Reductive Atmosphere Research Articles

Expanded graphite with boron-doping for cathode materials of high-capacity and stable aluminum ion batteries.

Recently, aluminum ion batteries (AIBs) have attracted more attention due to the reliable, cost-effective, and air-stable Al metal anode. Among various cathode materials of AIBs, graphite was paid more attention owing to its high-voltage plateau and stable properties in storing chloroaluminate anions (AlCl4 -). However, its low capacity limits the real application and can not satisfy the requirements of modern society. To solve the above issue, herein, boron (B)-doping expanded graphite (B-EG) was prepared by thermal treatment of expanded graphite and boric acid together in a reduction atmosphere. Based on the structural and electrochemical characterization, the results show that B-doping amplifies the interlayer space of expanded graphite (EG), introduces more mesoporous structures, and induces electron deficiency, which is beneficial to accelerating the transfer and adsorption of active ions. The results indicate that the B-EG electrode exhibits excellent rate capability and a high specific capacity of 84.9 mA h g-1 at 500 mA g-1. Compared with the EG electrode, B-EG shows better cycle stability with the specific capacity of 87.7 mA h g-1 after 300 cycles, which could be attributed to lower pulverization and higher pseudo-capacitance contribution of B-EG after the introduction of B species.

Controlling the europium oxidation state in diopside through flux concentration.

This paper explores the connection between the H3BO3 flux concentration and the co-existence of Eu2+ and Eu3+ dopants within CaMgSi2O6 crystals (diopside). The samples were synthesised using a solid-state synthesis method under varying atmospheric conditions, including oxidative (air), neutral (N2), and reductive (H2/N2 mixture) environments. Additionally, some materials underwent chemical modification by partially substituting Si4+ with Al3+ ions acting as charge compensation defects stabilizing Eu3+ luminescence. Depending on the specific synthesis conditions, the materials predominantly displayed either the orange-red luminescence of Eu3+ (under oxidising conditions) or the blue luminescence of Eu2+; however, the comprehensive results confirmed the co-existence of Eu3+/Eu2+ luminescence in both cases. This work shows that varying flux concentrations added during synthesis significantly affect the relative strength of Eu2+ and Eu3+ emissions in a manner dependent on the synthesis atmosphere. The emission of Eu2+ increases with a higher flux concentration in materials synthesised under oxidative and neutral atmospheres independent of the chemical modification. In contrast, for materials obtained under a reductive atmosphere, the changes in the Eu3+ emission intensity depended on the presence or absence of Al3+ ions namely the increase of flux increased the Eu3+ intensity in the case of unmodified materials and decreased in the Al-modified ones. All observed effects were qualitatively explained considering the double role of the flux in the studied system, which besides facilitating the diffusion of chemical species during synthesis acts as a charge compensating agent by creating B'Si centres stabilizing Eu3+ emission.

Unlocking color-tunable emission of Eu2+-activated phosphors through doping-free exploration of hidden sites

Reducing atmosphere modification (a doping-free strategy) leads to Eu2+ emission color changes from blue to cyan.

(Invited) Tuning the Activity of Iron Phosphide Electrocatalysts for Sustainable Energy Conversion

Electrocatalysis is a promising approach for the sustainable conversion of renewable energy sources, such as solar and wind power, into chemical energy that can be stored and used on demand. By harnessing renewable electricity to drive electrochemical reactions, we can produce fuels and chemicals in a way that is both clean and cost-effective. As we continue to develop new electrocatalytic materials and improve the efficiency of existing processes, the potential for electrocatalysis to transform our energy system will only continue to grow.We report the use of iron phosphide (Fe2P, FeP) in several electrocatalytic applications, such as reduction of nitrate ions (NO3), hydrogen and oxygen evolution studies. The electrochemical reduction of the nitrate ion (NO3), a widespread water pollutant, to valuable ammonia (NH3) is a promising approach to achieving green energy conservation. Particularly, FeP and Fe2P phases were successfully demonstrated as efficient catalysts for NH3 generation. Detection of the in-situ formed product using a bi-potentiostat was achieved by electrooxidation of NH3 to nitrogen (N2) on a Pt electrode. The Fe2P catalyst exhibits the highest Faradaic efficiency (96%) for NH3 generation with a yield (0.25 mmol h−1 cm-−2 or 2.10 mg h−1 cm−2) at −0.55 V vs. reversible hydrogen electrode (RHE). To get relevant information about the reaction mechanisms and the fundamental origins behind the better performance of Fe2P, density functional theory (DFT) calculations were performed.In addition to NH3 synthesis, the iron phosphide catalyst was used in electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) studies. To enhance the catalytic activities of the obtained iron phosphide particles, heat-treatments were carried out at elevated temperatures. Heat-treatment at 500°C under a reductive atmosphere induced structural changes in the samples: (i) Fe2P yielded a pure Fe3P phase (Fe3P−500°C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500°C). The electrocatalytic activities of heat-treated Fe3P−500°C, and Fe2P/FeP−500°C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The lowest HER electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2 was achieved with a Fe2P/FeP−500°C catalyst. The intrinsic activity of FeP catalysts was also tuned and studied for OER.

Effects of phosphorus on the fusion characteristics of synthetic ashes with different Al2O3/CaO ratios

In this paper, five series of synthetic ashes with different Al2O3/CaO ratio mass ratios were prepared, and the ash fusion temperatures (AFTs) of the samples with different percentages (5–20 wt%) of phosphorus pentoxide (P2O5) added were measured under a mild reducing atmosphere to study the effect of phosphorus on the fusion characteristics of the ashes in different compositions. X-ray diffraction (XRD), thermodynamic equilibrium calculations, and high-temperature heating stage microscopy (HHSM) were used to investigate the mechanism of phosphorus in changing the fusion characteristics of the ash. The results showed that the addition of P2O5 produced the least effect on AFTs of samples with an Al2O3/CaO ratio of 6:4. For lower Al2O3/CaO ratios (classified as peralkaline), the addition of P2O5 caused a decrease-increase-decrease trend in AFTs, while for higher Al2O3/CaO ratios (classified as peraluminous), the AFTs of samples were decreased by phosphorus. The stronger affinity of P2O5 for CaO and Al2O3, compared to that of SiO2, was noticed and led to a shift of main minerals in the slag from silicates to phosphates and to the isolation of SiO2. In addition, the phosphorus-bearing samples followed the same “melt-dissolution mechanism” as the phosphorus-free samples.

Sticking Behavior of Burdens During Reduction Process in Gas‐Based Shaft Furnaces

Gas‐based shaft furnaces (SFs) have garnered considerable attention because of their low CO2 emissions. The sticking behavior of their burden material influences the smooth operation of SFs. In this study, the effects of the reduction degree, temperature, and atmosphere on the sticking behavior of pellets are studied thoroughly under typical reduction conditions. The results demonstrate that the pellets will stick with each other as the reduction degree increases, the main phase of pellets at the maximum sticking index (SI) is iron, and the interconnection between iron whiskers results in the bonding phenomenon of pellets. The pellets exhibit a low SI at a relatively low reduction temperature. As the reduction temperature increases, the pellets stick, which is caused by thermal expansion and the large number of iron whiskers. With an increase in the proportion of H2 in the reducing gas, the iron particles become smaller, and the contact area between the particles decreases, effectively reducing the SI of the pellets. In general, choosing a reasonable reduction temperature and increasing the proportion of H2 in the reducing gas are helpful in controlling pellet sticking.

Palladium single atoms from melting nanoparticles on WO3−x for boosted hydrogen evolution reaction

Surface-supported isolated atoms in single-atom catalysts (SACs) grant maximum utilization of metals in heterogeneous catalysis. Herein, we report a feasible pyrolysis strategy to synthesize Pd single atoms by thermally melting Pd nanoparticles on an oxygen-vacancy-rich tungsten-oxide matrix at reduction atmosphere. Near ambient pressure X-ray photoelectron spectroscopy was used to monitor the formation of zero-valence Pd single atoms and the increased metallic feature of WO3−x substrate. Accordingly, the as-obtained zero-valence Pd single-atom catalyst exhibits a markedly boosted HER activity with a low overpotential (η10 = 70 mV) at the current density of 10 mA/cm2 and a small Tafel slope (b = 68 mV/dec), nearly 150 mV and a 3.0-fold enhancement than those of Pd nanoparticles (η10 = 220 mV, b = 133 mV/dec) under the same conditions. In addition, quasi in situ XPS results suggest the hydrogen spillover effect is more likely to occur on Pd single atoms during the electrochemical process. Our work may pave an interesting route for the rational design of highly-efficient single-atom catalysts, and the elucidation of corresponding enhanced reaction mechanisms by the utilization of advanced characterization techniques.

Synergistic recovery of copper, lead and zinc via sulfurization–reduction method from copper smelting slag

Cu, Pb and Zn were synergistically recovered from copper smelting slag via the sulfurization–reduction method. Pyrite was used as the sulfurizing agent to selectively sulfurize and recover valuable metals lost in the slag in the reductive atmosphere. Thermodynamic analysis and laboratory experiments were carried out to determine the feasibility and reliability of this process. The optimal experimental conditions were defined as follows: a dosage of sulfurizing agent (pyrite) of 26%, 6% coke addition of copper smelting slag mass, and smelting at 1350 °C for 3 h. Under the optimum conditions, Cu, Pb and Zn recoveries were 97.58%, 89.91% and 98.20%, respectively. Cu, Pb and Zn contents in the cleaned slag were 0.10%, 0.01% and 0.38%, respectively. The matte contained 7.28% copper. The proportions of Zn entering the gas, slag and matte phases were 80.93%, 10.09% and 8.98%, respectively. The proportions of Pb entering the gas, slag and matte phases were 40.12%, 1.79% and 58.09%, respectively. The matte phase mainly comprised Cu8S5, FeS, and some metals, such as Cu, Pb and Fe. Fe3O4 in the slag was reduced from 19.50% to 2.97%.

Role of Divalent Co-Dopant as Structure Stabilizer in Scandia-Stabilized Zirconia Electrolyte for SOFC

The present investigation reports the role of divalent binary co-dopant (Ca2+) in 11 mol% scandia stabilized zirconia (11SSZ) electrolytes to resolve its severe long-term aging issue for application in solid oxide fuel cells (SOFC). Dense electrolytes were formulated via the solid-state reaction method and their crystal structure was identified by X-ray diffractometer (XRD). To examine total electrical conductivity and its stability in oxidizing and reducing atmosphere DC four-point probe measurement was used. Among all the compositions, 0.2Ca11SSZ demonstrates the highest conductivity of 0.075 S cm−1 at 800 °C, with excellent stability of 6.7%/100 h in a reducing (97 vol% H2/3 vol% H2O) atmosphere. However, the presence of 0.5 mol% calcium in 11SSZ results in more than threefold suppression of aging rate compared to undoped11SSZ i.e. 2.19%/200 h in air atmosphere at 800 °C. Additionally, the doping of divalent Ca2+ widens the electrolytic domain up to pO2 ∼ 10−26 atm at 1000 °C compared to state-of-art 8YSZ (pO2 ∼ 10−22 atm), with 0.024% linear expansion on phase transition and 172 MPa flexural strength. Convincingly, the excellent structure stability and ionic conductivity of calcium co-doped 11SSZ compared to state-of-the-art electrolytes make them potential candidates to be used as an electrolyte for SOFC application.

Volatilization behavior of lead, zinc and sulfur from flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction

Existing methods are difficult to directly treat the tailings of Lanping Pb-Zn deposit because of low Pb + Zn content. According to the characteristics of high CaO content (11%) in the flotation products of Lanping low-grade Pb-Zn oxide ore, a carbon thermal reduction method based on rotary hearth furnace (RHF) process was developed. When reaction temperature was above 1000 °C, CaO could realize the transformation of metal sulfides to oxides. Increasing reducing atmosphere was favor of the efficient volatilization of Zn and Pb and the trapping of S. The volatiles in reducing agents could promote the volatilization of zinc. The reduction effect of anthracite and thermal coal was better than that of charcoal. The volatilization rates of Zn and Pb exceeded 98% and 96%, respectively, under the conditions of 1250 °C, 30 min, 20% thermal coal addition and air atmosphere. High quality ZnO dust with a ZnO purity of 83% was obtained.

Crystallization and activator reduction simultaneously for calcium sulfide nanophosphors and evaluation of red-light compensation - Environmental reliability

Calcium sulfide nanophosphors (CaS:Eu2+) with red emissions were synthesized by hydrothermal-derived 250 nm carbon-sphere templates to induce a reduction atmosphere to activate an activator valence transition and crystallize (Ca,Eu)S simultaneously at 800 °C without extra sulfur atmosphere. The cationic concentration z = [Ca2++Eu2+] and ionic ratio y = [S2−]/[Ca2++Eu2+] were controlled in an innovative chemical solution reflux process to synthesize a sulfide nanophosphor precursor on carbon-sphere template. The particle size and crystallinity of the prepared nanophosphors increased with the “y” value increase. The photoluminescence (PL) intensity of the 652 nm emission excited by 450 nm increased to y = 1 and kept nearly constant to y = 20. High PL intensity was achieved by 0.025CaS-1 and 0.025CaS-10 samples with individually sphere-like nanoparticles, enough crystallinity and homogeneous Eu doping as well as fully reduced Eu2+ in the nanophosphors. The CaS:Eu2+ nanoparticles prepared by carbon-sphere templates showed thermal quenching with temperature. The Eu2+-doped CaS emitted 652 nm red light by 450 nm but not by 380 nm excitation that was only for CaS host at 555 nm emission. The prepared 0.025CaS-10 paste of only 7 wt% was individually coated on a blue-light LED and commercially available YAG-LED. The red emission intensity was enhanced and broadened by the prepared sulfide nanophosphor compared to a commercially available red LED. The CRI value for R9 increased to higher than 90, and the measured Ra was higher than 95 for the prepared sulfide nanophosphor-coated commercial WLED. The prepared sulfide nanophosphors could keep the red-light brightness over six months' exposure at rainy marina to show the environmental reliability.

Experimental study on the catalytic effect of AAEMs on NO reduction during coal combustion in O2/CO2 atmosphere

During oxy-fuel combustion, the NO emission can be inhibited by the strongly reductive atmosphere caused by the high proportion of gasification reaction, which is a unique feature that differs from air combustion. The alkali and alkaline earth metals (AAEMs) contained in coal ash can catalyze gasification reactions, promoting the homogeneous reduction process of NO. Besides, AAEMs also suppress NO emission through catalyzing the NO heterogeneous reduction by char (CNO). Both catalytic effects of AAEMs have been studied at relatively low temperatures (below 1000 °C) in a simple atmosphere (pure CO2). However, the catalytic effect of AAEMs on NO reduction is still unclear during oxy-fuel combustion due to the more complex reaction atmosphere, higher reaction temperatures, and the presence of gasification reactions. In this work, the effect of different factors on the catalytic effect of AAEMs under O2/CO2 atmosphere is investigated. Results show that the order of the catalytic effect of AAEMs on NO reduction is Na > K > Ca > Mg, with the highest NO reduction efficiency of 30 % for Na. The catalytic effect of Na on NO reduction weakened as the temperature increases. When the temperature increased from 1373 K to 1573 K, the NO reduction efficiency (ηNO) of Na decreased from 30 % to 6 %. While the catalytic effect of Na on NO reduction strengthened as the oxygen concentration increases. When the O2 concentrations increased from 10 vol.% to 30 vol.%, the ηNO values of Na increased from 27 % to 35 %. The K-Na binary additive is more effective in reducing NO emissions than K and Na alone, with NO reduction efficiency as high as 46.8 % at a K/ Na is 1:2. Besides, the Raman test results reveal that K contributed to the conversion of amorphous carbon into a regular graphite crystal structure. Na disrupted the graphite structure resulting in more defective points appearing in the graphite lattice. These results are expected to provide a theoretical reference and new insights for the reduction of NO emission during oxy-fuel combustion.

Enhanced blue afterglow in Ce-doped boroaluminate glass modified by Na.

The alkali metal Na+ is commonly applied as a charge compensator to optimize afterglow performance but rarely reported as a structural regulator to modify afterglow behavior in long afterglow glass materials. In this paper, by preparing the Na + -modified Ce-doped boroaluminate glasses under a high-temperature reducing atmosphere, super-five times brighter blue-violet afterglow lasting up to 30 min was obtained. Results show that appropriate Na+ doping loosens the glass structure and widens the bandgap, thereby regulating most of the electron capture-release modes. This work provides new insights into the behavior of afterglow enhancement in alkali metal-doped glasses.

Numerical investigation on NOx formation of staged oxy-fuel combustion in a 35 MW large pilot boiler

In this study, high-fidelity simulations are conducted on a 35 MW pulverized coal oxy-fuel boiler to investigate NOx formation characteristics under staged oxy-fuel combustion, including both fuel-staged and oxygen-fuel two-way staged modes. Detailed volatile components are considered by using the chemical percolation devolatilization model. A skeletal reaction mechanisms consisting of 35 species developed for fuel-NOx formation under oxy-fuel conditions are employed for the gas phase combustion and NOx modeling. The radiative property models are also optimized for oxy-fuel combustion. The results show that in the fuel-staged mode, a reduction atmosphere is established in the reburning zone to reduce the NOx concentration in the flue gas. A reduction of 5.6% in the average NO concentration at the furnace outlet is observed relative to the baseline oxy-fuel case. Moreover, the application of oxygen-fuel two-way staged combustion leads to a further reduction in NOx formation. The average NO concentration at the furnace outlet is decreased by 17% compared to the baseline oxy-fuel case. Pathway analysis indicates a reduction in the NO formation pathway involving HCN → NCO → NO, while the NO reduction pathway of NO → HCN is enhanced.

Reduction of phosphogypsum for SO2 production: Insights into the release characteristics of SO2 following the solid–solid reaction of CaS and CaSO4 under different atmospheres

AbstractPhosphogypsum (PG) severely pollutes the environment and is difficult to recycle. PG is primarily composed of CaSO4 · 2H2O. In this study, the characteristics of SO2 released from the solid–solid reaction between calcium sulphide (CaS) and CaSO4 were thoroughly investigated using thermodynamic calculations. Experiments were performed by tuning the molar ratio of CaS to CaSO4, reaction atmosphere (S, CH4, N2, and air), and the heating rate. As shown by the phase diagram, high reaction temperatures favour CaO stability, and the corresponding maximum SO2 equilibrium partial pressure increases. The total SO2 production significantly increased with increasing molar ratio and slightly increased when the ratio exceeded 1:3. The SO2 productions were ranked from highest to lowest as follows: S, CH4, N2, CO, and air. The total SO2 production decreased with increasing heating rate. For the reaction between CaS and CaSO4, a higher molar ratio of CaS to CaSO4 no less than 1:3, both S and CH4 reductive atmospheres, and a lower heating rate (2°C/min) favour the total SO2 emission.

High‐Performance NIR Emission in Chromium‐Doped Garnet Phosphors Enabled by Structure and Excitation Regulation

AbstractThe burgeoning phosphor‐converted near‐infrared light‐emitting diodes (pc‐NIR LEDs) have important applications in special illumination and spectroscopy analysis. However, the development of efficient NIR‐emitting phosphors with high performance is still a challenge. In this work, a chemical unit co‐substitution strategy is proposed to realize the excitation transition regulation and successfully achieve high‐performance NIR luminescence in Ca3‐yNayMg1‐ySb2‐xAl2+yO12: xCr3+ (0 ≤ x ≤ 0.05, 0 ≤ y ≤ 1) garnet‐type solid solution phosphors. Through the excitation transition modulation from the 4A2 ground state to the 4T1(4P) and 4T1(4F) excitation state, the excitation intensity at the blue light region is largely enhanced by 25.6 times. Moreover, the NIR‐emitting efficiency and thermal stability are improved, with the optimal luminescence internal quantum efficiency of 90.6% and thermal stability of 97%@423 K, without any flux‐assisted sintering or reduction atmosphere protection. The structure regulation induced small Stokes shift, weak electron‐phonon coupling effect, and decreased non‐radiative transition are responsible for the excellent NIR‐emitting performance. Finally, the NIR pc‐LED is fabricated with photoelectric efficiencies of 18.7%@100 mA and NIR output powers of 63 mW@100 mA, presenting potential applications in nondestructive internal defect detection, veins imaging, and night vision surveillance.

Defect chemistry and transportation within La1.7Ba1.3In2O6.85 mixed ionic-electronic conducting membrane: Towards the application of solid oxide fuel cells

La1.7Ba1.3In2O6.85, as a representative material belonging to La2BaIn2O7-based family, is a novel and promising electrolyte material for solid oxide fuel cells (SOFCs). However, due to the co-existence of various mobile charged defects including oxygen vacancy, proton, and electron-hole, the conduction properties and behaviors of La1.7Ba1.3In2O6.85 are complex and not fully understood. In this work, we systematically explore La1.7Ba1.3In2O6.85 with a focus on defect chemistry and transportation. A theoretical model is built to analyze the experimentally measured conductivities of La1.7Ba1.3In2O6.85 at varying temperatures and oxygen partial pressures. Subsequently, the conduction properties and behaviors of La1.7Ba1.3In2O6.85 membrane at open circuit conditions and operation conditions are investigated thoroughly for the first time. Our findings reveal that in reducing and humidified atmospheres, La1.7Ba1.3In2O6.85 behaves as a dual-ion conducting oxide, with oxygen-ionic transport numbers exceeding 0.7. Our work can provide a new and overall understanding of the La2BaIn2O7-based material for SOFCs’ application.

CPFD modeling of hydrodynamics, combustion and NOx emissions in an industrial CFB boiler

The ultra-low NOx emission requirement (50 mg/m3) brings great challenge to CFB boilers in China. To further tap the NOx abatement potential, full understanding the fundamentals behind CFB boilers is needed. To achieve this, a comprehensive CPFD model is established and verified; gas-solid flow, combustion, and NOx emission behavior in an industrial CFB boiler are elaborated; influences of primary air volume and coal particle size on furnace performance are evaluated. Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace. Furnace temperature is highest in the bottom dense-phase zone (about 950 °C) and decreases gradually along the furnace height. Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace. NOx concentration gradually increases in the bottom furnace, reaches maximum at the elevation of secondary air inlet, and then decreases slightly in the upper furnace. Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere, which favors for NOx reduction and low NOx emission from CFB boilers.

Employing defect luminescence of LiGaO2 to realize dynamic readout and multiplexing of optical information

Optical data storage (ODS) materials have attracted much attention due to their unparalleled advantages, including outstanding low cost, high speed, and high storage density. The dynamic readout of high-resolution optical information in a single medium has always been a hotspot in the design of ODS materials. This work successfully developed a multi-mode dynamic luminescent material LiGaO2. By adjusting the defect states in different synthetic atmospheres, LiGaO2 materials with different luminescence properties were obtained, it appears green glow in air and nitrogen atmospheres and orange-red glow in reductive atmospheres. LiGaO2 material synthesized in a reduction atmosphere (R–LiGaO2) not only has the characteristics of rapid filling, but also has more abundant trap distribution, so it has a good optical information storage capacity, which is very suitable for the field of ODS. Through the analysis and characterization of R–LiGaO2 material in thermally-stimulated luminescence (TSL) and photostimulated luminescence (PSL), it is found that the dynamic optical information readout based on intensity-color-wavelength multiplexing in undoped single ODS materials is realized through the synergistic effect of trap centers and luminescence centers. This work provides a new strategy for the design and application of ODS materials.

About the nature of luminescent bands in undoped and Eu2+ doped SrAl2O4 phosphors

In this paper we report the luminescence properties of nanosized undoped and Eu2+ (1%) doped SrAl2O4 phosphors. The samples were prepared by combustion method at 600 °C followed by annealing of the resultant combustion ash at 1000 °C in a reductive (Ar + H2) atmosphere. Photo luminescence (PL) and cathodoluminescence (CL) analyses were applied to characterize the phosphors. The qualitative energy level scheme of doped crystal SrAl2O4:Eu2+ and nature of defects in undoped phosphor is proposed and discussed. Within a simplified model of a single vibration and linear vibronic coupling the shape-function of the vibrationally assisted band (Pekarian) is analyzed with the emphasis on the vibrational structure. We propose an approximate approach to pass from the discrete Pekarian distribution to the structureless crystal field spectra taking into account phonon dispersion. This approach is expected to be useful for the description of the shape of the bands when the electronic levels are close to the conduction band of the host crystal.