Abstract The burgeoning phosphor‐converted near‐infrared light‐emitting diodes (pc‐NIR LEDs) have important applications in special illumination and spectroscopy analysis. However, the development of efficient NIR‐emitting phosphors with high performance is still a challenge. In this work, a chemical unit co‐substitution strategy is proposed to realize the excitation transition regulation and successfully achieve high‐performance NIR luminescence in Ca 3‐ y Na y Mg 1‐ y Sb 2‐ x Al 2+ y O 12 : x Cr 3+ (0 ≤ x ≤ 0.05, 0 ≤ y ≤ 1) garnet‐type solid solution phosphors. Through the excitation transition modulation from the 4 A 2 ground state to the 4 T 1 ( 4 P) and 4 T 1 ( 4 F) excitation state, the excitation intensity at the blue light region is largely enhanced by 25.6 times. Moreover, the NIR‐emitting efficiency and thermal stability are improved, with the optimal luminescence internal quantum efficiency of 90.6% and thermal stability of 97%@423 K, without any flux‐assisted sintering or reduction atmosphere protection. The structure regulation induced small Stokes shift, weak electron‐phonon coupling effect, and decreased non‐radiative transition are responsible for the excellent NIR‐emitting performance. Finally, the NIR pc‐LED is fabricated with photoelectric efficiencies of 18.7%@100 mA and NIR output powers of 63 mW@100 mA, presenting potential applications in nondestructive internal defect detection, veins imaging, and night vision surveillance.
Abstract Cyan‐emitting phosphors have attracted widespread attention as an integral part to realize full‐spectrum lighting. Understanding the site occupation of luminescence centers is of great importance to design and clarify the luminescent mechanism for new cyan‐emitting phosphors. Here, we report a cyan‐emitting phosphor Ca 18 Na 3 Y(PO 4 ) 14 :Eu 2+ synthesized by the high‐temperature solid‐state method. The crystal structure is characterized by X‐ray diffraction and refined by the Rietveld method. The diffuse reflectance spectra, excitation/emission spectra, fluorescence decay curves, thermal stability, and related mechanism are systematically studied. The results show that Ca 18 Na 3 Y(PO 4 ) 14 :Eu 2+ crystallizes in a trigonal crystal system with space group R 3 c . Under excitation at 350 nm, a broadband cyan emission can be obtained at 500 nm with a half‐width of about 120 nm, which is caused by Eu 2+ occupying five different sites in host, namely, Na2O 12 (450 nm), (Ca3/Na1)O 8 (485 nm), Ca2O 8 (515 nm), Ca1O 7 (565 nm), and (Ca4/Y)O 6 (640 nm), respectively. Moreover, crystal structure, room and low temperature spectroscopy, and luminescence decay time are used to skillfully verify the site‐selective occupation of Eu 2+ . Finally, a full‐spectrum light‐emitting diode (LED) lamp is fabricated with an improved color rendering index (∼90.3), CCT (∼5492 K), and CIE coordinates (0.332, 0.318). The results show that Ca 18 Na 3 Y(PO 4 ) 14 :Eu 2+ has the potential to act as a cyan emission phosphor for full‐spectrum white LEDs.
To date, it is still a challenging topic to achieve a wide tunable emission from the same sample under the excitation of a single pump source. Herein, a new sort of nanophosphor NaYO 2 :Er 3+ /Yb 3+ is prepared and characterized. In particular, the wide tunable range crossing red–yellow–green–white regions can be realized only by modulating the power density of the 980 nm semiconductor laser. The mechanism of emitting white light is discussed, and two formulae for quantitatively defining the fluorescent material's tuning ability are also offered. At the same time, the nanophosphor on hand possesses a high degree of reversibility. The nanophosphor presents comprehensive application prospects in information security, anticounterfeiting, display, and other fields.
A series of Sr 2 MgSi 2 O 7 :Tb 3+ nanophosphors is prepared using a high-temperature solid-state reaction. The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb 3+ ions. However, the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb 3+ concentration. Unlike earlier investigations on down-conversion emission of Tb 3+ ion excited by deep ultraviolet light, in this work, the photoluminescence characteristics of Sr 2 MgSi 2 O 7 nanophosphors doped with different Tb 3+ concentrations are analyzed under 374-nm excitations. The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%. The main reason for the concentration quenching is due to the electric dipole–electric dipole interaction among Tb 3+ ions.
Currently, phosphor-converted light-emitting diode (pc-LEDs) are revolutionizing the industry of indoor plant cultivation lighting. The development of far-red emitting phosphors with emission wavelength covers 650-750 nm is of great importance because they correspond to the absorption spectrum of plant phytochrome PFR. Herein, a series of novel rare-earth free far-red emitting phosphor NaYBa4W2O12:xMn4+ (0.025 ≤ x ≤ 0.75 mol%, NYBW: Mn4+) are successfully synthesized toward application for near-ultraviolet light (n-UV) pumped plant cultivation LED. The phase purity, crystal structure, and luminescent properties of NYBW: Mn4+ are investigated in detail. The results indicate that all NYBW: Mn4+ phosphors are well crystallized in double perovskite structure with an optical band gap of 3.57 eV. Broad excitation band can be found with dominate wavelength at 365 and 520 nm, indicating NYBW: Mn4+ can be efficiently excited by commercial n-UV or green LED chip. Upon 365 nm excitation, NYBW: Mn4+ shows intense broad-band far-red emission center at 696 nm, attributed to the 2Eg-4A2g transition of Mn4+. The optimal doping concentration of Mn4+ is determined as 0.1 % and the concentration quenching mechanism is discussed as a dipole-dipole interaction. The decay lifetime decreases from 0.582 to 0.081 ms with Mn4+ concentration increasing from 0.025 to 0.75%. The temperature quenching behaviour of Mn4+ in NYBW are investigated with a thermal activation energy of 0.375 eV. Finally, a far-red emitting LED device is fabricated by coating NYBW: Mn4+ phosphors on a 365 nm n-UV LED chip. The above results revealed that the as-prepared far-red emitting phosphor NYBW: Mn4+ have great potential for application in indoor plant cultivation lighting.
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