to that of BSO crystal. The scintillation decay time of GSx glasses is consisted of fast (∼100 ns) and slow (∼560 ns) components. In thermally stimulated luminescence (TSL), GSS glass exhibits a strong TSL peak at approximately 440 K, with low intensity shoulders at about 520 K, implying different types of defects and traps. Therefore, GSx glass has promising prospects for X-ray imaging and high-energy physics applications.

Investigation of structural, optical characteristics of Gd3+ doped phosphate glass for radiation shielding applications

Gadolinium doped phosphate glass was created with a composition of 70 P2O5 + 5Al2O3 + 5 Ba2CO3 + 9 KF2 + 5 MnO2 + 5 SnO+1 Gd2O3 by using the melt-quenching process. The prepared glass sample’s amorphous nature was confirmed by the X-ray diffraction analysis. FT-IR examination confirms the presence of phosphate functional groups. Glass’s optical band gap was found to be 3.5 eV using Tauc’s plot method. The photoluminescence analysis indicates that the emission band at around 311 nm. The Commission International de I’Eclairage (CIE) was employed. It was identified that the computed chromaticity coordinate values (x = 0.3164 and y = 0.3371) were situated in the summer sunlight zone, close to the white light region. The attenuation capabilities of the gadolinium-doped phosphate glass sample were validated by the gamma ray shielding parameters. The mass attenuation coefficient and Mean free path of the prepared glass were fund to be 4.41 × 105 cm2/g at 0.015 MeV and 12.4 cm at 15 MeV respectively. In terms of infiltration deepness up to 40 MFP, the energy-related energy buildup factor (EBF) and energy absorption buildup factor (EABF) of glasses were calculated using the five (a, b, c, d, and Xk) parameters of the G-P fitting scheme. All of the results show that the synthetic glass can be used as shielding materials against gamma radiation.

A new approach toward enhancing the gamma-ray shielding efficiency: Zn ions effects on synthesized B2O3-PbO-BaO toward gamma-ray protection applications

In the present work, a newly produced PbO-BaO-B2O3 glass system’s mechanical, physical, and radiation absorption capabilities were studied to determine the effectivity of B2O3 substitution by ZnO. The melt-quench process produced the glasses utilized in the present investigation. The melting point used was 1000 °C, and the temperature at which they were annealed was 400 °C. The experimental measurement of the density for manufactured glass samples was conducted using Archimedes’ theory. It was observed that all density values of the fabricated glasses were raised when the concentration of ZnO was increased from 0 to 20 mol.%. Based on the model proposed by Makishima and Mackenzie from Young, bulk, shear, and longitudinal moduli, it was observed that there was a decrease as the concentration of ZnO was increased in the manufactured glasses. Microhardness was found to be reduced from 4.692 GPa to 4.218 GPa, while the Poisson ratio was found to be decreased from 0.234 to 0.229 when the percentage of ZnO was raised from 0 to 20 mol.%. In contrast, the assessment of radiation shielding qualities through the utilization of Monte Carlo software simulation demonstrates an augmentation in the radiation absorption capability of the manufactured glass samples due to the exchange between B2O3 and ZnO compounds. We used the MCNP5 code to study the radiation shielding properties in a wide energy range of 0.03–2.605 MeV. The linear attenuation coefficient LAC of the produced glass samples increased from 0.315 cm−1 to 0.369 cm−1 when the ZnO concentrations were enriched from 0 to 20 mol.%, respectively.

Significant improvement in the gamma ray attenuation properties of bismuth tellurite glass using molybdenum oxide reinforcement

Due to the high demand for protective materials against ionizing radiations such as gamma rays, X-rays and charged particles, it is necessary to focus more attention on several ways to improve the efficiency of the already existing radiation shielding materials. In the present study, experimental and theoretical approaches were followed to investigate the gamma ray attenuation performance of the bismuth tellurite glass composed of molybdenum oxide. 20MoO3-xBi2O3-(80-x)TeO2 was prepared by melt-quenching process with various compositions of Bi2O3. Absence of sharp peak in the XRD spectra revealed the amorphous nature of the 20MoO3-xBi2O3-(80-x)TeO2. Densities of the prepared 20MoO3-xBi2O3-(80-x)TeO2 was found to vary directly with Bi2O3 content. Additionally, Zeff significantly improved as a result of increase in mol% of Bi2O3 from 10 mol% to 25 mol%. Lowest values of MFP was obtained with MoBiTe4 which has the highest density of 4.819 g/cm3, hence demonstrated better gamma ray attenuation than other three samples. The current study found Bi2O3 in the 20MoO3-xBi2O3-(80-x)TeO2 good for gamma ray attenuation in the lower energy range.

Effect of Bismuth on Physical and Spectroscopic Properties of ZnO-Li2B4O7-TbF3 Glasses

The effect of Bismuth on zinc-lithium tetra borate glasses were discussed based on structural, physical, and spectroscopic properties. Glass systems of Bi2O3-ZnO-Li2B4O7-TbF3 [BZLT] were cast by melt-quench process. Transparent glasses were analysed by diffracted Roentgen X-rays. Peak free and broad nature X-ray diffraction revealed the amorphous arrangement prevailing in these glasses. Density was estimated using the Archimedes principle. Bismuth grossly affected the density of BZLT glasses by increasing its value 2.722 gm/cc [BZLT-0] to 4.6739 gm/cc [BZLT-40]. Optical absorption provides valuable information about optical band gap energy and Urbach energy and some of its derived physical quantities. The effect of bismuth is felt in decreased Eopt values [3.312 eV in BZLT-0] [2.619 eV in BZLT-40] in BZLT glasses. Bismuth altered the structure of the borate network by forming non-bridging oxygens which in turn reduced the band gap energy by large margin (ΔEopt = 0.693 eV). Fourier transform infrared spectroscpy and Raman studies revealed the presence of several triangular BO3 and tetrahedral BO4 and BiO3 units and also the existence of metal cation vibrations and supported the large deviations in the optical bandgap energies. Election paramagnetic resonance studies support the presence of Tb3+ ions and absence of Tb4+ions in BZLT glasses.

The impact of Bismuth Ion on the physical and optical characteristics of borate glasses

The bismuth doped borate (Bi2O3–B2O3) glasses were made using the melt quench process. The physico-optical characteristics, including their molar and density of the specimens were examined. The density readings were obtained using the Archimedes principle. The X-Ray differ actogram was used to verify that the specimens are amorphous. Using Tauc's approach, the optical characteristics of the specimens, including their direct and indirect forbidden energy gaps, were computed. The Urbach energy and steepness of the glass system were calculated to determine its disorderliness. The effect of Bi on physical and optical properties as density, poleron radius, forbidden energy gap, refractive index etc, were observed. The metallization criteria were used to examine the materials' non-metallic character.

Concentration-dependent physical, optical, and photoluminescence features of Pr3+-doped borate glasses

Lanthanum barium borate glasses doped with praseodymium were fabricated by a melt-quenching process, to study the effect of Pr2O3 on their properties. The addition of Pr₂O₃ in glass increases its density, molar volume, and refractive index. XRD confirms an amorphous nature of glass network, and XANES approves the praseodymium character as Pr3+ oxidation state in glass. Glasses absorb photons in ultraviolet and near-infrared region by the Pr3+ transitions from 3H4 ground state. The photoluminescence spectra of glasses exhibit the strongest emission at 602 nm (1D2 → 3H4) under 442 nm excitation (3H4 → 3P2). The optimal 0.5 mol% Pr2O3-doped glass possesses the highest emission intensity due to the concentration quenching effect. Judd-Ofelt theory was used to determine the Pr3+ site environment in glass and its dominant stimulated emission. Strong orange emission of this glass is suitable for orange solid-state lasers, LEDs, and emitting devices.

Radioluminescence and photoluminescence properties of Sm3+-doped Gd-Ba-Na borate glass scintillator

This study investigates the potential of Gd-Ba-Na borate glasses doped with Sm3+ ions as scintillation materials. The glasses were synthesized using a melt-quenching process, and their luminescence properties were examined. The results demonstrate that the glass sample with 0.5 mol% of Sm3+ exhibits the most promising scintillation performance, achieving the highest integral scintillation efficiency (24.11%) compared to the BGO crystal. For the photoluminescence study, the emission spectra, under 403 nm excitation wavelength, show emission bands centered at 563, 599, 646, and 706 nm, consistent with characteristic Sm3+ transitions. The highest energy transfer efficiency from Gd3+ to Sm3+ (64.37%) is also found in the glass sample with 0.5 mol% Sm3+. The emission color can be tuned by varying the excitation wavelength. Excitation at 403 nm primarily excites Sm3+ ions, resulting in orange emission. In contrast, excitation at 275 nm excites Gd3+ ions, leading to reddish-orange emission. The results demonstrate the potential of this glass composition for use as a highly efficient scintillation material due to its excellent performance in both radioluminescence and photoluminescence properties.

The role of ZnO in the radiation shielding performance of newly developed B2O3–PbO–ZnO–CaO glass systems

Glasses with varying compositions were prepared using the melt-quenching process within the 40B2O3–20PbO-xZnO-(40-x)CaO system, where x = 20, 25, 30 and 35 mol%. ZnO's influence on the prepared glasses' radiation shielding properties was studied in the 0.015–15 MeV energy range. The results demonstrated that ZnO has a significant shielding effect at low energies, where there is an increased in the linear attenuation coefficient from 279.96 to 319.17 cm−1 at 0.015 MeV due to the 20-to-35 mol% increase in ZnO. The values of the mean free path (MFP) for the prepared glasses are very small when the energy is less than 0.1 MeV, in the order of 0.013–0.015 cm at 0.03 MeV, 0.051–0.055 cm at 0.05 MeV and 3.051–3.248 cm at 1 MeV, which revealed an enhanced attenuation efficiency with increasing ZnO content. According to the MFP results, the Zn35Ca5 sample (which contains 35 mol% ZnO) offers the best shielding performance. The half value layer (HVL) was also evaluated, and we found that the HVL is in order of 1.5 cm at 0.6 MeV, and in order of 3 cm at 2 MeV, while at 15 MeV, the HVL is 4.30 cm for Zn20Ca20 and 3.74 cm for Zn35Ca5.

Influence of ZnO and Pr6O11 incorporation on the structural, thermal, optical, mechanical, and magnetic properties of calcium lithium borate glasses

A new glass of calcium lithium borate with the chemical formula (62.75-x)B2O3 + 20CaO + 0.25Pr6O11 + 17Li2O + xZnO, where x = 0, 2.5, 5, 10, 20 (mol%) have been prepared by conventional melt-quenching process. The amorphous character has been confirmed by the very short-range ordering structural matrices demonstrated through X-ray diffraction.The Raman spectra of the prepared glass revealed an enhancement of host lattice distortions. Differential scanning calorimetry (DSC) estimated the glass transition temperature (Tg), the onset temperature of crystallization (Tc), and the melting temperature (Tm). The glass transition decreased from 441 °C to 431 °C with increasing ZnO content up to 10 mol%. The criteria of glass samples up to 10 % ZnO have higher strength, rigidity and higher level of thermal stability. The physical quantities as density, molar volume, inter-atomic distance, polaron radius, packing density, and oxygen packing density were calculated. The glass density increases while the molar volume decreases with ZnO content. The optical properties of glasses were investigated using UV–Vis spectrophotometer. The addition of ZnO enhances the light absorption in UV–Vis. The results of the calculated direct and indirect optical band gaps decrease from 3.663 eV to 3.233 eV for and from 3.167 eV to 2.648 eV for direct and indirect transitions respectively with the increment of ZnO addition. Additionally, the dispersion energy and static refractive index clearly increase while the oscillator energy declines. The Makishima-Mackenzie’s (M−M) method was employed to ascertain mechanical parameters, including elastic moduli, and Poisson’s ratio. The study revealed an enhancement to the mechanical properties as the content of ZnO increased. Vibrating sample magnetometer (VSM) was used to investigate the magnetic properties of the prepared glass and all samples exhibited a ferromagnetic behavior. The incorporation of ZnO act as glass modifier controlling their physical, optical and mechanical properties making the investigated glasses suitable for various applications.

Cathodic Deposition-Assisted Synthesis of Thin Glass MOF Films for High-Performance Gas Separations.

Glass metal-organic framework (MOF) films can be fabricated from their crystalline counterparts through a melt-quenching process and are prospective candidates for gas separation because of the elimination of the grain boundaries in crystalline MOF films. However, current techniques are limited to producing glass MOF films with a thickness of tens of micrometers, which leads to ultralow gas permeances. Here, we report a novel cathodic deposition-assisted synthesis of glass ZIF-62 films with a thickness as low as ~1 μm. Electrochemical analyses and deposition experiments suggest that the cathodic deposition can lead to pure crystalline ZIF-62 films with a controllable thickness of ~2 μm to ~15 μm. Accordingly, glass ZIF-62 films with a thickness of ~1 μm to ~10 μm can be obtained after a thermal treatment. The fabricated defect-free glass ZIF-62 film measuring 2 μm in thickness shows a remarkable CO2/N2 and CO2/CH4 selectivity of 31.4 and 33.4, respectively, with a CO2 permeance which is over 30 times higher than the best-performing glass ZIF-62 films in literature.

Thermal, and radiation shielding properties of SrO–B2O3–TeO2–ZnO–Bi2O3 glasses doped with Dy2O3

The newly proposed materials demonstrated outstanding and effective radiation shielding capabilities and promising mechanical properties. A series of (20-x) SrO-(73)B2O3-(5)TeO2-(1)ZnO-(1)Bi2O3 doped with x-Dy2O3 have been produced employing the traditional melt-quench process, with the concentration of Dy2O3 varying from 0.05 to 1.5 mol%. This research examined glass samples' structural stability, mechanical and thermal characteristics, and radiation shielding capabilities. All of the glasses were amorphous, as confirmed by the X-ray examination, and the glass with the label SBTZBD6 had the maximum density because of the higher Dy2O3 content. The insert of Dy2O3 into the glass composition increased density values from 2.94 to 3.04 g/cm3 for SBTZBD1 and SBTZBD6 and improved mechanical properties such as Poisson ratio and elastic moduli. The hardness Vickers showed the maximum value at 1095.7 HV corresponding to Dy2O3 1 mol%, indicating the influence of Dy2O3 addition on the mechanical properties. The ability of the generated samples to shield against several forms of radiation, such as alpha, proton, neutron, and gamma radiation, was examined using SRIM and Phy-X software. The lowest HVL is 0.009 cm for SBTZBD6 at 0.02 MeV, the highest HVL was observed at 15 MeV with a value equal to 7.066 cm for the same sample. Dy2O3 was used instead of SrO, significantly increasing the μ/ρ values and improving radiation shielding. However, it was discovered that fast neutron shielding experienced a reduction in energy loss per unit mass (mass stopping power) when SrO was replaced with Dy2O3. However, the substitution also reduced energy loss per unit mass for alpha and protons and fast neutron shielding. To sum up, this study's glass samples are highly recommended for ionizing radiation shielding.

Manganese addition effect on structural and physical properties of calcium borovanadate glasses

New calcium borovanadate glass containing manganese ions within the system x Mn2O3-(30-x) V2O5-50 B2O3-20 CaO has been elaborated* in this work using melt quench process. The primary objective of this research is to examine the influence of introducing Mn2O3 upon the various properties of the elaborated glass specimens including physical, thermal, structural, optical and magnetic properties. X-ray diffraction indicated that the samples prepared were amorphous. The variation in density and molar volume revealed that the structure of the glass matrix cross-links and becomes more compact with increasing Mn2O3 content, which is confirmed when the glass transition temperature is increased. Furthermore, in order to check the group constitution of our glasses, a structural study was carried out using infrared (FTIR) and Raman spectroscopy. The optical characteristics of our vitreous materials were analyzed by UV solid, and the results of the band gap energy and refractive index values revealed an enhancement of non-bridging oxygen atoms (NBOs) with rising Mn2O3 concentration, also suggests that manganese acts as a structure modifier. The low Urbach energy values are an indication that the structure of our glasses is stable and uniform. The magnetic investigation highlighted the presence of the predominant antiferromagnetic order in the glass samples studied, which becomes stronger with the incorporation of more manganese ions into the structure.

Modifying of physical, biodegradation, drug delivery characteristics of bioactive borophosphate glass by addition of molybdenum

In this study, high valence MoO3 was added to bioactive glass based on (50-x) P2O5 - 20 B2O3 – 20 CaO - 10 Na2O (x = 0, 5, 10–15 mol. %; the corresponding samples encoded as 0-Mo, 5-Mo, 10-Mo, and 15-Mo) to modify its physical, biodegradation, drug delivery properties. The glasses were prepared via melt-quenching process. The obtained glasses were analyzed by XRD, FTIR, SEM, Raman, and zeta potential (-42, - 31.8, - 34.5, and - 26.4 mV for 0-Mo, 5-Mo, 10-Mo, and 15-Mo, respectively). The in vitro bioactivity and biodegradation were examined in the simulated body fluid (SBF). The glasses were checked for ability for drug delivery by using ciprofloxacin (CIP) antibiotic as a drug model to attain an anticipated therapeutic response to avoid infections, and the drug release kinetic was studied by fitting the release data with Higuchi and Hixon-Crowell models. Finally, the antibacterial activity of the glasses conjugated with drug and drug-free glasses was tested against gram positive bacteria (Streptococcus aureus), gram negative bacteria (Escherchia coli) and Pathogenic yeast (Candida albicans). The results showed that the glasses were characterized by amorphous structure, and it showed a good bioactivity after immersion in SBF. Moreover, the results presented that addition of molybdenum increased the degradation rate of the glasses and affected their surface charge to less negative. In addition, it increased the drug loading efficiency and drug release rate, where 11.2 %, 56.9 %, 75.4 %, and 83.6 % of the drug released from 0-Mo, 5-Mo, 10-Mo, and 15-Mo, respectively, at the end of incubation time. The drug release occurred by combined diffusion and dissolution mechanism. Finally, antibacterial activity showed that drug-free glasses possessed antibacterial activity against the bacterial, meanwhile the antibacterial activity increased by loading CIP on the glass particles. In conclusion, different physical properties, as well as biodegradation and drug release can be tailored by addition of molybdenum. On the other hand, the prepared glasses are expected to be used successfully as multifunctional bone grafting materials.

Studies on the fatigue failure behaviour of novel carbon nanotube–glass composites

Single walled carbon nanotubes (SWCNTs) based glass composites were fabricated through a melt-quench process and their fatigue failure properties were studied using a repeated indentation technique. The SWCNT–glass composites were found to exhibit significantly reduced damage in comparison to their respective base glasses, as corroborated by field emission scanning electron microscopy (FESEM). The fatigue resistance parameter (n) of the samples was determined where considerable increment in ‘n’ values in case of composites than that of the base glasses was observed. Moreover, a mathematical equation was also proposed for the theoretical estimation of the percentage enhancement in fatigue resistance parameter (In) of the composites and it was found to be in good agreement with the experimental values. Finally, the superior fatigue resistant behaviour of the SWCNT-glass composites was well elucidated with the help of cushioning effect and enhanced plasticity of the nanotube bundles embedded within the glass structure.

Cool white light generation of Dy3+ activated aluminum sodium calcium borate glass for W-LED application

The Dy3+-activated aluminum sodium calcium borate glass with white light emission might have been created through the melt-quenching process. This research explores the optical and luminescence characteristics of borate glasses. Dy3+-activated glasses exhibit absorption in the visible (VIS) and near-infrared spectrums. The absorption starts from the 6H15/2 ground state to the higher state concerning optical characteristics. The emission spectra of dysprosium-doped glasses' photoluminescence show greater intensity at 483 nm (blue light) and 575 nm (yellow light), which are critical wavelengths for white light-generating materials. The luminescence intensity of Dy3+ ions increased up to a 0.50 mol% concentration, while the decay time decreased with an increasing dysprosium ion concentration. The emission spectra were used to estimate the CIE 1931 chromaticity and corresponding color temperature, revealing a shift towards the cold white light location at that temperature. The stimulated emission cross-section is calculated via the Judd-Ofelt theory. All characteristic outcomes suggest that the existing dysprosium-enabled glasses are excellent materials for generating cool white light in W-LED applications.

Extraction of local structure differences in silica based on unsupervised learning.

Silica exhibits a rich phase diagram with numerous stable structures existing at different temperature and pressure conditions, including its glassy form. In large-scale atomistic simulations, due to the small energy difference, several phases may coexist. While, in terms of long-range order, there are clear differences between these phases, their short- or medium-range structural properties are similar for many phases, thus making it difficult to detect the structural differences. In this study, a methodology based on unsupervised learning is proposed to detect the differences in local structures between eight phases of silica, using atomic models prepared by molecular dynamics (MD) simulations. A combination of two-step locality preserving projections (TS-LPP) and locally averaged atomic fingerprints (LAAF) descriptor was employed to find a low-dimensional space in which the differences among all the phases can be detected. From the distance between each structure in the found low-dimensional space, the similarity between the structures can be discussed and subtle local changes in the structures can be detected. Using the obtained low-dimensional space, the β-α transition in quartz at a low temperature was analyzed, as well as the structural evolution during the melt-quench process starting from α-quartz. The proper differentiation and ease of visualization make the present methodology promising for improving the analysis of the structure and properties of glasses, where subtle differences in structure appear due to differences in the temperature and pressure conditions at which they were synthesized.