Near‐Infrared Mechanoluminescence of Cr³⁺ Doped Gallate Spinel and Magnetoplumbite Smart Materials

Abstract

Mechanoluminescence (ML), as an optical response to deformation stimuli, shows great potential in high-end stress sensing, ultrasonic field visualization, and multidimensional anti-counterfeiting. However, processive practical applications in bio-medicine are constrained by the discovery of nearinfrared (NIR) ML materials. Unlike lanthanides (Ln 3+ ) with sharp multiplets, two kinds of Cr 3+ -doped NIR ML materials, gallate spinel (ZnGa 2 O 4 :Cr 3+ , Zn 3 Ga 2 GeO 8 :Cr 3+ ) and gallate magnetoplumbite (SrGa 12 O 19 :Cr 3+ ) are here reported. Owing to the intrinsic cation antisite defects and cation vacancies in the matrix, these materials exhibit bright NIR ML under a relatively low load (20 N). In particular for SrGa 12 O 19 :Cr 3+ (750 nm, peak; 100 nm, FWHM) with low persistent luminescence (PersL) interference, the ML behavior can be further rejuvenated under UV and sunlight irradiation. SrGa 12 O 19 :Cr 3+ also shows bright NIR emission under photo-and thermo-stimulation. Owing to their excellent tissue penetration and concealment capability, NIR ML materials show great potential in the fields of bio-medicine and anti-counterfeiting.

Cr3+-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

“…The excitation bands peaking at 428 and 580 nm are ascribed to the 4 A 2g → 4 T 1g and 4 A 2g → 4 T 2g transitions of the Cr 3+ ions, respectively. 30 Therefore, BASO:0.024Cr 3+ can be matched not only with blue LED chips but also with yellow LED chips to reduced energy loss. Upon excitation at 428 nm, BASO:0.024Cr 3+ displays an intense NIR emission peaking at 695, 710, and 750 nm, which all come from the 2 E g → 4 A 2g transitions.…”

Electron Tunneling Charging upon Sunlight for Near‐Infrared Persistent Luminescence

“…The Ga II ( z = 0.257) site is deviated from the mirror ( z = 0.25) to relax the structural stress. [ 48,49 ] Consequently, this results in an weak bonded O 2− (negative charge center) with very long Ga─O bond length of 2.46 Å (Figure 4c), while attracting the vicinal Ga II cation (positive charge center) due to Coulomb attraction, as schematically shown in Figure 4b. However, this chemical state is metastable, and this positive‐negative charge center can achieve electrical neutrality after capturing the adventitious electrons and holes.…”

Broadband and Multimode Near‐Infrared Emitter Based on Cr3+‐Activated Stannate for Multifunctional Applications

“…However, most reported Cr 3+ -doped NIR PersL materials are dominated by gallate compounds, and exhibit short emission wavelength (λ em < 800 nm) and narrow bandwidth. [29][30][31][32][33][34][35] It is known that biological tissue shows a lower optical scattering coefficient in longer spectral region. Therefore, it is necessary to design PersL materials with emission wavelength longer than 800 nm to acquire highresolution imaging.…”