Fluorescence Lifetime as a Ruler: Quantifying Sm³⁺ Doping Levels in Na₄La₂ (CO₃)₅ Crystals via Time-Resolved Luminescence Decay

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled “Fluorescence Lifetime as a Ruler: Quantifying Sm³⁺ Doping Levels in Na4La2(CO3)5 crystals via Time-Resolved Luminescence Decay” by Sun and coauthors is focused on poorly characterized family of alkaline-lanthanide carbonates. This makes the manuscript particularly important in understanding the luminescence lanthanide ions in carbonate matrixes. The manuscript is well written with conclusions supported by the obtained results. However, there are few critical points that should be addressed:

 

1. In section 3.1 the authors claim that the addition of Sm3+ does not lead to change of the crystal structure. This does not seem to be quite accurate. On figure 1 it is clearly seen that after x=0.5 a new reflection appears around 16o 2theta. This is an obvious sign for the presence of the monoclinic phase (the particular peak is the (11-1) reflection), which leads to the conclusion that after x=0.5 the powders are actually a mixture of hexagonal and monoclinic phase.
2. It is unclear what the actual point of going beyond x=0.04 is for two reasons - As already mentioned in my first comment the samples are not single phase after x=0.5 and it seems that after x=0.04 significant concentration quenching occurs.
3. When reporting multiexponential fit for the lifetimes (table 1) it is important also to report the weight of each t.

The most critical point is that although the manuscript is generally in good condition it is not suitable for Coatings as it does not fall in the scope of the journal.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The paper ‘Fluorescence Lifetime as a Ruler: Quantifying Sm³⁺ Doping Levels in Na4La2(CO3)5 crystals via Time-Resolved Luminescence Decay’ is about a concentration study of a new Sm-doped phosphor. Authors have prepared the paper according to the generally common study of such kind of materials. The data are clearly presented, generally clearly illustrated, conclusions correctly come from the results. Authors use enough methods to support the results. Methodology is complete and is described according to the Journals’ rules. The literature is fully presented by relevant references. I see only minor revision here.

 

1. The first sentence of the Methods section gives a very comprehensible and laconic notation of the studied material “NLC:xSm3+”. However, the whole paper utilizes different notations – from full formula (for example, heading to Figure 1) to word explanation (see 3.2. first sentence). The Manuscript would look better if everywhere in the text the studied matter would be given as NLC:xSm3+, including tables and figures.
2. Figure 7 – can authors please try a different presentation here? For example, all dashed lines should be black, or more contrast?

Figure 8 – the same.

3. Figure 9 does not explain the abbreviation CR.
4. I recommend adding DOI to all cited literature

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors of the article presented interesting results concerning the synthesis and luminescent properties of a substance that is a promising optical sensor of double sodium-lanthanum carbonate doped with samarium. Optical sensors based on fluorescent materials are attracting increasing attention from researchers due to their ease of synthesis and operation, as well as their relatively high sensitivity to both external stimuli and many chemical reagents. The researchers proposed a method for the synthesis of a substance different from similar compounds, which makes it possible to obtain a hexagonal rather than a monoclinic modification, and analyzed the effect of the samarium content on the luminescence intensity and on the lifetime of the excited state. The observed results are explained in terms of the phenomenon of concentration quenching of luminescence primarily due to electric dipole-dipole interactions. It should be especially noted the successful approximation of the obtained data by a fairly simple equation. All the results are new, experimental studies are performed at a high level, the results are presented absolutely reliable. At the same time, when reading the article, a number of questions and comments arise.

1. What is the true composition of the resulting substance? The authors indicate that the Na:Ln ratio is equal to 1.12. Does this Na:Ln ratio depend on the samarium content in the sample?
2. The authors indicate that they have obtained a single-phase sample. However, additional peaks are clearly visible on the diffraction patterns of samples with x = 0.5 and x = 1 at around 15, 16.5, and 22 degrees. In addition, there is a strong broadening of the peaks for these samples, which would also be good to discuss.
3. In Figure 4, the luminescence band at 641 nm has a different maximum shape at low and high samarium concentrations. It is likely that there are two maxima and that there is a redistribution of energy between them. It would be nice to see a discussion of this fact.
4. When discussing the decay curves (Figure 8), the authors emphasize the need for multiple exponential equations. I would like to see a more detailed description of the selection of the optimal number of exponentials and the processes that determine this number.
5. The authors mention the similarity of the fluorescence lifetime values in the compound under study and a number of similar substances. However, there are certain differences. Could the authors provide some discussion of this fact?
6. In the introduction, the authors list specific compounds that can be identified using fluorescent materials. However, there is a much wider range of compounds that can be identified in this way. It may be necessary to expand this list or provide a more general description.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors addressed all of my questions/comments and the manuscript can be considered for publication in Coatings.

Author Response

Comments: The authors addressed all of my questions/comments and the manuscript can be considered for publication in Coatings.

Response: We appreciate your valuable feedback. Your suggestions will help us improve our future research. Thank you once again.

Reviewer 3 Report

Comments and Suggestions for Authors

In general, I azm quite satisfied vy the answers on my questions. The only exceptiion is the answer to questuion 1. If Na to Ln ratio is 1,12, that is less than in Na4Ln2(CO3)5 formulae, the actual composition of the salt should be different from given in the paper....

Author Response

Comments：In general, I am quite satisfied vy the answers on my questions. The only exception is the answer to question 1. If Na to Ln ratio is 1,12, that is less than in Na4Ln2(CO3)5 formulae, the actual composition of the salt should be different from given in the paper

Response：Thank you for your precise guidance. Although the chemical composition of the samples may vary, this difference is small. In our experiment, we repeated the experiment more than 6 times and obtained samples with nearly identical fluorescence emission intensities under the same reaction conditions. Therefore, this chemical formula can be used to express the product under these specific experimental conditions.