# Photochromic Sensors for Paper Marking

## TL;DR

This paper introduces photochromic sensors that change color when exposed to UV light, which can be used to mark and protect paper products.

## Contribution

The novelty lies in developing reversible UV sensors with a retarder to control color change for marking and security applications.

## Key findings

- The sensors change color reversibly under UVA radiation exposure.
- A UV radiation retarder was successfully applied to delay and weaken the color change.
- Potential applications include document security and UV dose measurement on paper products.

## Abstract

This study presents UV radiation sensors for use as paper marking. The sensors turn pink under exposure to UVA radiation and the color change is reversible. Additionally, a UV radiation retarder was applied to the sensor to delay the reaction and weaken the change in sensor color. The color changes of the sensors were analyzed depending on the absorbed dose of UVA radiation using reflectance spectrophotometry. Furthermore, the chemical analysis and surface morphology of the samples were performed using Raman Spectroscopy and Scanning Electron Microscopy, respectively. In addition, the structure of the sensors on the paper surface was assessed using X-ray Micro-Computed Tomography. Finally, possible potential applications for these types of sensors were presented, including marking, securing, and protecting against the counterfeiting of documents, paper packaging, and other paper products, and creating decorative elements, as well as measuring the 2D/3D dose distribution of UV radiation on paper products.