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. 2022 Jan 10;13:72. doi: 10.1038/s41467-021-27733-3

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© The Author(s) 2022

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a CO₂ sensing mechanism. b Spectral properties of the constituents of the CO₂ sensor: (A) Absorption spectrum of La₂O₂S:Eu; (B) Emission spectrum of La₂O₂S:Eu; (C) Absorption spectrum of the basic form of α-naphtholphthalein; and (D) Emission spectrum of the UV LED. c Relationship between the luminescence intensity and the CO₂ concentration fitted to the equation by Nakamura and Amao²⁵ (n = 5. Data are presented as mean values ± 1SD). d Response and recovery time of the developed sensor while increasing and decreasing CO₂ concentrations from 0% to 100% and vice versa.