LiGd_xY_1−xF₄ and LiGdF₄:Eu³⁺ Microparticles as Potential Materials for Optical Temperature Sensing

Round 1

Reviewer 1 Report

In this manuscript, high quality LiGd_xY_1-xF₄ single crystals were grown by Bridgman-Stockbarger technique. The characterization of the temperature-dependent spectrum of LiGdF₄:Eu³⁺ demonstrates its potential as an optical temperature sensor operating in the low temperature range. This research has certain innovations and can be published in this journal after minor revision.

1.      Why is the XRD pattern calculated by VESTA software deviated from both the experimental value and the standard card? The standard card corresponding to LiGdF4 should be drawn in Figure 1 to make the comparison more intuitive.

2.      The content expressed in Figures 3a and 4b is repeated and can be combined into one figure. The full name of “EDA” should be indicated in the article.

3.      Page 8, paragraph 17, “We associate this phenomenon with the radiation of defects, which is often found in fluorides and is associated with the formation of complexes of oxygen and fluorine [26].”

The authors attribute the disappearance of broadband emission with increasing temperature to the formation of oxygen and fluorine complexes. The authors should elaborate on the mechanism of this phenomenon.

4.      The authors should carefully correct citations and tagging errors in the article. For examples, the language used on the unit should be consistent in figure 6a and 6b；“Figure 5”should be changed to“Figure 7”in Page 8, paragraph 15 ；“Figure 7”should be changed to“Figure 9”in Page 10, paragraph 3 and Page 11, paragraph 1 ；“LiGd_XY_1-XF₄” should be changed to“LiGd_XY_1-xF₄”in the titles of 3.2 and 3.4.

     The author needs to further revise the English spelling and grammar and fill in the missing content. For examples，“wavelenght”should be corrected to“wavelength”；the annotation in Figure 9 should introduce 9a and 9b, respectively.

Author Response

In this manuscript, high quality LiGd_xY_1-xF₄ single crystals were grown by Bridgman-Stockbarger technique. The characterization of the temperature-dependent spectrum of LiGdF₄:Eu³⁺ demonstrates its potential as an optical temperature sensor operating in the low temperature range. This research has certain innovations and can be published in this journal after minor revision.

Dear Reviewer, thank you for careful examination of the manuscript and for your important comments. Here we answer the comments in detail. All the changes in the text we marked with color.

1. 1. Why is the XRD pattern calculated by VESTA software deviated from both the experimental value and the standard card? The standard card corresponding to LiGdF4 should be drawn in Figure 1 to make the comparison more intuitive.

Answer 1. Thank you for this observation. We presented the standard card at the bottom of the Figure 1 (JCPDS No 027-1236). In the case of the deviation, we performed simulation via VESTA software only for LiGdF₄ (the highest pattern of Figure 1). The simulation describes the LiGdF₄ XRD pattern very well (Δ2Θ is around 0.05 degrees). We believe that this difference is negligible and the phase composition is confirmed. In addition, this difference is notably less compared to S. Lepoutre et al. / Optical Materials 28 (2006) 592–596. You can also see our previous work “Morozov O. A. et al. Growth and characterization of optical and thermal properties of LiGdF₄ single crystal //Optical Materials. – 2023. – Т. 137. – С. 113490”. The deviation is observed for more complex sample LiGd_XY_1-XF₄ (X=0.05) that can be rewritten as Gd³⁺ (5%):LiYF₄.

2. The content expressed in Figures 3a and 4b is repeated and can be combined into one figure. The full name of “EDA” should be indicated in the article.

Answer 2. Thank you for this observation. We agree we omitted one picture. We left the picture containing EDX data, indicated the EDX full name and described the standard deviation  calculation procedure (just before Figure 3, marked with green).

3. Page 8, paragraph 17, “We associate this phenomenon with the radiation of defects, which is often found in fluorides and is associated with the formation of complexes of oxygen and fluorine [26].”

The authors attribute the disappearance of broadband emission with increasing temperature to the formation of oxygen and fluorine complexes. The authors should elaborate on the mechanism of this phenomenon.

Answer 3. Yes, this comment is absolutely fair and mechanism seems not to be well-grounded in literature devoted to optical sensing. We added this discussion in the text right after Figure 7 (marked with red).

“The presence of this broad emission can be explained by several mechanisms. In the work [39], the broad excitonic emission is observed for LiYF₄ (the same crystal structure has LiGdF₄) under X-ray excitation at 4.2 K. These excitons are of the type . However, this emission in the 200 – 400 K spectral range centered at 300 nm unlike the obtained results (Figure 7). Moreover, the excitonic emission is thermally quenched at T > 100 K. Here, we observe the broad emission at higher temperatures [40]. The second mechanism is related to the presence of oxygen impurities that is considered the most common impurity for fluorides. There are also fluorine vacancies (V_F). In this case, fluoride matrices where the fluorine ion is substituted by oxygen. The absorption band of these impurities is in the 250 – 300 nm range. Our excitation wavelength (274 nm) is almost at the center of the absorption band [41]. We found at least two consequences of the presence of the oxygen impurities (O_F). The first is O_F – RE³⁺ complex [41], the second is O_F – VF – RE³⁺ one [42]. Under UV excitation, both doping ion and the above-mentioned complexes are excited following the emission or non-radiative transitions. It can be suggested, that the  O_F – RE³⁺ and O_F – VF – RE³⁺ complexes have intricate energy level structure that provides broad band emission. At low temperature the energy transfer from the complex to RE is hindered. The energy transfer probability increases with the rise of the temperature that leads to the decrease of the complex emission intensity and the increase of RE emission. This hypothesis requires addition investigation”.

4. The authors should carefully correct citations and tagging errors in the article. For examples, the language used on the unit should be consistent in figure 6a and 6b；“Figure 5”should be changed to“Figure 7”in Page 8, paragraph 15 ；“Figure 7”should be changed to“Figure 9”in Page 10, paragraph 3 and Page 11, paragraph 1 ；“LiGd_XY_1-XF₄” should be changed to“LiGd_XY_1-xF₄”in the titles of 3.2 and 3.4.

Answer 4. Thank you for your attention to such important details. We’ve corrected them.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the LiGd_xY_1-xF₄ (x=0.05; 0.3; 0.7 and 1.0) and LiGdF₄: Eu³⁺ microparticles were prepared and their optical temperature sensing properties were studied. And LiGdF₄:Eu³⁺ is a suitable candidate for optical temperature sensor operating in the cryogenic temperature range. The following issues should be addressed and minor revision is needed before publication.

(1) The LiGd_xY_1-xF₄ single crystals were grown by the Bridgman-Stockbarger technique using a growth furnace with a specially designed heating unit. How about the LiGdF₄: Eu³⁺? Besides, the authors calculated the Gd³⁺ concentration through Scheil equation. And how is the concentration determined when Gd³⁺ and Eu³⁺ were co-doped?

(2) The type and content of doped rare-earth elements commonly affect the properties of crystal phase structure. In the XRD part, the authors should add some statements about the influence of different Gd³⁺ concentrations on the matrix.

(3) It is known that concentration quenching can lead to a decrease in luminescent efficiency, intensity, and also luminescent lifetime. The authors chose LiGdF₄, which has a concentration quenching effect, for the later study of doping Eu. Does the low luminescence energy of LiGdF₄ affect the energy transfer efficiency between Gd³⁺ and Eu³⁺? Authors mentioned that reabsorption of luminescence can lead to the increase of lifetime of the excited states, but the LiGdF₄­ sample, which owns at least two temperature-dependent processes: multiphonon relaxation on defects and reabsorption of luminescence, has lower t_decay than LiGd_0.05Y_0.95F₄. Please explain it.

(4)  In Figure 8, the curve equation obtained from the data fitting should be indicated in the figure.

(5) Some recent publications about studies of optical temperature sensing and effect of Eu³⁺ should be cited, such as J. Eur. Ceram. Soc., 43, 4408-4418 (2023).

There are many problems with the details of writing throughout the article, e.g. there should be space between number and unit. Many of the variable characters in the manuscript are not italicized, for example x, S_a and S_r. These should be checked carefully and then revised.

Author Response

In this work, the LiGd_xY_1-xF₄ (x=0.05; 0.3; 0.7 and 1.0) and LiGdF₄: Eu³⁺ microparticles were prepared and their optical temperature sensing properties were studied. And LiGdF₄:Eu³⁺ is a suitable candidate for optical temperature sensor operating in the cryogenic temperature range. The following issues should be addressed and minor revision is needed before publication.

Dear Reviewer! Thank you for detailed examination of our experimental work and important comments. Here we answer the comments in-depth.

(1) The LiGd_xY_1-xF₄ single crystals were grown by the Bridgman-Stockbarger technique using a growth furnace with a specially designed heating unit. How about the LiGdF₄: Eu³⁺? Besides, the authors calculated the Gd³⁺ concentration through Scheil equation. And how is the concentration determined when Gd³⁺ and Eu³⁺ were co-doped?

Answer 1. Thank you for this comment. It’s flair. For LiGd_xY_1-xF₄ (X = 0.05) we performed a big set of experiments detecting absorption spectra along the crystal. One of the main purpose was to physically characterize the LiGd_xY_1-xF₄ compound to choose appropriate host for Eu³⁺ doping. The ionic radii of Gd³⁺ and Y³⁺ are different and the presence of Gd³⁺ distribution was expected and we calculated it. The knowledge id Eu³⁺ distribution is also important. The Eu³⁺ and Gd³⁺ have neighboring position in the Periodic table occupying 63 and 64 numbers, respectively. They have closer ionic radii compared to yttrium and distribution is expected to be insignificant. In addition, as we proved that Gd³⁺ distributed inhomogeneously, we took the same part of the Eu³⁺:LiGdF₄ crystal for both concentration in order to carry out the experiments. However, the information about concentration distribution of rare-earth ions including Eu³⁺ is important. We’re going to perform it as new scientific paper with different RE³⁺ ions.

We added in “Materials and methods” part this specification:

The concentration of both Eu³⁺ and Gd³⁺ was calculated as a mass proportion of the EuF₃ and GdF₃ starting materials in the melt.

(2) The type and content of doped rare-earth elements commonly affect the properties of crystal phase structure. In the XRD part, the authors should add some statements about the influence of different Gd³⁺ concentrations on the matrix.

Answer 2.  Thank you for this comment, we agree. We added this discussion right after Figure 1 (marked with green).

“They also agree with JCPDS No. 027–1236 [22]. According to the literature data, the lattice parameters of LiGdF₄ are a = 0.5235(1) nm, c = 1.1019(2) nm [23]. In its turn, the lattice parameters of LiYF₄ are a = 0.5164 (1) nm, c = 1.074 (2) nm[24]. The XRD peaks also slightly shift toward higher angels with the decrease of Gd³⁺ content expressing the Bragg law. The calculated lattice parameters in agreement with the above-mentioned values and gradually increase with the increase of Gd³⁺ content (Table S1 of supplementary)”. 

(3) It is known that concentration quenching can lead to a decrease in luminescent efficiency, intensity, and also luminescent lifetime. The authors chose LiGdF₄, which has a concentration quenching effect, for the later study of doping Eu. Does the low luminescence energy of LiGdF₄ affect the energy transfer efficiency between Gd³⁺ and Eu³⁺? Authors mentioned that reabsorption of luminescence can lead to the increase of lifetime of the excited states, but the LiGdF₄­ sample, which owns at least two temperature-dependent processes: multiphonon relaxation on defects and reabsorption of luminescence, has lower t_decay than LiGd_0.05Y_0.95F₄. Please explain it.

Answer 3. Thank you for this important observation. We agree it should be discussed in more detail. Moreover, we did not find papers devoted to Gd³⁺ quenching in such a big concentration range (5 – 100%) in fluorine host. Moreover, many papers devoted to Gd-Ln energy transfer (not single-Gd-doped). We found in “Journal of Luminescence 42 (1988) 275 282”, that at 300 K the decay rate of ⁶P_7/2 (Gd³⁺) in LiYF₄-1%Gd³⁺ is equal to 115 (s^-1), hence, the decay time can be calculated as the inverse value = 8.7 ms. In our Gd³⁺ (5%):LiYF₄ the decay time is also around 8.5 ms. It can be suggested, that at lower concentrations the decay time of ⁶P_7/2 (Gd³⁺) is around 8.5%. With the higher concentrations, the contribution of reabsorption higher that contribution of concentration quenching. That leads to the increase of decay time. However, for LiGdF₄ sample, the contribution of concentration quenching is predominant, and the decrease of the decay time is observed.

We added this discussion after Figure 5 (marked with green)

The difference in decay times for LiGd_0.05Y_0.95F₄ and both LiGd_0.3Y_0.7F₄ and LiGd_0.7Y_0.3F₄ can be explained by the fact that there can be reabsorption of the luminescence that leads to the increase of the lifetime of the excited state. In more details, we found in [26], that at 300 K, the decay rate of ⁶P_7/2 (Gd³⁺) in LiYF₄-1%Gd³⁺ is equal to 115 (s^-1), hence, the decay time can be calculated as the inverse value = 8.7 ms. In our Gd³⁺ (5%):LiYF₄ sample, the decay time is also around 8.5 ms. It can be suggested, that at lower concentrations the decay time of ⁶P_7/2 (Gd³⁺) is around 8.5 ms. With the higher concentrations, the contribution of reabsorption is higher that contribution of concentration quenching. That leads to the increase of decay time. However, for LiGdF₄ sample, the contribution of concentration quenching is predominant, and the decrease of the decay time is observed.

   (4)  In Figure 8, the curve equation obtained from the data fitting should be indicated in the figure.

Answer 4. Thank you for this observation. Since the equation is relatively long, we indicated it in the Figure 8’s capture.

(5) Some recent publications about studies of optical temperature sensing and effect of Eu³⁺ should be cited, such as J. Eur. Ceram. Soc., 43, 4408-4418 (2023).

Answer 5. Thank you for advising interesting publication. It strengthened the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Oleynikova et al. present a photoluminescence investigation of two related fluoride systems: LiGdxY1-yF4 and Eu3+ doped LiGdF4. In general, the data presented in the manuscript leaves no questions. However, some language problems arise throughout the text, and there is a massive problem of omission of the mechanism and plausibility of Gd3+ -> Eu3+ energy transfer. Additionally, some information could be added to the text to make it more understandable to scientists who have less experience with Ln3+ luminescence.

The doubt, as mentioned earlier, regarding the Gd3+ -> Eu3+ mechanism arises from the text itself:
Line 140: "The Gd3+ – Eu3+ energy transfer process will be discussed below." - the authors only describe that the ET is present but do not discuss it. As Eu3+ has absorption lines in the region where Gd3+ is excited (250-300 nm), authors should provide a more solid proof of ET. With the missing excitation wavelengths in the text (only the transitions range is given for Figure 6), it might be that both ions were excited simultaneously.
Line 144: "The Gd3+ – Eu3+ energy transfer is phonon assisted" yet, as even the authors point out, fluoride matrices are known to be low phonon.

The authors should clarify this moment.

Another scientific problem is missing comparison with the literature, especially of Eu3+ luminescence in fluoride matrices, including luminescence decay times (and rises).

The emission spectra in Figure 6 are presented from 290 or 295 nm - so how was the sample excited at the 8S7/2 – 6PJ absorption band?

Further, regarding emission spectra presented in Figure 6 (text on line 174): "under Gd3+ excitation (8S7/2 – 6PJ absorption band)" - and which wavelength was used? Authors generally state either transition or wavelengths - combining both (throughout the text) is necessary. For example, in Figure 10, a description of which transitions are presented is desired.

Some language problems are present as well, including parts of the text presented not in English!
In line 27, "RE = lanthanides" in theory, authors are free to give any abbreviation they please to anything. However, RE conventionally abbreviates rare earth elements, while lanthanides are abbreviated as Ln.
The axes in Figure 6b are not in English. Parts of the SI are also written not in English.
Figure 10b: "t rize" - should be "t rise"
Lines 235-238: the same sentence is written twice.
Lines 241-243: it is extremely poorly written, so the sentence's meaning is lost. Besides, from the scientific language POV, conclusions should be drawn from data, not figures.

Some further minor problems:
The wrong figure is referenced in line 191. In lines 209 and 218 as well. Authors should check the correctness of all internal references and literature citations.
In the SI, for some decays, the legend is missing.

If the authors clarify the scientific points and the text is improved, this manuscript could be accepted in Ceramics.

As mentioned in the review, minor parts of the paper are presented in Russian, such as the axes in Figure 6b and the very end of the SI.

And again, as mentioned in the review, at least one sentence (lines 241-243) is not comprehensible.

Additionally, in some cases, a more passive voice (excluding "we") should be induced for scientific soundness, such as in lines 209-211:
"We see that for the sample we have obtained a competitive temperature sensitivity in the 50 – 180 К temperature range. " ->
The sample exhibits  a competitive temperature sensitivity.

And, one more example (line 110): "therefore, we measured the distribution coefficient of Gd3+ ions in the LiYF4 matrix" -> therefore, the distribution coefficient was measured.

There are more examples of this in the text, which, I assume, the authors can find themselves.

Author Response

Oleynikova et al. present a photoluminescence investigation of two related fluoride systems: LiGdxY1-yF4 and Eu3+ doped LiGdF4. In general, the data presented in the manuscript leaves no questions. However, some language problems arise throughout the text, and there is a massive problem of omission of the mechanism and plausibility of Gd3+ -> Eu3+ energy transfer. Additionally, some information could be added to the text to make it more understandable to scientists who have less experience with Ln3+ luminescence.

 Dear Reviewer! Thank you for detailed examination of our experimental work and for your attention to details. Here we answer the comments in-depth.

The doubt, as mentioned earlier, regarding the Gd3+ -> Eu3+ mechanism arises from the text itself:
Line 140: "The Gd3+ – Eu3+ energy transfer process will be discussed below." - the authors only describe that the ET is present but do not discuss it. As Eu3+ has absorption lines in the region where Gd3+ is excited (250-300 nm), authors should provide a more solid proof of ET. With the missing excitation wavelengths in the text (only the transitions range is given for Figure 6), it might be that both ions were excited simultaneously.
Line 144: "The Gd3+ – Eu3+ energy transfer is phonon assisted" yet, as even the authors point out, fluoride matrices are known to be low phonon.

The authors should clarify this moment.

 Answer. Thank you for this important comment, we agree. The Gd3+ – Eu3+ energy transfer process is complicated and deserves detailed discussion. To exclude the possibility of direct excitation of Eu³⁺ under 274 nm we carried out the same experiment for LiYF₄: Eu³⁺, where LiYF₄ host does not absorb this wavelength (274 nm). The pictures of both LiGdF₄: Eu³⁺ (0.1 %) and LiYF₄: Eu³⁺ (0.1 %) under 274 nm excitation are represented in Figure S4. For the LiGdF₄: Eu³⁺ (0.1 %), the characteristic red luminescence of Eu³⁺ is clearly observed. The LiYF₄: Eu³⁺ (0.1 %) does not show this emission. In the case of phonon-assisted nature of the energy transfer, we softened this statement in the manuscript, having written, that “It can be suggested…phonon assisted”. Because after literature analysis, we revealed, that this question requires total kinetic characterization and deserves a separated paper. Ouк arguments we show in the discussion section in the manuscript right after Figure 6 (marked with green).

It can be seen, that for LiGdF₄: Eu³⁺ (0.1 %) sample, the luminescence peaks of both Gd³⁺ and Eu³⁺ doping ions are clearly observed. To exclude the possibility of direct excitation of Eu³⁺ under 274 nm, we carried out the same experiment for LiYF₄: Eu³⁺, where LiYF₄ host does not absorb this wavelength (274 nm). The pictures of both LiGdF₄: Eu³⁺ (0.1 %) and LiYF₄: Eu³⁺ (0.1 %) under 274 nm excitation are represented in Figure S4. For the LiGdF₄: Eu³⁺ (0.1 %), the characteristic red luminescence of Eu³⁺ is clearly observed. The LiYF₄: Eu³⁺ (0.1 %) does not show this emission. According to the literature data, the energy transfer from Gd³⁺ to Eu³⁺ occurs via quantum cutting [29] and energy transfer between suitable energy levels of Gd³⁺ and Eu³⁺[30], [31]. The quantum cutting can be described at the Gd³⁺ excitation (λ_ex = 202 nm (⁸S_7/2 absorption band of Gd³⁺)) excitation “cuts” into the excitation of ⁵D₀ level of Eu³⁺ and ⁶P_J level of Gd³⁺. This process is possible only for above-mentioned excitation scheme (λ_ex = 202 nm). In the present work such quantum cutting is impossible. The energy transfer from Gd³⁺ to Eu³⁺ occurs via ⁶I_J (Gd³⁺) – ⁵F_J, ⁵I_J (Eu³⁺) and 6P_J - (Gd³⁺) – ⁵F_J, ⁵I_J (Eu³⁺). Gd³⁺ ions can be optically excited at 274 nm (⁸S_7/2–⁶I_J). Then the ⁶I_J states can decay non-radiatively populating ⁶P_J excited states. The excitation energy can be transfered to the ⁵H_J states of Eu³⁺, following the non-radiative transition to the lower ⁵D_J. The lowest ⁶P_J (J=7/2) of Gd³⁺ has energy around 32000 cm^-1 in LiGdF₄ [32]. In its turn, the highest ⁵D_J (J=4) state of Eu³⁺ has energy around 29000 cm^-1 [33]. The highest phonon energy for LiGdF₄ is around 570 cm^-1 [34], [35]. It required 3 – 4 phonons to “bridge” the ⁶P_7/2 - ⁵D₄ energy gap. In the case of ⁶I_J (Gd³⁺) – ⁵F_J, ⁵I_J (Eu³⁺) energy transfer, there are also the energy gap of the same order. It can be suggested, that this energy transfer is phonon-assisted at out excitation conditions.

Another scientific problem is missing comparison with the literature, especially of Eu3+ luminescence in fluoride matrices, including luminescence decay times (and rises).

 Answer. Thank you. It’s absolutely fair. The discussion of Gd³⁺ we provided in the above-mentioned part. The Eu³⁺ kinetic characterization we also discuss in the part right after Figure 10.

It can be seen from Figure 10 b that the decay times for the ⁵D₁ and ⁵D₀ states are around 7 and 3 ms at 300 K, respectively. The obtained results are in good agreement with the literature data in LiGdF₄ [47], [48]. The decay times demonstrate a weak tendency to decrease with an increase in temperature. This tendency can be attributed to increase the probability of non-radiative relaxation with the rise of temperature. The presence of the rise-time curve is explained by non-radiative relaxation from the higher-energy ⁵D_J levels to ⁵D_1,0 ones (the excitation of ⁵D_1,0 state is non-resonant). When the temperature is lowered, relaxation rates slow down, which is indicated by an increase in the rise-time [47]. Based on Figures 8 and 9 in the LiGdF₄:Eu³⁺ samples, it was found that the cross-relaxation process weakly depends on the temperature and concentration of Eu³⁺ ions and is not suitable for sensing purposes. The same tendency is observed in such important fluoride phosphors as Ka₅Li₂La_1-XEuXF₁₀ in the 80 – 300 K range. Specifically, ⁵D₁ lifetime decreases gradually from ~ 4 (80 K) to ~ 2 ms (300 K) [49]. The rise times for the ⁵D₁ and ⁵D₀ states are around 1 and 3 ms at 300 K, respectively. The same values were obtained for Eu³⁺:LiGdF₄ in work [47]. The rise times also demonstrate the decreasing tendency with the temperature increase. 

The emission spectra in Figure 6 are presented from 290 or 295 nm - so how was the sample excited at the 8S7/2 – 6PJ absorption band?

Further, regarding emission spectra presented in Figure 6 (text on line 174): "under Gd3+ excitation (8S7/2 – 6PJ absorption band)" - and which wavelength was used? Authors generally state either transition or wavelengths - combining both (throughout the text) is necessary. For example, in Figure 10, a description of which transitions are presented is desired.

 Answer. Yes, it is fair. We pointed the excitation wavelength 274 nm. We specified the transitions and wavelengths for Figure 10. In the case of Figure 6, we choose the 290 – 1100 nm scale in order not to show the excitation (274 nm) focusing on the ion emissions.

Some language problems are present as well, including parts of the text presented not in English!
In line 27, "RE = lanthanides" in theory, authors are free to give any abbreviation they please to anything. However, RE conventionally abbreviates rare earth elements, while lanthanides are abbreviated as Ln.
The axes in Figure 6b are not in English. Parts of the SI are also written not in English.
Figure 10b: "t rize" - should be "t rise"
Lines 235-238: the same sentence is written twice.
Lines 241-243: it is extremely poorly written, so the sentence's meaning is lost. Besides, from the scientific language POV, conclusions should be drawn from data, not figures. Some further minor problems:
The wrong figure is referenced in line 191. In lines 209 and 218 as well. Authors should check the correctness of all internal references and literature citations.
In the SI, for some decays, the legend is missing.

Answer. Thank you for detailed consideration of the manuscript. We corrected the mistakes. In addition, we have rewritten 241-243 lines:

In this work, physical characterization of LiGd_xY_1-xF₄ (x=0.05; 0.3; 0.7 and 1.0) and LiGdF₄: Eu³⁺ microparticles was carried out. XRD method confirmed that all the samples have tetragonal structure that corresponds to LiYF₄ and LiGdF₄ matrices.

If the authors clarify the scientific points and the text is improved, this manuscript could be accepted in Ceramics.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In this revised manuscript, the authors reply and modify the questions, I think the manuscript can be considered to be publish in this journal.

Reviewer 2 Report

The article has been well-revised and it can be accepted as it is.

Reviewer 3 Report

Authors reworked the manuscript in the way that it could be accepted in Ceramics