Recent Advances in Chromium‐Doped Near‐Infrared Luminescent Materials: Fundamentals, Optimization Strategies, and Applications

Abstract

Development of chromium-doped luminescent materials is pertinent to many emerging applications, ranging from agriculture, food industry to noninvasive health monitoring. The fundamental importance of chromium-activated luminescent materials in the field of optics and biomedicine makes the rapid development of novel materials and relevant applications. Herein, the recent advances on the luminescence principle and photoluminescence (PL) optimization for Cr 3+ -activated luminescent materials together with their potential applications are reviewed. The different types of most recently developed Cr 3+ -doped luminescent materials and the design principles are systematically summarized. The associations between crystal structure and nearinfrared (NIR) PL properties, as well as performance-evaluating parameters are introduced with the examples of known NIR emitting phosphors, which will be helpful to explore future NIR luminescent materials. Based on crystal field control, site engineering, and electron-phonon coupling, several efficient strategies for optimizing luminescence performances including bandwidth, thermal stability, and quantum efficiency of Cr 3+ -doped NIR luminescent materials are proposed. Then, potential applications in the fields of food analysis, night vision, information encryption, and optical sensors are surveyed. Finally, the challenges of promising Cr 3+ -doped luminescent materials are proposed.

An efficient and thermally stable near-infrared phosphor derived from the Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) garnet family

“…Recently, Cr 3+ -activated garnet-type materials with the formula A 3 B 2 C 3 O 12 have gained much attention because some of them show ultra-high IQE and outstanding thermal stability. 16,17 Typically, the garnet Gd 3 Al 2 Ga 3 O 12 :Cr 3+ (λ em = 730 nm) exhibits an IQE as high as 97.3% and an I 423 K of 96.8%. Disappointingly, its emission peak is located in the farred region limiting its applications in NIR spectroscopy.…”

Energy Conversion and Transfer in the Luminescence of CeSc3(BO3)4:Cr3+ Phosphor

“…According to quantum mechanics, the difference between two neighboring peaks corresponds to the energy Figure 3a presents the emission spectra of RESc 3 (BO 3 ) 4 :Cr 3+ (RE = Ce, Gd, Tb, Lu) under the excitation of 471 nm, in which the broadband emission is attributed to the 4 A 2 -4 T 2 ( 4 F) transition of Cr 3+ . By monitoring the emission of Cr 3+ at 822, 830, and 866 nm, the excitation spectra of RESc 3 (BO 3 ) 4 :Cr 3+ (RE = Ce, Gd, Tb, Lu) are given in Figure 3b-d, respectively, in which two strong excitation bands in regions of 400-575 nm and 575-800 nm are attributed to the electron transitions of 4 A 2 -4 T 1 ( 4 F) and 4 A 2 -4 T 2 ( 4 F), respectively [11][12][13]. Moreover, minor excitation bands in the region of 200-400 nm are observed, which should be caused by host excitation (as discussed below) in addition to the high-level excitation of Cr 3+ with the 4 A 2 -4 T 1 ( 4 G) transition.…”

“…However, the d-d transition of Cr 3+ is spin-forbidden, and accordingly, the absorbance of Cr 3+ is low, which results in the luminescence of the Cr 3+ -activated phosphor with poor efficiency. Recent progress achieved in the NIR phosphors activated by Cr 3+ is described in the latest review papers on references [ 11 , 12 , 13 ]. Generally, the absorbance and luminescence efficiency of the Cr 3+ -activated phosphors are far below those of the Eu 2+ - and Ce 3+ - activated phosphors.…”

Improving and broadening luminescence in Gd2−xAlxGaSbO7:Cr3+ phosphors for NIR LED applications

“…Near-infrared (NIR) spectroscopy, with distinct advantages of real-time monitoring, high penetration ability and minimal damage to biological organs, can be extensively applied in night vision, biological tissue detection, food composition and freshness analysis, plant cultivation, etc. [1][2][3][4][5][6][7][8] But traditional NIR-emitting sources, such as tungsten filaments and halogen lamps, are severely limited in emerging applications on account of their compactness, bulkiness, short lifetime and inefficiency. [8][9][10] In order to overcome these deficiencies and facilitate various functional applications of NIR light sources, NIR phosphor-converted light-emitting diodes ( pc-LEDs) with portability, energy saving, fast-response, long lifetime and efficiency are emerging continuously and are fabricated by coupling broadband NIR phosphors with commercial blue chips.…”