Review Reports - Down-Conversion Polymer Composite Coatings with Multipeak Absorption and Emission

Round 1

Reviewer 1 Report

I would like to thank the authors for a very good piece of original work that is rather clearly structured and depicted, addressing an interesting problem in the field of applicable down-conversion of light for which an interesting solution was found in the presented coatings. I wish the authors the best of luck to proceed with their scientific endeavours in the future.

I have no doubt that your data handling and analyses are of the highest standards and I do not see any unanswered questions in your paper. It clearly deserves publication in the 'Coatings' journal. I have revised your initial text with the greatest rigor to elevate your good work to the highest level of written English. I append the revised version of this text to the communication with you. The way I do this revision leads in some circumstances to the erasure of the Line Numbers. I am sure you will understand my corrections. Often they are of trivial nature. I have put the corrections in square brackets [] (from page 2 onwards) and sometimes given an explanation even. I still have to commend you for the high quality of the original text. I only found ONE slightly confusing sentence which is rare in such a long paper! Well done to the team.

Your figures are overall of publisable standard, however please consider the following:

Fig 1 has rather hard to read, small labelling in its current form. Please chose a larger typeset for the annotation and legend
* Fig 2. In order to stay consistent, please replace to 'Bandgap', also use bandgap=2.081 eV as an textbox above all the figure lines for clarity.
Fig. 3 is clearly too small in its current layout
Fig 4 should be expanded in horizontal width, as it is too small right now
Figs 5 & 6 . Ok as they are, a little horizontal expansion maybe?
Fig. 7 .. too small as they are. What is the relevance of the blue arrows shown in the upper left corners?
Fig 8 OK
Figs 9 & 10, too small as Fig 7

As for the tables:

General:. I am a 'big fan' of numerical values in tables aligned to the decimal point as it eases readability. You have centered values at the moment. Please align to decimal point OR Right align once you have made all values of the same decimal digit.

Table 2: Please check why it is in bold-font and then change to normal font.

Table 3: the current edition of the picture looks a little odd to me. I would strongly suggest that you conclude a special row with the heading: Schematic Diagram ABOVE the inserted pictures just below the rows for the polymers, that will ease the reader's efforts to understand why you put the picture in. I fully understand to give that guidance with the pictures for the paper, your strategy is clever and recommendable.

Table 4. Here you have the Schematic Diagram as a Column. Following the suggestion for Table 3, I would revert this diagram into a Row as you did for Table 3 anyhow, but, as suggested, a named by a heading row, as I suggested. IN the very moment the figure inserted looks truncated and whth my suggestion that would not be the case anymore and would make Table 3 and 4 much more consistently looking.

Table 5, same as for Table 4

Your literature review and citation is commendable too, but may I suggest contemplating the suitability of the inclusion of

D. Verma DOI: 10.1109/PVSC.2012.6318129, Conference: Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE

A. de Vos https://doi.org/10.1016/j.enconman.2008.09.012

and the very recent release by Wang et al. (Please do not hesitate, as surely that paper was published after the submission of your work, but never mind to include a very recent paper.

S. Wang https://doi.org/10.1016/j.jlumin.2020.117742 I also wanted to point out that I find the subscripts not rightly placed, as I would like to see them below the normal text lines. This however maybe a typeset issue with the editor and out of your control.

Comments for author File: Comments.pdf

Author Response

Dear Editor,

Thank you for considering our proposed manuscript (coatings-1124467) and offering us the opportunity to revise it. The manuscript was corrected according to the reviewers’ helpful comments point by point. The revisions are listed as following, which are highlighted in yellow both in the manuscript and the letter here.

We hope our corrections can match the expectation of the reviewers. And we are looking forward to your reply.

Sincerely,

Cheng Zhu, Ph.D

College of Materials Science and Engineering

Nanjing Tech University

Puzhu(s) 30, Nanjing, Jiangsu Province, China

E-mail: zhucheng415@163.com

Response to Reviewer 1 Comments

Point 1：I have no doubt that your data handling and analyses are of the highest standards and I do not see any unanswered questions in your paper. It clearly deserves publication in the 'Coatings' journal. I have revised your initial text with the greatest rigor to elevate your good work to the highest level of written English. I append the revised version of this text to the communication with you. The way I do this revision leads in some circumstances to the erasure of the Line Numbers. I am sure you will understand my corrections. Often they are of trivial nature. I have put the corrections in square brackets [] (from page 2 onwards) and sometimes given an explanation even. I still have to commend you for the high quality of the original text. I only found ONE slightly confusing sentence which is rare in such a long paper! Well done to the team.

Response 1: Thank you very much for revising this article, the relevant revisions have been revised in the article.

Point 2: Your figures are overall of publisable standard, however please consider the following: Fig 1 has rather hard to read, small labelling in its current form. Please chose a larger typeset for the annotation and legend.

Response 2: The annotation and legends are enlarged for easy reading. The changes are as follows:

Figure 1. (a) XRD patterns of the Sr₂CaMoO₆:Sm,Na (Sm20Na00-Sm30Na30). (b) Excitation spectra (λ_em = 648 nm) of the Sr₂CaMoO₆:Sm,Na samples. (c) Fluorescence emission spectra of Sr₂CaMoO₆:Sm,Na samples (λ_ex = 408 nm). (d) Fluorescence emission spectra of Sr_1.975-xCaMoO₆:0.025Sm,xNa series samples. (λ_em stands for the emission wavelength and λ_ex stands for the excitation wavelength.)

Point 3: Fig 2. In order to stay consistent, please replace to 'Bandgap', also use bandgap=2.081 eV as a textbox above all the figure lines for clarity.

Response 3: Bandgap=2.081 eV was used as a textbox above all the figure lines for clarity. The changes are as follows:

Figure 2. The calculated energy band structure of Sm25Na00 (a) and Sm25Na25 (b). Density of states of Sm25Na00 (c) and Sm25Na25 (d) near the Fermi energy level (the Fermi energy is the zero of the energy scale).

Point 4: Fig. 3 is clearly too small in its current layout.

Response 4: The picture layout has been adjusted to make the picture look clearer. The changes are as follows:

Figure 3. (a) XRD patterns of YVO₄:Bi,Eu. (b) Excitation (λ_em = 618 nm) spectra of YVO₄:Bi,Eu. (c) Emission (λ_ex = 365 nm) spectra of YVO₄:Bi,Eu.

Point 5: Fig 4 should be expanded in horizontal width, as it is too small right now.

Response 5: The horizontal width of Figure 4 was appropriately enlarged to make it look larger. The changes are as follows:

Figure 4. The calculated energy band structure and density of states of YVO₄:Bi,Eu (a、b). Partial densities of states of YVO₄:Bi,Eu (c、d、e、f) near the Fermi energy level (the Fermi energy is the zero of the energy scale).

Point 6: Figs 5 & 6. Ok as they are, a little horizontal expansion maybe?

Response 6: The horizontal width of Figs 5 & 6 was appropriately enlarged to make it look larger. The changes are as follows:

Figure 5. (a) The initial particle size distribution of Sm25Na25. (b) Particle size distribution of Sm25Na25 after grinding. (c) XRD spectra before and after grinding. (d) Emission spectra before and after grinding.

Figure 6. (a) The initial particle size distribution of Eu04. (b) Particle size distribution of Eu04 after grinding. (c) XRD spectra before and after grinding. (d) Emission spectrum before and after grinding.

Point 7: Fig. 7 .. too small as they are. What is the relevance of the blue arrows shown in the upper left corners?

Response 7: The layout and annotations of the pictures have been adjusted appropriately to make it easier to read. The blue arrow in the figure points to the coordinate axis corresponding to the curve. The changes are as follows:

Figure 7. (a) Transmission spectra and emission spectra (λ_ex = 408 nm) of M-1T20–M-4T20. (b) Transmission spectra and emission spectra (λ_ex = 408 nm) of M-1T30–M-4T30. (c) Transmission spectrum and emission spectra (λ_ex = 365 nm) of V-1T20–V-4T20. (d) Transmission spectra and emission spectra (λ_ex = 365 nm) of V-1T30–V-4T30. (The blue arrow in the figure points to the coordinate axis corresponding to the curve.)

Point 8: Figs 9 & 10, too small as Fig 7.

Response 8: The layout and annotations of the pictures have been adjusted appropriately to make it easier to read. The changes are as follows:

Figure 9. (a) Emission spectra of Z3R15T20 and Z3R15T30 upon the excitation at 365 and 408 nm, respectively. (b) Emission spectra of Z3R110T20 and Z3R110T30. (d) Emission spectra of Z4R15T20 and Z4R15T30. (d) Emission spectra of Z4R110T20 and Z4R110T30.

Figure 10. (a、b) Transmission spectrum of the bilayer coatings. (c) Emission spectra of Bi3R15SE and Bi3R15ES upon the excitation at 365 and 408 nm, respectively. (d) Emission spectra of Bi3R110SE and Bi3R110ES. (e) Emission spectra of Bi4R15SE and Bi3R15ES. (f) Emission spectra of Bi4R110SE and Bi4R110ES.

Point 9: General:. I am a 'big fan' of numerical values in tables aligned to the decimal point as it eases readability. You have centered values at the moment. Please align to decimal point OR Right align once you have made all values of the same decimal digit.

Response 9: Adjusted the data alignment to make it easier to read. The changes are as follows:

Table 1. The names and corresponding molar ratios of raw materials for the examined Sr₂CaMoO₆:Sm,Na phosphors samples.

Name	SrCO3	CaCO3	MoO3	Sm2O3	Na2CO3
Sm20Na00	1.980	1	1	0.0100	0.0000
Sm10Na10	1.980	1	1	0.0050	0.0050
Sm15Na15	1.970	1	1	0.0075	0.0075
Sm20Na20	1.960	1	1	0.0100	0.0100
Sm25Na25	1.950	1	1	0.0125	0.0125
Sm30Na30	1.940	1	1	0.0150	0.0150
Sm25Na00	1.975	1	1	0.0125	0.0000
Sm25Na15	1.960	1	1	0.0125	0.0075
Sm25Na20	1.955	1	1	0.0125	0.0100
Sm25Na30	1.945	1	1	0.0125	0.0150
Sm25Na35	1.940	1	1	0.0125	0.0175

Point 10: Table 2: Please check why it is in bold-font and then change to normal font.

Response 10: Adjust the font of Table 2 to make it the same as the full text. The changes are as follows:

Table 2. The names and corresponding molar ratios of raw materials for the examined YVO₄:0.04Bi³⁺, Eu³⁺ samples.

Name	Y₂O₃	NH₄VO₃	Bi₂O₃	Eu₂O₃
Eu01	0.475	1	0.02	0.005
Eu02	0.470	1	0.02	0.010
Eu03	0.465	1	0.02	0.015
Eu04	0.460	1	0.02	0.020
Eu05	0.455	1	0.02	0.025

Point 11: Table 3: the current edition of the picture looks a little odd to me. I would strongly suggest that you conclude a special row with the heading: Schematic Diagram ABOVE the inserted pictures just below the rows for the polymers, that will ease the reader's efforts to understand why you put the picture in. I fully understand to give that guidance with the pictures for the paper, your strategy is clever and recommendable.

Response 11: The layout of Table 3 has been appropriately adjusted to make it easier to understand. The changes are as follows:

Table 3. The name of the polymeric luminescent coatings with single phosphors.

Name^a	Sm25Na25 weight ratio	Thickness^b (μm)	Name^a	Eu04 weight ratio	Thickness^b (μm)
M-1T20	1‰	20	V-1T20	1‰	20
M-2T20	2‰	20	V-2T20	2‰	20
M-3T20	3‰	20	V-3T20	3‰	20
M-4T20	4‰	20	V-4T20	4‰	20
M-1T30	1‰	30	V-1T30	1‰	30
M-2T30	2‰	30	V-2T30	2‰	30
M-3T30	3‰	30	V-3T30	3‰	30
M-4T30	4‰	30	V-4T30	4‰	30
Schematic diagram

Molybdate			Vanadate

a: M and V stand for molybdate and vanadate phosphors, respectively. T stands for thickness in μm.

b: The uncertainty of coating thickness was ±1 μm.

Point 12: Table 4. Here you have the Schematic Diagram as a Column. Following the suggestion for Table 3, I would revert this diagram into a Row as you did for Table 3 anyhow, but, as suggested, a named by a heading row, as I suggested. IN the very moment the figure inserted looks truncated and whth my suggestion that would not be the case anymore and would make Table 3 and 4 much more consistently looking. Table 5, same as for Table 4

Response 12: The layout of Table 4 and5 has been appropriately adjusted to make it easier to understand. The changes are as follows:

Table 4. The name of the polymeric luminescent coatings that were directly mixed with two phosphors.

Name^a	Ratio (Eu04:Sm25Na25)	Total powder weight ratio	Thickness^b (μm)
Z3R15T20	1:5	3‰	20
Z3R15T30	1:5	3‰	30
Z3R110T20	1:10	3‰	20
Z3R110T30	1:10	3‰	30
Z4R15T20	1:5	4‰	20
Z4R15T30	1:5	4‰	30
Z4R110T20	1:10	4‰	20
Z4R110T30	1:10	4‰	30
Schematic diagram

a: Z means that vanadate and molybdate phosphors were mixed in polymer coatings. R and T stand for their weight ratio and coating thickness, respectively.

b: The uncertainty of coating thickness was ±1 μm.

Table 5. The name of the double-layer polymeric luminescent coatings with different phosphor weight ratios.

Name^a	Total powder weight ratio	Ratio (Eu04:Sm25Na25)		Upper layer	Lower layer
Bi3R15SE	3‰	1:5		Sm25Na25	Eu04
Bi3R110SE	3‰	1:10		Sm25Na25	Eu04
Bi4R15SE	4‰	1:5		Sm25Na25	Eu04
Bi4R110SE	4‰	1:10		Sm25Na25	Eu04
Bi3R15ES	3‰	1:5		Eu04	Sm25Na25
Bi3R110ES	3‰	1:10		Eu04	Sm25Na25
Bi4R15ES	4‰	1:5		Eu04	Sm25Na25
Bi4R110ES	4‰	1:10		Eu04	Sm25Na25
Schematic diagram of Sm25Na25 in the upper layer			Schematic diagram of Eu04 in the upper layer

a: Bi means that vanadate and molybdate phosphors were mixed separately in bi-layered polymer coatings. R stands for their weight ratio. The whole coating thickness was 30±1 μm.

Point 13: Your literature review and citation is commendable too, but may I suggest contemplating the suitability of the inclusion of D. Verma DOI: 10.1109/PVSC.2012.6318129, Conference: Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; A. de Vos https://doi.org/10.1016/j.enconman.2008.09.012, and the very recent release by Wang et al. (Please do not hesitate, as surely that paper was published after the submission of your work, but never mind to include a very recent paper. Author links open overlay S. Wang https://doi.org/10.1016/j.jlumin.2020.117742. I also wanted to point out that I find the subscripts not rightly placed, as I would like to see them below the normal text lines. This however maybe a typeset issue with the editor and out of your control.

Response 13: These excellent references are cited in this article.

De Vos, A.; Szymanska, A.; Badescu, V. Modelling of solar cells with down-conversion of high energy photons, anti-reflection coatings and light trapping. Energ Convers Manage. 2009, 50(2), 328-36.
Wang, S.; Yao, H.; Wu, D.; Lin, Z.; Ling, Q. Highly efficient white emission from UV-driven hybrid LEDs through down-conversion of arylmaleimide-based branched polymers. J Lumin. 2021;230.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper evaluates the effect of the rare-earth ions concentration to enhance the performance of Down-converter materials for solar cells and agricultural greenhouses applications. Overall, this is well-written and organized and provides some useful knowledge for the readers in polymeric luminescent coatings and DC materials. I advise the authors to consider the following points before submitting the final version of the manuscript:

There are some environmental effects of using rare-earth ions. It is better to highlight light some of these in the introduction.
Missing paper structure at the end of the introduction section
What basis set and the other important settings you used in the DFT analysis
Use higher resolution images for most of the figures.
In line 402, the word improved stands for what? i.e., what exactly was improved
In Figure 1, λem and λex stands for what?
As future work, you can test these modifications that you proposed with an actual solar cell device to evaluate the power conversion efficiency change.

Author Response

Point 1: There are some environmental effects of using rare-earth ions. It is better to highlight light some of these in the introduction.  

Response 1: The environmental effects of using rare-earth ions have been added to the introduction. The added content is as follows:

It is worth emphasizing that the rare earth ions used in down-conversion materials have no obvious negative impact on the environment, and different rare earth ions can be selected according to different spectral control requirements.

Point 2: Missing paper structure at the end of the introduction section.

Response 2: We appreciate this comment and agree with the reviewer that paper structure should be described at the end of the introduction section. We also think that we have given the logic flow of our manuscript to guide the reader for easy understanding.

Point 3: What basis set and the other important settings you used in the DFT analysis?

Response 3: Sorry for not mentioning some basic settings in the DFT analysis in the article. Relevant settings have now been added in " Characterizations and calculation ", as follows:

The calculation of the electronic structures of YVO₄:Bi and Sr₂CaMoO₆:Sm,Na was performed with the density functional theory (DFT) using the CASTEP code, in which the electron-ion interactions were described by pseudopotential method and electronic wave functions are represented by means of a plane-wave basis set. The first step was to use crystallographic data to construct a YVO₄ unit cell, in which one Y ion is replaced by Bi ion. Generalized Gradient Approximation (GGA) by the Perdew, Burke e Ernzerhof (PBE) formulation was chosen to optimize the crystal structure. The second step was to calculate the band structure and density of states of YVO₄ and YVO₄;Bi. The kinetic cutoff energy was 571 eV and Brillouin zone integration was represented using the K-point sampling scheme of 5 × 6 × 6 Monkhorst-Pack grid. Ultrasoft pseudopotentials were used to approximate the core electrons. The calculation method and setting parameters of the Sr₂CaMoO₆:Sm and Sr₂CaMoO₆:Sm,Na are the same as those of YVO₄:Bi.

Point 4: Use higher resolution images for most of the figures.

Response 4: The layout and clarity of the pictures have been adjusted accordingly to ensure that the pictures can be easily read.

Point 5: In line 402, the word improved stands for what? i.e., what exactly was improved?

Response 5: We am sorry that we did not express it clearly. Now some sentences are revised as follows:

Subsequently, by changing the concentration of rare-earth ions, the absorption capacity of YVO₄:Bi, Eu red molybdate phosphor in the ultraviolet region and the luminous intensity in the visible light region were improved.

Point 6: In Figure 1, λ_em and λ_ex stands for what?

Response 6: We explained the meaning of λ_em and λ_ex in the legend below Figure 1, as follows:

Point 7: As future work, you can test these modifications that you proposed with an actual solar cell device to evaluate the power conversion efficiency change.

Response 7: The coatings with multi-peaks absorption and multi-peaks emission are expected to be applied in the fields of solar cells. In future work, the impact of DC coatings on solar cells will be evaluated.

Author Response File: Author Response.pdf