Thermochromic Luminescent Nanomaterials Based on Mn⁴⁺/Tb³⁺ Codoping for Temperature Imaging with Digital Cameras

Abstract

A new thermographic nanocrystalline Sr₄Al₁₄O₂₅:Mn⁴⁺,Tb³⁺ phosphor was developed, and the concentrations of both dopants and the synthesis conditions were optimized. The combination of the thermally quenched luminescence from the Mn⁴⁺ ions to the almost temperature-independent emission from Tb³⁺ provides a sensitive luminescent thermometer (<i>S</i>_R = 2.8%/°C at 150 °C) with strong emission color variability. In addition, a figure of merit for this luminescence thermochromism was proposed, as the relative sensitivities of the <i>x</i> and <i>y</i> CIE coordinates, which for this phosphor reaches at 150 °C <i>S</i>_R(<i>x</i>) = 0.6%/°C and <i>S</i>_R(<i>y</i>) = 0.4%/°C, respectively. Noncontact thermal imaging was demonstrated with this phosphor using a single consumer digital camera and exploiting the ratio of red (R) and green (G) channels of the RGB images, thereby confirming the high application potential of Sr₄Al₁₄O₂₅:Mn⁴⁺,Tb³⁺ nanocrystals for thermal sensing and mapping.