Effect of tin doping and tin-bromine co-doping on electronic and optical properties of BiOCl crystal: density functional theory

Bismuth oxychloride (BiOCl) is a layered compound known for its exceptional physical, chemical, and optical characteristics, along with notable photocatalytic performance under visible light irradiation. This investigation employed density functional theory (DFT) to analyze the electronic band structure, projected density of states (PDOS), joint density of states (JDOS), and dielectric functions of both pristine BiOCl and various doped crystalline structures utilizing a projected augmented wave basis set. The crystallographic symmetry of doped and co-doped configurations exhibited congruency with the pristine crystals. Electronic band structures were evaluated for pristine, doped, and co-doped crystalline forms. In the case of the co-doped SnxBi1−xOBrxCl1−x crystal (x = 0.0625, 0.125, and 0.25), energy band gaps of 1.40 eV, 1.42 eV, and 1.5 eV were determined, respectively, signifying a reduction in the energy band gap compared to the single doped and undoped BiOCl crystal. Analysis of the PDOS revealed that the valence band (VB) of the SnxBi1−xOBrxCl1−x crystal was characterized by Cl (p), Br (p), O (p), and Sn (s, p) states, while the conduction band (CB) primarily consisted of Bi (p) states. JDOS calculations indicated a shift in peak energy towards lower values, indicating that dopants promoted electron transitions from Cl, Sn, O, and Br p states to the Bi p state. Moreover, investigation of the dielectric function for both pure and doped BiOCl demonstrated that tin-bromine co-doping induced modifications in the static dielectric constant and dielectric permittivity of the unmodified BiOCl crystal. Ultimately, the incorporation of tin and bromine through co-doping exerted a substantial influence on the electronic and optical properties of the doped crystalline materials. Based on our computational assessments, the SnxBi1−xOBrxCl1−x configuration with x = 0.25 showcased superior visible light absorption efficiency compared to other doped variations and pristine BiOCl.


Introduction
In recent years, there has been a surge in research interest surrounding bismuth-based materials, attributed to their diverse applications [1][2][3][4].Noteworthy characteristics such as layered structures [5], distinctive physicochemical properties [6], responsiveness to visible light [7], and adjustable band structures have established bismuth-based materials as crucial components in the realm of visible light photocatalysts [8,9].The presence of hybrid orbitals derived from Bi 6 s and O 2p within the valence band facilitates the efficient separation of photo-induced charge carriers, giving bismuth-based semiconductor photocatalysts an advantage over metal oxide counterparts like TiO 2 , ZnO, and Fe 2 O 3 , particularly in their broad absorption of visible light [10].Moreover, bismuth is recognized as an eco-friendly, cost-effective metal with inherent plasmon resonance properties [11].
The co-doping strategy enhances the efficacy of semiconductor material in visible-light photocatalysis.Introduction of metal elements through heteroatom doping modifies the conduction band (CB) edge, whereas non-metal doping alters the valence band (VB) edge [27,29,31].Additionally, heteroatom doping not only adjusts the band gap energy but also impedes the recombination of photoinduced charge carriers, thereby facilitating faster electron and/or hole transport.Various studies have demonstrated the effectiveness of metal doping, such as Nb, W, Sn, In, Al, Zn, Co, Ti, Ni, Mo, Cd, and Fe, in regulating the energy band width of BiOCl [26,[32][33][34][35]. Similarly, non-metal elements like sulfur (S), bromine (Br), boron (B), nitrogen (N), and carbon (C) have been utilized to fine-tune the band gap of BiOCl, enhancing its photocatalytic performance.Both metal and non-metal doping approaches have shown to enhance visible light absorption by adjusting the positions of CB or VB, or by introducing localized or doping energy levels.Recently, Attri and colleagues [26] developed metal (Ni, Mo, Cd and Co) doped BiOCl using a solvothermal synthetic route, incorporating Ni, Mo, Cd, and Co.Their findings indicate that the addition of Ni significantly enhances the photocatalytic and antibacterial properties of BiOCl compared to other metal-doped and pristine BiOCl materials.The presence of these dopants introduces donor ions, elevating the concentration of electron carriers within the material.This process also alters the band gap and optical characteristics of BiOCl, leading to a narrower band gap, broadened light absorption range, and improved separation of photogenerated carriers within the crystal [36].
Furthermore, a recent study reported the synthesis of Sn-doped BiOCl through the co-precipitation method, shows enhanced visible light photocatalytic activity [23].The Brunauer-Emmett-Teller (BET) analysis revealed that Sn-doped BiOCl possesses a notably larger specific surface area (ranging from 14.66 to 42.20 m 2 /g) compared to pristine BiOCl (13.49m 2 /g).Notably, the photocatalytic performance of 5% Sn-doped BiOCl exhibited the most efficient degradation of RhB dye, reaching 91.2% removal within 60 min.Another research study by Zulkiflee et al [37] confirmed the superior photocatalytic efficiency of Sn-doped BiOCl relative to pristine BiOCl, emphasizing Sn efficacy in tuning the band gap of BiOCl for enhanced photocatalytic capabilities.Additionally, Sn doping introduces Sn-related surface sites that aid in the separation of electronhole pairs, thereby enhancing the overall photocatalytic efficiency [23].
A significant challenge encountered when doping with metals or non-metals individually is striking a balance between achieving effective visible light absorption and mitigating rapid recombination of charge carriers.To address this issue, heteroatom or co-doping emerges as the preferred choice due to the advantageous synergistic effects it offers [38,39].An illustration of this is the recent work by Xie et al [39] who introduced In-Sco-doped BiOCl through simultaneous co-precipitation and ripening techniques.The co-doped BiOCl crystal exhibited promising photocatalytic performance in the degradation of tetracycline (TC).The literature on Sn-BiOCl crystal suggests that Sn is the best alternative for engineering the electronic and optical properties, which can boost the photocatalytic activity of the material [23,37].On the other hand, there is a lack of research on the co-doping of tin and bromine to enhance the electronic and optical properties of BiOCl crystals.This study examines the influence of tin-bromine co-doping on the electronic structure and optical properties using DFT calculations.Additionally, the influence of polarization direction on the dielectric function is explored across pristine, doped, and co-doped crystals within this paper.The results of this study contribute to the understanding of the impact of co-doping on the electronic and optical properties of the BiOCl crystal.Furthermore, our research has the potential to significantly contribute to the advancement of knowledge and opens up avenues for further exploration.

Computational methodology
The Density Functional Theory (DFT) method was used to perform theoretical calculations.The quantum espresso package [40,41] was used to implement all calculations.In this work, we utilized the projectoraugmented wave method (PAW) to calculate the electronic calculation.The generalized gradient approximation (GGA) proposed by Perdew, Burke and Ernzerhof (PBE) was used to describe the exchange and correlation potentials [23].Pseudoatomic calculations were performed for the valence electrons of the O, Cl, Br, Sn, and Bi orbitals, which were 2s 2 2p 4 , 3s 2 3p 5 , 4s 2 4p 5 , 5s 2 5p 3 and 6s 2 6p 3 respectively.The structural optimization was performed based on the convergence test for lattice parameters and cutoff energy.A cutoff energy of 320 eV was used for properties calculation.To perform the Brillouin zone (BZ) integral, a k-point mesh of (6 × 6 × 3) was generated using the Monkhorst-Pack scheme.For electronic minimization, the system was treated as nonmetallic.To consider the effect of doping concentration, a super cell of 2 × 2 × 1, and 4 × 2 × 1 were constructed using phonopy software.A convergence tolerance per atom of total energy of 1 × 10 −4 eV and a high-energy convergence tolerance of 1 × 10 −6 eV was used.Here we considered a model of Sn x Bi 1−x OBr x Cl 1−x , were x represents the replacement of 1, 2, or 3 Sn/Br atoms for every host atom in the supercell of BiOCl, which represents the concentration of 0.0625, 0.125, and 0.25, respectively.Using the optimized structure, we calculated the band structures, DOS, PDOS, JDOS, and optical properties.The band structure was calculated on a set of densely generated k points.The density of state was calculated using a set of (12 ×12 × 12) k-point sampling.The optical properties were calculated using norm-conserve pseudopotential.For comparison purposes, we incorporated an undoped and single Sn-and Br-dope BiOCl structure.

Result and discussion
3.1.Crystal structure BiOCl is matlockite-structured and crystallizes in the tetragonal space group P4 / nmm with Wyckoff Bi (2c), Cl (2c) and O (2a) [42].The pristine BiOCl crystal consists of six atoms in its unit cell.Figure 1 depict the top view of a 2 × 2 × 1 and 4 × 2 × 1 supercells of both the pure and doped crystals.The Bi 3+ atom is linked to four identical O 2− atoms and four identical Cl 1− atoms in a four-coordinate arrangement.The oxygen anion O 2− is linked to four identical Bi 3+ atoms to form a combination of corner-and edge-sharing OBi 4 tetrahedra.Additionally, the chlorine anion Cl 1 − is coordinated to four equivalent Bi 3+ atoms in a four-coordinate geometry.For a single component, all Bi-O, Bi-Cl and Bi-Bi bond lengths are 2.34 Å, 3.10 Å, and 3.91 Å, respectively.The optimized lattice parameters of the undoped and doped systems are summarized in table 1.Recently, Zulkiflee et al reported that the experimental lattice parameters for pristine and Sn-doped BiOCl were a = b = 3.885; 3.876 Å, and c = 7.371; 7.343 Å [37].Structural optimization results match experimental data and theoretical reports [22,36].However, only the lattice parameters were slightly different along the c-axis.For example, for Sn-doped and Sn/Br co-doped BiOCl structures, the bond length between Bi-O is reduced to 2.29 Å and 2.26 Å, respectively.These changes occur due to the small difference in atomic size between Sn and Bi as well as Br and Cl.All doped crystal structures appear to have the same structure as pristine BiOCl.In our current work, we employed the substitutional doping method.The dopant atoms, which are Sn and Br, possess similar sizes to the host atoms, which are Bi and Cl, respectively.This allows for a seamless fit into the crystal lattice without disturbing its overall symmetry.Consequently, the crystal symmetry remains unchanged for doped and codoped crystal [43].

Band structure and density of states
The band gap is a crucial parameter that influences the optical properties of the semiconductor material.The band structures of BiOCl, Sn x Bi 1−x OCl, Sn x Bi 1−x OBr x Cl 1−x , and BiOBr x Cl 1−x were calculated along a high The electronic band structure of pure BiOCl and Sn x Bi 1−x OBr x Cl 1−x crystals are plotted in figures 2(a)-(d).BiOCl is a semiconductor with a layered structure.Its band structure typically exhibits a valence band formed primarily by O 2p orbitals and a conduction band dominated by Bi 6p orbitals.There might be a small contribution from Cl 3p orbitals to the top of the valence band and some Bi 6 s character in the lower conduction band [29].The maximum valence band (MVB) of BiOCl crystal appears at X and Z points and the minimum conduction band (MCB) appears at the Γ point.The pristine BiOCl crystal has an indirect band gap energy nature.Its calculated energy band gap was 2.80 eV.When compared to the experimental result, the energy band gap of the pristine BiOCl crystal is underestimated [23], which can be attributed to the use of approximation methods in the GGA functional.However, the calculated result for both doped and undoped crystals is consistent with the literature [30,44].In doped and co-doped crystals, the band gap values undergo significant changes.Doping introduces impurity levels.These impurity levels can interact with the BiOCl electronic bands, leading to modifications in the band structure.As the doping concentration increases, the impurity levels can become more pronounced, altering the electronic states and causing shifts in energy levels.For all doped and co-doped crystals, the band gap values decrease as compared to the pure BiOCl.The calculated energy band gap of Sn 0.25 Bi 0.75 OCl and Sn 0.25 Bi 0.75 OBr 0.25 Cl 0.75 are estimated to be 2.25 eV and 1.50 eV respectively.Compared to single Sn or Br doped crystal, co-doped crystal has narrow band gap.This reduction might be because of new states that arise near the conduction and valence band edges due to the presence of dopant atoms.The change in energy levels near the valence or conduction band extremum can be correlated with the density of states (DoS).Furthermore, the electronic band structure analysis of the doped and co-doped crystal shows that MVB and MCB appear at different high symmetry points.This indicates that the doped crystals also have an indirect band-gap nature, as does the pristine BiOCl crystal.This result is in agrees with the previous report by [45,46].Sn-doped and Sn-Br co doped BiOCl exhibits metal-like characteristics in the visible light spectrum due to surface plasmon resonance (SPR) effects of Sn element.This phenomenon results in heightened light-matter interactions, such as increased light absorption, scattering, and confinement at the material's surface.The band gap directly influences the optical properties such as absorption spectra, emission, and recombination of charge carriers [38,39].Furthermore, doping can introduce defect states within the band gap, which could impact conductivity or carrier lifetimes [38].The concentration of dopants also has an effect on the electronic band gap.A smaller band allows crystals to absorb more visible light at longer wavelengths.Therefore, the Sn x Bi 1−x OBr x Cl 1−x crystals exhibit improved absorption in the visible light range than Sn x Bi 1−x OCl, BiOBr x Cl 1−x and pristine BiOCl crystal.Another very important property of semiconductor materials is their density of state (DOS).It describes how electrons are distributed over each energy state.Additionally, it provides us with the electronic states available to absorb photons of specific energies [47].The density of states (DOS) of pure BiOCl and doped  According to the result, the projected densities of each orbital confirm that the VB consists of hybridizations of Br (2P), Cl (3P), O (2P), and Sn (2S).On the other hand, the bottom CB mainly consists of Bi (3p).This result also agrees with the result of the DOS calculation.Joint density of states (JDOS) is a fundamental concept in the study of semiconductor materials.It provides a detailed picture of the available electronic states at different energy levels, which is valuable for understanding phenomena such as band gap engineering or carrier transport in the materials under study.It measures the density of available electronic energy levels that are formed by the conduction and valence bands.This measurement provides information about optical transitions, such as absorption, emission, scattering, etc, between valence and conduction states in the materials [49].The JDOS of pristine BiOCl, doped, and co-doped crystals is plotted in figure 5.The results demonstrate that a broad peak was observed at 3.5 eV, 2.10 eV, and 1.77 eV for pure BiOCl, Sn x Bi 1−x OCl (x = 0.25) and Sn x Bi 1−x OBr x Cl 1−x (x = 0.25) crystals, respectively.The peak in the JDOS plot indicates an electronic transition from the highest valence band to the lowest conduction band due to the absorption of photons.However, there is no peak observed in the energy range of (0-3) eV for pristine BiOCl crystal due to its wide band gap nature.Therefore, tin doping and tin-bromine co-doping significantly enhance the optical transition in the lower energy.Therefore, the JDOS result also conforms to the

Optical properties
The optical properties depend on how the materials respond to external fields applied on them.The crystal structure of a material has a significant influence on its optical properties.This is useful for analyzing energy band structure, contamination levels, excitons, lattice defects, lattice vibrations, and magnetic stimulation [44].It is well-known that the external field can polarize the material.The dielectric function describes the response of a material to an external applied field and is related to the material's ability to polarize and store electrical energy [51].The response of materials to the external field is described as dielectric functions, which is expressed using the equation (1) [52].
e w e w e w = +i 1 1 2

( ) ( ) ( ) ( )
Where e w ( ) is the linear response of electrons and optical transitions to photons expressed as a function of the angular frequency.The real part is related to the electronic polarizability of the crystal and is denoted by ò 1 (ω), while the imaginary part, which corresponds to the energy absorbance, is represented by ò 2 (ω).The imaginary part is computed from the momentum matrix between the occupied and unoccupied wave functions in the first Brillouin zone using equation (2) [53].The equation of the Kramer-Kronig relation (3) can be used to determine the real component of the dielectric function from the imaginary component for all positive frequencies [54].
where e is the charge on an electron, ò o is the permittivity of free space, V is the volume of the unit cell, and q is the momentum transfer and k is wave number with The dielectric constant ò is related to the ratio of the speed of light in a vacuum (c) to the speed of light in a medium (v) through ò = N 2 .The optical properties of a medium are directly linked to its dielectric constant using equation (4).
The refractive index (n) and the extinction coefficient (K) are typically not measured directly in optical experiments.Instead, the absorption coefficient (σ) and the reflectivity (R) are the measurable quantities [55].
Once the dielectric function is known, the absorption coefficient and reflectivity can be calculated using equations ( 5) and (6), respectively.where n and K are calculated using equation (7). and The imaginary part of the inverse dielectric tensor is proportional to the loss spectrum as expressed in equation (8).
The dielectric constant signifies the capacity of a material to store electrical energy within an electric field [56].The polarization direction can have a significant impact on the dielectric function of a material, given that it affects the refractive index of the material, which is interrelated with the dielectric function.
In an anisotropic material such as BiOCl, polarized photons experience varied phase shifts based on the orientation they possess relative to the crystal axes.The dielectric function of the pure and doped BiOCl systems is computed in three crystallographic directions.With the help of the two components of the dielectric function, several optical properties, including the absorption, refractive index, reflectivity, and conductivity [57], can be determined.Figures 6(a)-(f) depicts the dielectric function and electron energy loss function along the ZZpolarization directions.The peak position on imaginary part of dielectric function corresponding to electronic transitions from the valence to the conduction band.Both pristine BiOCl and doped BiOCl have an indirect band gap, the transition of electrons from the valence band to the conduction band requires the assistance of the phonon, resulting in peaks [44].For doped crystal the optical transition is from the Cl, Sn, Br and O p-states in the highest valence band to the Bi p-states in the lowest conduction band [44].An extra peak is observed at lower energy for tin-bromine co-doped crystal, indicating that the presence of dopants facilitates the transition of electrons from the top VB to the CB at lower energy, i.e., from the Sn and Br p-states to the Bi p-state.Furthermore, the peak observed in the imaginary curve indicates the presence of an absorption band, revealing energy ranges where photons are more likely to be absorbed by the material.The present results are consistent with the findings reported in the literature [56].These absorption characteristics are particularly important for applications such as solar cells, light-sensitive detectors, and photocatalysis applications.
The static dielectric constant for both pure and doped systems was calculated, and its values are summarized in table 2. When compared to pristine BiOCl, the static dielectric constants are larger for the doped system.The substitution of Bi with Sn and Cl with Br in the lattices can alter the charge distribution and polarization, leading to changes in the dielectric constants.This indicates that the dopants enhance the polarization and possess a strong binding capacity for electrons, which means they extend the lifespan of the photogenerated charge carrier on the conduction band, which is advantageous for photocatalytic activity.Another very important parameter in studying optical property is energy loss function.The energy loss corresponds to the difference between the initial and final states of the core electrons.The energy-loss spectrum is a useful way of examining the electronic, structural, and vibrational characteristics of materials [58].It reveals the energy-loss or absorption processes that take place when a material is exposed to external stimuli such as photons or electrons.By studying the energyloss spectrum, we can gain insight into the properties of the material.Figures 7(b)-(d) shows the energy loss function of a pure BiOCl, Sn x Bi 1−x OCl and Sn x Bi 1−x OBr x Cl 1−x crystal along the XX, YY and ZZ-polarization directions.The sharp maxima in the energy loss function correspond to plasmon oscillations [59].The plasmon frequency for the pure BiOCl crystal along the crystallographic polarization directions of XX, YY, and ZZ appears at 11.84 eV, 13.06 eV and 13.17 eV, respectively.However, for Sn x Bi 1−x OCl (x = 0.25), and Sn x Bi 1−x OBr x Cl 1−x (X = 0.25), crystal a plasmon frequency appears at energy of 11.55 eV, 10.86 eV, 11.11 eV; 11.30 eV, 11.55 eV and 10.56 eV along XX, YY, and ZZ-polarization direction respectively.The present results are in line with the findings of earlier studies [56].
In comparison to pristine BiOCl crystal, the plasmon frequency for the doped system appears at high energies.This shows that doping and co-doping can change the energy-loss properties of the BiOCl crystal.Sn x Bi 1−x OBr x Cl 1−x can absorb photons with lower energy and, consequently, experience higher energy losses.Band gaps narrowing caused by tin and bromine co-doping results in increased absorption of visible light.Thus, Sn x Bi 1−x OBr x Cl 1−x crystals have a small energy band gap and higher energy losses in the visible spectrum compared to those of pure BiOCl and single tin or bromine doped crystal.Additionally, there are optical absorption that arises from the promotion of electronic transitions enabled by the defect energy levels introduced by the Sn and Br impurities.Moreover, tin and bromine co-doping may also affect the plasmonic behavior of Sn x Bi 1−x OBr x Cl 1−x crystal [50].Plasmon are collective oscillations of electrons, and the introductions of Sn and Br impurities can alter the electron density and dielectric properties of the material.Extra electrons contribute to the overall electron density.As a result, the frequency of the plasmon tends to decrease with increasing Sn concentration.This decrease is due to the increased screening effect from the higher electron density, which reduces the strength of the collective electron oscillations.
We also evaluated the real values of the dielectric permittivity or complex dielectric function at the imaginary frequencies ò(iω) by utilizing the Kramers-Kronig formula as expressed in equation (9).The complex dielectric function of a material describes its electrical response to an applied external electric field.The dielectric function versus imaginary frequency graph provides important insights into the optical properties of a material.The complex dielectric function is plotted in figure 8 The findings demonstrate that doping alters the dielectric permittivity, which is consistent with the results from the real dielectric function curve.For the tin and bromine co-doped system, the complex dielectric function changes with concentration as a result of the alteration in the material's composition and structure.It affects the arrangement and density of atoms in the BiOCl crystal, resulting in modifications to the electronic and vibrational properties.

Conclusion
In this study, the impact of tin doping and co-doping with tin-bromine on the electronic structure and optical properties of BiOCl was examined employing density functional theory.The outcomes exhibited that despite the preservation of crystal symmetry, the substitution of Bi with Sn and Cl with Br induced slight modifications in the lattice parameters.Analysis of the energy bands validated the consistent nature of the band gap (indirect band gap) in both pure and doped crystals; however, the doped and co-doped crystals exhibited a reduced band gap width compared to the pure crystal.PDOS analysis elucidated that the VB in pure BiOCl comprised Cl 3p states and O 2p states, while in Sn x Bi 1-x OBr x Cl 1−x crystals, the VB encompassed Cl (3p), Br (3p), O (2p), and Sn (2s, 3p) states.The conduction band (CB) in all doped and pure BiOCl crystals was predominantly governed by Bi 3p states.Moreover, the investigation highlighted that the orientation of polarization significantly influenced the dielectric function of the material.The response of pure, doped, and co-doped crystals varied across different crystallographic directions due to the anisotropic nature of the parent crystal.Notably, the static dielectric constant was higher in the doped system compared to pristine BiOCl, indicating that dopants modified polarization and exhibited a robust binding affinity to electrons.Consequently, this extension prolonged the lifespan of photogenerated charge carriers in the conduction band, thereby augmenting the photocatalytic activity.Co-doping with tin and bromine notably impacted the optical properties of BiOCl crystals.Nevertheless, further exploration utilizing experimental techniques such as optical spectroscopy or energy-loss spectroscopy is warranted to comprehensively investigate this effect.
crystals were analyzed.Figures3(a)-(f) displays the DOS of BiOCl, Sn x Bi 1−x OCl, BiOBr x Cl 1−x and Sn x Bi 1−x OBr x Cl 1−x crystal calculated using the GGA method.In BiOCl crystals, the hybridization states between O-2p and Cl-3p states dominate the top VB, while the antibonding states of Bi p states dominate the bottom of the CB.The valence band in doped crystals consists primarily of Cl, Br, O, Br, and Sn p-states, whereas the conduction band is dominated by Bi p-states.When compared to the pure BiOCl crystal, the conduction band edge of the doped crystals is reduced, with co-doped crystals showing a further reduction compared to single Sn or Br doped crystals.The presence of Sn and Br atoms in the crystal results in changes to the electronic structure, causing a redshift in the energy state to a lower energy level (large wavelength).Our findings agree to the previously reported experimental results[23,48].These energy changes can affect the electronic transition and optical absorption properties of the materials.Furthermore, we calculated projected density of state (PDOS) for the pure and doped crystal.The PDOS provides the distribution of different atoms to the total density of states within the materials at specific energy levels and their localization on specific atomic orbitals[23].In figures 4(a)-(f), the orbital contributions to the total DOS of the Sn x Bi 1−x OBr x Cl 1−x crystal are shown.

Figure 4 .
Figure 4. PDOS of (a) the Sn 0.25 Bi 0.75 OBr 0.25 Cl 0.75 of each atom, (b) the Bi atom of each orbital, (c) the Br atom of each orbital, (d) the Cl atom of each orbital, (e) the O atom of each orbital, and (f) the Sn atom of each orbital.

Figure 7 .
Figure 7. (a) Complex dielectric function (b) Energy loss function along XX-polarization direction, (c) energy loss function along YYpolarization direction, (d) energy loss function along ZZ-polarization direction.

Table 1 .
Calculated value of bond angles, bond length, lattice parameters and band gap of pristine, doped and co-doped BiOCl crystal.

Table 2 .
The peaks values of energy loss function between (0-5) eV along different polarization direction and its corresponding plasmon energy and static dielectric constants of pure BiOCl and Sn x Bi 1−x OBr x Cl 1−x crystal.