Mechanoluminescence (ML) materials with long-wavelength emission bands are essential for future in vivo bioimaging, non-destructive testing of solids, etc. The lack of a defined mechanism, however, prevents the application of near infrared ML materials above 650 nm in several new fields. Here, the addition of Ga 3+ ions to Y 3 Al 5 O 12 : Cr 3+ manipulates matrix microstructure evolution, boosting near-infrared (NIR) zero-phonon line (ZPL) stress optical output of the Cr 3+ ion at 688 nm. The key factor changing the crystal field intensity D q /B due to the addition of Ga 3+ ions is what causes the luminescence amplification of ZPL. The ML fabricated by composite polydimethylsiloxane and Y 3 Al 4 GaO 12 : Cr 3+ (YAGG: Cr 3+ ) may penetrate chicken feet epidermal tissue and 4 mm pork tissue thanks to the strong NIR ZPL emission of YAGG: Cr 3+ phosphor. This discovery of enhancing near-infrared ZPL intensity by solid solution provides us with a new technique for optimizing NIR ML materials, as well as a new prospect for NIR ML materials in biological applications.
The emission of persistent luminescence nanoparticles (PLNPs) is in the second near infrared region (NIR-II, 1000–1700 nm), considered as ideal fluorescence imaging materials because of their special characteristic consist of no autofluorescence, weak scattering and deep tissue penetration depth in biological tissues. However, it is still a great challenge to enhance their persistent luminescence intensity. Herein, we reported a new MgGe 0.8 Ga 0.2 O 3 : Yb 3+ (MGGO: Yb 3+ ) PLNPs, which were synthesized through solvothermal liquid-solid-solution and salt microemulsion method. We found that partially replacing Ge 4+ with Ga 3+ ions in MgGeO 3 host can increase the density of traps, thus significantly improving the NIR-II persistent luminescence intensity of Yb 3+ ions (the decay time is more than 33 min). Moreover, X-ray could be used to repeatedly stimulate the NIR-II persistent emission of MGGO: Yb 3+ , which is pivotal for deep tissues long term imaging. The optical penetration length of Yb 3+ ions persistent luminescence was assessed to be 3.9 mm via capping tissue. The above results reveal that MGGO: Yb 3+ PLNPs are promising material to be applied to deep-tissue imaging field.
Xiaomeng Yin,Ming Qiang,Hui Lin,Dawei Zhang,Ruijin Hong,Zhaoxia Han
In this work, we fabricated a novel spinel-type phosphor material MgAl 2− x Ga x O 4 doped with Cr 3+ by the high-temperature solid-state sintering method. The crystal field environment of the spinel was tuned by replacing the Al ions with Ga 3+ ions of different concentrations. The cell volume and D q / B gradient increase from 2.82 to 2.62 with increasing Ga 3+ ion doping concentration. This also implies a gradual decrease in the field strength of the crystal. Based on this, the excitation spectra of MgAl 1.995− x Ga x O 4 :0.5%Cr 3+ phosphors yield a redshift. Increasing the Ga 3+ ion doping concentration also improves the emission intensity and thermal stability of the phosphors, and the emission intensity of the Ga 3+ -doped phosphors is significantly increased. For a Ga/Al ratio of 1, the thermal stability of the phosphor emission is optimal. The emission intensity at 140°C can maintain 76% of the emission intensity at room temperature, indicating that appropriate Ga 3+ ion doping can improve the emission efficiency and thermal stability of the phosphors.
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