Xinran Zhao

Photoluminescent properties of SrSi2O2N2 : Eu2+ phosphor: concentration related quenching and red shift behaviour

Highly efficient green phosphors SrSi2O2N2 : Eu2+, suitable for white light emitting diodes (LEDs), was synthesized by solid-state reaction and their photoluminescence properties were investigated. SrSi2O2N2 : Eu2+ phosphors can be effectively excited by ultraviolet (UV)–Vis light (300–460 nm) and yield green emission with a single, intense, broad band centred at around 540 nm. Concentration quenching occurs in the phosphors when the Eu2+ concentration exceeds 2 at%. The mechanism of concentration quenching is confirmed to be dipole–dipole interaction of Eu2+. With an increase in the Eu2+ concentration, the emission band of Eu2+ shifts to a longer wavelength due to the 5d-orbit hybridization of Eu2+ with the host crystal and the energy transfer between adjacent Eu2+ ions. All the results indicate that SrSi2O2N2 : Eu2+ is a promising green phosphor for UV or blue chip based white LEDs.

Photoluminescence properties of Eu2+-activated CaSi2O2N2: Redshift and concentration quenching

Highly efficient CaSi2O2N2:Eu2+ green phosphors were synthesized via solid-state reaction method. The produced phosphors are effectively excited with UV-vis light of wavelength between 300 and 460 nm and emit a single, intense, and broad emission band centered at 538 nm. The experimental results and their analysis suggest that the energy transfer mechanism should occur due to dipole-dipole interactions among Eu2+ ions, resulting in a shift in emission spectrum toward longer wavelengths with increasing Eu2+ concentration. The quenching concentration of Eu2+ (i.e., where the emission intensity maximizes) is approximately 2 at. %. Accordingly, the produced CaSi2O2N2:Eu2+ green phosphors are qualified for further consideration and experimentation for potential use in white light emitting diodes.

Li(2)SrSiO(4):Eu(2+) phosphor prepared by the Pechini method and its application in white light emitting diode

Eu 2+ -doped Li 2 SrSiO 4 phosphors were prepared by two different synthesis processes, the Pechini sol-gel route and solid-state reaction (SSR) method. Their morphology, crystal structure, and luminescence properties have been characterized. Li 2 SrSiO 4 :Eu 2+ phosphors show broad and intensive excitation in the range of 390–480 nm and emit yellow-orange light extending from 500 to 700 nm. The luminescence efficiency of Li 2 SrSiO 4 : Eu 2+ phosphors synthesized through the Pechini route is much better than that of phosphors prepared by solid-state reaction method. The application of phosphors from the Pechini route in white light emitting diodes (LEDs) has been investigated. The Commission Internationale de L’Eclairage (CIE) chromaticity coordinates and the correlated color temperature of these white LEDs have been calculated; they are comparable to corresponding values of commercial Y 3 Al 5 O 12 :Ce 3+ converted white LEDs.

Luminescence and Energy-Transfer Mechanism in SrSi2O2N2 : Ce3 + , Eu2 + Phosphors for White LEDs

A series of Ce 3+ and Eu 2+ co-doped SrSi 2 O 2 N 2 phosphors, whose features qualify them for consideration in white-light UV or blue light-emitting diodes (LEDs), was synthesized via a high temperature solid-state reaction under a reductive atmosphere. The dependence of luminescence properties of the produced powders on the concentration of an activator (Eu 2+ ) and a coactivator (Ce 3+ ) was investigated. The experimentally recorded luminescence spectra and the calculations of the efficiency of energy transfer from Ce 3+ to Eu 2+ and the critical distance between Ce 3+ and Eu 2+ suggest a resonance-type energy-transfer mechanism from Ce 3+ to Eu 2+ due to dipole-dipole interactions.

Observation of Fluorescence and Phosphorescence in Ca2MgSi2O7 : Eu2 + , Dy3 + Phosphors

This paper describes the experimental results of the fluorescence and phosphorescence observations in the Ca 2 MgSi 2 O 7 :Eu 2+ ,Dy 3+ phosphors. Discussions are made to elucidate the relationship between the photoluminescence of Eu 2+ and the crystal structure of the host, the luminescent quenching of the emission of Eu 2+ , and the role of Dy 3+ in the afterglow property. There exist two distinguishable Ca 2+ sites in the host, supported by two fluorescent emission bands located in the blue and green regions, respectively, originating from Eu 2+ doped into the host. The emission peak of Eu 2+ at about 474 nm quickly quenches as its concentration increases due to excitation energy transfer between the Eu 2+ ions doped into the two nonequivalent Ca 2+ sites. The answers to the question of why only one emission band was observed in some reports throughout the literature were supplied. Only the emission at 533 nm of Eu 2+ contributes to the long-lasting phosphorescence, whereas Dy 3+ ions do not act as the luminescent center. By investigating the decay time of the phosphorescence at 533 nm, preliminary conclusions were made that the co-doping of Dy 3+ obviously enhances the afterglow of Ca 2 MgSi 2 O 7 :Eu 2+ through electron trap-detrap and recombination processes by its electron trapping role.

Crystal Structure and Luminescent Properties of Eu2 + -Doped Li2BaSiO4 with a Polymorph for White LEDs

The crystal structure and photoluminescence of Li 2 BaSiO 4 :Eu 2+ phosphors were investigated. A preliminary conclusion was reached through X-ray diffraction, Fourier transform infrared absorption, photoluminescent excitation and emission investigations that a Li 2 BaSiO 4 polymorph was found. The Li 2 BaSiO 4 :Eu 2+ characterizes an intense blue emission with a peak at 465 nm and a broad excitation band in the UV/visible range. Warm white light with CIE coordinates (0.334, 0.347) and color temperature of about 5500 K is generated by mixing this blue phosphor with the Li 2 SrSiO 4 :Eu 2+ yellow phosphor. These results indicate that Li 2 BaSiO 4 :Eu 2+ with the polymorph of the host would be a promising blue phosphor candidate for UV-chip-based multiphosphor converted white light-emitting diodes (LEDs).