Average Coordination Number Research Articles

Dynamic Behavior Analysis of Wax Crystals during Crude Oil Gelation.

The motion behaviors, rheological properties, and mechanical properties of a wax crystal mesoscale force chain network of waxy crude oil during gelation were experimentally studied and simulated by rheo-optic in situ measurement and computational fluid dynamics-discrete element method (CFD-DEM) numerical simulation, respectively. The motion behavior characteristics of wax crystals and the changes in the average coordination number of wax crystal networks were obtained at different temperatures. The study investigates the rule of crude oil rheological deterioration, the increase of wax crystals, and the changes in wax crystal motion behaviors with decreasing temperature. The relationship between the structure of the mesoscale force chain of the wax crystal network and the motion behaviors of the wax crystal and its rheological properties was analyzed. The results show that the average motion velocity of wax crystals or aggregates decreases from 28.48 to 22.56 μm/s when the temperature decreases from wax appearance temperature (48 °C) to 25 °C. The rotation and rolling trend of wax crystals gradually flatten, and the average coordination number increases 4.39 times. The viscosity of waxy crude oil increases from 6.27 to 8369.7 mPa·s, and the average coordination number of wax crystals obtained by CFD-DEM also increases significantly, which confirms the experimental results. We also found that when the system tended to gelation, a complex and stable force chain network was formed between the wax crystals, with a force chain coverage of 87.93% and a significant increase in the pressure drop in the flow field, which is consistent with the variation pattern of the system viscosity. The micro-meso-dynamic behavior analysis of waxy crude oil combined with CFD-DEM coupling provides a new way to explore the rheological properties of waxy crude oil and the microscopic mechanism of its modification.

Study of correlations between glass-transition temperature and local structure of Ge-As-Se, Ge-As-Se-S chalcogenide glasses

ABSTRACT The local structure and glass transition of Ge-As-Se, Ge-As-Se-Schalcogenide glasses have been studied by X-ray diffraction and differential scanning calorimetry. By applying the theory of topological constraints and considering chemically ordered network models, it has been determined that Ge10As20S10Se60 (average coordination number = 2.4), Ge25As10S25Se40 ( = 2.6) are the compositions associated with the more stable glasses. This result is related to the larger differences between the glass transition (Tg ) and crystallization-transition (Tcr ) temperatures (ΔTg-cr ∼ 38 and 43 K) at these compositions. Relatively high values of short-range (d∼5.7–6.34 Å) and medium-range (L∼26.59–33.74 Å) order parameters of the local structure in the glass compositions satisfying the mentioned conditions affect the glass-transition temperature (Tg ) and cause its value to increase (Tg ∼589–689 K). As a result of comparative analyses of X-ray diffraction and differential scanning calorimetry curves it has been determined that there is a correlation between the glass-transition temperature (Tg ) with the short range (d) and medium range order (L) parameters of the local structure.

Compositional dependence of physical parameters of Sb-doped InSe nanochalcogenide alloys

ABSTRACT InSe is a III-VI semiconducting layered compound having potential applications in memories, solar cells, infrared sensors, switching devices and optical fibers. In this article various physical parameters of In0.1Se0.9-x Sb x (x = 0, 0.04, 0.08, 0.12) chalcogenide alloy depending on the varying composition of Se and Sb are discussed. The physical parameters include the theoretical calculations of average coordination number, number of constraints, floppy modes, number of lone pair electrons, deviation of stoichiometry, average heat of atomization, mean bond energy, density, molar volume, compactness, cohesive energy, electronegativity, energy band gap, conduction and valance band energy and glass transition temperature. The number of lone pair electrons and floppy modes is found to decrease, whereas the average coordination number, mean bond energy, average heat of atomization and density are found to increase with increasing Sb content. The theoretical values of glass transition temperature are calculated using the Tichy-Ticha and Lankhorst approach.

DEM study on evolution of soil arching in a deep trapdoor in seismic shaking conditions

In this study, the soil arching formed in a deep trapdoor model was investigated using the discrete element method, considering the magnitude, frequency, and direction in seismic shaking conditions. The parameters were validated using prior trapdoor test results. The results showed that the ultimate soil- arching ratio increased after shaking, indicating that the soil arching effect had degraded. The fluctuation range of the soil arching ratio increased with increasing shaking frequency. The ultimate average coordination number of the region above the trapdoor steadily increased as the shaking magnitude increased. Soil arching was more significantly influenced by shaking in the vertical (z-axis) direction than in the horizontal direction. The force chain in the arched region above the trapdoor progressively increased as the shaking magnitude increased, and clearly degenerated above the stationary region. As the shaking amplitude increased, the ultimate soil arching ratio increased; however, the ultimate coordination number decreased.

Evaluation of the microscale structure and performance of asphalt mixtures under different design methods

Asphalt mixture design methods have an important influence on both the microscale structure formed and the corresponding properties. This research compared the performance of asphalt mixtures with the Balanced design method, Marshall design method, and Superpave design method. CT scans were performed on the mixture specimens under different design methods to analyze the mixtures' void distribution law and skeleton structure stability. Then, the water stability of asphalt mixtures with different skeleton structures was evaluated by the water immersion Marshall test and freeze–thaw splitting test, and the effects of temperature and loading frequency on the dynamic modulus of asphalt mixtures under different skeleton structures were assessed by uniaxial compression dynamic modulus test. Finally, based on the time–temperature equivalence principle and Sigmoid model, the master curves of the dynamic modulus of asphalt mixtures under different design methods were constructed. The results showed that the number of coarse aggregate contact points and the average coordination number of asphalt mixtures were relatively larger under the Balanced design method, and the residual strength ratio of asphalt mixture under the Marshall design method was 1.4% larger than that of the Balanced design method, and the residual strength ratio of specimens under Superpave design method was 6.1% larger than that of the Balanced design method. At the same time, based on the differences in the air void of the specimens under different design methods and the different skeleton structures, the dynamic modulus laws under the action of different frequencies were obtained, and the mechanism of the influence of the skeleton structure on the dynamic modulus of the mixture was revealed. This research has important implications for the durability improvement of asphalt mixtures.

Characterization of internal pore size distribution and interconnectivity for asphalt concrete with various porosity using 3D CT scanning images

The open pore characteristics of asphalt mixtures play a crucial role in their resistance to water-induced damage. Accurate extraction and analysis of the pore structures at a micro level can reveal the seepage characteristics of asphalt pavements. However, existing studies mainly focus on the through-pore characteristics of porous asphalt mixtures and there is a lack of research on the open pore characteristics and interconnected paths of dense graded asphalt mixtures. This study aims to fill this gap by using 3D X-ray computed tomography technology to analyze the digital images of three typical asphalt mixtures with different porosities. The study quantitatively and statistically analyzes several new pore structure parameters at a micro level, such as porosity, equivalent diameter, coordination number, pore throat dimension, and tortuosity. The interconnected paths of the pores are also compared and analyzed. The results show that as the total pores content increases, the difference between the pore fraction and open pores fraction decreases. The porosity of porous asphalt mixtures is high, but mainly composed of interconnected pores with only a small proportion of closed pores. The coordination number determines the connectivity and thus the porosity of the asphalt mixture, and larger open pore channels lead to larger pore diameters and greater permeability. As the porosity of the asphalt mixture increases, the average coordination number of its internal pores also increases, leading to better pore connectivity and a more complex pore network.

Characterizing force-chain network in aggregate blend using discrete element method and complex network theory

The force chain network in aggregate blend indicates load transfer path and is the main carrier to resist external loads. The objective of this study is to analyze the force chain network characteristics of aggregate blend on the basis of complex network theory. The virtual aggregate blend models with three stone matrix asphalt (SMA) gradations and three dense asphalt concrete (AC) gradations were constructed using discrete element method (DEM). The force chain network topology structure of each aggregate blend was established according to the aggregate contact parameters extracted from DEM software and the introduced complex network theory. The characteristics of each force chain network were analyzed by the various network evaluation indicators. The results showed that there are two or more contacts between most particle pairs. The average coordination number and the average contact number of aggregate blend are not equal. The degree distribution of each gradation shows a good power-law distribution. The force chain network of aggregate blend is a scale-free network. Big particles have greater average strength and smaller average weight distribution difference compared with small particles. The reference lower limit has better clustering performance for SMA-16, and the reference upper limit has better clustering performance for AC-25. The average path length of SMA-16 is longer than that of AC-25, indicating that SMA-16 has better load transfer ability and skeleton properties.

Numerical Simulation of Mechanical Properties of Soil Considering the Effect of Internal Erosion

The loss of fine particles from the skeleton formed by coarse particles due to seepage action significantly affects the grading, void ratio, and mechanical properties of soil. This results in several issues of engineering hazards. In order to analyze the effect of internal erosion on the mechanical properties of gap-graded soils from macro and micro perspectives, triaxial consolidation and drainage shear tests were simulated in this paper using the particle flow discrete element software PFC3D. A linear contact model was employed to simulate internal erosion by randomly removing fine particles. The results showed that the void ratio of the specimens increased with the erosion degree. The variation in void ratios of the specimens with the erosion degree before loading was greater than those after loading. The peak deviatoric stresses of the specimens decreased with the increase of the erosion degrees. The larger the erosion degree, the more the maximum volumetric strain and the resistance capacity to deformation was also reduced. The average particle coordination number (Z) of the specimens generally tended to decrease as the erosion degree increased. When the average effective stress was not large, the critical state line gradually increased with the erosion degree, while the void ratio was also found to correlate with the erosion degree under the critical state of the specimens with zero average effective stress.

Experimental micro–macromechanics: particle shape effect on the biaxial shear response of particulate systems

The effect of particle shape on micro and macroscopic behaviour is investigated experimentally through a series of biaxial compression tests on round and angular rods. Dual-size assemblies of thousands of circular (round) or hexagonal (angular) particles were sheared under three confining pressures. The displacement, rotation and evolution of coordination number of all the particles during the shearing process were identified through image analysis. The macroscopic results show that the angular assemblies exhibit higher strengths and dilations. Angular particles tend to be more dilative and have higher critical state strengths. The microscale features show that the magnitude of particles' rotation is higher in circular assemblies. Particle rotations are normally distributed within both samples. However, rotating clusters are observed in angular samples. Angular particles are more resistant to rotations due to interlocking and clustering, causing higher strength at the macroscale. The absolute mean cumulative rotation for the circular assemblies at the end of shearing was approximately twice that of the angular assemblies. In circular assemblies, small particles rotate almost twice as much as big particles, which initiates a ball-bearing effect that further contributes to strength reduction. Particle rotation further governs the average coordination number, with hexagonal aggregates having higher coordination numbers.

Compositional effects of Ga incorporation on electrical and dielectric parameters in Ge-Se-Sb-Ga thin films

In this paper, the existence of new selenium-rich chalcogenide glassy systems i.e. (Ge20Se80)90-xSb10Gax (x = 2, 4, 6 and 10 at %) had been reported. (Ge20Se80)90-xSb10Gax glassy systems were prepared using melt-quenching technique. Thin films of (Ge20Se80)90-xSb10Gax were prepared on properly cleaned glass substrates using vacuum evaporation technique. Planar geometry of indium (In) electrodes (electrode spacing 0.08 cm) was used for electrical measurements. The physical parameters – average number of constraints, cohesive energy, mean bond energy, average coordination number, heat of atomization, glass transitition temperature and lone pair electrons had been estimated. The high values for the lone pair electrons proves the investigated system to be a good glass former. The increasing values of cohesive energy, glass transition temperature and mean bond energy with the incorporation of Ga, reveal that Ge-Se-Sb-Ga glassy systems are thermally stable glasses. The current transport mechanisms had been studied within the temperature range 173–363 K. Thermionic emission dominated in the high temperature region above 333 K. Within the intermediate temperature range 273–333 K, thermally-assisted tunneling of the charge carriers through grain boundary potential as well as thermionic emission over grain boundary potential contributed to the conduction mechanism. Below 273 K, Mott’s hopping process dominated the conduction mechanism. Dielectric measurements had been examined within the temperature range 173–363 K and the frequency range 50 Hz–1 MHz. Dielectric constant as well as dielectric loss decreased as the frequency was increased and increased as the temperature was increased. Orientation polarization described the temperature-dependence and frequency-dependence of dielectric constant. Temperature-dependence and frequency-dependence of dielectric loss was explained by conduction loss as well as hopping of charger carriers. The ac conductivity agrees with the power law: ωs where s < 1. The present investigation of dielectric parameters could be explained in terms of correlated barrier hopping (CBH) model. Profound analysis of the physical, electrical and dielectric properties and their variation as a function of Ga-content suggest the utilization of these glasses in optoelectronic devices.

Short range order of glassy KSb5S8 by diffraction, EXAFS, vibrational spectroscopy and DFT calculations

We report on a detailed experimental and simulation study of the short- and medium-range order of a potential phase change material – glassy KSb5S8. On the experimental side, diffraction techniques and EXAFS have been employed to record accurate structural data. Structural models have been generated by fitting multiple datasets simultaneously with the reverse Monte Carlo simulation technique. In addition, density functional theory was employed to study the structure and vibrational modes of selected clusters, representative of the glass structure. Unconstrained RMC simulation runs revealed that the average Sb-S coordination number is 3.18 ± 0.2, thus Sb is mostly threefold coordinated in the glassy state. The fraction of edge and corner sharing SbSn polyhedra and distribution of bridging S atoms (Qn distribution) have also been obtained. Distribution of bridging S atoms around Sb is similar in the crystalline and glassy states. DFT calculations assisted in the identification of a Raman mode at ∼468 cm−1, assigned to hypervalent bonding (quasi-tetrahedral units) in the glass structure.

Direct evidence and mechanism for biocrusts-induced improvements in pore structure of dryland soil and the hydrological implications

As a crucial living skin inhabiting the soil-atmosphere interface, biocrusts play a vital role in various soil properties and processes, especially surface soil pore structure and soil pore-related hydrological processes, such as infiltration and evaporation. However, it remains unclear how biocrusts affect pore structure in the micrometric point of view. In this study, X-ray computed tomography and image analysis were employed to quantify the differences in soil pore structure between bare soil and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) at 0–50 mm depth. Three-dimensional images were segmented and analyzed to assess morphological and geometrical properties, such as porosity, pore volume, degree of anisotropy, Euler number, pore shape, pore connectivity, and pore tortuosity. Our results showed that the porosity of three types of biocrusts was, on average, 100% higher than bare soil, and the porosity ranked in order of moss crusts > mixed crusts > cyanobacterial crusts > bare soil. In comparison to bare soil, pore surface area density, mean pore volume, and node density of biocrusts were increased by 45%, 422%, and 52% on average, respectively. Biocrusts had larger fractal dimensions but lower degrees of anisotropy, mean tortuosity, and Euler number, which indicates the pore structure of biocrust became more complex and stable with higher connectivity compared to bare soil. Additionally, elongated pores had the largest contribution to porosity, and these pore proportions were significantly higher in biocrusts than bare soil. More importantly, the pore network model and network analysis revealed that biocrusts have a higher connected porosity (17% vs. 4%), connected porosity/isolated porosity (11.7 vs. 0.6), average coordination number (8 vs. 5), and number of channels (14,480 vs. 807), but a lower average channel length (2.7 vs. 3.8 mm), which indicates that the physical and topological structures of pore network in biocrusts were reconfigured and exhibited a better pore network connectivity. Moreover, the biocrusts increased soil water holding capacity by 87% on average, but decreased saturated hydraulic conductivity by 55% as compared to bare soil. From the reshaped pore structure, improved soil water holding capacity, and decreased infiltrability of the biocrusts in comparison to bare soil, we conclude that biocrusts play a vital role in surface soil water balance, which subsequently affect surface hydrological processes (e.g., runoff generation and evaporation) in drylands.

Hydration of Phosphate Ion in Polarizable Water: Effect of Temperature and Concentration

The hydration of phosphate ions, an essential component of many biological molecules, is studied using all-atom molecular dynamics (MD) simulation and quantum chemical methods. MD simulations are carried out by employing a mean-field polarizable water model. A good linear correlation between the self-diffusion coefficient and phosphate anion concentration is ascertained from the computed mean-square displacement (MSD) profiles. The HB dynamics of the hydration of the phosphate anion is evaluated from the time-dependent autocorrelation function CHB(t) and is determined to be slightly faster for the phosphate–anion system as compared to that of the water–water system at room temperature. The coordination number (CN) of the phosphate ion is found to be 15.9 at 298 K with 0.05 M phosphate ion concentration. The average CN is also calculated to be 15.6 for the same system by employing non-equilibrium MD simulation, namely, the well-tempered meta-dynamics method. A full geometry optimization of the PO43−·16H2O cluster is investigated at the ωB97X-D/aug-cc-pVTZ level of theory, and the hydration of the phosphate anion is observed to have both singly and doubly bonded anion–water hydrogen bonds and inter-water hydrogen bonds in a range between 0.169–0.201 nm and 0.192–0.215 nm, respectively. Modified Stokes–Einstein relation is used to calculate the conductivity of the phosphate ion and is found to be in good agreement with the experimentally observed value.

Ab-Initio molecular dynamics simulations of binary NaCl-ThCl4 and ternary NaCl-ThCl4-UCl3 molten salts

Molten salt reactor (MSR) with Thorium (Th) fuel cycle has attracted growing attention due to its merits such as safety, low radioactive waste production, and non-proliferation. The design and safe operation of MSR rely on a thorough understanding of the thermophysical properties of molten salts over a wide range of composition and temperature. However, experimental data of Th-based molten salts are limited due to the inherent challenges of dealing with corrosive molten salts and the radioactive nature of actinides. In this work, thermophysical properties including density, heat capacity, thermal expansion coefficient, and mixing energy of binary NaCl-ThCl4 and ternary NaCl-ThCl4-UCl3 molten salts are explored using ab-initio molecular dynamic simulations (AIMD) with the dDsC dispersion correction. The calculated mixing energy of binary NaCl-ThCl4 exhibits a minimum close to the eutectic composition. The heat capacity of the mixtures is linearly dependent on the mole fraction of each component. 7-fold and 6-fold coordinated Th complexes are dominant in the mixtures. 8-fold coordinated Th complex increases with ThCl4 fraction due to the formation of network structures. The average coordination number of Th exhibits a minimum near the eutectic composition. The minimum mixing energy for the ternary mixtures is observed in systems with a composition close to [NaCl]0.5[ThCl4]0.25[UCl3]0.25. The density positively deviates from the ideal solution in mixtures near this composition. These results are important to fill the data and knowledge gap of ThCl4 molten salts.

Method for estimating the structural parameters of ceramics

A simplified method is proposed for determining the structural parameters of composite ceramics using porcelain as an example from the average coordination number of random packing and optical microscopy data. This eliminates the ambiguity in the representation of structural parameters. The calculated average distance between quartz particles in porcelain agrees well with experiment. Ill. 1. Ref. 9. Tab. 2.

Short- and medium-range structure synergistically control fracture toughness of densified aluminoborate glasses

Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.

Structural and thermal characteristics of Ge30−xSbxTe10Se60 (0 ≤ x ≤ 20) glasses for electronic devices

Thermal characterization of different compositions of Ge30−xSbxTe10Se60 (x = 0, 5, 10, 15, 20 at.%) glassy materials has been investigated through differential scanning calorimetry (DSC). The tested glasses have been synthesized by melt-quench technique. Glassy materials display compositional phase separation at x = 0, 5, 10, 15 at.%. For additional increase in Sb content at x = 20 at.%, the separation of phases combines in the glass matrix. The glass transition temperature (Tg), initial temperature of crystallization (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) were found to be affected by both heating rate and composition. It is noticed that the increasing of antimony mass percentage in the glassy matrix is leading to decrease in Tg, Tc, Tp and Tm values. The melting temperature (Tm) of these glasses was found in the range 733–746 K for the first phase and in the range 740–792 K for the second phase. The activation energy of glass transition (Eg), activation energy for crystallization (Ec), Avrami index (n) and fragility index (Fi) were calculated using these specific temperatures. Eg decreases with increasing Sb content in all studied samples, but Eg is increasing in the sample with Sb content of 20%, and hence, it varies between 102.7 and 110.6 kJ approximately, whereas (Ec) decreases with the increase in the Sb content in all the tested samples and varies between 283 and 339 kJ. The fragility index varies between 10 and 26 indicating that the melts of these glasses are strong, and the fragility is minimum. The results were discussed in terms of the average coordination number NC and chemical bond approach.

Modeling the physical properties of hydrate‐bearing sediments: Considering the effects of occurrence patterns

Investigating the dependence of the physical properties of hydrate-bearing sediments (HBS) on hydrate occurrence patterns and saturation levels is crucial for exploring gas hydrate resources. However, precise analysis of these effects remains challenging due to limitations in current experimental techniques and numerical modeling methods that cannot accurately control the hydrate saturation and distribution patterns. In this work, to address such issues, we propose a novel hybrid modeling approach integrating X-ray CT imaging technology, morphological operation algorithm, and quartet structure generation set method. Then, we generate 75 samples containing pore-floating, cementing, as well as bridging hydrates, each with predefined saturation levels, and comprehensively investigate the effects of the hydrate distribution patterns and saturation on the pore radius, coordination number, correlation functions, permeability, electrical conductivity, and elastic moduli of HBS. The findings indicate that the heterogeneity of pore and throat radius distributions varies across different hydrate types. The increase in pore-floating hydrate leads to the most rapid decline in the pore and throat radii, tortuosity, and pore-space correlation, but it makes the average coordination number larger while the others decrease the number. Moreover, the cementing patterns cause the weakest damage to the permeability and electrical conductivity with low hydrate saturation. When the hydrate saturation is larger than about 45%, the bridging pattern has the greatest effect on the mass transport properties. Furthermore, the pore-floating and bridging patterns cause the largest and smallest increase in the elastic moduli, respectively. The hydrate occurrence pattern causes a larger effect on the bulk modulus than the shear modulus.

Numerical simulation of direct shear tests on gas hydrate-bearing sediments using the discrete element method

Natural gas hydrate is a potential unconventional energy resource. Understanding the mechanical behavior of gas hydrate-bearing sediments (GHBS) is important to ensure the safe and efficient exploitation of natural gas hydrate and prevent geohazard problems. This study employs discrete element method to investigate the mechanical properties of GHBS with different hydrate saturations under various vertical stresses, and a series of direct shear tests, which requires less computational consumption than triaxial or biaxial tests. Comprehensive analyses of macroscopic and microscopic mechanical behaviors, including shear strength, internal friction angle, cohesion, shear band, average coordination number, and crack number evolution, are carried out, as an effort for understanding the shear strength breakpoint, which is recognized in laboratory experiments, probably caused by the transition in hydrate morphology in sediment pores. The results obtained reveal that: (1) the way of hydrate in strengthening GHBS is to enhance cohesion; (2) the increasing rate of the strength difference between the sediment matrix with and without hydrate remarkably increases when the hydrate saturation is over certain value at which the shear strength breakpoint is observed, and this rate decreases with the increase in median particle diameter (D50) of host sediments; (3) the transition in hydrate morphology in sediment pores is recognized when the hydrate saturation increases at microscale; and (4) the shear strength breakpoint in the curve of strength difference versus hydrate saturation is explained based on the micromechanical properties of GHBS, including shear bandwidth, average coordination number, average normal force, and crack number evolution.

Structural features and optical-luminescent properties of the Pb-containing germanate and silicate oxyfluoride glasses

The XRD, IR transmission, EPR, optical absorption, luminescence spectra and decay kinetics in new un-doped 0.5PbO–0.3GeO2–0.2AlF3 and 0.53PbO–0.226SiO2–0.244AlF3 glasses were investigated. The XRD patterns were analysed in order to obtain the radial distribution functions and define the average interatomic distances and coordination numbers in the network of investigated glasses. The IR transmission, EPR, and UV–vis optical absorption spectra of the studied glasses were interpreted. Optical band gap and Urbach energy were obtained from analysis of the fundamental absorption edge. Under UV photoexcitation the 0.5PbO–0.3GeO2–0.2AlF3 and 0.53PbO–0.226SiO2–0.244AlF3 glasses demonstrate broad emission band at 493 nm and 499 nm, respectively. Fast (band-to-band recombination) and slow (recombination with a contribution of defects levels) mechanisms of intrinsic luminescence have been proposed from a detailed analysis of luminescence spectra and decay kinetics curves. The CIE chromaticity diagram shows a variation in emission colour of studied glasses with the change in their composition.