Phase Transformation, Optical and Emission Performance of Zinc Silicate Glass-Ceramics Phosphor Derived from the ZnO–B₂O₃–SLS Glass System

Round 1

Reviewer 1 Report

I have following comments:

1. p. 3, line 108 - Authors wrote that the precursor glass frit sample is of the light yellowish color due to high concentration of ZnO. ZnO is white and also Zn2+ compounds are in majority white. This corresponds with the fact that zinc in fact is not the transition element as its d orbitals are fulfilled both in the elemental form and in the oxidation state +II.

Did the authors find out the composition of the pollutant SLS glass? The color could be caused by impurities becoming from these glasses.

2. Glasses were melted in alumina crucibles. Did the authors find out the content of aluminum in the glasses? Aluminum can affect the properties of the glass.
3. I recommend editing of Table 2, there are some vibrations listed here twice and the assignment of the bands is not unambiguous, see e.g. 570 cm(-1) symmetric stretch of ZnO4 X 500-570 cm(-1) asymmetric stretch of ZnO4 .
4. The absorption spectra and the thermal dependence of some properties are explained by the existence of ZnO particles in samples prepared at lower temperatures (600 oC). Do the authors have any evidence of the existence of these particles? I think this explanation is very debatable and from chemical point of view possibly wrong. During the synthesis of the precursor glass, chemical reactions of the starting oxides took place and it is difficult to imagine that in the structure there is unreacted zinc oxide. Even from IR spectrum it follows that Zn is in the structure as ZnO4. Authors are advised to consult the results with an inorganic chemist.
5. p. 5, line 154 - What does it mean: “these NBOs are easily excited”?
6. English should be checked.

Author Response

Response to Reviewers

Reviewer 1

1. p.3, line 108 - Authors wrote that the precursor glass frit sample is of the light yellowish color due to the high concentration of ZnO. ZnO is white and also Zn²⁺ compounds are in majority white. This corresponds with the fact that zinc in fact is not the transition element as its d orbitals are fulfilled both in the elemental form and in the oxidation state +II. Did the authors find out the composition of the pollutant SLS glass? The color could be caused by impurities becoming from these glasses.

Answer: Thank you for the comment. This glass samples are highly transparent with very light yellowish in color. We are really sure that there is no contamination or impurity in the sample. We also sorry because cannot provide any additional data such as EDX or XRF to confirm this statement due to COVID19 where all the synthesis and measurement laboratory in the university are closed until today.

2. Glasses were melted in alumina crucibles. Did the authors find out the content of aluminum in the glasses? Aluminum can affect the properties of the glass.

Answer: We sure that there is no content of aluminum in the glasses because we are using high purity alumina crucible that can withstand high temperature up to 1700 °C. There is not any reaction occur in the alumina crucible. We also sorry because cannot provide any additional data such as EDX or XRF to confirm this statement due to COVID19 where all the synthesis and measurement laboratory in the university are closed until today.

3. I recommend editing of Table 2, there are some vibrations listed here twice and the assignment of the bands is not unambiguous, see e.g. 570 cm^-1 symmetric stretch of ZnO₄ X 500-570 cm^-1 asymmetric stretch of ZnO₄.

Answer: Table 2 has been edited and revised in the manuscript.

4. The absorption spectra and the thermal dependence of some properties are explained by the existence of ZnO particles in samples prepared at lower temperatures (600 °C). Do the authors have any evidence of the existence of these particles? I think this explanation is very debatable and from chemical point of view possibly wrong. During the synthesis of the precursor glass, chemical reactions of the starting oxides took place and it is difficult to imagine that in the structure there is unreacted zinc oxide. Even from IR spectrum it follows that Zn is in the structure as ZnO4. Authors are advised to consult the results with an inorganic chemist.

Answer: The absorption spectra for 600 °C is concluded as ZnO spectra as referred to the previous research ghoul et al. (2012) and Omri et al. (2013) state that the absorbance spectrum for ZnO is 370-390 nm.

5. p. 5, line 154 - What does it mean: “these NBOs are easily excited”?

Answer: The statement has been change to; The increase of NBO’s will promote the replacement of oxide that lead to higher the formation of crystal.

6. English should be checked.

Answer: The English language has been checked and revised in the recent manuscript.

Reviewer 2 Report

The manuscript contains results of XRD, FTIR, UV-Vis, and PL investigation of the complex glass system produced from the ZnO, B2O3 and SLS powders.

Different experimental methods show that a zinc silicate crystals appear after heat treatment of 700 degrees and above. This fact is known for Zn2SiO4 formation in silica after ion implantation.

There are few questions and remarks to be addressed:

1. English language revision is required throughout the text. Minor mistakes make a reader stumble here and there.
2. The list of literature isn't numbered, so it is hard to find a reference from the text.
3. Bar charts like Fig. 2 are rarely used in the materials science... It contrasts very much with the Fig. 1. What is the error for linear shrinkage measurement?
4. What is the reason for a kink in the optical absorption spectra near 600 nm?
5. How do you think, which type of optical transitions (direct or indirect) form the optical band gap, as shown in Fig. 4?
6. XRD and PL spectra for samples annealed at 700 and 900 deg. are almost identical, though they look quite differently in Fig. 9. Why?

Of course it is difficult to draw sound conclusions for a multicomponent glass-ceramic system. May the questions posed help the authors to enrich the conclusion.

Author Response

Response to Reviewers

Reviewer 2

1. English language revision is required throughout the text. Minor mistakes make a reader stumble here and there.

Answer: The English language has been revised throughout the text.

2. The list of literature isn't numbered, so it is hard to find a reference from the text.

Answer: Literature numbered has been checked. All the literature was numbering cited format and can be referred in the references section in the manuscript.

3. Bar charts like Fig. 2 are rarely used in the materials science. It contrasts very much with the Fig. 1. What is the error for linear shrinkage measurement?

Answer: Thank you for the comment. The bar chart has changed to linear graph with standard error.

4. What is the reason for a kink in the optical absorption spectra near 600 nm?

Answer: We not very sure about the broad hump occur near 600 nm occur for sample heat treated at 600 °C. However, we suggest that, the hump occur due to the some condition during experimental/apparatus during the measurement. Generally, some intense peak will appear if the glass containing transition metal or rare-earth ions (as a doping). For our case, the precursor glass sample is fully amorphous without any crystal peak (as shown in XRD measurement).

5. How do you think, which type of optical transitions (direct or indirect) form the optical band gap, as shown in Fig. 4?

Answer: Normally, the direct transition optical band gap was used for glass and glass-ceramic materials.

6. XRD and PL spectra for samples annealed at 700 and 900 deg. are almost identical, though they look quite differently in Fig. 9. Why?

Answer: Refer to Fig. 9, the intensity/emission color of the sample is influenced by the amount or progress of crystal growth in the glass-ceramic structure. In comparison to XRD and PL data, the intensity in the XRD and PL support the result in Fig. 9. For heat-treatment at 700 and 800 °C, the zinc silicate crystal start to growth. With the increasing of heat-treatment temperature up to 900 °C, the optimum of Zn₂Si₄ crystal growth has been achieved. Subsequent, these progress causes the emission color change to high intensity green emission of Zn₂SiO₄ crystal phase.

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript reports the synthesis of ZnO doped silica-lime-soda glass using glass waste. The synthesized glass was heat treated and characterized at different temperatures. According to the results, somewhere between 600 and 700 C crystallization of Zn₂SiO₄ occurs which prevails in the studied temperature range. Change of physical properties is supposed to be related to change of crystallinity.

However, no evidences of changing crystallinity are presented (e.g. FWHM of XRD peaks). Evidence of the presence of ZnO phase (lines 197-197) also lacks.

Crystallization process and characteristic temperatures of the glass can be better followed by thermal measurements (e.g. DTA).

Discussion of the results is mostly speculative.

References in brackets [] mentioned in the text cannot be identified, as the reference list do not contain reference numbers.

2.) Figures 1 and 2 can be merged. Also, the slope of the linear part above 600 C can serve as a basis for further discussion.

3.) Figures 3 and 4 can be also merged. Legend in Figure 3 is inappropriate.

4.) lines 168-169: shift of the Si-O band should be indicated.

5.) lines 197-198: is there any evidence for the presence of ZnO particles? Volume ratio? particle size?

6.) lines 203-204: the shift of the absorption edge towards shorter wavelengths should be demonstrated.

What do the Authors think about the presence of B2O3 (or (BO3) group)? How does it affect measured physical properties? What is the structural role of borate in the crystallized silicate phase?

Author Response

Response to Reviewers

Reviewer 3

This manuscript reports the synthesis of ZnO doped silica-lime-soda glass using glass waste. The synthesized glass was heat treated and characterized at different temperatures. According to the results, somewhere between 600 and 700 C crystallization of Zn2SiO4 occurs which prevails in the studied temperature range. Change of physical properties is supposed to be related to change of crystallinity.

1. However, no evidences of changing crystallinity are presented (e.g. FWHM of XRD peaks). Evidence of the presence of ZnO phase (lines 197-197) also lacks.

Answer: The discussion about the formation and crystallinity of Zn₂SiO₄ has been corrected in the revised manuscript. According to work by Khalkhali et al., [24], the increased composition of (ZnO/B₂O₃) emerge the formation of Zn₂SiO₄ phase which leads to more intense crystallization as ZnO react as a network modifier that can cause formation non-bridging oxygen’s (NBO’s).

2. Crystallization process and characteristic temperatures of the glass can be better followed by thermal measurements (e.g. DTA).

Answer: Thank you for the suggestion. However, we cannot provide the DTA data for this work because due to COVID19 where all the synthesis and measurement laboratory in the university are closed until today.

3. Discussion of the results is mostly speculative.

Answer: Several part of the discussion has been revised

4. References in brackets [] mentioned in the text cannot be identified, as the reference list do not contain reference numbers.

Answer: Literature numbered has been checked. All the literature was numbering cited format and can be referred in the references section in the manuscript.

4. Figures 1 and 2 can be merged. Also, the slope of the linear part above 600 °C can serve as a basis for further discussion.

Answer: Thank you for suggestion. However, we prefer to separate this results into 2 different graph for comprehensive discussion

5. Figures 3 and 4 can be also merged. Legend in Figure 3 is inappropriate.

Answer: Thank you for suggestion. However, we prefer to separate this results into 2 different graph for comprehensive discussion. Figure 3 has been corrected.

6. lines 168-169: shift of the Si-O band should be indicated.

Answer: The shift of the Si-O band has been list in revised manuscript.

7. lines 197-198: is there any evidence for the presence of ZnO particles? Volume ratio? particle size?

Answer: There is some error in the discussion. Rapid rises in the absorbance toward lower wavelengths are present in the optical absorption spectrum of glass material. This rapid rise of absorption coefficient can be referred as fundamental absorption edge known as UV cut-off. It was clear that no sharp absorption edge after the glass sample heat treated at 600°C which corresponds to the characteristic of glassy state was observed.

8. lines 203-204: the shift of the absorption edge towards shorter wavelengths should be demonstrated.

Answer: The shift of the absorption edge towards shorter wavelengths has been pointed in the revised manuscript.

9. What do the Authors think about the presence of B₂O₃ (or (BO₃) group)? How does it affect measured physical properties? What is the structural role of borate in the crystallized silicate phase?

Answer: In this work, B₂O₃ acts as a glass former, together with SiO₂. The addition of B₂O₃ in the glass structure makes the melting point and crystallization temperature of the glass decrease. Besides, the ability of the material to form a glass also increases with the addition of B₂O₃ in the structure.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I am satisfied with the authors' answers and the changes made.

Author Response

Reviewer 1

1. I am satisfied with the authors' answers and the changes made.

Answer: Thank you for the comment.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript reports the synthesis of ZnO doped silica-lime-soda glass using glass waste. The synthesized glass was heat treated and characterized at different temperatures. According to the results, somewhere between 600 and 700 C crystallization of Zn2SiO4 occurs which prevails in the studied temperature range. Change of physical properties is supposed to be related to change of crystallinity.

1. However, no evidences of changing crystallinity are presented (e.g. FWHM of XRD peaks). Evidence of the presence of ZnO phase (lines 197-197) also lacks.

Answer: The discussion about the formation and crystallinity of Zn₂SiO₄ has been corrected in the revised manuscript. According to work by Khalkhali et al., [24], the increased composition of (ZnO/B₂O₃) emerge the formation of Zn₂SiO₄ phase which leads to more intense crystallization as ZnO react as a network modifier that can cause formation non-bridging oxygen’s (NBO’s).

I do not see any modifications in the manuscript regarding crystallinity.

lines 240-243 from the revised manuscript:

"The emission spectra emitted at heat treatment of 700 °C, 800 °C and 900 °C which the intensity of the emission is increased with the increase of heat treatment temperatures. This is because of the improvement in
crystallinity inside the sample as the progress in heat treatment  temperature [41]."

I still ask why the crystallinity has not been checked based on XRD pattern.

Additionally, there are still no evidence of ZnO.

3. Discussion of the results is mostly speculative.

Answer: Several part of the discussion has been revised

The indicated changes in the manuscript do not contribute to a better interpretation and of improvement of scientific content.

4. Figures 1 and 2 can be merged. Also, the slope of the linear part above 600 °C can serve as a basis for further discussion.

Answer: Thank you for suggestion. However, we prefer to separate this results into 2 different graph for comprehensive discussion

5. Figures 3 and 4 can be also merged. Legend in Figure 3 is inappropriate.

Answer: Thank you for suggestion. However, we prefer to separate this results into 2 different graph for comprehensive discussion. Figure 3 has been corrected.

Due to the parallel presentation of Figures 1 and 2, and Figures 3 and 4,  the number of figures unnecessarily increases in the manuscript.

6. lines 168-169: shift of the Si-O band should be indicated.

Answer: The shift of the Si-O band has been list in revised manuscript.

Only the position of the Si-O band has been included into Table 2, the shift has not been indicated. This shift is definitely not straightforward from Figure 5.

7. lines 197-198: is there any evidence for the presence of ZnO particles? Volume ratio? particle size?

Answer: There is some error in the discussion. Rapid rises in the absorbance toward lower wavelengths are present in the optical absorption spectrum of glass material. This rapid rise of absorption coefficient can be referred as fundamental absorption edge known as UV cut-off. It was clear that no sharp absorption edge after the glass sample heat treated at 600°C which corresponds to the characteristic of glassy state was observed.

See point 1.

Author Response

Reviewer 3

1. This manuscript reports the synthesis of ZnO doped silica-lime-soda glass using glass waste. The synthesized glass was heat treated and characterized at different temperatures. According to the results, somewhere between 600 and 700 C crystallization of Zn₂SiO₄ occurs which prevails in the studied temperature range. Change of physical properties is supposed to be related to change of crystallinity.

However, no evidences of changing crystallinity are presented (e.g. FWHM of XRD peaks). Evidence of the presence of ZnO phase (lines 197-197) also lacks.

Answer: The FWHM of the XRD has been check, it is as the heat treatment temperature increase the values for FWHM decrease.

2. The indicated changes in the manuscript do not contribute to a better interpretation and of improvement of scientific content.

Answer: Deep explanation about the results has been added in the revised version of the manuscript.

3. Figures 1 and 2 can be merged. Also, the slope of the linear part above 600 °C can serve as a basis for further discussion.

Answer: Thank you for suggestion. The figures has been merged as suggested by the reviewer.

4. Due to the parallel presentation of Figures 1 and 2, and Figures 3 and 4, the number of figures unnecessarily increases in the manuscript.

Answer: Thank you for suggestion. The figures has been merged as suggested by the reviewer.

5. Only the position of the Si-O band has been included into Table 2, the shift has not been indicated. This shift is definitely not straightforward from Figure 5.

Answer: Fig. 5 has been revised.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

The authors have made serious efforts to improve their manuscript and also provided new information supporting the changing degree of crystallinity. My only remark is regarding Figure 1: units of axis y are missing, please add units. Maybe, additional axis on the right hand side could be used.

Author Response

Reviewer 3

1. The authors have made serious efforts to improve their manuscript and also provided new information supporting the changing degree of crystallinity. My only remark is regarding Figure 1: units of axis y are missing, please add units. Maybe, additional axis on the right hand side could be used.

Answer: Thank you for the comment. Fig. 1 has been revised following the suggestion from the reviewer.

Author Response File: Author Response.docx