The near-infrared (NIR) light source is desirable for realtime nondestructive examination applications, which include the analysis of foodstuffs, health monitoring, iris recognition, and infrared cameras. The emission spectra of such an infrared light source should also be as broad as possible for effective performance, in view of the fact that the broad absorption and reflection of light by the organic elements present in foodstuffs and human health fall in the blue and NIR regions of the electromagnetic spectrum, respectively. In this letter, a blue light-emitting diode (LED) excitable super broadband NIR phosphor light source is developed with a high fwhm of 330 nm and radiant flux of 18.2 mW for the first time. The observation of superbroad-band luminescence from two distinct luminescence centers is studied and evidenced by electron paramagnetic resonance, X-ray absorption near-edge structure, steady-state luminescence, and timeresolved luminescence at ambient and high-pressure environments. Finally, the luminescence mechanism is discussed with the relevant configurational coordinate diagrams.

Recently, infrared (IR) light-emitting diodes (LEDs) have attracted considerable interest in the research field worldwide. IR phosphors, the basic materials utilized in LEDs, have become a research hotspot as well. Here, we introduce the high-quantum-efficiency IR ScBO 3 :Cr 3+ phosphor, which provides a spectral range of emission from 700 to 1000 nm with a peak maximum at 800 nm. Electron paramagnetic resonance spectroscopy, with high element selectivity, was used to elucidate the unusual small peak in the photoluminescence spectrum. Phonon structure and electron−lattice interaction were well observed and discussed via temperature-dependent measurements. Moreover, the high quantum efficiency of 72.8% was achieved. To evaluate their potential practical application, phosphor-converted LED packages were designed, which revealed high stability and high output power of 39.11 mW. Furthermore, the fabricated IR LED demonstrated a remarkable ability to penetrate biological tissues. This study provides insights into the luminescent properties and the practical applications of IR LEDs.

Red phosphors AMF6:Mn(4+) (A = Na, K, Cs, Ba, Rb; M = Si, Ti, Ge) have been widely studied due to the narrow red emission bands around 630 nm. The different emission of the zero-phonon line (ZPL) may affect the color rendering index of white light-emitting diodes (WLED). The primary reason behind the emergence and intensity of ZPL, taking KNaSiF6:Mn(4+) as an example, was investigated here. The effects of pressure on crystal structure and luminescence were determined experimentally and theoretically. The increase of band gap, red shift of emission spectrum and blue shift of excitation spectrum were observed with higher applied pressure. The angles of ∠FMnF and ∠FMF(M = Si, Ti, Ge) were found clearly distorted from 180° in MF6(2-) octahedron with strong ZPL intensity. The larger distorted SiF6(2-) octahedron, the stronger ZPL intensity. This research provides a new perspective to address the ZPL intensity problem of the hexafluorosilicate phosphors caused by crystal distortion and pressure-dependence of the luminescence. The efficacy of the device featuring from Y3Al5O12:Ce(3+) (YAG) and KNaSiF6:Mn(4+) phosphor was 118 lm/W with the color temperature of 3455 K. These results reveal that KNaSiF6:Mn(4+) presents good luminescent properties and could be a potential candidate material for application in back-lighting systems.

Light-emitting diodes (LEDs) are attracting considerable attention around the world. Phosphor materials, as crucial color-converted components, play central roles in LED development. The demands for phosphor materials have become increasingly stringent over the past decades, from high brightness to narrowband emission or function-dependent spectrum engineering. Although substantial progress has been made for currently developed phosphor materials, simultaneously satisfying all requirements for high-level applications remains challenging. In this review, we aim to provide a comprehensive understanding of the development of phosphor materials in different generations and to elucidate the key designed mechanisms concerning the activators and the host structures to fulfill the aforementioned aspects. We highlight the developments in phosphor materials through the classification of demands for high luminescence, high thermal stability, narrowband emission for high color gamut, and broadband emission for near-infrared. We also focus on elucidating the key designed mechanisms of phosphor materials in different generations. Furthermore, future perspectives about micro-LED applications and nanoluminescent materials are provided. This study opens up an avenue for designing the luminescent materials of the future.

A one-step approach to synthesize Na 2 SiF 6 :Mn 4+ and K 2 SiF 6 :Mn 4+ red phosphors by co-precipitation is reported in this paper. The phosphors were precipitated from a silicon fluoride solution with NaF and Na 2 MnO 4 (Na 2 SiF 6 :Mn 4+ preparation) or KF and K 2 MnO 4 (K 2 SiF 6 :Mn 4+ preparation) using H 2 O 2 to reduce Mn 7+ to Mn 4+ at room temperature. Na 2 SiF 6 :Mn 4+ was also prepared through a convenient two-step route with K 2 MnF 6 as a raw material. The obtained Na 2 SiF 6 :Mn 4+ phosphors have hexagonal structures with space group D 3 2 -P321 and no impurity phase when they were examined via X-ray diffraction. Photoluminescence, photoluminescence excitation, thermal luminescence, and luminescence decay time were considered to determine the optical properties of the fluoride complexes. The prepared phosphors exhibited bright red emission under 460 nm light excitation and low-thermal quenching ($92% of the luminescent intensity at 423 K). Increasing the concentration of Mn 4+ enhanced the luminescence intensity. A warm white light LED with high color rendering index (R a ¼ 86 and R9 ¼ 61) was fabricated by employing Na 2 SiF 6 :Mn 4+ as red phosphors and commercial Y 3 Al 5 O 12 :Ce 3+ as yellow phosphors on a blue-InGaN chip.