# Synergistic Optimization Between Chromium Local Coordination States Toward Self‐Powered High‐Repeatability Near‐Infrared Mechanoluminescence

## TL;DR

This paper introduces a high-repeatability near-infrared self-powered mechanoluminescent material optimized through chromium ion coordination states for advanced sensing and imaging applications.

## Contribution

The novel contribution is the optimization of Cr3+ local coordination states to achieve tunable, high-repeatability near-infrared mechanoluminescence.

## Key findings

- Cr3+ local coordination states in MgO host enable high-repeatability (>10,000 times) near-infrared mechanoluminescence.
- Electron transfer among Cr3+ states is linked to stress-driven electron tunneling and photoelectric output.
- A proof-of-concept application model for NIR bio-imaging and sensing is demonstrated.

## Abstract

Self‐powered mechanoluminescence (S‐ML) elastomer with near‐infrared (NIR) emission exhibits great potential for the next generation of bio‐imaging, bio‐sensing, and human‐machine interaction fields. However, due to the lack of understanding of the mechanical‐photon conversion mechanism, the emission efficiency and cycling stability of ML materials reported so far are still unable to meet the application needs. Herein, high‐repeatability (>10000 times) and tunable near‐infrared (650–1000 nm) mechanoluminescent materials are reported by optimizing Cr3+ local coordination states in a simple centrosymmetric MgO host. The constructed electron transfer model among multiple Cr3+ ion states (isolated Cr3+, Cr3+ pair, and Cr3+ cluster) reveals the structure‐activity relationship between local piezoelectricity and photoelectric output. Theoretical calculations and experimental results reveal that the heterovalent substitution of Cr3+ ions promotes the [MgO6] distortion to activate the nearest neighboring defect to form suitable intermediate gap states, facilitating stress‐driven electron tunneling to Cr3+ states. Proof‐of‐concept multi‐layered bright field sensing and imaging is developed with all‐round interactive NIR tactile perception. This work not only provides a high‐repeatability NIR ML phosphor but also establishes the integrated thinking mode for material‐performance‐device rational design.

Herein, a Cr3+‐activated tunable near‐infrared (650–1000 nm) self‐powered mechanoluminescence material with high intensity and repeatability is innovatively developed. This work focuses on optimizing multiple Cr3+ local coordination environments (isolated Cr3+, Cr3+ pair, and Cr3+ cluster) to deeply understand the electron transfer mechanism behind the self‐powered mechanoluminescence, and proposes a proof‐of‐concept application model in the field of NIR bio‐imaging and sensing, showing extraordinary potential for intelligent sensors, wearable technology, and biomedical applications.