Luminescent polyurethane composite with real-time thermal response via visible signal

Abstract

Visible signals are vital to human communication. Thermal signals are often difficult to observe unless they are in physical contact with the subject or an infrared thermal imaging system is used. In this study, we prepared a luminescent polyurethane composite (LPC), which can intelligently alter its colour and luminescence based on temperature. The LPC is fabricated from rare-earth luminescent materials (Sr₂ZnSi₂O₇: Eu²⁺, Dy³⁺ and Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺), a heat-sensitive rose-red TF-R1 thermochromic pigment (TP), polyurethane (PU), and polyester fabric. Microstructure and crystal structure analyses were carried out to determine the basic material properties of the LPC. The reflectivity and K S⁻¹ value under different temperatures indicate that blue and green light were absorbed by LPC at 25 °C and the absorption decreased at 45 °C. This results in the LPC turning white. The emission spectra demonstrate that the quinoid structure of TP blocked the light of Sr₂ZnSi₂O₇: Eu²⁺, Dy³⁺. Meanwhile, the lactone structure of TP allowed the light emission of Sr₂ZnSi₂O₇: Eu²⁺, Dy³⁺ and Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺. As a result, LPC emits red light at low temperatures and blue light at high temperatures. The advantage of the fabricated LPC is that the output can be easily manipulated into patterns. The uncured PU could form various graphics to cooperate with visible signals. Therefore, the LPC has significant potential as a functional material in smart clothing, flexible electronics, and wearable devices.