Review Reports - Synthesis and Characterization of Nd:YAG Ceramics for Laser Applications

Round 1

Reviewer 1 Report

This is a original and interesting study on the synthesis and characterization of Nd: YAG material with varying Nd contents using the solid-state sintering method. Although this is a traditional method, this work includes crucial supporting descriptions for the necessary understanding. Before publication, a few minor clarifications & additions must be made. Thus, with a few minor modifications, I agree to approve the publication document.

1. There is considerable interest in this study project around the world due to the topic's importance. Therefore, it is important for the authors to make some comparative descriptions of their results against the literature values -processing conditions, performance, etc. That will make this article a contribution to the scientific community.

2. Rephrase the sentences on page 1, lines 41-43, for better understanding for the reader.

3. On page 2, lines 104-106, there is no mention of the particle size measurement techniques mentioned in the experimental section.

4. On page 2, lines 114-116, it is important to mention the atmosphere of the furnace.

5. The authors could explain a bit more details on the emission spectrum results as its important outcome of this work that needs more clarity in the statements.

The english language is acceptable no major issues, however few sentences were not described properly which needs further improvement.

Author Response

We are thankful to the reviewers for their constructive and important comments. By taking in account of their suggestions, some sections of the manuscript have been modified for clarity (highlighting with yellow those parts that have been modified). Below, we give our rebuttal to their comment.

Reviewer 1 This is an original and interesting study on the synthesis and characterization of Nd: YAG material with varying Nd contents using the solid-state sintering method. Although this is a traditional method, this work includes crucial supporting descriptions for the necessary understanding. Before publication, a few minor clarifications & additions must be made. Thus, with a few minor modifications, I agree to approve the publication document.

Comment 1: There is considerable interest in this study project around the world due to the topic's importance. Therefore, it is important for the authors to make some comparative descriptions of their results against the literature values -processing conditions, performance, etc. That will make this article a contribution to the scientific community.

Response to comment 1: Although a comparative table of the luminescent properties of the laser manufactured here was not included. It is mentioned in the sections 3.5 and 3.6 that optical properties of our compounds are very similar to those of commercial lasers and lasers obtained by more complex methodologies. In this sections also, they are compared these properties with those of other works and suggests possible applications of the laser fabricated here.

Comment 2: Rephrase the sentences on page 1, lines 41-43, for better understanding for the reader.

Response to comment 2: The sentences were revised and modified.

Comment 3: On page 2, lines 104-106, there is no mention of the particle size measurement techniques mentioned in the experimental section.

Response to comment 3: A brief note on the technique for carrying out the measurement on the equipment used has been added.

Comment 4: On page 2, lines 114-116, it is important to mention the atmosphere of the furnace.

Response to comment 4: A note was added indicating the type of atmosphere used in the furnace chamber.

Comment 5: The authors could explain a bit more details on the emission spectrum results as its important outcome of this work that needs more clarity in the statements.

Response to comment 5: A more in-depth discussion was added in the emission spectrum results part.

Reviewer 2 Report

The authors reported Nd:YAG ceramic bulk samples prepared by solid state reaction for potential optical source or laser application. The effect of different ratio of Nd in samples were studied and compared. Chemical and optical properties of samples were explored and summarized in this manuscript, the prepared samples are reasonably good but still need to be further analyzed. While the paper is quite clear, it could be further improved by the following suggestion or discussion.

1) Authors state that sample density reducing is resulting from Nd content and unclosed pores in the sintered samples. But all samples including pure YAG sample densities in the manuscript are relative lower than normal Nd:YAG density (~4.5g/cc), any reason cause that density reduction (high porosity or metrology issue)? If further increasing sintering temperature and duration, would it resolve this issue?

And in the density evolution figure 1, it would be better to use Nd concentration as X-axis label (0, 0.25, 0.5 and 1 atomic %) rather than sample number.

2) Particle size distributions of samples with different Nd concertation show unclear and abnormal trend. Authors state that Nd composition prevents the pores closing, however 1% Nd sample shows a not only smaller but a more uniform particle size distribution, which is not consistent with 0.5% Nd sample case. I would like to know more explanation and thought about this abnormal phenomenon.

3) In this manuscript, authors analyzed several samples synthesized at different temperature, which is helpful to monitor the actual reaction transition. However, seems in final sample sintered at 1500C still contains some undesirable phases, I wonder if authors have any thoughts or plan to remove impurities of samples, like additional annealing, higher temperature synthesis, longer reaction time? Is the selected 1500C due to any particular reason or equipment limitation?

4) In the microstructure section, authors discussed and presented the morphologies of samples taken by the optical microscope. From the figures, there are some visible white particles in the surface of samples. I wonder if authors could distinguish what the whitish particles are.

5) Since this manuscript emphasize the importance sample density and porosity contributions, it would be better to further explore the microstructures of samples with the help of SEM, which would be helpful to determine to porosity of samples with different composition. I am also interested to see the Nd element distribution inside the crystal and among the grain boundaries based on some SEM chemical analysis of samples.

6) In the Materials and Methods section, the unit of powders cannot be presented well (shows as 1m) in the manuscript: Powders of Y2O3 and Al2O3 (Sigma-Aldrich, 99.9 % purity and 1 m size). Please double check if that is correct.

Author Response

Reviewer 2

Comment 1:

Authors state that sample density reducing is resulting from Nd content and unclosed pores in the sintered samples. But all samples including pure YAG sample densities in the manuscript are relative lower than normal Nd:YAG density (~4.5g/cc), any reason cause that density reduction (high porosity or metrology issue)? If further increasing sintering temperature and duration, would it resolve this issue?

And in the density evolution figure 1, it would be better to use Nd concentration as X-axis label (0, 0.25, 0.5 and 1 atomic %) rather than sample number.

Response to comment 1:

An explanation related to the control mechanisms during sintering was added, which explains the low density of the samples.

Figure 1 has been modified.

Comment 2:

Particle size distributions of samples with different Nd concertation show unclear and abnormal trend. Authors state that Nd composition prevents the pores closing, however 1% Nd sample shows a not only smaller but a more uniform particle size distribution, which is not consistent with 0.5% Nd sample case. I would like to know more explanation and thought about this abnormal phenomenon.

Response to comment 2:

A possible explanation of the phenomenon occurring here has been added to the manuscript.

Comment 3:

In this manuscript, authors analyzed several samples synthesized at different temperature, which is helpful to monitor the actual reaction transition. However, seems in final sample sintered at 1500C still contains some undesirable phases, I wonder if authors have any thoughts or plan to remove impurities of samples, like additional annealing, higher temperature synthesis, longer reaction time? Is the selected 1500C due to any particular reason or equipment limitation?

Response to comment 3:

A note was added in the manuscript indicating that in order to remove the impurities still present at 1500, the samples would have to be sintered at a higher temperature.

Comment 4:

In the microstructure section, authors discussed and presented the morphologies of samples taken by the optical microscope. From the figures, there are some visible white particles in the surface of samples. I wonder if authors could distinguish what the whitish particles are.

Response to comment 4:

New SEM figures were attached together with an EDS analysis indicating that the presence of these white particles corresponds to regions where Nd is present.

Comment 5:

Since this manuscript emphasize the importance sample density and porosity contributions, it would be better to further explore the microstructures of samples with the help of SEM, which would be helpful to determine to porosity of samples with different composition. I am also interested to see the Nd element distribution inside the crystal and among the grain boundaries based on some SEM chemical analysis of samples.

Response to comment 5:

New SEM figures were added and the discussion of microstructures in the manuscript was expanded.

Comment 6:

In the Materials and Methods section, the unit of powders cannot be presented well (shows as 1m) in the manuscript: Powders of Y₂O₃ and Al₂O₃ (Sigma-Aldrich, 99.9 % purity and 1 m size). Please double check if that is correct.

Response to comment 6:

Certainly, there was an error in the units, the correct unit is microns, this has been corrected in the corresponding part of the manuscript.

Reviewer 3 Report

In this study, a simple and inexpensive alternative to producing Nd:YAG materials via solid-phase reactions was proposed.

The work can be accepted but with the following remarks

-The topic of obtaining Nd:YAG crystals is very common and many breakthroughs have been made. I ask to make a comparative table with characteristics of translucency of ceramics obtained from polycrystalline samples (SPS, HIP, CIP and others). (10.1016/j.ceramint.2018.09.123, 10.1016/j.matchar.2021.110883)

-Figure 3 please use the Rietveld method to recalculate the semi-quantitative phase content. Please specify the deciphering in the legend of the phase reductions and indicate the numbers of the cards of the received connections through the PDF database.

-Not enough pictures of the obtained samples on how persistent the crystals turn out

-Why this operating temperature mode is chosen, missing the aforementioned table comparing the properties

-As I know that YAG-based crystals are very demanding to purity, please indicate how the

-Please expand the number of references to works for 2017-2022, as well as add links to Ceramics Journal itself

Author Response

Reviewer 3

In this study, a simple and inexpensive alternative to producing Nd:YAG materials via solid-phase reactions was proposed.

The work can be accepted but with the following remarks

Comment 1:

The topic of obtaining Nd:YAG crystals is very common and many breakthroughs have been made. I ask to make a comparative table with characteristics of translucency of ceramics obtained from polycrystalline samples (SPS, HIP, CIP and others). (10.1016/j.ceramint.2018.09.123, 10.1016/j.matchar.2021.110883).

Response to comment 1:

Although a comparative table of the luminescent properties of the laser manufactured here was not included. It is mentioned in the sections 3.5 and 3.6 that optical properties of our compounds are very similar to those of commercial lasers and lasers obtained by more complex methodologies.

In this sections also, they are compared these properties with those of other works and suggests possible applications of the laser fabricated here.

Comment 2:

Figure 3 please use the Rietveld method to recalculate the semi-quantitative phase content. Please specify the deciphering in the legend of the phase reductions and indicate the numbers of the cards of the received connections through the PDF database.

Response to comment 2:

We are sorry we do not have the software to perform Rietvelt analysis to quantify the phases. However, considering that in a future work we will sinter at temperatures higher than those worked here (1500°C), with the idea of eliminating the remaining phases to obtain pure YAG garnet, a Rietvelt analysis would not be very necessary.

Comment 3:

Not enough pictures of the obtained samples on how persistent the crystals turn out.

Response to comment 3:

New SEM figures were added, together with an analysis by eds, and the discussion of the microstructure section was deepened.

Comment 4:

Why this operating temperature mode is chosen, missing the aforementioned table comparing the properties.

Response to comment 4:

The working temperature of 1500°C was chosen considering that with the mechanical activation of the powders, the sintering and occurrence of reaction 1 would be sufficient at that temperature. However, from the results obtained and from the accurate observations of the referees, it is clear that it is necessary to work at higher temperatures, 1550 or 1600°C.

Comment 5:

As I know that YAG-based crystals are very demanding to purity, please indicate how the…

Response to comment 5:

Although the sentence is incomplete, we assume that it refers to the purity of the ceramic obtained after the reaction at 1500°C, as another referee also observed. We established in the manuscript that persistent impurities (alumina and yttria) in the material after sintering at 1500°C could be removed by sintering at higher temperatures and thus obtain a YAG-based ceramic with high purit.

Comment 6:

Please expand the number of references to works for 2017-2022, as well as add links to Ceramics Journal itself.

Response to comment 6:

The number of references of papers from 2017-2023 has been extended, including the 2 suggested by the referee.

Round 2

Reviewer 2 Report

I think the authors have addressed all my concerns and those of the other reviewers thoroughly and to my satisfaction, and I recommend publication in Ceramics.

Reviewer 3 Report

completely satisfied the reviewer's comments. The article can be accepted for publication