Design of a Novel Near-Infrared Phosphor by Controlling the Cationic Coordination Environment

Abstract

Phosphors with the emission spectra located at the biological window I (650–950 nm) are significant for biological imaging. In this work, a series of deep red and near-infrared phosphors InMgGaO4: xCr3+ and In0.9‑y MgGaO4: 0.1Cr3+, yAl3+ are designed and successfully synthesized by a high temperature solid state method. InMgGaO4 is selected as the host considering its special crystal structure that one of the Mg/Ga–O bonds is affected by the surrounding environment. Therefore, when Cr3+ is substituted into the lattice, the longer Mg/Ga–O bonds are easily broken, which provides a tunable crystal field. The emission spectra of InMgGaO4: xCr3+ cover from 650 to 1200 nm, including one sharp line emission peak (peak 1) and two broad emission bands (peak 2 and peak 3). The Racha parameters D q/B and the decay curves are analyzed to distinguish the origins of these three peaks. Meanwhile, these three emission peaks show different degrees of red shift, which is related to the covalency, crystal field splitting (D q), bond breaking of Mg/Ga–O, and decrease of band gap. However, comparing with the luminescent property of Cr3+ single doped samples, In0.9‑y MgGaO4: 0.1Cr3+, yAl3+ shows a contrasting luminescence property and the reason is analyzed. In summary, the emission spectra of these samples can be tuned between a narrow peak and broad band continuously by controlling the concentration of Cr3+ ions or Al3+ ions, which shows a potential application in biological imaging.

Multi-Site Cation Control of Ultra-Broadband Near-Infrared Phosphors for Application in Light-Emitting Diodes

“…Conversely, the LGGO-CrSnBaSc sample shows a different kind of emission with the Cr1/Cr3 peak by exhibiting a redshift and less pronounced R-lines. Given the crystal field strength, Dq is greatly dependent on the interatomic bond distances and is given by ,,− where Dq is the crystal field strength, z is the charge of the anion, e is the charge of the electron, < r 4 > is the expected value of fourth power of radius operator with respect to 3d electronic wave function, and R is the bond distance. Since <r 4 > is usually considered as a parameter, the simplified expression can be used where C is a constant that can be determined from the experimental data.…”

Broadband near-infrared (NIR) emission realized by the crystal-field engineering of Y3−xCaxAl5−xSixO12:Cr3+(x= 0–2.0) garnet phosphors

“…As the strength of the crystal field decreases, the broadband emission attributed to the spinallowed 4 T 2 -4 A 2 transition appears. 18 Several kinds of broadband phosphors with weak crystal fields have been reported recently, such as SrSc 2 O 4 :Cr, 19 Ca 2 MgWO 6 :Cr, 20 ScBO 3 :Cr, 21 and Sr 8 MgLa(PO 4 ) 7 :Cr. 22 In addition, broadband emissions can be achieved by decreasing the crystal field strength of a strong crystal field material by a substitution strategy.…”

Competitive Cr3+ occupation in persistent phosphors toward tunable traps distribution for dynamic anti‐counterfeiting

“…The PLE and PL spectra of LZG: xCr 3+ are depicted in Figure 2A,B. The excitation peaks were found at 284, 408, and 580 nm corresponding to the 4 A 2 ‐ 4 T 1 ( 4 P), 4 A 2 ‐ 4 T 1 ( 4 F), 4 A 2 ‐ 4 T 2 ( 4 F) spin allowed Cr 3+ d–d transitions respectively 26‐27 . The low temperature spectrum of LZG: 0.8% at 5 K was tested (Figure 2C), showing three peaks at 677, 708, and 728 nm, and the lifetime decay curves at these three peaks were monitored in Figure 2D, which were 3.32, 3.06, and 2.68 ms, respectively.…”

“…The excitation peaks were found at 284, 408, and 580 nm corresponding to the 4 A 2 -4 T 1 ( 4 P), 4 A 2 -4 T 1 ( 4 F), 4 A 2 -4 T 2 ( 4 F) spin allowed Cr 3+ d-d transitions respectively. [26][27] The low temperature spectrum of LZG: 0.8% at 5 K was tested (Figure 2C), showing three peaks at 677, 708, and 728 nm, and the lifetime decay curves at these three peaks were monitored in Figure 2D, which were 3.32, 3.06, and 2.68 ms, respectively. The electron has a long lifetime of milliseconds at the 2 E level, while the orbital lifetime at the 4 T 2 ( 4 F) level is usually microseconds, indicating the emission comes from the 2 E level.…”