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The series of novel phosphors Ca9La(PO4)5 [(Si1-xGexO4)]F2:0.15Dy3+ with x = 0, 0.25, 0.50, 0.75 and 1 (CLPS1-xGxF:0.15Dy3+) with apatite-type structure (space group P63/m) has been synthesized. The crystal structure and electronic structure have been studied by powder X-ray diffraction (PXRD) in combination with the atomic-scale density functional theory (DFT) calculations. A combination of Raman, nuclear magnetic resonance (29Si NMR) spectroscopy and the evolution of Dy3+ ions photoluminescent properties was used to characterize the local crystal structure features. Based on the variation of the [SiO4] by [GeO4] tetrahedral substitutions in the apatite-type structure, the difference in the thermal stability and decay curves of CLPS1-xGxF:0.15Dy3+ phosphors were referred to crystal chemical stability of as-prepared compounds, which is also confirmed by the values of polyhedral distortion, bond valence sum (BVS) and DFT calculations. The present study provides new insights the synthetic methodology and fundamental characterizations into the design of new phosphors combined with theoretical methods.

Porous geopolymers are energy saving, environment-friendly and simple in preparation. However, the thermal conductivity (TC) of present porous geopolymers as well as other inorganic thermal insulation materials can be hardly below 0.050 W m-1 K-1 in the markets. In order to further decrease the TC of porous geopolymers, it is vital to understand the heat transfer mechanism of this type of materials. In this work, we made a comparison among the main heat transfer models for porous two-component system reported so far including series model, parallel model, geometric mean model, Maxwell-Eucken equation, Hashin spherical structure model and novel effective medium theory (NEMT) based on the data reported in references and obtained by our group for porous geopolymers, and found that NEMT could describe the heat transfer mechanism of porous geopolymers better. Then we systematically studied the relationship among the effective TC (ke), porosity (e), TC of solid skeleton (ks) and TC of the uniform medium reflecting the heat conduction of the solid skeleton to air (km) based on the calculations with NEMT. It was found that it is essential to increase e and decrease ks and km for reducing the TC of porous geopolymers. Under the guidance of above calculations, we successfully designed and obtained some porous geopolymers with TC as low as 0.040 W m-1 K-1. This paper offers not only several porous geopolymers with low TC, but also an idea to design novel thermal insulation materials.

A set of Eu3+, Dy3+ and Tb3+ doped novel scheelite-type LiCaGd(WO4)3 (LCGW)-based phosphors was prepared via a conventional solid-state reaction method. The X-ray diffraction (XRD), transmission electron microscopy (TEM) analysis, characteristics of luminescence, PL thermostability, decay lifetimes, as well as CIE coordination were investigated to characterize the as-prepared samples in detail. The XRD analysis indicated that the Eu3+, Dy3+ and Tb3+ ions were incorporated into the LCGW host lattice. Under the ultraviolet radiation, the characteristic emission lines of Eu3+ (5D0–7F2), Dy3+ (4F9/2–6H13/2) and Tb3+ (5D4–7F5) ions were observed. The Eu3+ and Tb3+ single-doped LCGW fluorescent powders showed bright red and green emissions, respectively, without concentration quenching. As well as the Dy3+ doped LCGW phosphors radiate a strong yellow light at optimal Dy3+ concentration 0.08 mol. The efficient energy transfer phenomenon was observed for the Eu3+/Dy3+ and Tb3+/Dy3+ ions. The emission color of the LCGW:xTb3+/0.08Dy3+ samples was tuned from yellow (0.4074, 0.4727) to green (0.3604, 0.5521) via adjusting the Tb3+ concentration. The emission color of LCGW:yEu3+/0.08Dy3+ can be tuned from yellow (0.491, 0.3856) to red (0.5694, 0.3512) by variation of the Eu3+/Dy3+ ratio. Additionally, the thermal stability of the luminescence in the LCGW phosphors doped by Eu3+, Tb3+, Dy3+ ions was studied. The results verified that the LCGW:Ln3+ (Ln = Tb, Eu, Dy) phosphors are promising for applications in white LEDs.

Tb 3+ -Sm 3+ co-doped Sr 9 Gd(PO 4 ) 5 (SiO 4 )F 2 (SGPSF) phosphors were prepared through a solid-state reaction, and their luminescence properties as well as energy transfer mechanism have been investigated in detail. The SGPSF:Tb 3+ , Sm 3+ phosphors system could be efficiently excited at wavelengths ranging from 200 to 500 nm, which is well matched with the spectra of near ultraviolet chips. The emission of SGPSF:Tb 3+ , Sm 3+ phosphor covers the entire visible region with sharp peaks in the blue, green, and red regions. The emission color of SGPSF:Tb 3+ , Sm 3+ could be adjusted from green (0.275, 0.378) to red (0.519, 0.295) by controlling the doping content of Sm 3+ /Tb 3+ .

In this paper, a series of novel luminescent Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors with apatite structure were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the PL thermal stability were investigated. Sr 9.92 (SiO 4 ) 3 (SO 4 ) 3 O:0.08Eu 2+ phosphor exhibits better thermal quenching resistance, retaining the luminance of 66.55% at 150 °C compared with that at 25 °C. The quenching concentration of Eu 2+ in Sr 10 (SiO 4 ) 3 (SO 4 ) 3 O was about 0.08 (mol) with the dipole–quadrupole interaction. The Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors exhibited a broad-band green emission at 538 nm upon excitation at 396 nm. The results indicate that Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs.

In this paper, a series of novel luminescent Sr 1− x Al 12 O 19 : x Eu 2+ phosphors were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the decay curves were investigated. The quenching concentration of Eu 2+ in SrAl 12 O 19 was about 0.15 (mol). Upon excitation at 378 nm, the composition-optimized Sr 0.85 Al 12 O 19 :0.15Eu 2+ exhibited strong broad-band green emission at 530 nm with the CIE chromaticity (0.2917, 0.5736). The results indicate that Sr 1− x Al 12 O 19 : x Eu 2+ phosphors have potential applications as green-emitting phosphors for UV-pumped white-light LEDs.

Ba 3 Sc(PO 4 ) 3 :Eu 2+ ,Tb 3+ (BSP:Eu 2+ ,Tb 3+ ) phosphors were successfully prepared via conventional high-temperature solid-state reaction, their luminescence properties as well as energy transfer mechanism have been investigated in detail. The energy transfer mechanism was proposed to be the dipole–quadrupole mechanism, and the energy transfer efficiency was also estimated. BSP:Eu 2+ ,Tb 3+ phosphors showed a broad emitting band centered at 518 nm and several sharp emission peaks, which were assigned to the 5 d →4 f allowed transitions of Eu 2+ ions and characteristic optical 5 D 4 – 7 F J ( J =6, 5, 4, and 3) transitions of Tb 3+ ions, respectively. The emission color of BSP:Eu 2+ , y Tb 3+ exhibited a controlled luminescence evolution in the green area owing to the Eu 2+ –Tb 3+ energy transfer process.

A novel blue-emitting phosphor Sr8La2(PO4)6O2:Eu2+ was synthesized via the conventional high-temperature solid-state method and its photoluminescence (PL) properties were investigated for application in white light-emitting diodes. The phosphor exhibited strong broad absorption band in the near ultraviolet (n-UV) range, and generated bright blue emission centered at 442 nm upon 365 nm excitation light. The critical Eu2+ quenching concentration (QC) mechanism was verified to be the dipole–dipole interaction. The fluorescence decay curves, temperature dependence photoluminescence and CIE value of Sr8La2(PO4)6O2:Eu2+ phosphors were discussed. The above results indicated that Sr8La2(PO4)6O2:Eu2+ phosphor is a good candidate as a blue component for potential application in UV-excited w-LEDs.