Luminescence Properties of Phosphate Phosphor: Barium Tungstate Doped with Dy

A series of barium-tungstate-based phosphors doped with different concentrations of Dy3+ were synthesized by solid-state reaction method. Photoluminescence properties and decay lifetime of Dy3+-doped BaWO4 samples were studied. The results indicated that luminescent properties of BaWO4:Dy3+ depended on the Dy3+ concentration, and the inner energy could transfer from to Dy3+. The quality of the light was checked by estimating CIE parameters, and the results showed that BaWO4:Dy3+ was a potential candidate as blue-green luminescent materials in white LED because of its excellent emission spectrum excited by UV light.

Cool white light and tunable multicolor emission from Tb^(3+)/Dy^(3+)co-activated glasses under different excitations for WLEDs

A set of co-doped(Tb^(3+)/Dy^(3+))lithium zinc borate(LZB)glasses were developed by melt quenching.The structural evaluation was performed for synthesized glassy matrices.The Dy^(3+)and Tb^(3+)individually doped glasses exhibit intense yellow and green luminescence bands at 575 nm(^(4)F_(9/2)→^(6)H_(13/2))and543 nm(^(5)D_(4)→^(7)F_(5)),respectively.The sensitization effect of Dy^(3+)on Tb^(3+)was analyzed by increasing the Tb^(3+)content with respect to the optimum Dy^(3+)content(0.5 mol%)in Dy^(3+)/Tb^(3+).The spectral overlay of Dy^(3+)luminescence and Tb^(3+)absorption profiles,Dy^(3+)/Tb^(3+)PL spectra under different excitations 352,362,376,and 385 nm,shortening decay lifetimes of Dy^(3+)in Dy^(3+)/Tb^(3+)co-activated glasses,energy transfer(ET)parameters,chromaticity coordinates and their corresponding correlated temperatures all help to explain ET from Dy^(3+)to Tb^(3+).At 385 nm of Dy^(3+)excitation,the optimized co-activated(0.5Dy^(3+)+1.0Tb^(3+)):LZB glass displays cool white light emission.The non-radiative ET from Dy^(3+)to Tb^(3+)is dominated by electric dipole-dipole interaction and its ET efficiency was calculated to be 63%.At the same time,reverse ET from Tb^(3+)to Dy^(3+)was also analyzed.The shift in color coordinates from dominant yellow to greenish-yellow,green and white light emission suggests that Dy^(3+)/Tb^(3+)coactivated LZB glasses can be a potential candidate for UV converted multicolor and white light emitting devices.

Structural and optical properties of Dy^(3+):YAlO3 phosphors for yellow light-emitting diode applications

The spectroscopic properties of a series of Dy^(3+)single-doped and Dy^(3+)/Nd^(3+),Dy^(3+)/Tb^(3+),and Dy^(3+)/Tm^(3+)co-doped YAlO_(3)(yttrium aluminum perovskite,YAP)phosphors were investigated and compared through the measurements of optical absorption,emission spectra,and fluorescence decay curves.For the Dy^(3+)ion single-doped samples,the intensity of each absorption band increases with an increment in Dy^(3+)ion doping concentration,and the identified strong absorption peak at 447 nm indicates that Dy^(3+):YAP phosphors are suitable to be pumped by a blue laser diode(LD).For all co-doped samples,absorption peaks of Dy^(3+)ion along with some of the absorption bands of Nd^(3+),Tb^(3+),and Tm^(3+)ions are observed.Under 351 and 447 nm excitation,a prominent emission peak at 572 nm was obtained in all the samples,corresponding to Dy^(3+):^(4)F_(9/2)→^(6)H_(13/2)transition.Here,2 at%Dy^(3+):YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping.Among the three kinds of Dy^(3+)co-doped phosphors,Dy^(3+)/Tb^(3+):YAP phosphor possesses the dominant yellow emission.The fluorescence decay curves show exponential behaviour and are fitted well.The Commission International de L’Eclairage(CIE)chromaticity coordinates were calculated following the respective emission spectra,and it is found that all the coordinates locate in the yellow region.The energy transfer(ET)processes were investigated and the concentration quenching mechanism was discussed.The obtained results suggest that Dy^(3+)-activated YAP phosphors are good candidates for yellow LED applications.

Novel Properties of Photochromic Spirooxazine Nanoparticles

The nanoparticles of a spirooxazine （SPO） and its photomerocyanine （PMC） were prepared through the reprecipitation method. Two distinct features were observed. One is that the decaying lifetime for PMC nanoparticles was 600 times of that for the dispersed molecules, and the other is that the fluorescence intensity of SPO nanoparticles was enhanced by 240 times of that of the dispersed monomer.

Optical Studies of Fluorescent Mesoporous Silica Nanoparticles

Spherically shaped mesoporous silica nanoparticles （MSNs） having honeycomb like porous structure were synthesized by sol-gel method. Transmission electron microscopy （TEM）, surface area measurement and X-ray diffractometry were used, revealing the hexagonal shaped pores in MSNs. MSNs with surface area of 1104.47 m^2/g and large porosity of 2.8 nm in pore diameter and 0.87 cm^3/g in pore volume were synthesized. TEM images showed spherical nanoparticles of - 200-300 nm having honeycomb like pores. Stilbene 420 laser dye was incorporated in MSNs and photoluminescence spectra of stilbene 420 in MSNs and in ethanol had been studied. Stilbene 420 laser dye showed high fluorescence intensity in the fluorescence spectra of MSNs than that of ethanol. The prolonged fluorescence lifetime decay of stilbene in MSNs and the increase in fluorescence intensity for stilbene 420 in MSNs would make these nanomaterials more useful for nanosensors and nanolasers application.

Luminescent properties of Tm^(3+)/ Ho^(3+) co-doped LiYF_4 crystals

Ho3+ with various concentrations and Tm3+ with molar concentration of 1.28% are co-doped in Li YF4(YLF) single crystals. The luminescent properties of the crystals are investigated through emission spectra, emission cross section and decay curves under the excitation of 808 nm. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission of Ho3+ around 2.05 μm are investigated. The emission intensity at 2.05 μm keeps increasing with the molar concentration of Ho3+ improved from 0.50% to 1.51% when the molar concentration of Tm3+ is kept at 1.28%. Moreover, for the co-doped crystals in which the molar concentrations of Tm3+ and Ho3+ are 1.28% and 1.51%, respectively, the maximum emission cross section reaches 0.760×10–20 cm2 and the maximum fluorescence lifetime is 21.98 ms. All the parameters suggest that these materials have more advantages in the future 2.0 μm laser applications.

Luminescence of Eu^2＋ and Eu^2＋-Mn^2＋ in sodium scandium diphosphate NaScP2O7 crystal

In this work, the photoluminescence（PL） of NaScP2O7：Eu^2＋ and NaScP2O7：Eu^2＋,Mn^2＋ was investigated. Phase purity was checked using X-ray powder diffractometry（XRD）. PL excitation and emission spectra were recorded to elucidate the PL properties of NaScP2O7：Eu^2＋ and NaScP2O7：Eu^2＋,Mn^2＋. Furthermore, fluorescence lifetime measurements were performed. PL and lifetime measurements were carried out from 10 to 525 K. Moreover, the Eu^2＋ site occupation was discussed. It turned out that the incorporated Eu^2＋ ions substituted for Na＋ site and occupied two different sites. Temperature dependent PL measurements indicated the emission intensity decreased with increasing temperature due to temperature quenching in NaScP2O7：Eu^2＋. Fluorescence lifetimes of Eu^2＋ in NaScP2O7：Eu^2＋ almost did not change with a decay constant τ=~0.53 μs in the temperature range of 10–280 K, and then shortened due to temperature quenching. The luminescent lifetime reached ~0.05 μs at T=525 K. Finally, it was found that energy transfer occurred from Eu^2＋ to Mn^2＋ in co-doped NaScP2O7：Eu^2＋,Mn^2＋.