Chem. Mater., 2017, 29, 3, 1430–1438. https://doi.org/10.1021/acs.chemmater.7b00006

Local structure modification in solid solution is an essential part of photoluminescence tuning of rare earth doped solid state phosphors. Herein we report a new solid solution phosphor of Eu2+-doped xSr2Ca(PO4)2–(1–x)Ca10Li(PO4)7 (0 ≤ x ≤ 1), which share the same β-Ca3(PO4)2 type structure in the full composition range. Depending on the x parameter variation in xSr2Ca(PO4)2–(1 – x)Ca10Li(PO4)7:Eu2+, the vacancies generated in the M(4) site enable the nonlinear variation of cell parameters and volume, and this increases the magnitude of M(4)O6 polyhedra distortion. The local structure modulation around the Eu2+ ions causes different luminescent behaviors of the two-peak emission and induces the photoluminescence tuning. The shift of the emission peaks in the solid solution phosphors with different compositions has been discussed. It remains invariable at x ≤ 0.5, but the red-shift is observed at x > 0.5 which is attributed to combined effect of the crystal field splitting, Stokes shift, and energy transfer between Eu2+ ions. The temperature-dependent luminescence measurements are also performed, and it is shown that the photoionization process is responsible for the quenching effect.

Chem. Mater., 2017, 29, 17, 7563–7570. https://doi.org/10.1021/acs.chemmater.7b02724

Eu²⁺ local environments in various crystallographic sites enable the different distributions of the emission and excitation energies and then realize the photoluminescence tuning of the Eu²⁺ doped solid state phosphors. Herein we report the Eu²⁺-doped Ca₁₀M(PO₄)₇ (M = Li, Na, and K) phosphors with β-Ca₃(PO₄)₂-type structure, in which there are five cation crystallographic sites, and the phosphors show a color tuning from bluish-violet to blue and yellow with the variation of M ions. The difference in decay rate monitored at selected wavelengths is related to multiple luminescent centers in Ca₁₀M(PO₄)₇:Eu²⁺, and the occupied rates of Eu²⁺ in Ca(1), Ca(2), Ca(3), Na(4), and Ca(5) sites from Rietveld refinements using synchrotron power diffraction data confirm that Eu²⁺ enters into four cation sites except for Ca(5). Since the average bond lengths d(Ca–O) remain invariable in the Ca₁₀M(PO₄)₇:Eu²⁺, the drastic changes of bond lengths d(M–O) and Eu²⁺ emission depending on the variation from Li to Na and K can provide insight into the distribution of Eu²⁺ ions. It is found that the emission band at 410 nm is ascribed to the occupation of Eu²⁺ in the Ca(1), Ca(2), and Ca(3) sites with similar local environments, while the long-wavelength band (466 or 511 nm) is attributed to Eu²⁺ at the M(4) site (M = Na and K). We show that the crystal-site engineering approach discussed herein can be applied to probe the luminescence of the dopants and provide a new method for photoluminescence tuning.

Inorg. Chem., 2017, 56, 19, 11837–11844. https://doi.org/10.1021/acs.inorgchem.7b01816

Exploring high-performance narrow-band red-emitting phosphor is an important challenge for improving white light LEDs. Here, on the basis of three interesting nitride phosphors with similar vierer rings framework structure, two phosphor series, Eu2+-doped Sr(LiAl)1–xMg2xAl2N4 and Sr(LiAl3)1–y(Mg3Si)yN4 (x, y = 0–1), are successfully synthesized by a solid state reaction. They show narrow-band red emission with tunable emission peaks from 614 to 658 nm and 607 to 663 nm. The varying luminescence behaviors with composition and structure are discussed based on centroid shift, crystal field splitting and Stokes shift. On the basis of experimental data, we construct the host referred binding energy (HRBE) and vacuum referred binding energy (VRBE) schemes of divalent/trivalent lanthanide-doped end-member compounds, and further give thermal quenching mechanism of these series phosphors.