Shucai Gan

Preparation and luminescent properties of CaAl2O4:Eu3+,R+ (R=Li, Na, K) phosphors

CaAl2O4:Eu3+, R+(R=Li+ Na+, K+) red phosphors were synthesized by solid state reaction method. X-ray diffraction (XRD) and photoluminescence (PL) were employed to characterize their structural and luminescent properties. It was found that the optimal sintering temperature and sintering time were 1200 degrees C and 4 h, respectively. The optimal concentration of doped Eu3+ was 3 mol.%. Furthermore, under ultraviolet excitation with a wavelength of 254 nm, these samples showed red luminescence which were probably attributed to the transitions from D-5(0) excited state to F-7(J) (J=0-4) ground states of Eu3+ ions. The feature and the high intensity of hypersensitive transition from D-5(0)-> F-7(2) indicated that Eu3+ preferred to occupy a low symmetry site. The incorporation of alkali metal ions greatly enhanced the luminescence intensity probably due to the influence of charge compensation of alkali metal ions.

Synthesis and luminescence properties of a novel red-emitting phosphor SrCaSiO4: Eu3+ for ultraviolet white light-emitting diodes

Abstract A novel red phosphor based on Eu 3+ -activated SrCaSiO 4 was successfully synthesized by conventional solid state reaction method and the photoluminescence properties were investigated. X-ray diffraction (XRD) patterns indicated that SrCaSiO 4 : Eu 3+ phosphors belong to orthorhombic crystal system (space group= Pmnb ). The photoluminescence (PL) excitation spectrum showed broad-band absorption and the strongest excitation peak at 397 nm contributed to the 7 F 0 → 5 L 6 transition which matched well with the emission of a UV chip. The PL emission spectrum with the peaks at 577, 586, 592, 612, 650 and 685 nm, were probably attributed to the transitions from 5 D 0 to 7 F J ( J =0, 1, 2, 3, 4) of Eu 3+ ions. The quenching concentration of Eu 3+ was 10 mol.%, and the critical distance ( R c ) was about 1.2 nm. The fluorescence lifetime of Eu 3+ ions was found to be 3.2 ms. The results indicated that the SrCaSiO 4 : Eu 3+ might become an important red phosphor candidate for white-light-emitting diodes with near-UV LED chips.

Photoluminescence properties of Tb3+ and Ce3+ co-doped Sr2MgSi2O7 phosphors for solid-state lighting

Abstract Sr 2 MgSi 2 O 7 :Tb 3+ ,Ce 3+ phosphors were synthesized by solid-state reaction and placed in a muffle furnace in a reducing atmosphere at 1300 °C for 3 h. Photoluminescence properties and energy transfer were investigated. The Ce 3+ /Tb 3+ energy transfer was thoroughly investigated by their emission/excitation spectra and photoluminescence lifetime, there was shortened lifetime of Ce 3+ (from 51.31 to 50.06 ns) which could support evidence of energy transfer from Ce 3+ to Tb 3+ in the host. The varied emitted color of Sr 1.97– y MgSi 2 O 7 :0.03Tb 3+ , y Ce 3+ phosphors could be achieved by altering the concentration of Ce 3+ , the chromaticity coordinates ( x, y ) varied from (0.225, 0.376) to (0.172, 0.231). In Sr 1.96 MgSi 2 O 7 :0.03Tb 3+ ,0.01 Ce 3+ phosphors, the results indicated that Sr 2 MgSi 2 O 7 :Tb 3+ ,Ce 3+ might be useful as tunable phosphors for ultraviolet white-light-emitting diodes.

Synthesis and luminescence properties of a novel phosphor Ca2−x/2Si1−xPxO4:Eu2+ for near UV-excited white-light-emitting diodes

Abstract A novel green-emitting phosphor, Eu 2+ -doped Ca 2− x /2 Si 1− x P x O 4 (0.25≤ x ≤0.30), was prepared through a conventional solid- state reaction. X-ray diffraction (XRD), photoluminescence (PL) and decay studies were employed to characterize the sample, which was assigned to P 63 mc space group in the hexagonal system. The effect of P-doping on the α-Ca 2 SiO 4 was studied and P 2 O 5 broken down by the raw material of (NH 4 ) 2 HPO 4 played an important role in stabilizing α-Ca 2 SiO 4 which can only be stable at high temperature. The XRD patterns of the Ca 2− x /2 Si 1− x P x O 4 host were found pure and optimized when the mole fraction of P 2 O 5 was 14.5%. The diffuse reflectance spectra of the Ca 1.855 Si 0.71 P 0.29 O 4 and Ca 1.845 Si 0.71 P 0.29 O 4 :0.01Eu 2+ covered the spectral region of 230–400 nm, implying that the phosphor was suitable for UV or near-UV LED excitation. The phosphor could be effectively excited in the near UV region with the maximum at 372 nm. The emission spectrum of the Ca 1.845 Si 0.71 P 0.29 O 4 :0.01Eu 2+ phosphor showed an asymmetrical single intensive band centered at 513 nm, which corresponded to the 4f 6 5d 1 →4f 7 transition of Eu 2+ . Eu 2+ ions might occupy two types of Ca 2+ sites in the Ca 1.855 Si 0.71 P 0.29 O 4 lattice and form two corresponding emission centers, which led to the asymmetrical emission of Eu 2+ in Ca 1.855 Si 0.71 P 0.29 O 4 . The effects of Eu 2+ -doped concentration in Ca 1.855− x Si 0.71 P 0.29 O 4 : x Eu 2+ on the PL were also discussed, the optimum doping concentration of Eu 2+ was 1 mol.% and the critical distance of the energy transfer was also calculated by the concentration-quenching method. The non-radiative energy transfer between Eu 2+ seemed to be caused by the multipole-multipole interaction. The fluorescence lifetime of Eu 2+ was found to be 0.55711 μs. The results suggested that these phosphors might be promising candidates used for near UV light excited white LEDs.

Synthesis and Luminescent Characteristics of Ce3+-Activated Borosilicate Blue-Emitting Phosphors for LEDs

The phosphors Sr3B2SiO8:Ce3+ have been successfully synthesized via solid-state reaction process. Emission/excitation spectra and photoluminescence decay behaviors were investigated in detail. Under the excitation of 340u2009nm, the emission spectrum presented an asymmetry emission band extended from 350 to 600u2009nm, which with the main peak at 425u2009nm can be fitted in two peaks (23940u2009cm−1 and 21934u2009cm−1). The chromaticity coordinates of : Ce3+ are fixed in the blue region; when the intensity of Ce3+ reached the maximum, the chromaticity coordinate is (0.154, 0.088) which is more close to the standard CIE of blue light (0.140, 0.080). The results showed the kind of phosphor may have potential applications in the fields of UV-excited white LEDs.