The concentration quenching and crystallographic sites of Eu^(2+) in Ca_2BO_3Cl

A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.

Enhancing the water-resistance stability of CaS:Eu^(2+),Sm^(2+) phosphor with SiO_2-PMMA composite coating

This work was aimed at improving the water-resistance stability of CaS：Eu2＋,Sm2＋ phosphor. An organic-inorganic com- posite coating method was adopted in order to obtain ideal phosphor. The phosphor was coated with SiO2 via sol-gel technique and it was also covered by polymethyl methacrylate （PMMA） via dissolution-cohesion technique. Powder X-ray diffraction （XRD） patterns, fluorescence spectroscopy and transmission electron microscopy （TEM） were employed to characterize the phase structures, emission spectrum and surface morphologies, respectively. In addition, the water-resistance stability of the phosphor was tested by soaking the phosphor into deionized water. The results showed that the phase structures remained the same as the uncoated phosphor and the po- sition of the fluorescence peak did not shift after surface treatment. Results showed that the water-resistance stability of the phosphor was improved to some degree. Moreover, the photoluminescence （PL） intensity of the coated phosphors reduced less than 10% of the original phosphors. Though being soaked into deionized water for 50 h, the phosphor coated with 10 wt.%SiO2-10 wt.%PMMA retained 85.9% PL intensity compared to that of the uncoated phosphor. Therefore, it could be concluded that the 10 wt.%SiO2-10 wt.%PMMA composite coating effectively improved the phosphor water resistance and retained its good optical properties.

Luminescence properties of red phosphors Ca_(10)Li(PO_4)_7:Eu^(3+)

A series of red phosphors Ca10Li （PO4）7：Eu3＋ were synthesized by high temperature solid-state reaction method. Their luminescence properties were characterized by means of photoluminescence excitation and emission spectra,CIE chromaticity and quantum efficiency. Results indicated that the phosphors could be effectively excited by the near ultraviolet （NUV） light （393 nm）. The main emission peaks of the phosphor were ascribed to the transition 5D0–7F2 （613 and 617 nm） of Eu3＋ ion when samples were excited by 393 nm. The CIE chromaticity （x,y） of Ca9.9Li （PO4）7：0.10Eu3＋ was x=0.638,y=0.361 and the quantum efficiency of this phosphor was 75% excited by 393 nm. Therefore,this phosphor could be a promising red component for the applications in white LEDs.

Combustion synthesis and luminescence properties of Ca4Y6（SiO4）60：Eu3＋ red phosphor for white LEDs

Eu3＋ activated Ca4Yt（SiO4）60 phosphors were prepared by combustion synthesis method, and their morphologies and lu- minescent properties were investigated. Field scanning electron microscopy （FSEM） confirmed that the crystallite sizes of nanoparti- cles with narrow diameter ranging from 30 to 60 rim. The excitation spectra of CaaY6（SiO4）60：Etl3＋ showed that there existed two strong excitation bands at around 399 nm （TFo----~SL6） and 469 nm （TF0---＊SD2）, which were consistent with the output wavelengths of near-UV and blue LEDs, respectively. The emission spectra of Ca4Y6（SiO4）60：Eu3＋ were dominant by a red peak located at 614 nm due to the 5Do→7TF2 transition of Eu3＋. With the increase of Eu3＋concentration, the luminescence intensity of the red phosphor reached maximum and then decreased. The optimum concentration for Eug＋in Ca4Y6（SiO4）60 was 21 mol.%.

Synthesis and photoluminescence properties of novel red-emitting Ca_(14)Mg_2(SiO_4)_8:Eu^(3+)/Sm^(3+) phosphors

Novel red-emitting Eu3＋, Sm3＋ singly doped and co-doped Ca14Mg2（SiO4）8 phosphors were prepared by conventional solidstate reaction. Powder X-ray diffraction patterns were employed to confirm phase pttrity. Ca14Mg2（SiO4）8：Eu3＋ phosphors exhibited intense red emission under 394 nm excitation and Ca14Mg2（SiO4）8：Sm3＋ phosphors, excited at 405 nm, also showed strong red emitting at 602 nm. The concentration quenching mechanism of Cal4Mg2（SiOa）s：Eu3＋ was dipole-dipole interaction, while that of CalnMg2（SiOn）8：Sm3＋ was energy migration among nearest neighbor ions. The results indicated that Ca14Mg2（SiOn）8：Eu3＋ and Ca14Mg2（SiOn）s：Sm3＋ were promising red-emitting phosphors for WLEDs. Meanwhile, the effect of co-doping Sm3＋ ions on photoluminescence properties of CalaMg2（SiO4）s：Eu3＋ was studied and energy transfer from Sm3＋ to Eu3＋ was discovered in Eu3＋, Sm3＋ co-doped phosphors.

Effects of crystal field on photoluminescence properties of Ca_2Al_2SiO_7:Eu^(2+) phosphors

A series of single-phased Ca2Al2SiOT：EU2＋phosphors were synthesized by the solid-state reaction. Their structure and photoluminescence properties were investigated by the X-ray powder diffraction （XRD） and excitation and emission spectra in detail. The emission spectra of Ca2Al2SiO7：Eu2＋ phosphors consisted of blue and green band located at 419 and 542 nm, respectively. The relative intensities of the blue and green emission changed with Eu2＋ concentration and were sensitive to the excitation wavelength. The unique photoluminescence property originated from the 4f^7→4f65d transition of Eu2＋ at different energy levels, on which the effect of the crystal field strength was con- sidered to be tailed by adjusting the host composition.