Sustainable Smart Tags with Two‐Step Verification for Anticounterfeiting Triggered by the Photothermal Response of Upconverting Nanoparticles

Abstract

Quick‐response (QR) codes are gaining much consideration in recent years due to their simple and fast readability compared with conventional barcodes. QR codes provide increased storage capacity and safer access to information, fostering the development of optical or printed smart tags as preferred tools for the Internet of Things (IoT). Herein, the combination of Yb3+/Er3+‐doped NaGdF4 upconverting nanoparticles (UCNPs) with recovered plastic for the fabrication of sustainable screen‐printed QR codes is reported. Their photothermal response under distinct power densities of the 980 nm laser irradiation (15–115 W cm−2) induces color‐tuning and temperature sensing. This power dependence is exploited to design a double key molecular keylock accessed by a smartphone camera through the red (R), green (G), and blue (B) (RGB) additive color model and upconversion thermometry. The latter is based on the integrated areas of the 2H11/2→4I15/2 and 4S3/2→4I15/2 Er3+ transitions using the interconnectivity and integration into the IoT network of the mobile phone to download the temperature calibration curve of the UCNPs from a remote server. These findings illustrate the potential of QR codes‐bearing UCNPs toward the design of smart tags for mobile optical sensing and anticounterfeiting.

Upconverting nanoparticles as primary thermometers and power sensors

“…Since the population of the 2 H 9/2 level is reached via a threephoton upconversion process, the intensity of radiative transitions from the 2 H 9/2 level shows a different behavior with P D than the 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions (Renero-Lecuna et al, 2011;Zhou et al, 2013;Cho et al, 2017). A similar trend is observed for 4 F 9/2 → 4 I 15/2 , where, at higher P D , the upper levels, 2 H 11/2 and 4 S 3/2 become saturated favoring the population of the 4 F 9/2 emitting level due to nonradiative relaxations upon the local heating induced by the laser excitation (Kraft et al, 2018;Maturi et al, 2021). The emission spectra of 2 and 3 measured at the lowest measured P D display analogous emission spectra of 1, except for the worse SNR (Supplementary Figure S1).…”

Luminescence Thermometry Beyond the Biological Realm

“…Luminescence thermometry has also been applied to inform thermal management strategies for optoelectronics and integrated photonics 248 and guide the design of thermally actuated photonic devices; 249 alternatively, optoelectronic devices themselves can also serve as thermometers. 250 While UCNPs have longstanding anticounterfeiting applications based on their unique optical properties, Maturi et al 251 recently reported QR codes containing NaGdF 4 :Yb 3+ ,Er 3+ UCNPs that rely on emission changes resulting from laserinduced heating as part of a two-step verification process.…”

Multifunctional optical sensing platform of temperature, pressure (vacuum) and laser power density: NaYF4: Gd3+, Yb3+, Er3+ nanomaterial as luminescent thermometer, manometer and power meter

“…[3][4][5][6][7][10][11][12][13] Although, there are currently not many pumping power sensors, so their use as power meters is limited, for the moment. 20,21 Materials containing Nd 3+ , Er 3+ and Tm 3+ are commonly used as luminescent thermometers for temperature sensing. This is due to the presence of thermally coupled levels (TCL) that are separated by a small energy difference a Universidad de La Laguna, Departamento de Fı ´sica, MALTA-Consolider Team, IMN and IUdEA Apdo.…”

“…, all this properties are related with the 4f–4f electronic transitions. 3–7,16–20 Other advantage that have the inorganic materials doped with lanthanide ions is the good responses to pressure and temperature, so they can function as luminescent manometers and thermometers. 3–7,10–13 Although, there are currently not many pumping power sensors, so their use as power meters is limited, for the moment.…”

“…15 The great interest in lanthanide (Ln) ions for optical methods is due to their wide variety of useful spectroscopic properties, among them wide-range multicolor emission, long short Stokes shift, luminescence lifetimes, narrow emission lines, etc., all this properties are related with the 4f-4f electronic transitions. [3][4][5][6][7][16][17][18][19][20] Other advantage that have the inorganic materials doped with lanthanide ions is the good responses to pressure and temperature, so they can function as luminescent manometers and thermometers. [3][4][5][6][7][10][11][12][13] Although, there are currently not many pumping power sensors, so their use as power meters is limited, for the moment.…”