Minimizing Bond Angle Distortion to Improve Thermal Stability of Cr³⁺ Doped Near‐Infrared Phosphor

Abstract

Broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes are next‐generation smart NIR light sources. However, the NIR phosphor suffers from serious thermal quenching (TQ), resulting in efficiency reduction and spectral shift. Here, a novel strategy is realized to suppress TQ by minimizing bond angle distortion, completely different from the conventional TQ suppression approach through bond length variation. Li(Sr1−xCax)AlF6:Cr3+ NIR phosphor is taken as an example in which rotation between the two parallel fluorine planes perpendicular to the C3 axis in the [AlF6] octahedron is found to dominate TQ. Increasing x from 0 to 1 reduces the amplitude of the rotation from 16.17° to 5.06°, weakening the electron–phonon coupling and, consequently, raising the TQ temperature significantly from 320 to 570 K. This mechanism is elucidated from both theoretical calculations and spectroscopic studies. The findings open a new horizon for the exploration of thermally stable NIR phosphors.

Host Dependency of Boundary between Strong and Weak Crystal Field Strength of Cr3+ Luminescence

“…Otherwise, sharp R-line emission, as seen in the case of the first solid-state Ruby laser invented in 1960, will be obtained . An effective strategy to attain this wide-band emission is to construct the host with large ionic-size cations, such as Ga 3+ , Sc 3+ , Li + , etc., to serve as the coordinated polyhedron accommodating Cr 3+ . , On the contrary, when Cr 3+ substitutes at a compressed site such as at Al 3+ , the wide-band emission originating from 4 T 2 ( 4 F) to 4 A 2 ( 4 F) is diminished, and sharp-line emission from 2 E­( 2 G) to 4 A 2 ( 4 F) emerges . Hence, it is essential for researchers to modulate the host in both composition and structure in order to tune the Cr 3+ luminescence.…”

Developing and optimizing novel Cr3+-activated inorganic NIR phosphors by combining triple-objective optimization and crystal field engineering

“…Near-infrared (NIR) spectroscopy is widely used in medicine, food safety, chemical industries, agriculture, and other fields. 1–6 In this case, NIR phosphors as key components are required to have long emission wavelengths, high internal quantum efficiencies (IQE), and thermal stability. 7–11 Recently, researchers have developed a series of Cr 3+ -activated NIR phosphors based on traditional trial-and-error experiments.…”

Spectrally tunable near-infrared photoluminescence in MP3O9:Cr3+ (M = Al, Ga, In) phosphate phosphors

“…Near-infrared (NIR) spectroscopy is extensively used in night vision, health monitoring, non-destructive testing, and biological imaging due to its convenient and fast response characteristics. 1–5 The route of combining blue LEDs with NIR phosphors has been proven to be an effective and feasible approach, benefiting from the rich experience acquired during the development and application of white LEDs. 6–8 The phosphor performance almost ultimately determines the device performance; therefore, the development of broadband NIR phosphors that are thermally stable and can be efficiently excited by InGaN LED chips is crucial.…”