Unlocking The Inherent Luminescence of Eu 2+ /Eu 3+ by Light‐Induced Oxidation for Invisible Optical Storage

Mechanoluminescence (ML) is a fascinating phenomenon with diverse applications in pressure sensing, damage detection, and stress distribution visualization. However, most ML materials exhibit instantaneous photon emission that requires real‐time recording with a photodetector, and thereby circumscribing their applicability predominantly to real‐time stress‐sensing scenarios. In this work, a novel method is introduced for non‐real‐time stress sensing utilizing Li0.1Na0.9NbO3:Pr3+ phosphor, which allows for the retrieval of pressure location and intensity even 20 days after the event. The influence of heat and pressure on the trap depth distribution is analyzed using thermoluminescence (TL) and ML measurements, and it is proved that both heat and pressure release the captured electrons in the same traps. Leveraging the intricate competition between mechanical and thermal detrapping processes, stress information can be accessed through TL imaging. Furthermore, an algorithm is proposed based on this phenomenon to authenticate the stress information. This research not only advances the fundamental understanding of ML phenomena but also introduces a novel approach for applications such as mechano‐history indicators, security papers, and advanced data storage systems.

Controllable Modulation of Trapped Carriers in Mechano/Thermo Dual‐Responsive Particles for Advanced Stress‐Encoded Information Storage

Peng,

Sun,

Deng

et al. 2024

Europium Ions Self‐Reduction Benefiting from AlO₄/Si(Al)O₄ Network Structure for Multimode Optical Thermometry Manometry

Lu,

Zhang,

Fang

et al. 2024

Mixed‐valence europium ions‐activated phosphors have distinct advantages in color modulation, dynamic anti‐counterfeiting, and optical sensors. Nevertheless, it is still a challenge to obtain mixed‐valence europium ions in single compounds by facile self‐reduction. Herein, the crystal structure of a 3D hexagonal network formed by SiO4/AlO4 tetrahedra is demonstrated to play a significant role in the spontaneous reduction of Eu3+ to Eu2+ based on SrAl2Si2O8, Sr2SiO4, SrAl2O4 hosts. The crystal field theory and Judd‐Ofelt theory provide a deeper understanding of Eu2+ and Eu3+ luminescence behavior, namely, the low energy spectra of Eu2+ are more easily observed in crystal structure with high polarizability and octahedral coordination, whereas the spectra properties of Eu3+ are affected by the symmetry of local environment and crystal rigidity. For SrAl2Si2O8: 0.02Eu2+/Eu3+, multi‐mode thermometry is explored in terms of the luminescence intensity ratio (LIR) of Eu2+/Eu3+, luminescence intensity (LI) and full‐width at half maximum (FWHM) of Eu2+ with maximal relative sensitivity reaching 3.83% K−1. This study presents the first exploration of optical manometry based on the LIR mode of Eu2+/Eu3+ with excellent sensitivity (Sr = 18.13% GPa−1). This work not only provides a novel strategy for the design of mixed‐valence ions‐activated materials but also constructs promising optical thermometry, and manometry candidates.

Crystallographic Engineering to Develop Ultra‐Narrow‐Band Cyan‐Emitting UCr₄C₄‐Type Phosphor for Healthy LED Lighting and Display

Wan,

Dang,

Liu

et al. 2024

Narrow‐band cyan‐emitting materials for white light‐emitting diode (wLED) application have shown great potential in increasing the maximum accessible display gamut and improving the color rendering of full‐spectrum healthy lighting. However, the discovery of novel narrow‐band cyan emitters with excellent luminescence performances remains challenging. Here, an ultra‐narrow‐band cyan‐emitting Na5K3(Li3SiO4)8:Eu2+ (N5K3:Eu2+) phosphor (λem = 483 nm) with full width at half maximum (FWHM) of only 18 nm is developed from some typical UCr4C4 frameworks phosphors by slightly modifying crystal structure and symmetry. Through controllable regulation of the ratio of Na and K from Na4K4(Li3SiO4)8:Eu2+ (N4K4:Eu2+) and Na6K2(Li3SiO4)8:Eu2+ (N6K2:Eu2+) to N5K3:Eu2+, the lattice sites forming shoulder peaks are further squeezed to generate the narrowest cyan emission. Moreover, the N5K3:Eu2+ exhibits low photoluminescence thermal quenching (90%@150 °C) and high internal quantum efficiency (IQE) of 50%. The color rendering index of wLED for full‐spectrum health lighting is enhanced from 92 to 94. Using this short‐wavelength cyan emission instead of a part of the emission from a blue chip can effectively prevent “blue hazard”. This work provides basic principles for the design of ultra‐narrow‐band phosphors, thus achieving their applications in the fields of healthy lighting and eye‐friendly display.