Spectral Characterization of CeF₃-YF₃-TbF₃ Nanoparticles for Temperature Sensing in 80–320 K Temperature Range

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study reports the synthesis of Ce0.5Y0.5-XTbXF3 (X = 0–0.05) nanoparticles via a water-based co-precipitation method, yielding 17–20 nm hexagonal-phase particles consistent with CeF3. The luminescence properties were investigated under 266 nm excitation, revealing temperature-dependent variations in the spectral shape of Ce3+ (5d–4f) and Tb3+ (5D4–7FJ) emissions. The authors employed the integrated luminescence intensity ratio (LIR) between Ce3+ and Tb3+ (5D4–7F3) peaks as a quantitative parameter for temperature sensitivity. Results demonstrated a linear decay of LIR with increasing temperature, with the decay rate decreasing as Tb3+ concentration increased, attributed to enhanced Ce3+ → Tb3+ energy transfer at higher Tb3+ levels. The study provides novel insight into the cross-relaxation mechanisms and their influence on luminescence temperature sensitivity in CeF3-TbF3-YF3 nanoparticles over a low-temperature range of 80–320 K. While the study is interesting, several aspects require clarification and refinement to meet the standards of the Condensed Matter journal.

The author are encouraged to consider the following recommendations when revising their manuscript.

1. Authors should clearly describe the novelty of the presented research.
2. It is requested that the magnification for the photograph depicted in Figure 1 be specified. Furthermore, it is required that EDS mapping, along with the percentage of individual elements, be attached and discussed.
3. The numeric data presented in Table 1 should contain dots, not commas. In addition, the table caption should be adequate for its content.
4. The following sentences: „Note that integrated intensities were calculated according to Figure 5“, „Here, there is an activation energy of the Ce3+ luminescence quenching process. “ should be rewritten.
5. To what extent does nanoparticle size distribution (17–20 nm) impact the luminescence efficiency and temperature sensitivity of these materials?
6. How does the Ce3+ → Tb3+ energy transfer mechanism influence the linearity of LIR decay across varying Tb3+ concentrations?
7. What role does cross-relaxation among Tb3+ ions play in modulating the thermal quenching behavior of Ce3+ luminescence?
8. Figure 8e is not mentioned in the discussion part.
9. How could the observed temperature dependence of LIR be theoretically modeled using energy transfer kinetics in multi-doped fluoride nanoparticles?
10. How might extending the study to sub-80 K or above 320 K temperature ranges alter the observed spectral and LIR behaviors?
11. Please rewrite the following sentence: „In order to discuss the obtained results we need to discuss the chemical composition. “ as „discuss “ is mentioned twice.
12. The following sentence: „It can be seen, that we achieved competitive values. “ should be discussed in more detail, as well as the results presented in Figure 10.
13. Could the methods used here for spectral characterization be adapted to investigate dynamic energy transfer processes under pulsed excitation conditions?
14. It is mentioned at the end of the manuscript that some results can be found in the Supplementary Materials file. However, the manuscript lacks this information, and the file does not exist.
15. The English language of the manuscript needs correction.

Author Response

Dear Editors and the Reviewer. Thank you very much for careful examination of our work and for valuable comment and questions. Here we answer them in detail. All the changes we marked with blue.

Reviewer 1

The study reports the synthesis of Ce0.5Y0.5-XTbXF3 (X = 0–0.05) nanoparticles via a water-based co-precipitation method, yielding 17–20 nm hexagonal-phase particles consistent with CeF3. The luminescence properties were investigated under 266 nm excitation, revealing temperature-dependent variations in the spectral shape of Ce3+ (5d–4f) and Tb3+ (5D4–7FJ) emissions. The authors employed the integrated luminescence intensity ratio (LIR) between Ce3+ and Tb3+ (5D4–7F3) peaks as a quantitative parameter for temperature sensitivity. Results demonstrated a linear decay of LIR with increasing temperature, with the decay rate decreasing as Tb3+ concentration increased, attributed to enhanced Ce3+ → Tb3+ energy transfer at higher Tb3+ levels. The study provides novel insight into the cross-relaxation mechanisms and their influence on luminescence temperature sensitivity in CeF3-TbF3-YF3 nanoparticles over a low-temperature range of 80–320 K. While the study is interesting, several aspects require clarification and refinement to meet the standards of the Condensed Matter journal.

The author are encouraged to consider the following recommendations when revising their manuscript.

Comment 1. Authors should clearly describe the novelty of the presented research.

Answer 1. Thank you for this important remark, we added this text about the novelty in the Introduction (marked with blue):

One of the main novelties of this work is that here we consider a double-doped system (Ce³⁺/Tb³⁺), where the donor ion (Ce³⁺) is optically excited via 4f – 5d transition.  This class of materials is significantly less studied compared to double-doped materials excited via f-f transitions (Nd³⁺/Yb³⁺, Tm³⁺/Yb³⁺, etc). Due to the high sensitivity of 5d electrons to the surroundings, this class of materials has potentially higher temperature sensitivities.  No less important thing is that we consider several samples having different Tb³⁺ concentrations in order to manipulate and maximize the thermometer performances.

 

Comment 2. It is requested that the magnification for the photograph depicted in Figure 1 be specified. Furthermore, it is required that EDS mapping, along with the percentage of individual elements, be attached and discussed.

Answer 2. Thank you for this comment, we pointed x300k magnification in the Figure 2 (TEM) capture. In the case of EDS mapping, we agree, that this method allows visualizing the chemical element distribution. However, this method has a threshold around 0.5 % and our samples with low Tb³⁺ concentrations can not be studied correctly. In the case of our Hitachi electron microscope, we don’t have such option as EDS mapping, along with the percentage of individual elements. We are going to perform such experiments in future. Here we consider the ration of chemical elements according to the chemical reaction.

 

Comment 3. The numeric data presented in Table 1 should contain dots, not commas. In addition, the table caption should be adequate for its content.

Answer 3. We corrected the Table 1 according to your recommendations (marked with blue).

 

Comment 4. The following sentences: „Note that integrated intensities were calculated according to Figure 5“, „Here, there is an activation energy of the Ce³⁺ luminescence quenching process. “ should be rewritten.

Answer 4. Thank you for this comment, we absolutely agree. We replaced this sentence by “

 

Comment 5. To what extent does nanoparticle size distribution (17–20 nm) impact the luminescence efficiency and temperature sensitivity of these materials?

Answer 5. Thank you for this question. Indeed, the size influence of physical properties is a very interesting topic of nanotechnology. There are several opinions about the influence of the size. For instance, in [1], the influence of the synthesis method on the size of nanoparticles and their luminescent properties was studied. This suggests that, unlike ions in the bulk of a nanoparticle, ions in its surface layer are subject to a low-symmetry crystal field and are also influenced by the surrounding environment. Moreover, a significant influence of the surface occurs at nanoparticle sizes less than 15 nm. Specifically, there is a sharp decrease in the quantum yield, a shortening of the luminescence lifetime, and a predominance of nonradiative relaxation over other energy transfer processes.

[1] Vanetsev A. Relation of Crystallinity and Fluorescent Properties of LaF3: Nd3+ Nanoparticles Synthesized with Different Water‐Based Techniques / A. Vanetsev, K. Kaldvee, L. Puust, K. Keevend, A. Nefedova, S. Fedorenko, Y. Orlovskii // Chemistry Select. – 2017. – Т. 2. – №. 17. – P. 4874-4881.

We did not set a task to study the size effect in the present work, however, thank you for the idea. It is very interesting to perform these experiments in the future.

 

 

Comment 6. How does the Ce3+ → Tb3+ energy transfer mechanism influence the linearity of LIR decay across varying Tb3+ concentrations?

Answer 6. Thank you for this very important question. The LIR decay function is a very difficult topic. Some results are well-fitted by Arrhenius function, some results by the Boltzmann one. The same linear decay of the LIR was obtained in Journal of Luminescence 217 (2020) 116807. The physical interpretation of the linear decay required further investigation. However, the decrease of decay rate with the increase of Tb³⁺ concentration we explain by the decreasing contribution of Ce³⁺ thermal quenching (the discussion after Figure 8. The configurational coordinate diagram of the ground states and the excited states of Ce³⁺ and Tb³⁺).

 

 

 

Comment 7. What role does cross-relaxation among Tb³⁺ ions play in modulating the thermal quenching behavior of Ce³⁺ luminescence?

Answer 7. Thank you for this important question.  The role of cross-relaxation of Tb³⁺ was discussed in our previous work “Optical Materials 148 (2024) 114831”. Based on the data from this work, the main contribution of Ce³⁺/Tb³⁺ temperature sensitivity if related to Ce³⁺ thermal quenching. The role of cross-relaxation seems to be negligible. Indeed, the cross-relaxation depopulates ⁵D₃ excited level of Tb³⁺ only without affecting the Ce-Tb energy transfer.

 

Comment 8. Figure 8e is not mentioned in the discussion part.

Answer 8. Since the numbering was changed, now it is Figure 9. We added this sentence “In particular, the Ce³⁺ intensity gradually decreases with the increase of Tb³⁺ concentration (Figure 9a -9e)”.

 

Comment 9. How could the observed temperature dependence of LIR be theoretically modeled using energy transfer kinetics in multi-doped fluoride nanoparticles?

Answer 9. Thank you very much for this very important question. Indeed, the theoretical description of the obtained dependence is very important and, by and large, is not described anywhere. For example, the conventional Mott–Seitz model describes the double-doped systems for f-f transitions. Here, we have Ce³⁺ thermal quenching as well as phonon assisted energy transfer. The theoretical model is the next part of this investigation.

 

Comment 10. How might extending the study to sub-80 K or above 320 K temperature ranges alter the observed spectral and LIR behaviors?

Answer 10. The extended temperature range (320 K and higher) was discussed in our previous work “Optical Materials 148 (2024) 114831. Here the LIR functions demonstrated the same tendencies. However, the decay behavior is “less linear”. The decay rates are higher. Probably is was related to the higher temperatures and more efficient thermal quenching.

 

Comment 11. Please rewrite the following sentence: „In order to discuss the obtained results we need to discuss the chemical composition. “as „discuss “ is mentioned twice.

Answer 11. Thank you, we corrected.

 

 

Comment 12. The following sentence: „It can be seen, that we achieved competitive values. “ should be discussed in more detail, as well as the results presented in Figure 10.

Answer 12. We absolutely agree, we added the discussion about the comparison of the Sr values after equation 3 (marked with blue). We considered modern papers.

 

Comment 13. Could the methods used here for spectral characterization be adapted to investigate dynamic energy transfer processes under pulsed excitation conditions?

Answer 13. Thank you for this question. The difference between the regime of excitation (including CW or pulse excitation) is a very complex question. However, in this particular case, there is no difference between CW or pulse excitation because here we consider the Ce³⁺ excitation. The main difference between these types of excitation is the power density. For pulse excitation, the power density in the pulse is to high to trigger ionization of some two phonon processes. We do not use such high energies and we believe that the CW or pulse excitation are the same. However, it is interesting to experimentally perform such comparison.

 

Comment 14. It is mentioned at the end of the manuscript that some results can be found in the Supplementary Materials file. However, the manuscript lacks this information, and the file does not exist.

Answer 14. Thank you for this comment. We excluded supplementary.

 

Comment 15. The English language of the manuscript needs correction.

Answer 15. Thank you, we corrected the English. The corrections were marked with blue.

 

Reviewer 2 Report

Comments and Suggestions for Authors

see pdf attached

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have effectively and sufficiently addressed all the observations and concerns I raised in my previous review. The modifications made to the text, along with the detailed explanations in the author response  letter, are satisfactory.