[en] A series of novel luminescent phosphors Sr_1_0(PO_4)_6O:Eu"2"+ with apatite structure were synthesized via a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples, and the selected Sr_9_._9_7(PO_4)_6O:0.03Eu"2"+ phosphor exhibits strong thermal quenching resistance, retaining the luminance of 88.73% at 150 °C. The quenching concentration of Eu"2"+ in Sr_1_0(PO_4)_6O was about 0.03 attributing to the dipole–quadrupole interaction. The Sr_1_0(PO_4)_6O:Eu"2"+ phosphor exhibited a broad-band blue emission at 439 nm upon excitation at 346 nm. The results indicate that Sr_1_0(PO_4)_6O:Eu"2"+ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Graphical abstract: Sr_1_0(PO_4)_6O:Eu"2"+ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Highlights: • Sr_9_._9_7(PO_4)_6O:0.03Eu"2"+ phosphor exhibits strong thermal quenching resistance. • Two different Eu"2"+ emission centers exists in Sr_1_0(PO_4)_6O. • The activation energy was also estimated for the Eu"2"+ luminescence center

[en] In this paper, La_1.45Ce_0.05Ba_3.5(SiO₄)_1.5(PO4)_1.5F compound with apatite structure was synthesized via solid state reaction method. The phosphor exhibits two strong excitation bands at 279 nm and 345 nm in near ultraviolet light region. When excited at 345 nm, the emission peaks of the phosphor give a red-shift from 406 nm to 418 nm compared with that of 279 nm excitation. Besides, the site occupation of Ce³⁺ was proposed based on structure refinement, luminescence, fluorescence decay curves, as well as CIE diagram. All the results indicated that Ce³⁺ can occupy sites of La³⁺ with nine and seven coordination and a possible mechanism was proposed to explain the luminescence properties observed.

[en] A series of new luminescent emission-tunable phosphors La₆Ba₄(SiO₄)₆F₂:Ce³⁺,Tb³⁺ with apatite structure have been synthesized by a high temperature solid-state reaction. X-ray diffraction, photoluminescence (PL) emission and excitation spectra, lifetime, as well as the effect of Tb³⁺ concentration were employed to characterize the resulting samples. The PL spectrum of La₆Ba₄(SiO₄)₆F₂:Ce³⁺,Tb³⁺ phosphor contains both the asymmetric broad-band blue emission (Ce³⁺ ion) and the line-type green emission (Tb³⁺ ion). The increased Tb³⁺ concentration induced the emitting colors to shift from blue to green region by the naked eye. Meanwhile, the energy transfer between Ce³⁺ and Tb³⁺ is thoroughly investigated, and the energy-transfer efficiency from Ce³⁺ to Tb³⁺ ion is also calculated. The results indicated that these phosphors could be considered as double emission phosphors for n-UV excited white light-emitting diodes. -- Highlights: • Color-tunable blue–green La₆Ba₄(SiO₄)₆F₂:Ce³⁺,Tb³⁺ phosphors were prepared. • The phase structures of the La₆Ba₄(SiO₄)₆F₂ apatites compounds were analyzed. • Ce³⁺–Tb³⁺ energy transfer process and mechanism were discussed

[en] A series of new luminescent emission-tunable phosphors Sr_2La_8(SiO_4)_6O_2:Ce"3"+, Tb"3"+ with apatite structure have been synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence emission and excitation spectra, lifetime, as well as the effect of Tb"3"+ concentration are investigated to characterize the resulting samples. The critical distance was calculated to be 8.26 Å by using the concentration quenching method. The intense green emission was observed in the Sr_2La_8(SiO_4)_6O_2:Ce"3"+, Tb"3"+ phosphors on the basis of the efficient energy transfer from Ce"3"+ to Tb"3"+ with an efficiency of 68.55%. And a possible mechanism of the energy-transfer from Ce"3"+ to Tb"3"+ ion is also proposed. The results indicate that Sr_2La_8(SiO_4)_6O_2:Ce"3"+, Tb"3"+ phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes because of the broad excitation in the near-ultraviolet range and the efficient green emission light. - Graphical abstract: Crystal structure and luminescence properties of Sr_2La_8(SiO_4)_6O_2:Ce"3"+,Tb"3"+ phosphors have been discussed. - Highlights: • Ce"3"+ and Tb"3"+ ions entered both La sites in SLSO. • The energy transfer efficiency can reach at 68.55%. • The emitting color of SLSO phosphors shifted from the blue to green region

[en] A series of blue-emitting La_5.90−xBa_4+x(SiO₄)_6−x(PO₄)_xF₂:0.10Ce³⁺ (x= 0, 1, 2, and 3) phosphors with apatite structure were synthesized by a solid-state reaction. The crystal structure and the photoluminescence properties were investigated in detail. The crystallographic occupancy of Ce³⁺ in La_2.90Ce_0.10Ba₇(SiO₄)₃(PO₄)₃F₂ and La_5.90Ce_0.10Ba₄(SiO₄)₆F₂ were studied based on Rietveld refinements results and the crystal chemistry rules. La_5.90−xBa_4+x(SiO₄)_6−x(PO₄)_xF₂:0.10Ce³⁺ exhibited strong blue light emission in the range of 407–414 nm with high thermal stability upon excitation at 276 nm. Besides, the activation energy E of La_5.90Ce_0.10Ba₄(SiO₄)₆F₂ and La_2.90Ce_0.10Ba₇(SiO₄)₃(PO₄)₃F₂ phosphors were calculated to be 0.152 and 0.177 eV. These results suggest that La_5.90−xBa_4+x(SiO₄)_6−x(PO₄)_xF₂:0.10Ce³⁺ is a potential blue phosphor candidate for near-UV-pumped w-LEDs.

[en] Single-phase Ba_1_0_−_x_−_y(PO_4)_6O:xEu"2"+,yMn"2"+ samples with apatite structure have been synthesized via a solid-state reaction method. The phase structure, luminescence properties, lifetime, PL thermal stability, as well as fluorescence decay curves of the samples were investigated. Effective energy transfer occurs from Eu"2"+ to Mn"2"+ in Ba_1_0(PO_4)_6O and a possible mechanism of the energy-transfer from Eu"2"+ to Mn"2"+ is proposed. The critical distances R_c was calculated by concentration quenching and turned out to be about 0.817 nm (x_c=0.21). The CIE and thermally stable luminescence behaviors of Ba_9_._9_4(PO_4)_6O:0.06Eu"2"+ phosphor were also studied in detail. All the results indicate that Ba_1_0_−_x_−_y(PO_4)_6O:xEu"2"+, yMn"2"+ phosphors have potential applications as near UV-convertible phosphors for white light-emitting diodes. - Graphical abstract: Crystal structure and luminescence property of Ba_1_0_−_x_−_y(PO_4)_6O:xEu"2"+,yMn"2"+ have been discussed. - Highlights: • Ba_1_0_−_x_−_y(PO_4)_6O:xEu"2"+,yMn"2"+ was firstly reported. • Ba_9_._9_4(PO_4)_6O:0.06Eu"2"+ exhibits high thermal quenching resistance. • The energy transfer between Eu"2"+ and Mn"2"+ was investigated.

[en] The Ca₉La(PO₄)₅(SiO₄)Cl₂:Dy³⁺ (CLPSCl:Dy³⁺) powder phosphor with apatite structure has been successfully synthesized via high-temperature solid state method. Single phase in such phosphor was verified through X-ray diffraction (XRD) technique. The Dy ions concentration dependent luminescence properties including emission, excitation and lifetimes of Dy ions were characterized using photoluminescence (PL) spectroscopy. The results showed that CLPSCl:Dy³⁺ phosphor could efficiently assimilate the n-UV light and emit blue (~486 nm) and yellow light (~578 nm), originating from the f-f transitions of Dy³⁺. The critical Dy³⁺ quenching concentration (QC) was determined to be about 12 mol%. The concentration quenching mechanism was also determined to be dipole–dipole interaction.

[en] Tb³⁺–Sm³⁺ co-doped Ba₃NaLa(PO₄)₃F phosphors with apatite structure have been prepared by a high temperature solid-state reaction, and their luminescence properties have been investigated in detail. The energy transfer (ET) mechanism was verified as the dipole–quadrupole mechanism, and the ET efficiency as well as the critical distance is also estimated. As a result of fine-tuning of the emission composition of the Tb³⁺ and Sm³⁺ ions, tunable luminescence properties can be realized by combining the emission of Tb³⁺ and Sm³⁺ in a single host lattice under UV light excitation. The emission color of the obtained phosphors can be modulated from green to yellow by controlling the doping content of the Sm³⁺ ions with the fixed Tb³⁺ content. Additional, as the temperature increases from RT to 150 °C, the PL intensities of Ba₃NaLa_0.7(PO₄)₃F:0.10Tb³⁺,0.20Sm³⁺ decreased to 80.4% and 78.6% of the initial PL intensity, corresponding to the intensity of transition of Sm³⁺ and transition of Tb³⁺ in the Ba₃NaLa_0.7(PO₄)₃F:0.10Tb³⁺,0.20Sm³⁺ phosphor, respectively. These results indicate the series of Ba₃NaLa_1−x−y(PO₄)₃F:xTb³⁺,ySm³⁺ phosphors can be acted as a good candidate for the application in white light-emitting diodes. - Highlights: • Tb³⁺,Sm³⁺-codoped Ba₃NaLa(PO₄)₃F phosphors have been synthesized. • The emission color of the obtained phosphors can be modulated from green to red. • This phosphor has a good thermal stability.

[en] A new kind of multicolor phosphor Ba₂La₃(SiO₄)₃Cl:0.15Tb³⁺,xEu³⁺ (BLSOCl:0.15Tb³⁺,xEu³⁺) has been acquired through the traditional high temperature solid phase synthesis method. The structure information of the phosphor was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rietveld refinement. The optical properties of the phosphor have also been studied in detail, including photoluminescence spectra (PL), photoluminescence excitation spectra (PLE), fluorescence decay curves, energy transfer mechanism and thermal quenching spectra. The CIE values have also been studied. All the properties are good and can contribute to the promotion from the laboratory to practical application for the phosphor.

[en] Highlights: • The typical evolution patterns of PM_2.5 in each season of Beijing were depicted. • A novel method was developed to elucidate the driving species of PM_2.5 pollution. • Organic matters were the driving species in the winter and nitrate contributed more than sulfate during severe hazes. • Aqueous pathway was dominant in the winter while multiple pathways coexisted in the other seasons. • The variation of fine particle pH during pollution episodes was revealed. In recent years, air pollution has become a major concern in China, especially in the capital city of Beijing. Haze events occur in Beijing over all four seasons, exhibiting distinct characteristics. In this study, the typical evolution patterns of atmospheric particulate matter with a diameter of less than 2.5 μm (PM_2.5) in each season were illustrated by episode-based analysis. In addition, a novel method was developed to elucidate the driving species of pollution, which is the largest contributor to the incremental PM_2.5 (ΔPM_2.5), not PM_2.5. This method revealed a temporal variation of the driving species throughout the year: nitrate-driven spring, sulfate-driven summer, nitrate-driven early fall, and organic matters (OM)-driven late fall and winter. These results suggested that primary organic particles or volatile organic compounds emissions were dominant in the heating season due to residential heating, while NOx and SO₂ emissions dominated in the other seasons. Besides, nitrate formation seemed more significant than sulfate formation during severe pollution episodes. It was also found that the pollution formation mechanism in the winter showed some unique features in comparison with the other seasons: aqueous reactions were more important in the winter, while multiple pathways coexisted in the other seasons. Furthermore, this study confirmed that the PM_2.5 in Beijing was moderately acidic despite a fully neutralized system. In addition, the acidity variation during pollution episodes displayed different patterns between seasons and was driven by both the variation of aerosol water and chemical compositions. These results provide a new perspective to understand the characteristics and mechanisms of aerosol pollution in Beijing. However, more accurate measurements are necessary for effective air pollution control that depends on the seasonal variation of fine particle formation in Beijing and the surrounding areas.