[Differentiated fluorescence centers in europium acetylacetonate hydrate doped poly methyl methacrylate].

Poly methyl methacrylate (PMMA) was doped with europium acetylacetonate hydrate. Judd-Ofelt parameters Ω2 (19.73 x 10(-20) cm2) and Ω4(2.19 x 10(-20) cm2) indicate a high inversion asymmetry and strong covalent environment arounc Eu3+ in PMMA. The maximum stimulated emission cross-sections for the 5D0 --> 7F(J); (J = l, 2 and 4) transitions in EAH doped PMMA were calculated to be 0.38 x 10(-21), 4.90 x 10(-21) and 0.36 x 10(-21) cm2, respectively. Efficient purplish-red and red fluorescence was obtained from ediropium acetylacetonate hydrate doped PMMA under 365 and 254 nm excitation respectively, indicating that it can be used as UV sensitive components for fiber optic sensors. Because of the suitable refractive index difference between doped sample and pure PMMA, it is expected to fabricate standard 9 µm/125 µm optical fiber which supports multimode transmission, providing basis of further development for medical fiber, flexible communication fiber and fiber optic sensor.

[The enhancement of 1.5 microm near infrared luminescence in Er3+ and Yb3+ codoped Y2O3 nanocrystalline].

Y0.96 Er0.02 Yb0.02)O3 nanocrystals of 10 and 40 nm average particle size were prepared by combustion method. And bulk materials of the same components were obtained by annealing at 1 200 degrees C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, transmission electron microscope (TEM), and scanning electron microscopy (SEM) were used to characterize the crystal structure and morphology of the samples. The upconversion emission spectra and NIR (near-infrared) emission spectra were measured, under 980 nm excitation. The research result indicates that as the particle size decreases, the upconversion red emission and NIR emission components increase in the emission spectra. This phenomenon is attributed to the large ratio of surface area to volume in nanocrystals. This characteristic makes the nanocrystals absorb more OH-, whose vibrational energy is 3 200-3 800 cm(-1). The increase in the OH- number enhances the rate of nonradiative relaxation from Er3+ 4I11/2 to 4I13/2 energy level (energy gap is 3 600 cm(-1)). This nonradiative relaxation process depopulates the 4I11/2 level and makes the green emission weaker. Meanwhile, this process populates the 4I3/2 level and makes the red and NIR emissions stronger. The intensity of 1.5 microm main peak is 1.6 times that of bulk materials. This result has great significance in actual applications of nanophosphors.

[Study on concentration quenching and energy transfer in Ln3+ (Ln = Tb, Tm, Eu) in Y2O3 nanocrystal powders].

Nano-powders Y2O3 with various particle sizes and different doping concentrations of Ln (Ln = Tb, Tm, Eu) were prepared by using a combustion technique. The bulky powders doped with concentrations corresponding to nano-powders were obtained by annealing the nano-powders at high temperature. The emission spectra, XRD spectra and TEM were used in the present study. The concentration quenching of luminescent centers and energy transfer between luminescent centers in Y2O3 : Ln nanocrystal powders were investigated. It was found that the behaviors of luminescence concentration quenching for 5D4 --> 7F5 : Tb3+ and 5D0 --> 7F2 : Eu3+ in nano-powders are similar to that in bulky powders. On the contrary, the quenching concentrations for 5D3 --> 7F5 : Tb3+ and 1D2 --> 3H4 : Tm3+ are distinctly higher than that in bulk powders. This owes to the size confinement effect: the interface of nanocrystal particles can stop a portion of the energy transfer, which happens in the bulk ones, between luminescent centers. The size confinement effect can bring different influences to the different types of energy transfer. For instance, it will restrain the energy transfer (governed by electric dipole-dipole interaction) between the ions in long distances, and will hardly affect the energy transfer (governed by exchange interaction) between the ions locating at near intervals.

[Preparation of alpha-Gd2 (MoO4)3 red emitting phosphor for white light emitting diodes and its luminescence study].

A novel red phosphor alpha-Gd2 (MoO4)3: Eu was synthesized by conventional solid state reaction method with the starting materials: Gd2O3, MoO3 and Eu2O3. The effects of flux and Eu concentration on the crystal structure, morphology and luminescent properties of the phosphors were investigated. The results showed that non-agglomeration phosphors with regular morphology and fine size were produced after the mixture being calcined at 800 degrees C for 4h with 3% NH4F as flux. The main emission peak of the samples is at 613 nm. The excitation spectrum showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, nicely fitting in with the widely applied output wavelengths of ultraviolet or blue LED chips. The alpha-Gd2 (MoO4)3 phosphor may be a good candidate phosphor for solid state lighting application.

[Quantum efficiency of the 5D0 level of Eu3+ at C2 site in cubic nanocrystalline Y2O3].

In the present the authors are trying to work out how the quantum efficiency depends on the nanocrystalline size. Cubic nanocrystalline Y2O3 : Eu3+ samples were prepared by chemical self-combustion. The bulk Y2O3 : Eu3+ was obtained by annealing the nanocrystalline at 1 000 degrees C for 2 h. The emission spectra, XRD and fluorescence decay showed that the emission intensities are increased and fluorescence decay becomes slow with an increase in particle diameter of the samples. Two routes were used to estimate the quantum efficiency of the 5D0 level of Eu3+ at C2 site. The quantum efficiencies of 5D0 level of Eu3+ at C2 site in the samples depend on the nanocrystalline sizes. Finally, a detailed discussion about these two approaches for estimating the quantum efficiencies was made.

[Synthesis and luminous characteristics of Y (P, V)O4: Eu3+ phosphors for PDP].

Y(P, V)O4 :Eu3+ phosphors with good morphology for plasma display panels have been prepared via coprecipitation reaction. The phosphor was characterized by SEM and photoluminescence under UV (325 nm)and VUV (147 nm) excitation. The emission spectra depending on temperature under 325 nm excitation by laser indicated that there exist energy transfer between VO4(3-) group and Eu3+ ion. Under 147 nm excitation, the most intense emission peaks of commercial (Y,Gd)BO3 :Eu3+ phosphor range around 593 nm, and those of Y(P, V)O4 :Eu3+ phosphors prepared by coprecipitation reaction ranged around 619 nm. The red emission color purity of Y(P, V)O4 :Eu3+ phosphor is much better than that of (Y,Gd)BO3: Eu3+, and its relative emission intensity is almost close to that of the commercial phosphor.

[High efficiency and low threshold upconversion from IR to red for Er3+ and Tm3+ co-doped fluoride-oxide glass-ceramic].

In this paper, high efficiency and low threshold upconversion from IR to red is reported, for Er3+ and Tm3+ co-doped fluoride-oxide glass-ceramic under 978 nm LD excitation. The component of sample in experiment is 65GeO2-25NaF-8.5BaF2-1Er2O3-0.5 Tm2O3, and the prepared method is obtained. The upconversion emission spectra under 978 nm LD excitation is measured at room temperature. Analyzing it, we find that introduction of Tm3+ into Er3+ doped system preferentially quenches the green upconversion fluorescence from 4S3/2 level of Er3+ duo to the efficient cross-relaxation of 4I13/2-->4I15/2 (Er): 3H6-->3H4 (Tm) which can significantly reduce the upconversion efficiency from 4I13/2 level to the emitting 4S3/2 level, and the Tm3+ behaves as a good sensitizer of the red upconversion from the 4F9/2 level of Er3+ which is mainly populated by the cross-relaxation of 3H4-->3H6 (Tm): 4I11/2-->4F9/2 (Er). However, at low Er3+ concentration (2 mol%), it is impossible for strong red upconversion. X-ray analysis is done, there are lots of nanocrystallites in MFG glass-ceramic. So we think, this red upconversion is attributed to Er3+ enriched fluoride microcrystallites, which makes the cross-relaxation of 3H4-->3H6 (Tm): 4I11/2-->4F9/2 (Er) more effective, therefore their active optical properties may be optimised. In the end, the relationship between LD working current and intensity of upconversion luminescence is discussed, the results confirm that both red and green upconversion processes are consisted by two photons.