DiscussionIncrease in both glass tr

Discussion
Increase in both glass transition temperature and onset crystallization temperature of BaPF glasses with increase in CaF2 content can be attributed to the increase in compactness of the glass structure [26] and [27]. Incorporation of Ca2 + ions into the glass matrix, which is having larger field strength (0.69) compared to Ba2 + (0.51) results in more tightened and compact glass structure due to shortening of phosphate chains and increase in both cross-link density and bond strength between phosphate chains [3], [28] and [29], whereas the lower melting temperature of glasses with higher CaF2 content may be due to the action of CaF2 as a flux to reduce the viscosity of glass melt [30].

Refractive index of glasses depends on electron density and polarizability of ions present in the glass matrix. Low atomic number and high field strength ions exhibit both low electron densities and polarizabilities [31]. So, partial substitution of Ba2 + having less field strength and higher atomic number by Ca2 + or the partial substitution of more polarizable oxygen ion by fluorine leads to reduction in refractive index of BaPF glasses with the increase in CaF2 content [32]. Reduction in the values of optical basicity of glasses and electronic polarizability of oxide/fluoride ions with the increase in CaF2 content also substantiates the reduction in the measured refractive index of prepared glass samples with CaF2 addition [33].

Optical band gap energy (Eopt) increases from 2.92 eV to 3.39 eV with the increase in CaF2 content in the batch composition. This increase in Eopt can be attributed to decrease in the concentration of non-bridging oxygen atoms, formation of non-bridging fluorine atoms and substitution of Ba2 + having smaller field strength (0.51) and polarizing power with Ca2 + having larger field strength (0.69) and polarizing power [34], [35] and [36]. In insulators optical absorption arises due to electron transfer from valence band of anion to conduction band of cations [37]. So, in glasses containing both oxides and fluorides, optical transitions emerge from the transfer of electron from valence band of oxygen and fluorine to conduction band of metal ions. Non-bridging oxygen atom, which binds excited electrons less tightly than bridging oxygen and non-bridging fluorine atoms possess higher magnitude of negative charge on them. This larger magnitude of negative charge on the non-bridging oxygen atoms helps in easy excitation of their electrons to the conduction band of cations, whereas fluorine atom, which is having larger electronegativity (3.98) than oxygen atom (3.44) stabilizes more electrons than bridging and non-bridging oxygen atoms. High-field-strength alkali and alkali-earth ions like Ca2 + also raise the UV edge, because they bind the oxygen ions more strongly in their oxides, even though they break up the tetrahedral structure [35] and [36]. Hence, the replacement of barium oxide by calcium fluoride leads to decrease in contribution of electrons from nearby ions by reducing number of non-bridging oxygen atoms and increasing the average number of bridging oxygen atoms in the barium phosphate glass network, resulting in the lowering of top of valence band.

Reduction in Urbach energy of glasses from 0.8 eV to 0.52 eV indicates that defect concentration in glasses decreases with the increase in CaF2 content. It is a fact that in amorphous and crystalline systems, Urbach energy can be used to characterize the degree of disorderliness present in them [35] and [36]. The Urbach energy indicates the extent of the absorption edge smearing due to disordering caused by structural features like lack of long range order as well as those induced by external factors such as density fluctuations, phonon-assisted indirect electron transitions and charged impurities [38]. Thus, reduction in Urbach energy also shows that extension of tails of states into the mobility gap reduces with replacement of barium oxide by calcium fluoride.

It can be noted from Table 3 that theoretical optical basicity of glasses decreases with the increase in CaF2 content. It indicates that the addition of CaF2 into glass batch will reduce the electron donating ability of the glass matrix. Thus, addition of CaF2 into the barium phosphate glasses will result in shift of UV cutoff towards shorter wavelength, resulting in increase of optical band gap energy, which substantiates our experimental result, while increase in values of metallization parameter indicates that insulating nature is increasing with addition of CaF2 to the glass batch. It also gives the idea that the width of both valence and conduction bands is reducing thereby increasing the forbidden band, resulting in an increased band gap.

Fig. 5 depicts that values of theoretical average optical basicity (λth) of glass system under investigation fall very close to the average optical basicity (λ) predicted using the relation given by Velli et al. [19]. Thus, for the pres

ผลลัพธ์ (ไทย) 1:

สนทนาเพิ่มอุณหภูมิการเปลี่ยนแก้วและอุณหภูมิเริ่มตกผลึก BaPF แว่นเพิ่มขึ้น CaF2 เนื้อหาอาจเป็นเพราะการเพิ่มขึ้นในความกระทัดรัดของโครงสร้างแก้ว [26] [27] รวมตัวกันของ Ca2 + ไอออนในเมตริกซ์แก้ว ซึ่งมีขนาดความเข้มของสนาม (0.69) เทียบกับ Ba2 + (0.51) ผลลัพธ์ในแก้วขนาดกะทัดรัด และต้องเพิ่มเติมโครงสร้างเนื่องจากเนยขาวฟอสเฟตโซ่ และเพิ่มทั้งสองลิงก์ข้ามพันธะและความหนาแน่นแข็งระหว่างกลุ่มฟอสเฟต [3], [28] [29], และในขณะที่อุณหภูมิหลอมเหลวต่ำกว่าของแก้วกับเนื้อหา CaF2 สูงอาจเนื่องมาจากการกระทำของ CaF2 เป็นฟลักซ์เพื่อลดความหนืดของแก้ว ละลาย [30]ดัชนีหักเหของแสงของแก้วขึ้นอยู่กับความหนาแน่นอิเล็กตรอนและ polarizability ของไอออนที่อยู่ในเมตริกซ์แก้ว เลขอะตอมต่ำและประจุไฟฟ้าแรงสูงฟิลด์แสดงความหนาแน่นอิเล็กตรอนต่ำและ polarizabilities [31] ทดแทนดังนั้น บางส่วนของ Ba2 + มีน้อยกว่าความเข้มของสนามและเลขอะตอมสูงขึ้น โดย Ca2 + หรือแทนบางส่วนของ polarizable เติมออกซิเจนไอออนโดยฟลูออรีนที่นำไปสู่การลดดัชนีหักเหของแสงของแว่นตา BaPF เพิ่มเนื้อหา CaF2 [32] ลดค่า basicity เลนส์แว่นตาและอิเล็กทรอนิกส์ polarizability ของไอออนออกไซด์/ฟลูออไรด์ CaF2 เนื้อหาเพิ่มยัง substantiates การลดดัชนีหักเหของแสงวัดได้ของตัวอย่างพร้อมกระจกจาก CaF2 [33]Optical band gap energy (Eopt) increases from 2.92 eV to 3.39 eV with the increase in CaF2 content in the batch composition. This increase in Eopt can be attributed to decrease in the concentration of non-bridging oxygen atoms, formation of non-bridging fluorine atoms and substitution of Ba2 + having smaller field strength (0.51) and polarizing power with Ca2 + having larger field strength (0.69) and polarizing power [34], [35] and [36]. In insulators optical absorption arises due to electron transfer from valence band of anion to conduction band of cations [37]. So, in glasses containing both oxides and fluorides, optical transitions emerge from the transfer of electron from valence band of oxygen and fluorine to conduction band of metal ions. Non-bridging oxygen atom, which binds excited electrons less tightly than bridging oxygen and non-bridging fluorine atoms possess higher magnitude of negative charge on them. This larger magnitude of negative charge on the non-bridging oxygen atoms helps in easy excitation of their electrons to the conduction band of cations, whereas fluorine atom, which is having larger electronegativity (3.98) than oxygen atom (3.44) stabilizes more electrons than bridging and non-bridging oxygen atoms. High-field-strength alkali and alkali-earth ions like Ca2 + also raise the UV edge, because they bind the oxygen ions more strongly in their oxides, even though they break up the tetrahedral structure [35] and [36]. Hence, the replacement of barium oxide by calcium fluoride leads to decrease in contribution of electrons from nearby ions by reducing number of non-bridging oxygen atoms and increasing the average number of bridging oxygen atoms in the barium phosphate glass network, resulting in the lowering of top of valence band.Reduction in Urbach energy of glasses from 0.8 eV to 0.52 eV indicates that defect concentration in glasses decreases with the increase in CaF2 content. It is a fact that in amorphous and crystalline systems, Urbach energy can be used to characterize the degree of disorderliness present in them [35] and [36]. The Urbach energy indicates the extent of the absorption edge smearing due to disordering caused by structural features like lack of long range order as well as those induced by external factors such as density fluctuations, phonon-assisted indirect electron transitions and charged impurities [38]. Thus, reduction in Urbach energy also shows that extension of tails of states into the mobility gap reduces with replacement of barium oxide by calcium fluoride.It can be noted from Table 3 that theoretical optical basicity of glasses decreases with the increase in CaF2 content. It indicates that the addition of CaF2 into glass batch will reduce the electron donating ability of the glass matrix. Thus, addition of CaF2 into the barium phosphate glasses will result in shift of UV cutoff towards shorter wavelength, resulting in increase of optical band gap energy, which substantiates our experimental result, while increase in values of metallization parameter indicates that insulating nature is increasing with addition of CaF2 to the glass batch. It also gives the idea that the width of both valence and conduction bands is reducing thereby increasing the forbidden band, resulting in an increased band gap.
Fig. 5 depicts that values of theoretical average optical basicity (λth) of glass system under investigation fall very close to the average optical basicity (λ) predicted using the relation given by Velli et al. [19]. Thus, for the pres