Preparation and Luminescent Properties of BAM Blue Phosphor for PDP and CCFL

The Ba x-0.05MgAl 10O 16+x∶Eu 2+ 0.05 (0.88≤x ≤1.02) phosphors with different Ba 2+ content and the Ba 0.85MgAl 10O 16.94∶Eu 2+ 0.09 phosphors with different fluxes (BaF 2, MgF 2, AlF 3, BaCl 2, MgCl 2, AlCl 3, H 3BO 3) were prepared by high temperature solid-state reaction method and their luminescence characteristics were studied under 254 nm excitation and vacuum ultraviolet (VUV) excitation. With the increase of the Ba 2+ content, there is an increase in the emission intensity, and when x=0.94, it reaches a maximum. Then, as the Ba 2+ content increases, the emission intensity slowly falls. The fluorides have better flux-effects than chlorides and H 3BO 3. The possible mechanism in the process of particle growth was discussed when fluorides were used as fluxes. The effect of the activator concentration on this system was also investigated. The quenching concentration is 0.13 mol in per mole host.

Luminescence properties of Sr2MgB2O6：Tb3＋,Li＋ green-emitting phosphor

A novel green phosphor,Sr2MgB2O6：Tb3＋,Li＋ for white light-emitting diodes was prepared by solid-state reactions,and its structure and luminescence properties were investigated.The excitation and emission spectra indicated that this as-prepared phosphor could be effectively excited by ultraviolet 368 nm,and exhibited bright green emission centered at 545 nm corresponding to the^5D_4→~7F_5 transition.9 mol.%of Tb^（3＋） was shown to be optimal.Good green emissions with the CIE chromaticity coordinates（0.262,0.583） could be achieved.Furthermore,the integrated emission intensity of Sr_2MgB_2O_6：0.09Tb^（3＋）,0.09Li~＋ phosphor decreased continuously to 72.1%at 300 ℃ with increasing temperature,and the activation energy of thermal quenching（E_a） was calculated to be0.175 eV,moreover,the quantum yield excited by 368 nm was measured as 11.1%.A green emission LED was made by coating Sr_2MgB_2O_6：0.09Tb^（3＋）,0.09Li~＋ phosphor on a NUV（365-370 nm） chip.Our results showed that Sr_2MgB_2O_6：Tb^（3＋）,Li~＋ is a kind of potential green-emitting phosphor and features good thermal stability.

Two-color spectroscopy of UV excited ssDNA complex with a single-wall nanotube photoluminescence probe： Fast relaxation by nucleobase autoionization mechanism

DNA autoionization is a fundamental process wherein ultraviolet （UV）- photoexcited nucleobases dissipate energy by charge transfer to the environment without undergoing chemical damage. Here, single-wall carbon nanotubes （SWNT） are explored as a photoluminescent reporter for the study of the mechanism and rates of DNA autoionization. Two-color photoluminescence spectroscopy allows separate photoexcitation of the DNA and the SWNTs in the UV and visible range, respectively. A strong SWNT photoluminescence quenching is observed when the UV pump is resonant with the DNA absorption, consistent with charge transfer from the excited states of the DNA to the SWNT. Semiempirical calculations of the DNA-SWNT electronic structure, combined with a Green＇s function theory for charge transfer, show a 20 fs autoionization rate, dominated by hole transfer. Rate-equation analysis of the spectroscopy data confirms that the quenching rate is limited by thermalization of the free charge carriers transferred to the nanotube reservoir. This approach has great potential for monitoring DNA excitation, autoionization, and chemical damage, both in vivo and in vitro.

Ce^(3+)ion-doped α-NaYF_4 single crystal for UV laser

A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the molar ratio of30∶18∶48∶4, where the KF is shown to be an effective assistant flux. The x ray diffraction, absorption spectra,excitation spectra, and emission spectra of the Ce^（3＋）t-doped α-Na YF_4 single crystal are measured to investigate the phase and optical properties of the single crystals. The absorption spectrum of the Ce^（3＋）t：α-Na YF_4 shows a strong band that peaks at the wavelength of 300 nm. The emission spectrum of the Ce^（3＋）t：α-Na YF_4 emits an intense ultraviolet（UV） band at the wavelength of 332 nm under the excitation of 300 nm light. Two separated luminous bands of 330 and 350 nm, which correspond to the transitions 5d → 2F25∕2and 5d → F7∕2, can be obtained by Gauss fitting. The strong emission intensity at the UV band and the excellent optical transmission in the range of UV wavelengths indicate that Ce^（3＋）t：α-Na YF_4 single crystals can be considered as a promising material for UV lasers.

Improved luminescent properties of SrZn_2(PO_4)_2:Sm^(3+) doped with Li^+, Na^+ and K^+ ions

SrZn2(PO4)2:Sm3+ phosphor was synthesized by a high temperature solid-state reaction in atmosphere. SrZn2(PO4)2:Sm3+ phosphor is efficiently excited by ultraviolet(UV) and blue light, and the emission peaks are assigned to the transitions of 4G5/2-6H5/2(563 nm), 4G5/2-6H7/2(597 nm and 605 nm) and 4G5/2-6H9/2(644 nm and 653 nm). The emission intensities of SrZn2(PO4)2:Sm3+ are influenced by Sm3+ concentration, and the concentration quenching effect of SrZn2(PO4)2:Sm3+ is also observed. When doping A+(A=Li, Na and K) ions, the emission intensity of SrZn2(PO4)2:Sm3+ can be obviously enhanced. The Commission Internationale de l'Eclairage(CIE) color coordinates of SrZn2(PO4)2:Sm3+ locate in the orange-red region. The results indicate that the phosphor has a potential application in white light emitting diodes(LEDs).

Growth and optical properties of Dy^(3+)/Eu^(3+) co-doped NaYF_4 single crystals with cubic lattice for white LED application

Dy3+/Eu3+ co-doped cubic lattice Na YF4 single crystal with high quality in the size of ~Φ1.0 cm×10.0 cm was grown by an improved Bridgman method using potassium fluoride(KF) as assistant flux. X-ray diffraction(XRD), absorption spectra, excitation spectra and emission spectra are measured to investigate the phase and luminescent properties of the crystal. The effects of excitation wavelength and concentrations of Dy3+ and Eu3+ ions on the luminescent characteristics are analyzed. The Na YF4 single crystal with the doping molar concentrations of 1.205% Dy3+ and 0.366% Eu3+ exhibits an excellent white light emission with chromaticity coordinates of x=0.321, y=0.332. It indicates that the Dy3+/Eu3+ co-doped cubic lattice Na YF4 single crystal can be a potential luminescent material for the ultraviolet(UV) light excited white light emitting diode(w-LED).

Luminescence and energy transfer of Ce^(3+)-Eu^(2+) in Ca_9Al(PO_4)_7

A series of Ce^(3+),Eu^(2+) and Ce^(3+)-Eu^(2+) doped Ca_9Al(PO_4)_7 phosphors are synthesized by a high temperature solid-state method.Under 291 nm excitation,Ca_9Al(PO_4)_7:Ce^(3+) has one emission band at 356 nm,which is attributed to4f°5d^1→4f^1 transition of Ce^(3+).Under 305 nm excitation,Ca_9Al(PO_4)_7:Eu^(2+) presents one emission band at 445 nm,which is assigned to 4f^65d^1→4f^7 transition of Eu^(2+).Energy transfer from Ce^(3+) to Eu^(2+) in Ca_9Al(PO_4)_7 is validated and proved to be a resonant type via a quadrupole-quadrupole interaction.Critical distance(R_c) of Ce^(3+) to Eu^(2+) in Ca_9Al(PO_4)_7 is calculated to be 1.264 nm.Moreover,the emission intensity of Ca_9Al(PO_4)_7:Ce^(3+),Eu^(2+) can be tuned by properly adjusting the relative doping composition of Ce^(3+)/Eu^(2+).