Shortwave Infrared Luminescence of Tetravalent Chromium and Divalent Nickel: Phosphor Design Principles and Applications

Abstract

Shortwave infrared radiations (SWIR, 900–1700 nm) emitting inorganic luminescent materials are key components for multiple applications, which range from optical communication and anticounterfeiting purposes to chemical and medical diagnosis. The blue light excitable SWIR phosphors activated with the transition metal ions Cr4+/Ni2+ are considered prospective light sources for an upcoming compact modern device using phosphor converter technology. In this review, the crystal field theory and Tanabe-Sugano diagram are briefly discussed to understand the splitting of energy levels and the concurrent effect. Several possible strategies to achieve and enhance the luminescence efficiency of Cr4+/Ni2+ SWIR emission are disclosed as is the reported chemical system. Finally, the domains for the potential practical application of SWIR phosphors are introduced. This review will provide information on the recent advances and the luminescence mechanism of Cr4+/Ni2+-activated SWIR phosphors and will also assist researchers in developing next-generation SWIR phosphors and exploring new applications.

Advances in Chromium‐Activated Phosphors for Near‐Infrared Light Sources

“…The intersection of 4 T 2 and 2 E levels is generally used to divide the strong ( Dq / B > 2.3) and weak crystal field ( Dq / B < 2.3). [ 9 ] Figure 2 presents the Cr 3+ emission profiles in the strong and weak octahedral fields, respectively, based on the T–S energy level diagram and configuration coordinate model. As shown in Figure 2a, when Cr 3+ ion is in a strong crystal field, 2 E energy level is the lowest excited state.…”

“…[ 8 ] Besides, NIR solid‐state laser diodes present good spectral stability, however, the requirements of high electrical consumptions and massive housing arrangements obstruct them to be used as light sources for handheld portable spectrometers or miniature spectrometers. [ 9 ] Subsequently, a new strategy for making miniature NIR light source was proposed by coating efficient broadband NIR luminescent materials on the commercial blue LED chips to fabricate phosphor‐converted light‐emitting diode (pc‐LED) devices.…”

Unraveling Luminescent Energy Transfer Pathways: Futuristic Approach of Miniature Shortwave Infrared Light-Emitting Diode Design

“…Octahedrally coordinated Ni 2+ ions can emit SWIR emissions in the range of 1100–1700 nm, but the practicality of Ni 2+ -activated SWIR phosphors is hindered by its rapid concentration quenching effect, weak blue light absorption, and low quantum efficiency . To the best of our knowledge, the introduction of a codopant and the fluxing agent is a potential strategy to counteract the current bottlenecks, and the energy transfer process is mainly reported between the isolated Cr 3+ and Ni 2+ ions in the host structures of phosphates and inverse spinel. − Nevertheless, designing the energy transfer process between the Cr 3+ –Cr 3+ ion pair and Ni 2+ ion has been unexplored, and approaches for increasing SWIR efficiency have not been established.…”

Advancing Reporting Guidelines for Optimal Characterization of Inorganic Phosphors

“…When designing phosphor materials with transition metal ions as activators, such as Mn-based red/near-infrared phosphors, Cr-based infrared phosphors, Fe-based near-infrared phosphors, and Ni-based shortwave infrared phosphors, understanding the local structure is crucial for proposing new luminescence mechanisms. Electron paramagnetic resonance (EPR) in correlation with a superconducting quantum interference device (SQUID) is an effective approach for estimating the local structural features around the transition metal .…”

“…In contrast, Eu 3+ emission exhibits sharp red lines and is considered less attractive in this context. Similarly, Cr 3+ emits near-infrared light, while Cr 4+ emits shortwave infrared light. , XAS and XPS are valuable techniques in X-ray spectroscopy, but they have distinct characteristics. XAS provides information about the average electronic structure of a material with limited depth sensitivity, while XPS is surface-sensitive, typically probing within a few nanometers.…”