How to Realize Ultrahigh Photochromic Performance for Real-Time Optical Recording in Transparent Ceramics

A combination of transparency and photochromic (PC) properties in ferroelectrics has promising application potential in smart windows and optical storage/imaging. Nonetheless, limited by understanding the underlying PC mechanism, a splendid PC performance is rarely achieved in transparent ferroelectrics. Here, a strategy to construct deep-lying traps by ion-doping induced defect engineering in (K_0.5Na_0.5)NbO₃-based ferroelectric ceramics is proposed. Based on the improved density functional theory simulations, a high concentration of vacancy defects can be realized by codoping 1 mol % Pr and 4 mol % Ba in (K_0.5Na_0.5)NbO₃, which helps achieving deep-lying traps and then superior PC performance. Through traditional pressureless sintering, highly transparent ceramics with designed optimal composition have been fabricated in a wide sintering temperature range (1170-1210 °C), exhibiting an ultrafast PC feature, i.e., 0.1 s response time (by illumination of 400 nm light), along with high PC efficiency (5.8 cm²·W^-1) and PC rate (7.1 s^-1), preeminent among reported inorganic PC transparent materials. Additionally, the ceramics have been utilized for real-time optical recording, displaying unambiguous patterning with long-time preservation (21 days). This research supplies a paradigm for designing high-performance PC transparent materials in optical applications and helps deepen the comprehensive understanding of the PC mechanism.

Reversible Modulated Upconversion Luminescence of MoO3:Yb3+,Er3+ Thermochromic Phosphor for Switching Devices

Reversible modulation of upconversion luminescence induced by the external field stimuli exhibits potential applications in various fields, such as photoswitches, optical sensing, and optical memory devices. Herein, a new MoO₃:Yb³⁺,Er³⁺ thermochromic phosphor was synthesized via a high-temperature solid-state method, and the reversible color modification of the MoO₃:Yb³⁺,Er³⁺ phosphor was obtained by alternating the sintering conditions either in a reducing atmosphere or in air. The color of the MoO₃:Yb³⁺,Er³⁺ phosphor changed from light-yellow to blue under sintering in the reducing atmosphere and returned back after sintering again in air. The influence of reversible thermochromism on the upconversion luminescence of MoO₃:Yb³⁺,Er³⁺ phosphor was investigated. The MoO₃:Yb³⁺,Er³⁺ phosphor prepared in air exhibited visible upconversion luminescence, while the MoO₃:Yb³⁺,Er³⁺ phosphor has no upconversion luminescence after sintering in the reducing atmosphere. This up-conversion luminescence modulation shows excellent reproducibility after several cycles. The thermochromic MoO₃:Yb³⁺,Er³⁺ phosphor with reversible modulated upconversion luminescence shows great potential for practical applications in optical switches and optoelectronic multifunctional devices.

Thermomchromic Reaction-Induced Reversible Upconversion Emission Modulation for Switching Devices and Tunable Upconversion Emission Based on Defect Engineering of WO3:Yb3+,Er3+ Phosphor

Reversible luminescence modulation of upconversion phosphors has the potential applications as photoswitches and optical memory and data storage devices. Previously, the photochromic reaction was extensively used for the realization of reversible luminescence modulation. It is very necessary to develop other approaches such as thermomchromic reaction to obtain the reversible upconversion luminescence modulation. In this work, the WO₃:Yb³⁺,Er³⁺ phosphors with various colors were prepared at various temperatures, exhibiting tunable upconversion luminescence attributed to the formation of oxygen vacancies in the host. Upon heat treatment in the reducing atmosphere or air, the WO₃:Yb³⁺,Er³⁺ phosphors show a reversible thermomchromic property. The reversible upconversion luminescence modulation of WO₃:Yb³⁺,Er³⁺ phosphors was observed based on thermomchromic reaction. Additionally, the upconversion luminescence modulation is maintained after several cycles, indicating its excellent stability. The WO₃:Yb³⁺,Er³⁺ phosphors with reversible upconversion luminescence and excellent reproducibility have potential applications as the photoswitches and optical memory and data storage devices.