Expedient Red Emitting and Transparency Dual Modulation in KNN-Based Transparent Ceramics via Sensitive Photothermochromic Behavior

An up-conversion luminescence (UCL) transparent ferroelectric oxide (KNN) introduced by rare-earth ions (Er3+ and Bi3+) has been demonstrated to exhibit a unique, high-purity, red emitting, high transparency, reversible, photothermochromic (PTC) reaction. And, its associated transmittance/red emitting modulations are realized via the continuous alternating of UV light irradiation and heat treatment (200 °C). The effects of the phase structure, microstructure, and oxygen vacancy defects on their optical transmittances and the corresponding optical modulation based on PTC reaction at different sintering temperatures were systematically studied. Because of the sufficiently small grain size, dense structure, and appropriate concentration of oxygen vacancy defects, excellent optical transparency (∼70%, at 900 nm) and moderate PTC modulation contrast (ΔAbs = 13.9%, ΔR = 48.9%) are obtained in KNNEB-1155. The decreased and increased transmittance/red emitting can represent two pairs of “off” and “on” codes, which makes the red-emitting KNNEB transparent ceramics very competitive in the application of multifunctional transparent sustainable warning equipment and optical storage materials.