Water-Stable Perovskite Quantum Dots for Wide-Color-Gamut White-Light-Emitting Diodes

Comments 1:  What do you want to achieve from time-resolved photoluminescence (TRPL) fitting parameters for the mentioned samples? and how you tune the performance parameters.

Response 1: Thank you for the comment. We agree that the purpose and physical meaning of the TRPL fitting parameters should be clarified. In the revised manuscript, we expanded the TRPL discussion to explicitly explain: what information the multi-exponential fitting provides (trap-assisted vs. radiative recombination contributions), how the relative amplitudes and lifetime components reflect changes in non-radiative pathways, and how APTES passivation and subsequent silica encapsulation tune these parameters by reducing surface defects and suppressing moisture-related degradation.

Revision in manuscript: Section 3 (TRPL analysis). (Page 6, Lines 231–239).

The fitting results show a progressive increase in τavg from 2.5 ns (CsPbBr₃) to 22.8 ns (CsPbBr₃-APTES) and further to 36.9 ns (CsPbBr₃-APTES@SiO₂) (Table 1). This substantial extension of carrier lifetime, together with a systematic decrease in the amplitude ratio A1/(A1+A2+A3) from 0.99 to 0.02, confirms the effective suppression of non-radiative decay channels through sequential surface engineering. The improvement in radiative recombination efficiency, which scales with , correlates well with the observed enhancement in PL intensity, demonstrating that the combined strategy of APTES passivation and silica coating significantly improves both the optical performance and photophysical stability of CsPbBr₃ PQDs.

Comments 2: In your proposed research work, how you achieve spectral observations with the macroscopic luminescence behavior of the samples? What is the novelty in such results?

Response 2: We appreciate this important question. We have clarified the linkage between spectral observations (PL intensity retention, peak position/FWHM stability, and TRPL evolution) and macroscopic luminescence behavior (photographs under UV illumination during water immersion). In the revised manuscript, we explicitly state that consistent preservation of spectral signatures directly explains the persistent visible emission under UV light after immersion.

Revision in manuscript: Section 3 (water-immersion stability discussion) (Page 8, Lines 284-287); related photo/spectral linkage text in Results and Discussion (Page 9, Lines 317-320).

The consistent peak position and narrow FWHM in the PL spectra explain the preserved macroscopic luminescence observed in the corresponding photographs during water immersion.

Spectral analysis shows that only the device incorporating CsPbBr₃–APTES@SiO₂ retains a distinct PQD emission peak at 533 nm without an obvious spectral shift after water exposure, whereas the PQD-related emission nearly vanishes in devices based on the other two PQDs.

Comments 3: In the mentioned Television system what novel improvements you are getting out of the proposed generated results?

Response 3: Thank you for pointing this out. We clarified that the “television system” relevance refers to wide-color-gamut display backlighting. The key improvement enabled by our PQDs is the realization of a color-converted WLED with wide color-gamut coverage and stable chromaticity, supported by narrowband green emission and improved environmental stability after encapsulation. We revised the Discussion to more clearly articulate the display-backlight relevance.

Revision in manuscript: Section 3 (WLED and wide color gamut) (Page 9, Lines 305-319); Figure 5(d–e) and caption.

To further verify the impact of environmental stability on device performance, WLEDs fabricated with water-treated PQDs—CsPbBr₃, CsPbBr₃–APTES, and CsPbBr₃–APTES@SiO₂—were comparatively examined. Spectral analysis shows that only the device incorporating CsPbBr₃–APTES@SiO₂ retains a distinct PQD emission peak at 533 nm without an obvious spectral shift after water exposure, whereas the PQD-related emission nearly vanishes in devices based on the other two PQDs. This result provides direct evidence that the silica-derived stability enables CsPbBr₃–APTES@SiO₂ PQDs to maintain reliable color-conversion functionality under humid or demanding conditions, highlighting the material’s promise for display backlight applications. Fabrication and measurement details.

Comments 4: What are the optimum results/novelty by which you can claim with supporting proposed methodology that demonstrate that rational surface engineering can simultaneously address the efficiency and stability challenges of perovskite PQDs, establishing a viable pathway toward their practical implementation in demanding optoelectronic applications? Have you compared your results with the already existing similar research work?

Response 4: We are grateful for this suggestion to better contextualize our work. In the revised manuscript, we more clearly summarize the optimum outcomes (simultaneous enhancement of PLQY/TRPL and water-immersion stability) enabled by the stepwise strategy, and we added a comparison with representative prior reports on passivation and silica-coated perovskite PQDs. This comparison highlights the combined merits of high optical efficiency, direct water-immersion tolerance, and device-level validation within one workflow.

We added a short literature comparison paragraph (Page 2, Lines 73-88) and revised the Introduction accordingly.

Despite the substantial progress in PQD stabilization, creating an ideal protective shell remains a challenge. For instance, Wang et al. [34] synthesized CsPbBr3@mSiO2 composites within mesoporous silica, yet the confinement often induces QD aggregation and subsequent fluorescence quenching. Alternatively, Sun et al. [35] employed the hydrolysis of (3-aminopropyl) triethoxysilane (APTES) with ambient moisture to form silica shells; however, the slow hydrolysis kinetics result in prolonged exposure of the perovskite core to water molecules, causing structural degradation. While Zhao et al. [36] and Li et al. [37] optimized the hydrolysis rate to achieve uniform morphologies, the resulting silica shells were typically too thin (1–2.7 nm) to provide robust protection against harsh aqueous environments. These limitations, combined with recent atomic-scale insights into water-induced degradation pathways, highlight that an effective encapsulation strategy must simultaneously minimize the exposure time of QDs to water during synthesis and ensure the formation of a dense, sufficiently thick barrier. Building on this foundation, we employ a stepwise surface-engineering strategy (APTES-mediated defect passivation followed by TMOS-derived silica encapsulation) to concurrently enhance PLQY/TRPL and water-immersion stability.

34. WANG H C， LIN S Y， TANG A C， et al. Mesoporous silica particles integrated with all-inorganic CsPbBr3 perovskite quantum-dot nanocomposites（MP-PQDs） with high stability and wide color gamut used for backlight display ［J］. Angew. Chem. Int. Ed.， 2016， 55（28）： 7924-7929.  doi: 10.1002/anie.201603698.

35. SUN C， ZHANG Y， RUAN C， et al. Efficient and stable white LEDs with silica-coated inorganic perovskite quantum dots ［J］. Adv. Mater.， 2016， 28（45）： 10088-10094.  doi: 10.1002/adma.201603081.

36. ZHAO H F， WEI L F， ZENG P， et al. Formation of highly uniform thinly-wrapped CsPbX3@silicone nanocrystals via self-hydrolysis： suppressed anion exchange and superior stability in polar solvents ［J］. J. Mater. Chem. C， 2019， 7（32）： 9813-9819.  doi: 10.1039/c9tc01216h.

37. MENG C F， YANG D D， WU Y， et al. Synthesis of single CsPbBr3@SiO2 core‐shell particles via surface activation ［J］. J. Mater. Chem. C， 2020， 8（48）： 17403-17409.  doi: 10.1039/d0tc03932b.

Comments 5: How the water immersion level in perovskite quantum dots affects the performance and how you overcome those challenges to achieve optimum results?

Response 5: Thank you for this query regarding the degradation mechanism. We have expanded the mechanistic explanation. Water immersion can accelerate ligand detachment and ion dissolution, leading to defect formation, structural degradation, and rapid PL quenching. In our system, APTES improves surface defect passivation and strengthens surface binding, while the in-situ silica shell provides a physical barrier that slows water penetration and suppresses dissolution pathways.

Revisions were made in the Section 3 (water-stability) (Page 10, Lines 356-359).

Mechanistically, water exposure can trigger ligand desorption, ion solvation, and facet-dependent dissolution of perovskite nanocrystals; the APTES anchoring and the SiO2 shell act as a physical diffusion barrier and reinforce surface passivation, thereby suppressing these pathways.

4. Response to Comments on the Quality of English Language

Point 1:

Response 1: We have carefully proofread the manuscript and corrected grammar, punctuation, terminology inconsistencies, and formatting issues across the text, figures, and references.

Comments 1:  While FTIR and stability tests imply encapsulation, the TEM images show cubic particles without a distinct visual contrast between the core and the silica shell. Energy-dispersive X-ray spectroscopy (EDS) elemental analysis would provide more definitive proof of the core-shell architecture.

Response 1: We thank the reviewer for this excellent recommendation. We have added EDS elemental analysis to provide direct evidence of the core–shell architecture. The revised manuscript now includes EDS spectra and elemental mapping, showing the presence of Si signal associated with the silica coating around the PQD regions.

Added as a new figure (Figure 2 c-g) and discussed in the structural characterization section (Page 5, Lines 186-187,195-197).

Figure 2. (a) XRD patterns of pristine CsPbBr₃, CsPbBr₃-APTES, and CsPbBr₃-APTES@SiO₂, high-lighting the peak shifts and intensity variations. (b) FTIR spectra comparing pristine CsPbBr₃ and CsPbBr₃-APTES@SiO₂, confirming the presence of the silica network. (c) TEM image of the final CsPbBr₃-APTES@SiO₂ PQDs showing uniform cubic morphology. (d-g) mapping images including the elements of Cs, Pb, Br and Si in sequence.

Comments 2: The paper covers water stability, which is vital for perovskites. However, for LED applications where temperatures can rise significantly, the data on thermal quenching are essential. The Authors mention thermal stress as a degradation factor but do not provide experimental data on the thermal stability of their specific core-shell samples. Such data and the corresponding discussion would strengthen the manuscript.

Response 2: We agree completely that thermal stability is critical for LED applications. We have performed temperature-dependent PL measurements (thermal quenching tests) for the silica-coated samples. The new data confirms that silica encapsulation effectively mitigates thermally activated non-radiative recombination, resulting in superior emission retention at elevated temperatures compared to controls.

Added as a new figure (Figure 4 (a)) and discussed in (Page 7, Lines 261-265).

Figure 4. (a) Normalized PL intensity curves of CsPbBr3, CsPbBr3-APTES, and CsPbBr3-APTES@SiO2 measured during heating at 80 °C to evaluate PL thermal stability.

To systematically evaluate the environmental stability of the samples, we investigated their thermal tolerance and water resistance. As shown in Figure 4a, the silica-coated CsPbBr₃–APTES@SiO₂ shows the most stable normalized PL intensity under continuous heating at 80 °C, indicating effective suppression of thermally activated non-radiative losses.

Comments 3: Although the Authors report CIE coordinates (0.323, 0.331) and NTSC gamut coverage, the manuscript lacks values for the Correlated Color Temperature (CCT) and Color Rendering Index (CRI). These are fundamental metrics for characterizing white light sources. Presenting CCT and CRI is necessary to fully evaluate the quality of the white light and assess the device’s suitability for practical lighting applications compared to commercial standards.

Response 3: We appreciate this suggestion to align our metrics with lighting standards. We have added CCT (6362 K) and CRI (60) values calculated from the measured device emission spectrum using standard CIE colorimetry procedures. These metrics are now reported together with the chromaticity coordinates and color-gamut coverage to provide a more complete evaluation of the WLED performance.

Added in the WLED characterization section (Section 3) and corresponding captions (Page 9, Lines 302-304, 325-326).

The correlated color temperature (CCT) and color rendering index (CRI) of the WLED are 6362 K and 60, respectively.

Comments 4: The water stability test was conducted for only 100 minutes. While this time period is sufficient to demonstrate the immediate protective effect of the coating compared to pristine samples (which quench in minutes), commercial applications typically require more extensive aging tests lasting hundreds or even thousands of hours to ensure long-term reliability. This limitation should be acknowledged in the manuscript. Also, the Authors are encouraged to propose possible ways for overcoming these limitations in the future.

Response 4: We thank the reviewer for this fair observation. We have explicitly acknowledged that the current water-immersion test primarily demonstrates the immediate protective effect of the silica shell under direct contact with water and longer-term damp-heat storage and operational aging tests will be investigated in future work.

Added in Conclusions (Page 10, Lines 376-378).

We note that the current direct-immersion test (100 min) primarily demonstrates short-term water resistance; longer-term damp-heat storage and operational aging tests will be investigated in future work.

Comments 5: The manuscript refers to the "electroluminescence" stability or performance of the PQDs. However, the described device employs a color conversion architecture where the PQDs are optically excited by a blue LED chip. By definition, electroluminescence implies light emission resulting from application of electric current across the structure. In this case, the QDs exhibit photoluminescence driven by the blue light source. It is technically more accurate to describe this device as a color-converted LED or to refer to the mechanism as the emission frequency down-conversion, rather than electroluminescence.

Response 5: We sincerely apologize for this terminological inaccuracy. The reviewer is correct. We agree and have corrected the terminology throughout the manuscript. We now clearly describe the PQDs (and red phosphor) as photoluminescent color converters excited by the blue LED chip, and we use “Electrically driven device” instead of “electroluminescence of PQDs” where appropriate.

Revised in the WLED section and figure captions (Page 8, Line 304, Page 9, Line 328, Page 10, Lines 362).

Comments 6: The synthesis temperatures should be indicated across Subsection 2.2.

Response 6: Thank you for noting this detail. We have revised Subsection 2.2 to explicitly state the reaction temperatures for each key step (including room-temperature processes where applicable), improving reproducibility.

Revision in manuscript: Section 2.2(Page 3, Lines 119-120).

Unless otherwise specified, all synthesis and purification steps were performed at room temperature (25°C) under ambient conditions.

Comments 7: The data for CsPbBr3-APTES seem to be missing from Fig. 3(b). The authors should include these data for completeness or explain their absence.

Response 7: We apologize for this omission. We have updated Figure 4(b) to include the CsPbBr₃-APTES dataset for a complete comparison among pristine, APTES-passivated, and silica-coated PQDs during water immersion. The corresponding text has also been revised accordingly.

Revision in manuscript: Figure 4(b) and caption.

Figure 4. (b) Time-dependent normalized PL intensity of three samples during water immersion.

Comments 8: The measurement units (ns) should be indicated in Table 1 for τ_i.

Response 8: Thank you for the comment. We have added the lifetime unit (ns) in Table 1 and its caption.

Revision in manuscript: Table 1 (add “ns” units for τ₁/τ₂/τ₃/τavg in header or caption).

Comments 9: Technical remarks. Line 191: In “τ_avg”, “avg” should be a subscript. There is a typo in Fig. 4(a): “substaute” should be “substrate”. There are some spaces missing, e.g., line 188 (“andA3”), refs. 4 and 5 in the reference list. Incorrect punctuation appears in line 196 (“, ,”). In Table 1, “CsPbBr3APTES” should be “CsPbBr3-APTES”; this inconsistency should be checked throughout the text as well. Some DOIs in the reference list are complete “clickable” links (e.g., ref. 10) and some are just DOI numbers (e.g., ref. 11). Thus, the manuscript should be carefully proofread.

Response 9: We are grateful for the reviewer's careful proofreading. We have carefully proofread the manuscript and corrected: (i) formatting of τ_avg (subscript), (ii) the typo “substaute” → “substrate”, (iii) spacing and punctuation issues, (iv) naming consistency (e.g., “CsPbBr₃-APTES”), and (v) standardized DOI formatting across the reference list.

Revision in manuscript: Section 3 (τ_avg subscript formatting and equation typography); Figure 5(a) text correction (Page 9, Line 320); Table 1 sample naming consistency (“CsPbBr₃-APTES”) (Page 7, Line 251); reference list formatting (spaces/punctuation/DOI format unified).

Comments 1: For clarity and consistency, please harmonize the PLQY values reported for the silica-coated sample. In the current draft, the PLQY is reported as 95.6 percent in some locations, while 98.6 percent is also stated in the Results and Discussion text. Please confirm the correct value, clarify whether it is an average over repeated measurements, and ensure consistent reporting across the Abstract, Results, figure captions, and Conclusions.

Response 1: We sincerely apologize for any confusion caused by our typographical error. We have carefully re-checked the PLQY data for the silica-coated sample (CsPbBr₃-APTES@SiO₂). The correct PLQY is 95.6%; the previously stated 98.6% was a typographical error. We have corrected this value and harmonized the PLQY reporting throughout the manuscript, including the Abstract, the Results and Discussion text, relevant figure captions, and the Conclusions.

Revision in manuscript: Discussion; Section 3 (PLQY discussion) (Page 6, Line 235).

Comments 2: The Introduction and Discussion on moisture and water-induced degradation would be even more convincing with a citation to a recent in situ mechanistic study that clarifies water-induced degradation pathways and highlights how surface passivation can modify degradation behavior. A suitable example is Ma et al. (Water-Induced Degradation Mechanism of Metal Halide Perovskite Nanocrystals. Matter 2025, 8, 102083.), which provides mechanistic insight that can support the authors framing.

Response 2: We thank the reviewer for suggesting this highly relevant literature. We agree that a recent in situ mechanistic study would strengthen the discussion of moisture/water-driven degradation and the rationale for surface engineering. Accordingly, we have added the suggested work by Ma et al. to the Introduction/Discussion and used it to support our mechanistic framing (e.g. water-triggered ligand desorption/ion solvation and facet-dependent dissolution of perovskite nanocrystals) and to motivate how robust surface passivation/encapsulation can alter degradation trajectories. This citation is now also referenced in the Discussion when interpreting why APTES anchoring and the dense SiO₂ shell jointly suppress water-induced quenching pathways in our system.

Revision in manuscript: Introduction (water/moisture degradation context) (Page 2, Lines 54-56); Section 3 (water stability mechanism discussion) (Page 10, Lines 346-349); reference list (new citation added) (Page 12, Lines 469-470).

Recent in situ studies have provided atomic-scale insights into water-induced degradation of perovskite nanocrystals, highlighting the need for robust encapsulation strategies

Mechanistically, water exposure can trigger ligand desorption, ion solvation, and facet-dependent dissolution of perovskite nanocrystals; the APTES anchoring and the SiO2 shell act as a physical diffusion barrier and reinforce surface passivation, thereby suppressing these pathways.

32.  Ma, H.; Ahn, E.; Lee, D.; Kim, H.; Lee, K.; Lee, H. C.; Lee, S.; Ji, S.; Kim, K.; Ahn, H.; Zheng, H.; Yang, J. Water-induced degradation mechanism of metal halide perovskite nanocrystals. Matter 2025, 8(6), 102083, doi: 10.1016/j.matt.2025.102083. 

Comments 3: The TMOS-based silica encapsulation is a key enabling step, and adding a few small details would make the protocol more reproducible for readers. In particular, since the coating is performed in nonpolar or weakly polar media, it would be helpful to specify the water source for hydrolysis (intentional water addition versus ambient moisture), whether any catalyst or base was used (if none, stating that explicitly is also helpful), total reaction volume and solvent composition, and whether the reaction was performed in a sealed vial or in open air. These clarifications can be brief but would substantially strengthen the Methods section.

Response 3: We appreciate this feedback regarding reproducibility. We have expanded the Methods section to make the TMOS-derived silica encapsulation more reproducible, particularly given the weakly polar/nonpolar reaction medium. The revised text now explicitly states (i) the water source for TMOS hydrolysis (ambient water vapor in laboratory air, ~40% RH; no intentional water addition), (ii) that no acid/base catalyst or base was used, (iii) the solvent environment and approximate reaction volume (the PQDs dispersed in hexane, followed by addition of 40 μL APTES and 40 μL TMOS), and (iv) the reaction configuration (open vessel in laboratory air under vigorous stirring at room temperature). These brief clarifications preserve readability while enabling practical replication.

Revision in manuscript: Section 2.2.4 (silica encapsulation procedure: water source for hydrolysis, sealed/open condition, catalyst/base statement, solvent composition/volume) (Page 4, Lines 142-145).

For the TMOS-based silica encapsulation, TMOS was hydrolyzed using ambient water vapor as the sole water source (laboratory air) under vigorous stirring; the reaction was carried out in an open vessel at room temperature without adding extra water or any acid/base catalyst.

Comments 4: To further enrich the context of the color-conversion WLED design, it would be helpful to cite a recent example where quantum dot color conversion layers explicitly use multi-stacked, layer-by-layer architectures to suppress interparticle energy transfer compared with mixed configurations, supported by time-resolved photoluminescence analysis and clear WLED performance metrics. This citation would fit naturally in the Introduction where the authors discuss design strategies for color conversion layers and challenges such as energy transfer and spectral balance in mixed phosphor or QD systems. For example, Lee et al. (Transfer-Printed Multi-Stacked Quantum Dot Color Conversion Layers for White Light-Emitting Diodes. Applied Surface Science 2025, 687, 162196.) reported transfer-printed multi-stacked quantum dot color conversion layers that mitigate energy transfer and achieve high-quality white emission with balanced chromaticity and high color rendering, providing a directly relevant benchmark and complementary design perspective for the WLED discussion in this manuscript.

Response 4: We agree that discussing layer-by-layer architectures provides a valuable perspective on suppressing energy transfer. That can help further enrich the WLED context, especially regarding interparticle energy transfer and spectral balance in mixed phosphor/QD systems. We therefore added the recent example by Lee et al. in the Introduction where we discuss design strategies for color-conversion layers. This work demonstrates transfer-printed multi-stacked QD color conversion layers that suppress energy transfer compared with mixed configurations, supported by time-resolved photoluminescence analysis and clear WLED performance metrics. We cite it as a directly relevant benchmark and complementary design perspective to our color-conversion WLED, while emphasizing that our primary advance is achieving high PLQY plus direct water-immersion tolerance with device-level validation in a scalable workflow.

Revision in manuscript: Introduction (design strategies for color conversion layers; suppressing energy transfer) (Page 2, Lines 69-71); reference list (new citation added) (Page 13, Lines 471-473).

In addition, multi-stacked color-conversion architectures have been reported to suppress interparticle energy transfer and improve the spectral quality of WLEDs.

33.  Lee, J.; Kim, Y.; Lee, K.; Yoo, J.; Kim, K.; Kim, J. W.; Lee, S.; Kim, C.; Choi, M. K.; Yang, J. Transfer-printed multi-stacked quantum dot color conversion layers for white light-emitting diodes. Applied Surface Science 2025, 687, 162196, doi: 10.1016/j.apsusc.2024.162196.

Comments 5: Adding a little more device fabrication and measurement details on WLED applications would enhance reproducibility: the encapsulant type and the mixing or stacking ratio of PQDs and the red phosphor, approximate loading amount or layer thickness if known, curing conditions, EL measurement conditions, etc.

Response 5: Thank you for the comment. We have added more details on device fabrication and characterization to enhance reproducibility. The revised manuscript now specifies the encapsulation approach, component ratio (PQDs and red phosphor), curing conditions, and measurement conditions for the device emission spectra.

Revision in manuscript: Section 3 (WLED fabrication details: encapsulant type, mixing/stacking ratio, loading amount/thickness if available, curing and EL measurement conditions) (Page 9, Lines 314-319).