Emerging phototherapy in a clinic and plant photomorphogenesis call for efficient red/far-red light resources to target and/or actuate the interaction of light and living organisms. Rare-earth-doped phosphors are generally promising candidates for efficient light-emitting diodes but still bear lower quantum yield for the far-red components, potential supply risks, and high-cost issues. Thus, the design and preparation of efficient non-rare-earth activated phosphors becomes extremely important and arouses great interest. Fabrication of Cr3+-doped Na3AlF6 phosphors significantly promotes the potential applications by efficiently converting blue excitation light of a commercial InGaN chip to far-red broadband emission in the 640–850 nm region. The action response of phototherapy (∼667–683 nm; ∼750–772 nm) and that of photomorphogenesis (∼700–760 nm) are well overlapped. Based on the temperature-dependent steady luminescence and time-resolved spectroscopies, energy transfer models are rationally established by means of the configurational coordinate diagram of Cr3+ ions. An optimal sample of Na3AlF6:60% Cr3+ phosphor generates a notable QY of 75 ± 5%. Additionally, an InGaN LED device encapsulated by using Na3AlF6:60% Cr3+ phosphor was fabricated. The current exploration will pave a promising way to engineer non-rare-earth activated optoelectronic devices for all kinds of photobiological applications.
The fluorinated tris-thiolate compounds Ln(SC(6)F(5))(3) can be isolated as THF, pyridine, or DME coordination complexes. In THF, the larger Ce forms dimeric [(THF)(3)Ce(SC(6)F(5))(3)](2) (1) with bridging thiolate ligands, while the smaller lanthanides (Ln = Ho (2), Er (3)) form monometallic (THF)(3)Ln(SC(6)F(5))(3) compounds. There is a tendency for fluoride to coordinate to Ln throughout the lanthanide series (Ce-Er). The cerium compound 1 contains a pair of bridging thiolates connecting two eight-coordinate Ce(III) ions. Of the two terminal thiolates, only one exhibits a distinct Ce-F bond. In contrast, the Ho derivative (THF)(3)Ho(SC(6)F(5))(3) is a molecular compound in the solid state, with two monodentate thiolates and one thiolate that again coordinates through both S and F atoms. Incorporation of a stronger Lewis base reduces but does not necessarily eliminate the tendency to form Ln-F bonds. Structural characterization of the eight-coordinate (pyridine)(4)Sm(SC(6)F(5))(3) (4) reveals a single, clearly defined Ln-F interaction, while in (pyridine)(4)Yb(SC(6)F(5))(3) (5) there are no Yb-F bonds. In the structure of (DME)(2)Er(SC(6)F(5))(3) (6) the DME ligands completely displace F from the Er coordination sphere.
A pair of mer-octahedral lanthanide chalcogenolate coordination complexes [(THF)(3)Ln(EC(6)F(5))(3) (Ln = Er, E = Se; Ln = Yb, E = S)] have been isolated and structurally characterized. Both compounds show geometry-dependent bond lengths, with the Ln-E bonds trans to the neutral donor tetrahydrofuran (THF) significantly shorter than the Ln-E bonds that are trans to negatively charged EC(6)F(5) ligands. Density functional theory calculations indicate that the structural trans influence evidenced by the differences in these bond lengths results from a covalent Ln-E interaction involving ligand p and Ln 5d orbitals.
Experimental SectionGeneral Methods. All syntheses were carried out under ultrapure nitrogen (JWS), using conventional drybox or Schlenk techniques. Solvents (Fisher) were refluxed continuously over molten alkali metals or K/benzophenone and collected immediately prior to use. Anhydrous pyridine (Aldrich) was purchased and refluxed over KOH. Hg(SC6F5)2 was prepared in a variation of literature procedures. 24 HSC6F5 was purchased from Aldrich. Sm and Eu were purchased from Strem. Melting points were taken in sealed capillaries and are uncorrected. IR spectra were taken on a Mattus Cygnus 100 FTIR spectrometer and recorded from 4000 to 600 cm -1 as a Nujol mull on NaCl plates. Electronic spectra were recorded on a Varian DMS 100S spectrometer with the samples in a 0.10 mm quartz cell attached to a Teflon stopcock. Elemental analyses were performed by Quantitative Technologies, Inc. (Whitehouse NJ). 19 F NMR spectra were obtained on a 400 MHz NMR spectrometer with an external HSC6F5 reference, and chemical shifts are reported in δ (ppm). Direct probe-EI mass spectra were obtained at the Rutgers University Department of Food Science.Synthesis of Hg(SC6F5)2. In a modification of the original literature procedure, Hg(CH3COO)2 (1.169 g, 3.676 mmol) and HSC6F5 (1.468 g, 7.335 mmol) were combined in deionized water (∼100 mL). The solution was stirred overnight, and the white precipitate was collected by vacuum filtration and recrystallized by slowly cooling a saturated hot toluene solution to give white crystals (3.194 g, 87%) that were identified by IR and melting point. 12 Synthesis of [(THF)2Sm(µ2-SC6F5)(SC6F5)2]2 (1). Sm (0.150 g, 0.997 mmol) and Hg(SC6F5)2 (0.895 g, 1.50 mmol) were combined in THF (25 mL), and the mixture was stirred until all the Sm was consumed (1 h). The solution was filtered to separate the elemental Hg (0.25 g, 78%), the volume was reduced (ca. 15 mL), and the solution was layered with hexane (12 mL) and then cooled slowly (-20 °C) to give yellow-orange (0.293 g, 33%) crystals that turn darker orange at 74 °C, start becoming lighter yellow at 150-185 °C, and melt at 252-254 °C.
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