M. Yin

Luminescence of nanometric scale Y2SiO5:Eu3+

Abstract We report what is to our best knowledge the first results of spectroscopic properties of X1-Y2SiO5:Eu3+. The sample under UV or dye laser excitation at room temperature exhibits a strong orange-red fluorescence. By using selective excitation at low temperature, dissimilar photoluminescence (PL) spectra from different sites were obtained. The fluorescence spectra, the excitation spectra of the fluorescence and the radiative lifetime were studied.

SITE SELECTIVELY EXCITED LUMINESCENCE AND ENERGY TRANSFER OF X1-Y2SIO5:EU AT NANOMETRIC SCALE

Two different types of structure called X1 and X2 are existing in Y2SiO5 at normal conditions. In X1 type, Y3+ ions occupy two sites where they are surrounded respectively by nine and seven oxygen ions, while in X2 structure, only six and seven oxygen ions are involved. Nanometric scale X1-Y2SiO5 crystals were prepared by sol-gel method with particle size around 50 nm. Site selective excitation at low temperature has shown four different luminescent centers. Two of them belong to Eu3+ embedded in X1-Y2SiO5, the other two are attributed to Y2O3:Eu phase and to a particular site on the surface. The occurrence of the latter site may be related to the nanometric size of the sample. A pronounced excitation energy transfer from site 2 to site 1 was also observed on excitation spectra. The energy transfer rate increases rapidly with increasing Eu3+ concentration and for x=0.7 in Y2−xSiO5:Eux, no fluorescence takes place in site 2 at 15 K. The lifetimes of the 5D0 levels of Eu3+ in the two sites were measured as ...

Spectroscopic properties of Eu3+ ions in X1-Y2SiO5 at nanometric scale

Abstract The influence of concentration and temperature on the luminescence properties of the Eu 3+ activated X 1 –Y 2 SiO 5 are investigated for the first time. For high Eu 3+ concentration, a cross relaxation process between Eu 3+ ions results in the quenching of 5 D 1 emission. At low temperature and high concentration, the excitation transfer between Eu 3+ ions in the two sites enables the fluorescence of site 2 disappears entirely. In addition, the samples showed some interesting phenomenon related to size effect.

Spectroscopic studies of Er3+ centers in KYF4

Abstract A systematic spectroscopic study of KYF 4 :Er 3+ (5%) in the visible region is reported. By using site selective excitation (emission) at 12 K, emission (excitation) spectra originating in Er 3+ in two different crystallographic sites are distinguished. Transient measurement shows that the 4 S 3/2 Er 3+ level in the two sites decays exponentially with lifetimes of 0.53 ms for site A and 0.82 ms for site B, respectively. The phenomenon of green up-conversion emission under red excitation to 4 F 9/2 level is explained by 4 F 9/2 , 4 F 9/2 → 4 F 7/2 , 4 I 11/2 up-conversion excitation.

Ab initio calculation of electronic structures and 4f-5d transitions of some rare earth ions doped in crystal YPO4

Abstract The ab initio self-consistent DV-X α (discrete variational X α ) method was used in its relativistic and spin-polarized model to investigate the ground-state electronic structures of the crystal YPO 4 and YPO 4 :RE 3+ (RE=Ce, Pr and Sm) and f-d transition energies of the lattice. The calculation was performed on the clusters Y 5 P 10 O 32 and REY 4 P 10 O 32 embedded in a microcrystal containing about 1500 ions, respectively. The ground-state calculation provided the locations of the 4f and 5d crystal-field one-electron levels of RE 3+ relative to the valence and conduction bands of host, the curve of total and the partial density of states, and the corresponding occupation numbers, etc. Especially, the transition-state calculation was performed to obtain the 4f → 5d transition energies of RE 3+ in comparison to the experimental observations. The lattice relaxation caused by the dopant ion RE 3+ was discussed based on the total energy calculation and the transition-state calculation of the f-d transition energies.

Infrared to green up-conversion in LaCl3: U3+

Abstract Investigations of the optical properties of LaCl 3 : U 3+ (0.1%) single crystal have revealed an interesting up-conversion phenomenon. When the 4 G 7 2 level of U 3+ is excited by an infrared laser set at 748.6 nm, a strong green fluorescence from the 2 K 15 2 level is observed. From the analysis of the dynamics of the excited states, we conclude that the observed phenomenon occurs mainly via two mechanisms: (i) excited-state absorption and (ii) an energy transfer up-conversion (ETU) process involving pairs of U 3+ ions in 4 G 5 2 and 4 F 9 2 states.

Study on spectroscopic properties of GdOBr:RE3+ (RE=Eu, Tb, Ce)

Abstract Rare earth ions doped gadolinium oxybromide phosphors GdOBr:RE3+ (RE=Eu, Tb, Ce) were synthesized by the method of solid-state reaction at high temperature, and the VUV-VIS spectroscopic properties of the phosphors were systematically investigated. Under the excitation of VUV or UV source, the phosphors doped with Eu3+ and Tb3+ show a bright and sharp emission at around 620 nm corresponding to the forced electric dipole 5D0 → 7F2 transition of Eu3+, and at around 544 nm corresponding to the 5D4 → 7F5 transition of Tb3+, respectively. For GdOBr:Ce3+, a broader and intense emission spanned 370–500 nm corresponding to the d-f transition of Ce3+ was observed. The excitation spectra were also analyzed.

Theoretical study on complex f–f transition: simulation of luminescence spectra of nanocrystalline X1–Y2SiO5:Eu3+1

Abstract Based on the electrostatic crystal-field model of M. Faucher, in which the induced electric dipoles of ligands are obtained from a set of self-consistent combined equations and the contributions from far ligands are considered, the crystal-field energy parameters of nanocrystalline X 1 –Y 2 SiO 5 :Eu 3+ at two sites both with C 1 symmetry are calculated by using related data of its crystal structure and physical properties. Moreover, we successfully extend the above model to calculate the transition intensities, therefore giving a computed simulation of luminescence spectroscopy consistent with the experimental one which we measured before, supporting the model and the data we adopted here.

New paths of excitation of up-conversion emissions in LaCl3:U3+

Green and red up-conversion emissions centred at 555 and 681 nm, respectively were investigated in LaCl 3 :U 3+ . They were observed after IR excitation in resonance with transitions between excited states. The green 2 K 15/2 → 4 1 9/2 emission is excited via two different processes and the red 4 F 9/2 → 4 I 9/2 one via one excited state process only. Excitation paths of these emissions as well as possibilities of a two-photon absorption and an avalanche up-conversion in this material are discussed.

EXCITATION TRANSFER BETWEEN THE TWO SITES IN THE NANOMETRIC SCALE X1-Y2SIO5:EU

Abstract We have measured the photoluminescence spectra of nanometric scale X1-Y2SiO5:Eux. The spectra were recorded at 15K and room temperature using site selective excitation by a dye laser in addition to conventional UV excitation. We found that at low temperature there is a pronounced excitation transfer from site 2→1. The transfer rate increases rapidly with increasing concentration and for x=0.7 no fluorescence from site 2 can be observed. Decaycurve measurement revealed this transfer process directly. The lifetimes of the 5Do levels of the two sites were also measured as a function of Eu3+ concentration. The results show that the lifetimes of the 5D0 level of site 2 decreases with increasing concentration. The mechanism of the excitation transfer is discussed. Wavelengths of the 5D0→7D0–4 transitions of the two sites were also tabulated.