Effect of Preparation Method on the Optical Properties of Novel Luminescent Glass-Crystalline Composites

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript reports on the preparation of tellurite‑zinc‑sodium (TZN) glass composites containing 5 wt.% LaAlO₃:Eu³⁺ (LAO:Eu) phosphor, using three different methods (remelt, direct‑doping, co‑sintering). The authors compare structural (XRD, SEM/EDS), optical (transmittance), and luminescence (emission spectra under 266 nm and 393 nm excitation) properties to identify which route best preserves the crystalline phase while maintaining acceptable transparency.

Major Comments/Questions/suggestions

1. The Introduction (lines 24–44) nicely outlines the trade‑off between transparency and luminescence in PiG materials. However, it would help to state more clearly why the specific combination TZN + LAO:Eu was chosen over other hosts. Is it mainly refractive‑index matching (n≈1.97 vs. n≈2.09), chemical durability, or prior art?

1. In Figure 1e and its description (lines 147–152), % transmittance values of only 5–10 % in the visible range are reported even for the “as‑prepared” TZN glass. These values seem very low compared to typical PiG materials, which often exceed 60 %–80 % transparency. Could the authors clarify whether the transmittance is measured on a 1 mm pellet, and whether multiple scans or baseline corrections were applied? Include thickness and surface‑finish details, and consider reporting specular vs. diffuse transmittance or haze.
2. Intrusuction: It would be useful for readers to also see a summary Table where one could see comparative Eu luminescence data for a series of compounds such as Al₂O₃, La₂O₃, Y₃Al₅O₁₂ and studied here LAO. See, for example:

Đorđević, V., Antić, Ž., Nikolić, M. G., & Dramićanin, M. D. (2014). Comparative structural and photoluminescent study of Eu3+-doped La2O3 and La (OH) 3 nanocrystalline powders. Journal of Physics and Chemistry of Solids, 75(2), 276-282.

Klement, R., Drdlíková, K., Kachlík, M., Drdlík, D., Galusek, D., & Maca, K. (2021). Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics. Journal of the european ceramic society, 41(9), 4896-4906.

Zhunusbekov, A.M.; Karipbayev, Z.T.; Tolegenova, A.; Kumarbekov, K.K.; Nurmoldin, E.E.; Baizhumanov, M.M.; Kotlov, A.; Popov, A.I. Comparative VUV Synchrotron Excitation Study of YAG: Eu and YAG: Cr Ceramics. Crystals 2024, 14, 897. https://doi.org/10.3390/cryst14100897

 

1. The study appears to report single samples per method without error bars or multiple replicates. For a robust comparison: How many independent samples were prepared for each method? Provide standard deviations for transmittance and integrated emission intensities (Figure 4d) to demonstrate reproducibility.
2. The co‑sintering method uses only 330 °C for 1 h (lines 115–117), which is surprisingly low compared to the T₉ (glass transition) of many tellurite glasses (~350–380 °C). Was the pellet sufficiently consolidated at 330 °C? Were density measurements performed? Discuss whether higher sintering temperatures or longer dwell times were explored to improve transparency without decomposing LAO:Eu.
3. Depth of Crystallite Dissolution: SEM line scans (Figure 3) reveal a “soft and gradual” glass/crystal interface for direct‑doping (lines 187–191). Could the authors quantify the diffusion depth of Eu³⁺ (e.g., via EDS line profiles) to better compare methods? A table summarizing the thickness of the interdiffusion zone for each method would help.
4. References: The reference list contains several recent works (e.g., Bardins et al. 2025 [15], Wu et al. 2024 [14], Sangwan et al. 2024 [16]). This is good.  Are there any very recent reports (2025) specifically on PiG composites with perovskite phosphors that should be discussed?  Consider citing any 2024–2025 studies on YAG:Ce or other oxide phosphors in tellurite hosts, to position this work within the latest advances.

Author Response

1. The Introduction (lines 24–44) nicely outlines the trade‑off between transparency and luminescence in PiG materials. However, it would help to state more clearly why the specific combination TZN + LAO:Eu was chosen over other hosts. Is it mainly refractive‑index matching (n≈1.97 vs. n≈2.09), chemical durability, or prior art?

R: The motivation behind the choice of this particular pair was clarified in Introduction:

“This particular pairing was based on several premises, mainly: the low melting temperature of TZN glass, vast research and known luminescence properties of Eu-doped LAO, and similar refractive indices of TZN and LAO, making it a useful example for further refractive index engineering studies aimed at matching these values to obtain transparent composite material.”

2. In Figure 1e and its description (lines 147–152), % transmittance values of only 5–10 % in the visible range are reported even for the “as‑prepared” TZN glass. These values seem very low compared to typical PiG materials, which often exceed 60 %–80 % transparency. Could the authors clarify whether the transmittance is measured on a 1 mm pellet, and whether multiple scans or baseline corrections were applied? Include thickness and surface‑finish details, and consider reporting specular vs. diffuse transmittance or haze.

R: Thank you for bringing our attention to the importance of proper baseline correction. We revised our results and realized we did not applied proper correction, which lead to underestimation of some samples’ transmittance. The results of transmittance were also corrected for thickness of the samples. Now the transmittance in Figure 1e shows the value for 1 mm thick samples. The relevant mention was added in the Materials and Methods: “The thickness of the TZN glass, RM, DD and CS samples were 2.7, 2.65, 2.5 and 1.1 mm, respectively, and the results were corrected to exhibit the value for 1 mm thick samples.” As for a diffuse transmittance, we would measure and report it only if we were unable to measure a regular transmittance.

3. Introduction: It would be useful for readers to also see a summary Table where one could see comparative Eu luminescence data for a series of compounds such as Al₂O₃, La₂O₃, Y₃Al₅O₁₂and studied here LAO. See, for example:

Đorđević, V., Antić, Ž., Nikolić, M. G., & Dramićanin, M. D. (2014). Comparative structural and photoluminescent study of Eu3+-doped La2O3 and La (OH) 3 nanocrystalline powders. Journal of Physics and Chemistry of Solids, 75(2), 276-282.

Klement, R., Drdlíková, K., Kachlík, M., Drdlík, D., Galusek, D., & Maca, K. (2021). Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics. Journal of the european ceramic society, 41(9), 4896-4906.

Zhunusbekov, A.M.; Karipbayev, Z.T.; Tolegenova, A.; Kumarbekov, K.K.; Nurmoldin, E.E.; Baizhumanov, M.M.; Kotlov, A.; Popov, A.I. Comparative VUV Synchrotron Excitation Study of YAG: Eu and YAG: Cr Ceramics. Crystals 2024, 14, 897. https://doi.org/10.3390/cryst14100897

R: This valuable suggestion to prepare a table comparing Eu³⁺ luminescence properties of various Eu-doped materials allowed us to further clarify our motivation behind choosing LAO host:

“Compared to other Eu³⁺ - doped materials (Table 1), LAO:Eu exhibit low electric dipole to magnetic dipole transition ratio, which allows for utilization as an optical probe, as well as relatively low charge transfer band ( CTB) energy, which allows for excitation by 266 nm laser diode.

 

Table 1. Comparison of charge transfer band (CTB) energies and electric dipole to magnetic dipole transition (ED/MD) ratio for common Eu³⁺-doped crystalline powder materials.

Compound	CTB (eV)	ED/MD ratio	Source
La2O3	4.38	8.5	[26]
Al2O3	4.23	3.4 - 3.6	[27]
Y3Al5O12 (YAG)	6.64	0.7	[28,29]
LaAlO3 (LAO)	3.94	1.4	[18], this work

“

4. The study appears to report single samples per method without error bars or multiple replicates. For a robust comparison: How many independent samples were prepared for each method? Provide standard deviations for transmittance and integrated emission intensities (Figure 4d) to demonstrate reproducibility.

R: Yes, this study reports the results of single samples per method. The number of samples prepared for each method varied, depending on the possibility of optimization of method parameters, such as temperature and duration. Co-sintering method allows for such optimization, but the rest of the methods do not (they both require the melting temperature and the same process as glass melting). For this reason, with exception for the samples prepared by co-sintering, we did not perform multiple trials for the same method. As for the reproducibility, remelt and direct-doping method are not unique enough to warrant extensive reproducibility studies, in our opinion.

5. The co‑sintering method uses only 330 °C for 1 h (lines 115–117), which is surprisingly low compared to the T₉ (glass transition) of many tellurite glasses (~350–380 °C). Was the pellet sufficiently consolidated at 330 °C? Were density measurements performed? Discuss whether higher sintering temperatures or longer dwell times were explored to improve transparency without decomposing LAO:Eu.

R: Glass transition temperature for TZN is around 310 °C (ref. [20]), and on that basis the sintering temperature was chosen to be 330 °C. There were attempts to perform co-sintering up to 350 °C and dwell time up to 3 h, but the resulting composites exhibit the same features, so the lower temperature samples was used for measurement to ensure lower dissolution of LAO:Eu. Unfortunately, we could not perform density measurements.

6. Depth of Crystallite Dissolution:SEM line scans (Figure 3) reveal a “soft and gradual” glass/crystal interface for direct‑doping (lines 187–191). Could the authors quantify the diffusion depth of Eu³⁺ (e.g., via EDS line profiles) to better compare methods? A table summarizing the thickness of the interdiffusion zone for each method would help.

R: Thank you for this valuable comment. This suggestion persuaded us to look closely at the cross-section analysis results and try to estimate the thickness of the interdiffusion zone. We could not trace specifically Eu³⁺, due to very low concentration, but we could use La₂O₃ and Al₂O₃ for the same purpose. We checked the distance between the beginning of the LAO detection across the line and the point at which the LAO concentration reached the approximate maximum. We concluded, to our surprise, that this distance is around 30 nm for both DD and CS samples. This result enriched our conclusion about the dissolution phenomenon in PiG composites:

“Although the elemental mapping indicates different stages of LAO dissolution in glass matrix for samples prepared by DD and CS method, the cross-section analysis shows, that the glass-crystal interface is similarly sharp for both methods– see around the 160-170 and 260-270 μm marks in Figure 3e – contrasting with the sharp glass/crystal boarded in CS sample – see 105 and 250 μm marks in Figure 3f. The interdiffusion zone for both these samples was estimated to be around 30 nm (see Supplementary). This result may suggest that the thickness of the interdiffusion zone does not depend on the method, but rather is the result of the types of crystal and glass used for the composite preparation.”

7. References: The reference list contains several recent works (e.g., Bardins et al. 2025 [15], Wu et al. 2024 [14], Sangwan et al. 2024 [16]). This is good.  Are there any very recent reports (2025) specifically on PiG composites with perovskite phosphors that should be discussed?  Consider citing any 2024–2025 studies on YAG:Ce or other oxide phosphors in tellurite hosts, to position this work within the latest advances.

R: Thank you for this suggestion. Based on this advice, we referenced the following recent studies on PiG composites:

6. Qi, Y.; Ye, R.; Hua, Y.; Huang, L.; Jin, C.; Jiang, T.; Zhao, J.; Cai, M.; Li, B.; Bai, G.; et al. High Efficiency and Thermal Stability LuAG: Ce3+ Converter Based on Phosphor-in-Glass-Ceramics for Laser-Driven Lighting. Ceram Int 2025, 51, 31609–31617, doi:10.1016/j.ceramint.2025.04.352.
7. Sun, X.; Liang, Y.; Zheng, J.; Zhao, C.; Fang, Z.; Tian, T.; Liang, X.; Huan, W.; Xiang, W. Advancing Laser Lighting: High-Brightness and High-Stability Ce:YAG Phosphor-in-Glass. Ceram Int 2024, 50, 48909–48917, doi:10.1016/j.ceramint.2024.09.341.
8. Niu, L.; Liu, C.; Zhang, K.; Wang, C.; Liu, L.; Chu, Y.; Ren, J.; Zhang, J. Net Gain at the Near‐Infrared from CsPbBr 3 Quantum Dots Sensitized Nd 3+ ‐activated Tellurite Glass Under Solar Excitation. Adv Opt Mater 2024, 12, doi:10.1002/adom.202302953.
9. Sun, Y.; Wang, Y.; Chen, W.; Jiang, Q.; Chen, D.; Dong, G.; Xia, Z. Rapid Synthesis of Phosphor-Glass Composites in Seconds Based on Particle Self-Stabilization. Nat Commun 2024, 15, 1033, doi:10.1038/s41467-024-45293-0.

and expanded the Introduction:

“The motivation behind development of PiG is usually focused on the high luminescence efficiency, whether it is in the visible range, as in LuAG:Ce/YAG:Ce in silicate glass [6,7], or near infrared, as in CsPbBr₃ Quantum Dots embedded in Nd³⁺- activated tellurite glass [8].”

“Tellurite glass was used as a host for YAG:Ce phosphor in recent study by Sun et al. [21] on tellurite-based PiG.”

Reviewer 2 Report

Comments and Suggestions for Authors

In this research work, three Methods were adopted to prepare Eu3+ glass-crystal composites doped with perovskite-shaped LaAlO3 in TZN glass, namely remelting method, direct doping method and co-sintering method. And found that crystals in the glass matrix can affect the material’s emission properties, which is interesting. After answering the following questions, it cab be published in appl sci.:

1. Materials and Methodssection mentioned that decarburization treatment might not have been carried out in all three methods. But is decarbonization here a necessary processing step? During processes such as remelting and sintering, is it possible for the accumulation of carbon to cause a reduction in surface transparency? Please provide an explanation.
2. The direct-doping (DD) should be explained in the methods.
3. In Figure 2a, it is mentioned that independent aluminum clusters can be identified. Please mark them in the figure.
4. In fig.3, the element scanning gives the element fractions, not oxide fractions. As one element has two oxides, which will not be reflected by the line scanning.  
5.  In the explanation text of Figure 4, what does ED/MD represent? Please explain in detail. How does the author determine the decomposition degree of LAO: Eu based on the value of ED/MD?
6. The format of references should be unified.

Author Response

1. Materials and Methods section mentioned that decarburization treatment might not have been carried out in all three methods. But is decarbonization here a necessary processing step? During processes such as remelting and sintering, is it possible for the accumulation of carbon to cause a reduction in surface transparency? Please provide an explanation.

R: The decarbonization was performed in all three methods. The RM method description mentions omittance of the decarbonization step during the SECOND melting treatment. Please notice, that the as-prepared glass used in the RM method has already been subject to the decarbonization process during the initial melting.

2. The direct-doping (DD) should be explained in the methods.

R: The direct-doping method was described in Material and Methods section:

“In the direct-doping method, the fresh batch of the TZN glass was prepared and melted according to the aforementioned procedure. 5wt.% of LAO:Eu was added to the glass melt right before quenching. The quenched material was treated the same way as the as-prepared TZN glass.”

3. In Figure 2a, it is mentioned that independent aluminum clusters can be identified. Please mark them in the figure.

R: The aluminum clusters were marked in Figure 2a.

4. In fig.3, the element scanning gives the element fractions, not oxide fractions. As one element has two oxides, which will not be reflected by the line scanning.  

R It is correct that the element scanning provides element fractions. The oxide fractions were calculated based on the element fractions e.g. the amount od Na2O N_Na2O was calculated as N_Na/2, then the fraction of Na2O was calculated as N_Na2O/total sum of all oxides. The detail of calculation was added to the Supplementary.

5. In the explanation text of Figure 4, what does ED/MD represent? Please explain in detail. How does the author determine the decomposition degree of LAO: Eu based on the value of ED/MD?

R:The ED/MD was explained in the figure caption as “electric dipole- (ED) to magnetic dipole-type (MD) transition ratios for each spectrum”, as well as expanded upon in the text:

“As the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ are magnetic dipole- (MD) and electric dipole-type (ED), respectively, the relative intensity of these transitions (ED/MD) can be used as an indicator of the Eu³⁺ ions’ environment. Decomposition can be evidenced as the ED/MD ratio increasing and diverging from the value for original phosphor (1.4) becoming closer to the value for TZN:Eu glass [34].”

6. The format of references should be unified.

R: The references were formatted to fit the journal requirements. Unfortunately, some journal do not provide page ranges, only article numbers (e.g. Nature Communication), in which case the reference could not be formatted in this way.

Reviewer 3 Report

Comments and Suggestions for Authors

After reviewing the manuscript entitled "Effect of preparation method on the optical properties of novel luminescent glass-crystalline composites", the research done is straightforward and concise. It is interesting to note the systematic approach to evaluating the three methods for incorporating crystalline phosphors into glass matrices for LED applications. Overall, the research is sound and serves as a standpoint for choosing a method to fabricate PiGs. There are minor issues to address before publication, which are listed below:

 

1. Figures 1 and 3 require improvement. The graphs appear pixelated and even distort when digitally zooming in. Please adjust the DPI resolution for a better presentation.
2. On page 4, line 174, the manuscript refers to "Supplementary" to find the elemental mapping of the samples; however, on page 8, line 260, it states that the study does not refer to any supplementary information. Please correct accordingly.
3. Preparing a supplementary document with the detailed cross-section elemental line analysis of the analyzed samples is suggested.
4. Did the authors normalize the emission spectra to a specific Eu3+ transition (like the ⁵D₀ -> ⁷F₄) or just the maximum intensity? Please provide the information.

Author Response

1. Figures 1 and 3 require improvement. The graphs appear pixelated and even distort when digitally zooming in. Please adjust the DPI resolution for a better presentation.

R: The DPI resolution of the figures was adjusted.

2. On page 4, line 174, the manuscript refers to "Supplementary" to find the elemental mapping of the samples; however, on page 8, line 260, it states that the study does not refer to any supplementary information. Please correct accordingly.

R: We apologize for the omittance and the lack of Supplementary document in an initial submission.

3. Preparing a supplementary document with the detailed cross-section elemental line analysis of the analyzed samples is suggested.

R: The detailed cross-section elemental line analysis was included in Supplementary.

4. Did the authors normalize the emission spectra to a specific Eu3+ transition (like the ⁵D₀-> ⁷F₄) or just the maximum intensity? Please provide the information.

R: The normalization was done to maximum intensity. This information was added to the figure caption.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

After successful revision,  this manuscript can be recommended for publication.