Precisely Manipulating the Self‐Reduction of Manganese in MgGa₂O₄ through Lithium Incorporation for Optical Thermometry and Anti‐Counterfeiting

Abstract

Manganese (Mn) doped MgGa2O4 (MGO) phosphors are prepared by a solid‐state reaction technique in air. Upon UV light excitation, the featured green and red emissions of Mn2+ and Mn4+, respectively, are detected in the Mn‐doped MGO phosphors, indicating the incomplete self‐reduction behavior of Mn in the MGO host lattices. To clarify the incomplete self‐reduction behavior, theoretical calculations based on density functional theory and bond energy theory are performed. Moreover, the self‐reduction behavior of Mn can be manipulated by the incorporation of Li+, leading to the precise regulation of the Mn2+ and Mn4+ contents in the MGO host lattices. Based on the ionic radii, the inhibited self‐reduction mechanism is triggered by Li+ occupying the tetrahedral Mg2+ site, leading to the reduced occupancy of tetrahedral Mg2+ sites by Mn ions, and forcing Mn to take up the octahedral Ga3+ sites. Furthermore, the afterglow properties of phosphors with wide and continuous multiple traps are studied in detail. Finally, based on unique luminescence properties of the phosphors, their potential application in ratiometric optical thermometer and optical anti‐counterfeiting is also systematically exploited.

Mg4InSbO8 Spinel: Double 2:1 Ordering in Tetrahedral and Octahedral Sublattices and Perspective Application as an Optical Thermometer via Mn2+/4+ Doping

“…Plots of S a and S r values for MISO/Mn as a function of temperature in Figures d and S9 reveal that MISO:0.002Mn shows significantly higher sensitivities than those of MISO:0.008Mn over the entire temperature range (303–483 K). The highest S r value of 2.10% is obtained for MISO:0.002Mn at 453 K. This high S r value is comparable to those Mn 2+ /Mn 4+ -based spinel-type optical thermometers, such as 1 wt %Li-MgGa 2 O 4 : Mn 2+ /Mn 4+ ( S r = 1.81% K –1 ), ZnGa 1.5 Al 0.5 O 4 :Mn 2+ /Mn 4+ ( S r = 2.166% K –1 ), ZnAl 2 O 4 :Mn 2+ /Mn 4+ ( S r = 2.85% K –1 ), and much higher than those of previously reported other optical thermometric materials, such as Na 3 Sc 2 P 3 O 12 :Eu 2+ /Mn 2+ ( S r = 1.56% K –1 ), CaBaZn 2 Ga 2 O 7 :Bi 3+ (S r = 1.45% K –1 ), and LaMg 0.402 Nb 0.598 O 3 : Pr 3+ ( S r = 0.73% K –1 ) . Therefore, MISO:Mn 2+ /Mn 4+ phosphors are promising candidates for noninvasive and remote temperature monitoring via the FIR technique.…”

“…Multiple tetrahedral and octahedral sites in MISO spinel are appropriate for Mn 2+ and Mn 4+ doping, thereby realizing perspective applications in solid-state lighting, as observed for many AB 2 O 4 -type spinels. − A phosphor series MISO/ x Mn was thus rationally designed to functionalize and expand the application of this newly discovered spinel. The PLE spectra of MISO/ x Mn monitored at 496 nm are depicted in Figure a.…”

“…According to the above spectroscopic analysis, we can conclude that green-emitting Mn 2+ and deep-red-emitting Mn 4+ ions coexist in MISO/xMn. The coexistence of Mn 2+ and Mn 4+ ions was also reported in other Mn-activated phosphors such as Mg(Ga/Al) 2 O 4 /Mn 50,62 and Mn-rich spinel like CuMn 2 O 4 . 63 Note that our MISO/xMn phosphors were prepared by using MnO 2 as the Mn source.…”

Structure and photoluminescence of Mn2+/4+-activated doubly ordered spinel Mg4(Ga/Al)SbO8: site-selective Al3+-to-Ga3+ substitution enabling Mn4+ accumulation, excellent anti-thermal quenching of Mn2+ green emission, and optical thermometry

“…Such an incomplete self-reduction has been frequently reported for Mn-doped AB 2 O 4 -type spinels (A = Mg 2+ , Zn 2+ ; Ga 3+ , Al 3+ ) and attributed to the release of electrons from the negatively charged A 2+ -cation vacancies. 34,50…”

Eulytite-type Ba3Yb(PO4)3:Tm/Er/Ho as a high sensitivity optical thermometer over a broad temperature range

“…Lanthanide elements (Pr, Nd, Eu, Ho, Er, Tm) and transition metal elements (Cr, Mn) have proven to be highly effective luminescent centers for optical thermometry. 19–22 For instance, Back, M et al discussed the potential of Nd 3+ -activated bismuth silicate systems as ratio thermometers, demonstrating relative sensitivity values of 1.43%·K −1 and 1.33%·K −1 at 300 K for Bi 2 SiO 5 :Nd@SiO 2 and Bi 4 Si 3 O 12 :Nd@SiO 2 , respectively. 23 Furthermore, the Cr 3+ -doped Bi 2 Ga 4 O 9 system reported by the same group as a novel radiometric luminescent thermometer, exhibited remarkable relative sensitivity values across a broad temperature range, with a maximum value of 2.74%·K −1 at 80 K and 0.70%·K −1 within the physiological range.…”