MULTIPLEXED LUMINESCENT QR CODES FOR SMART LABELLING, FOR MEASURING PHYSICAL PARAMETERS AND REAL-TIME TRACEABILITY AND AUTHENTICATION

Abstract

The present technology discloses smart labels to monitor physical parameters, and for traceability and authentication of objects, documents or people. This active and multifunctional label is based on spectrally and spatially multiplexed Quick Response (QR) codes (A). Spectrally selectivity is achieved using luminescent materials and spatially multiplexing is achieved using different patterns (B) combining both to design improved QR codes able to store information at different layers of accessibility. This brings advantages over the actual scenario of QR codes wherein the amount of storage information increases up to three times, adding the capability to sense physical parameters and allow to control the provided information, creating public and restricted access. To access and read the content of each layer, different illumination is used (C) to (E) and is processed using a device or via dedicated applications.

Claims

1. A multiplexed luminescent QR code comprising at least two layers, composed each by an individual QR code with different shapes, wherein it is configured to act as a sensor to monitor physical parameters that influence the layer′s material optical properties, and store information, wherein a color and/or pixel intensity of the code changes when exposed to physical parameters, and wherein the code is processed when exposed to a specific radiation source and by a device comprising a camera.

2. The multiplexed luminescent QR code according to claim 1, wherein each layer is composed by a different luminescent material.

3. The multiplexed luminescent QR code according to claim 1, wherein the materials are lanthanide ions, luminescent polymers, luminescent nanoparticles, luminescent micro powders.

4. The multiplexed luminescent QR code according to claim 1, wherein the materials are organic-inorganic hybrid materials doped with trivalent europium (Eu.sup.3+) and terbium (Tb.sup.3+) ions.

5. The multiplexed luminescent QR code according to claim 1, wherein the material is di-ureasil (600) doped with bi-nuclear Eu0.25Tb0.75 (1,1,1-trifluoro-2,4-pentanedione)3.H2O complex.

6. The multiplexed luminescent QR code according to claim 1, wherein the layers overlap.

7. The multiplexed luminescent QR code according to claim 1, wherein the physical parameters are temperature, UV exposure, humidity.

8. The multiplexed luminescent QR code according to claim 1, wherein the layer changes from transparent to color upon exposure to an excitation source.

9. The multiplexed luminescent QR code according to claim 1, wherein it is made by dip-coating, spin-coating, inkjet print or other film deposition technics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present technology will be further explained with example figures attached where the different materials are represented by different colors:

[0026] FIG. 1 Photographs of luminescent QR codes at different temperature values. Schematic of the temperature measurement by a conventional smartphone (Charge-coupled device (CCD) camera) based on the quantification of the color exhibited at different temperatures.

[0027] FIG. 2 spectrally and spatially multiplexed Quick Response (QR) codes (A). (B) different patterns used. (C)-(E) different illumination used to access and read the content of each layer.

[0028] FIG. 3 (A) Illustrative example of a QR code version 1 with dimensions 15×5 cm.sup.2 used as first layer with regular module as established in ISO 18004/2001. (B) Illustrative example of a QR code version 1 with dimensions 15×15 cm.sup.2 used as second layer with square modules with an area 0.72 smaller than layer 1. (C) Illustrative example of a QR code version 1 with dimensions 15×15 cm.sup.2 used as third layer with circle modules with an area 0.44 smaller than layer 1. (D) Illustrative example of a QR code version 1 with dimensions 15×15 cm.sup.2 using the QR codes presented in figures (A)-(C).

[0029] FIG. 4 Illustrative example of (A) public and (B) restrict access based on FIG. 3D, granted using different excitation energies (e.g. (A) solar and (B) UV).

[0030] FIG. 5 Traceability and authenticity of the object to which the label is attached to made using a smartphone in connection with a server/could service.

DETAILED DESCRIPTION

[0031] The multiplexed luminescent QR codes of the present application are formed by overlapping different layers, composed each one by an individual QR code with different shapes, and produced with a different material.

[0032] To have a multiplexed QR code at least two QR code layers are needed, produced with two different materials, and at most to maintain the orthogonality of the color space used the maximum are three QR code layers produced with different materials, and overlapped, being only limited by the detection device capability to recognize the color exhibited and by the minimum physical dimensions necessary to produce the QR code.

[0033] The QR codes of the present technology are formed by materials that are sensitive to temperature variation and/or UV exposure, or other physical parameters, not being expected a variation of those parameter due to exposure to visible light. It is expected that other physicals parameters such as humidity, or other parameters capable of changing the emission spectra of the layer materials, which can have implications in the color and/or pixel intensity of the materials, are also able to me monitored by the present technology.

[0034] So, the present technology encompasses the enhancement of storage capacity limits, since the different layers comprise different information, and the evolution to a smart label for devices decryption applications.

[0035] In one embodiment, the materials of the layers are luminescent materials.

[0036] In one embodiment, the materials of the layers are any material (inorganic, organic or organic-inorganic hybrids, nanoparticles, crystals) incorporating any optical center, whose emission properties depend on the physical parameters above mentioned(the example selected in the present document are organic-inorganic hybrids with trivalent europium (Eu.sup.3+) and terbium (Tb.sup.3+) ions, whose emission color is thermal—or other physical parameters above mentioned—dependent) were processed as luminescent QR codes with the ability to simultaneously double the storage capacity and sense temperature in real time using a photo taken with the CCD camera of a smartphone.

[0037] In one embodiment the material used in the present technology is di-ureasil (600) (d-UPTES (600)) doped with bi-nuclear Eu0.25Tb0.75(tfac).sub.3.H.sub.2O complex, wherein tfac is 1,1,1-trifluoro-2,4-pentanedione.

[0038] In another embodiment, the materials used for the layers of the multiplexed QR code of the present application are complexes with lanthanide ions, luminescent polymers, luminescent nanoparticles, luminescent micro powders. The materials chosen for the present technology should be transparent and only change color and/or intensity when exposed to the physical parameters herein described.

[0039] These materials are capable of changing from transparent to colorful ones because they absorb radiation in the UV/Blue spectral region and downshift this radiation towards de visible and/or near-infrared spectral region through photoluminescence processes (radiative and non-radiative).

[0040] If near infrared is used as excitation source downshifting emission in the near infrared spectral region and upconversion emission towards the visible spectral range (non-linear absorption process).

[0041] The methods of deposition/printing of the materials in a QR code format are: [0042] (1) dip-coating—immersing a transparent substrate made with a QR code format inside a container with the material of the layer intended to make the code, creating a coating around the substrate. In this case, to obtain the multiplexed QR code of the present application, it is necessary to have more than one substrate, each made with a different code shape; [0043] (2) spin-coating—put a subtract with a QR code format in a rotating machine and apply the material on top of it. The centrifuge force will spread the material across the substrate forming a coating; [0044] (3) Inkjet print—use of an inkjet material printer to print the material in the QR code format onto a substrate. [0045] (4) General film deposition technics known to the skilled person.

[0046] The materials used to produce the QR are transparent until irradiated with an excitation source, and at that point the material exhibits a characteristic color.

[0047] The reading and decoding of the multiplexed QR code is made by exposing it to specific radiation, a specific wavelength (UV/visible), to retrieve specific information. Since one of the basic features of QR codes is that it can be decoded very fast, this exposure to the excitation source will be also very fast, so it should not affect the measured value for UV exposure.

[0048] The excitation source wavelength ranges from UV to visible to infrared depending on the material intrinsic characteristics and can be provided by:

[0049] (1) external lamp, LED, LASER;

[0050] (2) sun;

[0051] In one embodiment, the luminescent QR codes of the present application are capable of revealing different colors at distinct temperature values, as shown in FIG. 1.

[0052] In another embodiment, the luminescent QR codes of the present application are capable of revealing different colors depending on the UV exposure they are subject to, as shown in FIG. 2 (c-e).

EXAMPLES

[0053] The developed methodology based on the intensity of the red and green pixels of the photo yielded a maximum relative sensitivity and minimum temperature uncertainty of the QR code sensor of 5.14% K-1 and 0.194 K, respectively, both at 293 K. As added benefit, the intriguing performance results from an efficient energy transfer involving the thermal coupling between the Tb3+-excited level (5D4) and the low-lying triplet states of organic ligands, being the first example of an intramolecular primary thermometer.

[0054] The use of different materials, with different properties lead to different exhibited color, so is predicted a wide range of colors possible to be used, being the color analyse develop in the RGB orthogonal color space for visible emitting QR codes. In the case of near infrared QR codes the image analysis is based on the relative intensity in gray scale.

Example 1

[0055] Synthesis of Eu0.25Tb0.75(tfac)3.H20 Complex

[0056] The Eu0.25Tb0.75(tfac)3.H20 was synthesized according to the literature [1].

Synthesis of di-ureasil, dU(600), Doped With the Eu0.25Tb0.75(tfac)3.H20 Complex

[0057] The organic-inorganic hybrid precursor, d-UPTES(600), was prepared according to the literature [2]. In order to get the optimal doping concentration for the QR code fabrication, two doping contents corresponding to the final concentrations in the gels of 0.87 wt % (dU6TbEu-1) and 3.39 wt % (dU6TbEu), were adopted. For synthesis of sol doped with higher concentration of Eu0.25Tb0.75(tfac)3.H20, typically, 6.0 g (5.484 mmol) of d-UPTES(600) was mixed with 8 mL of EtOH under stirring. Then 168.0 mg of Eu0.25Tb0.75(tfac)3.H20 was added, and the mixture was treated under ultrasonic condition until a clear solution was obtained. Next 0.592 mL of HCl acidified water (pH=2) was added under stirring to catalyse the hydrolysis and condensation reactions. The molar ratio of d-UPTES(600):H20 is 1:6. The resulting sol (dU6EuTb) was stirred at room temperature for further 2 hours and then it was deposited by dip-coating, as detailed below. The resulting materials were characterised by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy, as detailed in the following section.

Materials

[0058] The bi-nuclear Eu.sub.0.25Tb.sub.0.75(tfac).sub.3H2O complex (tfac=1,1,1-trifluoro-2,4-pentanedione, Sigma-Aldrich), was synthesized as previously reported, (Ramalho, António et al. 2018). Elemental analyses for C and H were performed with a TruSpec 630-200-200 CNHS Analyser. The doping concentrations of Eu.sup.3+and Tb.sup.3+ were determined by ICP-OES (inductively coupled plasma-optical emission spectroscopy). The analytical results are: calcd. (wt %): C 28.38, H 2.21, Eu 5.99 and Tb 18.80; found (wt %): C 27.97, H 2.24, Eu 5.97 and Tb 18.10. To process the complex as films it was incorporated into a di-ureasil organic-inorganic hybrid host, so-called d-U(600), which is formed by polyether chains (with average molecular weight of 600 gmol-1) covalently linked to a siliceous inorganic skeleton by urea bridges, as previously reported(Brites, Fuertes et al. 2017). The resulting material, hereafter termed as dU6EuTb, was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy

QR Code Processing

[0059] Luminescent QR codes version 1 (21×21 modules2) with error correction level L (7% of codewords can be restored by a Reed-Solomon error algorithm) and dimensions 5×5 cm.sup.2 with the different messages, “SMART LABELLING”, “UNIVERSITY OF AVEIRO”, and “INST. DE TELECOMUNICACOES”, were implemented. Aiming at preparing a luminescent layer, QR codes produced on a 5.0×10.sup.−4 m thickness acetate substrate layer were laser cut (the acetate on the inactive modules region was removed). These QR codes were vertically immersed in a solution of the dU6EuTb (3.39 wt %) at a velocity of 1.4×10.sup.−3 m.s.sup.−1 using a homemade dip-coating system. After the deposition, the substrates with the luminescent QR codes were transferred to an oven at 45° C. for 48 h. The QR codes are transparent under day light, enabling color-based multiplexing. This strategy to multiplex distinct colored QR codes consists in overlapping a conventional black/white QR code by the luminescent QR code. Under daylight the acetate-based luminescent code is transparent, and the base code is readily accessed, whereas under UV illumination the acetate-based QR code becomes luminescent, enabling the color-multiplexing of the overlapped codes.

Optical Characterization

[0060] Image acquisition: The photographs of the luminescent QR codes under UV illumination were taken with a smartphone camera with resolution of 2238×3986 pixel.sup.2, aperture of f/2 and a sensor dimension of 1/4.2″.

Luminescent QR Codes

[0061] FIG. 1 shows a dU6EuTb-based luminescent QR code at distinct temperature values, revealing different emission color coordinates. The emission is ascribed to the intra-4f6 (Eu3+) and intra-4f8 (Tb.sup.3+) transitions, whose relative intensity is thermal sensitive. As the temperature is raised from 283 to 323 K, the relative intensity of the 5D4.fwdarw.7F6-3 transitions decreases, whereas that of the 5D0.fwdarw.7F0-4 transitions remains nearly constant. Consequently, the emission color coordinate deviates from the orange (0.578, 0.356) to the red (0.636, 0.234) spectral regions.

[0062] This color variation with temperature was also quantified in the RBG color space calculated from photographic records of the luminescent QR codes in the same temperature range, FIG. 2a, taking advantage of the ability of the smartphone CCD camera that simultaneously allows the QR code reading (decryption) and the photo acquisition for further processing and temperature sensing, through the quantification of the RGB color coordinates of the image avoiding the need of a spectrometer to record emission spectra.

[0063] In this example, photographs taken with the CCD camera of a mobile phone enable the temperature readout with a maximum relative sensitivity and a minimum uncertainty of 5.14 % K.sup.-1 and 0.194 K, respectively, both at 293 K. These figures of merit result from the thermal coupling between the 5D4 Tb.sup.3+excited level and the low-lying triplet states of the organic ligands and are among the best ones known for luminescent thermometers. The ratio between the intensity of the green and red pixels of the photos are the basis for the temperature sensing through a unique intramolecular primary thermometer opening the possibility for the implementation of QR codes in mobile IoT without the need of any technological adaptation of current smartphones.

[0064] This is the first example in which smartphones are used as an effective alternative to portable spectrometers to calculate the temperature using the induced color temperature change. The methodology constitutes an innovation in the area, assigning technological value to the QR codes and leveraging the area of IoT devices towards smart labels using a smartphone in its original configuration, as there is no need to adapt neither the tag decoding nor the CCD detector for temperature sensing, in which e-health is a target application. Additional features are envisaged to the luminescent QR codes (e.g. traceability, data storage and security alerts) through dedicated applications, that establish connections and information exchanging between the QR code reader and the cloud, in which the encrypting connection may appear as an optional tool.

Emission Spectra and Temperature Calibration

[0065] The temperature-dependent emission spectra of the QR codes were measured using a portable spectrometer (OceanOptics Maya 2000 Pro) coupled with an optical fiber, under a UV lamp excitation (254 nm). The QR code response to temperature was calibrated using either the emission spectra or the smartphone photographic records of the codes. For calibration, a homemade Peltier-plate based temperature controller and a K-type thermocouple were used. The temperature was set in the temperature controller and the QR code was let to thermalize for 5 minutes to ensure a constant temperature value reading in the thermocouple. An emission spectrum (integration time of 1.0 s, recorded at a central location of the code) and a photograph of the whole code were collected using the portable spectrometer and the smartphone's camera, respectively. The procedure was repeated in the 283-323 K range (step of 1 K). To independently monitor the temperature attesting its uniformity within the QR code surface, a thermographic camera FLIR DGOO1U-E (sensitivity of 0.1 K, accuracy of ±2 K, according to the manufacturer) was used. The IR camera temperature profiles result from an averaging of four thermal images acquired in distinct regions of the QR code (Figure S3, Supporting Information). To estimate the dU6EuTb layer emissivity (ε) we adopted the procedure described elsewhere,(Ramalho, António et al. 2018) resulting ε=0.85. The emission colour coordinates were calculated from the emission spectra using the 1931 Commission Internationale de Éclairage (CIE) methodology defined for the 2.sup.nd standard, whereas the colour coordinates from the photographs were determined using the RGB model (Supporting Information for details).

Photoluminescence

[0066] The emission and the excitation spectra were recorded at 300 K using a modular double grating excitation spectrofluorimeter with an emission monochromator (Fluorolog-3 2-Triax, Horiba Scientific) coupled to a photomultiplier (R928 Hamamatsu), using the front face acquisition mode. The excitation source was a 450 W xenon arc lamp. The excitation spectra were weighed for the spectral distribution of the lamp intensity using a photodiode reference detector. The absolute emission quantum yields were measured at room temperature using a system (Quantaurus-QY Plus C13534, Hamamatsu) with a 150 W xenon lamp coupled to a monochromator for wavelength discrimination, an integrating sphere as the sample chamber, and a multichannel analyzer for signal detection. The method is accurate to within 10%.

RGB color model

[0067] The RGB color model is an additive model that creates color through the mix of three primaries colors Red, Green and Blue. Based on this every image can be decomposed into that three channel, one corresponding to each primary being possible afterwards to determine the mean value for each channels (μR,G,B) using an histogram fitted whit a Gaussian function and their associated error defined by the standard error of the mean, Eq. 1.

[00001]$\begin{array}{cc}{\mu }_{R,G,B,}=\frac{{\sigma }_{R,G,B}}{\sqrt{n}}& \left(1\right)\end{array}$

where n is the sample number of points and σR,G,B is the standard deviation of each fit.

[0068] The R, G and B values were normalized using Eq. 2.

[00002]$\begin{array}{cc}r=\frac{R}{R+G+B};g=\frac{G}{R+G+B};b=\frac{B}{R+G+B}& \left(2\right)\end{array}$

[0069] Lisbon,