Guo Qing-Lin

Luminescence characteristics of Eu 2+ activated Ca 2 SiO 4 Sr 2 SiO 4 and Ba 2 SiO 4 phosphorsfor white LEDs

This paper investigates the luminescence characteristics of Eu2+ activated Ca2SiO4, Sr2SiO4 and Ba2SiO4 phosphors. Two emission bands are assigned to the f–d transitions of Eu2+ ions doped into two different cation sites in host lattices, and show different emission colour variation caused by substituting M2+ cations for smaller cations. This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence. These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes (LEDs) based on ultraviolet chip/phosphor technology.

Luminescent Characteristics of LiSrBO3:Eu3+ Phosphor for White Light Emitting Diode

LiSrBO3:Eu3+ phosphor is synthesized by a high solid-state reaction method, and its luminescent characteristics are investigated. The emission and excitation spectra of LiSrBO3:Eu3+ phosphors exhibit that the phosphors can be effectively excited by near ultraviolet (401 nm) and blue (471 nm) light, and emit 615 nm red light. The effect of Eu3+ concentration on the emission spectrum of LiSrBO3:Eu3+ phosphor is studied; the results show that the emission intensity increases with increasing Eu3+ concentration, and then decreases because of concentration quenching. It reaches the maximum at 3 mol%, and the concentration self-quenching mechanism is the dipoledipole interaction according to the Dexter theory. Under the conditions of charge compensation Li+, Na+ or K+ incorporated in LiSrBO3, the luminescent intensities of LiSrBO3:Eu3+ phosphor are enhanced.

Energy Transfer from Ce3+ to Eu2+ in LiSrBO3 and Its Potential Application in UV-LED-Based White LEDs

Ce3+/Eu2+ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3:Ce3+,Eu2+ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-type energy transfer from Ce3+ ion to Eu2+ ion and tuning the relative proportion of Ce3+/Eu2+ properly. Energy transfer mechanism in LiSrBO3:Ce3+, Eu2+ phosphor is dominated by the dipole-dipole interaction, and the critical distance of the energy transfer is estimated to be about 2 nm by both spectral overlap and concentration quenching methods. Under UV radiation, white light is generated by coupling 436 and 565 nm emission bands attributed to Ce3+ and Eu2+ radiations, respectively.

Preparation and luminescence characteristics of Eu2+ activated silicate phosphor

This paper synthesizes the Sr2SiO4 : Eu2+ phosphor by high temperature solid-state reaction. The emission spectrum of Sr2SiO4 : Eu2+ shows two bands centred at 480 and 547 nm, which agree well with the calculation values of emission spectrum, and the location of yellow emission of Sr2SiO4 : Eu2+ is influenced by the Eu2+ concentration. The excitation spectrum for 547nm emission has two bands at 363 and 402 nm. The emission spectrum of white light emitting diodes (w-LEDs) based on Sr2SiO4 :Eu2+ phosphor + InGaN LED was investigated.

Preparation and Luminescence Characteristics of Ca3Y2(BO3)4:Eu3+ Phosphor

Ca3Y2(BO3)4:Eu3+ phosphor is synthesized by high temperature solid-state reaction method, and the luminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole 5D0–7F2 transition of Eu3+ under 365 nm excitation, the reason is that Eu3+ substituting for Y3+ occupies the non-centrosymmetric position in the crystal structure of Ca3Y2(BO3)4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet (UV) (254 nm, 365 nm and 400 nm) and blue (470 nm) light. The effect of Eu3+ concentration on the emission intensity of Ca3Y2(BO3)4:Eu3+ phosphor is measured, the result shows that the emission intensities increase with increasing Eu3+ concentration, then decrease. The CIE colour coordinates of Ca3Y2(BO3)4:Eu3+ phosphor is (0.639, 0.357) at 15 mol% Eu3+.

Luminescence and Site Occupancy of Eu2+ in Ba2 Ca(BO3)2

A green phosphor Ba2Ca(BO3)2:Eu2+ was synthesized by a high temperature solid-state reaction method under a reductive atmosphere. The luminescence and site occupancy of Eu2+ in Ba2Ca(BO3)2 are investigated. Ba2Ca(BO3)2:Eu2+ shows one green band (537 nm) under 400 nm near ultraviolet excitation which is suitable for UV LED. Ca2+ and Ba2+ ions in Ba2Ca(BO3)2 are replaced by Eu2+ ions, the Ba2Ca(BO3)2:Eu2+ shows a dissymmetrical emission band. The influence of Eu2+ doping concentrations on the emission intensity of Ba2Ca(BO3)2:Eu2+ is studied. It is found that the emission intensity is influenced by the Eu2+ concentration and reaches the maximum value at 2% Eu2+. According to the Dexter theory, the concentration quenching mechanisms of Eu2+ in Ba2Ca(BO3)2 are the d-dinteraction.

Improving luminescent property of SrIn2O4:Eu3+ by co-doped A+ (A = Li, Na, K) or Sm3+

A series of SrIn2O4:Eu3+ phosphors are synthesized by a high temperature solid-state method, and their luminescent properties are investigated. They can be excited by 395-nm radiation, and produce red emission (619 nm); however, they have a low absorption of near-ultraviolet light with the wavelength of 400 nm?405 nm. When co-doped with A+ (A = Li, Na, K), the emission intensity of SrIn2O4:Eu3+ is significantly enhanced, but its emission and excitation spectral profile is unchanged. With co-doping Sm3+, not only is the emission intensity of SrIn2O4:Eu3+ enhanced, but also the absorption is broadened and strengthened in the range of 400 nm?405 nm. The effect of Sm3+-doped content on the emission intensity of SrIn2O4:Eu3+, Sm3+ is investigated, and the optimal Sm3+ content is 0.02 mol.

Solitons with Periodic Behavior in an SBN:75 Photorefractive Crystal

We study the formation of spatial solitons in an SBN:75 photorefractive crystal by a 532 nm continuous-wave laser beam. The output beam from the crystal cannot be compressed proportionally to the voltage of the applied electric field. Quasi-steady-state spatial solitons are formed instantaneously at a voltage of 900 V. Interestingly, the quasi-steady-state solitons exhibit a periodic behavior consisting of formation/broken/reformation cycles. If we increase the input intensity of the soliton beam but keep the same signal-to-background intensity ratio, the solitons stay for a longer time in the quasi-steady state and a longer period of soliton formation/broken/reformation cycle is also observed.

Spectral feature with sub-natural linewidth due to quantum interference in a four-level system

This paper studies the narrow spectral feature appearing in a four-level system coupled by two strong coherent fields and probed by a weak laser field. The linewidth is examined as a function of the Rabi frequencies of coupling fields, and the result is explained by using the dressed-state formalism.

Study of ψ(4415) in the QPC model

Some authors consider the ψ(4415) to be the 4S or 5S excited state of a c pair. Starting from this assumption, we study the decays of the ψ(4415) to D, D**, DSS, DS*S*, and get the corresponding branching ratios in terms of the Quark-Pair-Creation (QPC) model. Compared with the experimental data, we find that the results of 4S state agree much better than those of the 5S state. Therefore, it is more reasonable to assume the ψ(4415) to be a 4S state.