Ln 3+ doped (Yb 3+ ,Tm 3+ codoped and Yb 3+ ,Er 3+ ,Tm 3+ tridoped) NaYF 4 /poly(vinyl pyrrolidone)(PVP) (M w ≈ 1 300 000) composite fibers with an average diameter of 300-800 nm were prepared by electrospinning and characterized by X-ray diffraction, field emission scanning electron micrography, and Fourier transform infrared spectra. Their upconversion (UC) luminescence properties were studied in contrast to the corresponding Ln 3+ doped NaYF 4 nanoparticles (15-20 nm) under 980-nm excitation. The results demonstrate that in the Yb 3+ ,Tm 3+ codoped composite fibers the blue emission of 1 G 4 -3 H 6 is dominantly strong, while in the nanoparticles the red emission of 3 F 2,3 -3 H 6 contributes considerably to the increase of the excitation power. This indicates that the color purity of blue is improved greatly by the modification of PVP. In the tridoped Yb 3+ ,Er 3+ ,Tm 3+ composite fibers, white light with more stable color balance (blue 1 G 4 -3 H 6 of Tm 3+ , green 2 H 11/2 / 4 S 3/2 -4 I 15/2 , and red 4 F 9/2 -4 I 15/2 of Er 3+ ) was obtained. The improved UC properties in the composite fibers are attributed to the suppressed local thermal effect. The energy transfer and UC populating processes are discussed.

The effects of size and europium concentration on photoluminescence properties of La 2 O 2 S: Eu 3+ nanocrystals (∼20 nm) and the corresponding bulk were studied. The results indicate that in nanocrystals, the absorption edge largely shifted to blue in comparison to the bulk, which was mainly attributed to the variation of phononexcitation relaxation. Two excitation bands were observed, located at ∼250 and ∼330 nm, respectively, corresponding to the charge transfer (CT) transitions of Eu-O and Eu-S. Relative to the CT transition of Eu-O, that of Eu-S increased greatly with europium concentration. The dependence of photoluminescence intensity on concentration showed that in the nanocrystals and the bulk, Eu 3+ ions had two different quenching mechanisms, respectively, the exchange interaction and electric dipole-dipole interaction.

Three-dimensionally ordered macroporous (3DOM) ZrO 2 :Eu 3+ inverse opal materials prepared by polystyrene (PS) colloidal crystal templating, using the sol-gel method, were successfully fabricated. Their crystal structure, morphology, and photoluminescence (PL) properties and the effect of the photonic stop-band on the spontaneous emission of Eu 3+ ions were studied and compared with those of the nonporous sample. In the 3DOM ZrO 2 : Eu 3+ , significant suppression for the 5 D 0 -7 F 1 transition peaking at 590 nm was observed, which was in good agreement with the photonic band gap calculated (∼586 nm). After grinding the 3D ZrO 2 :Eu 3+ inverse opal material, the suppression of emission was restored due to the disappearance of the photonic band gap. In the 3DOM ZrO 2 :Eu 3+ , the luminescent lifetime of 5 D 0 -7 F J depended strongly on emission wavelengths, which was mainly attributed to the appearance of different Eu 3+ centers. In the 3DOM ZrO 2 :Eu 3+ , three symmetry sites for Eu 3+ were identified by site-selective excitation, differing from the nonporous sample, in which only one site was identified.

Ternary terbium complexes were fully encapsulated and uniformly distributed into the channels of unmodified and modified mesoporous molecule sieves of SBA-15 and characterized by transmission electron micrographs (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) absorption spectra, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and elemental analysis. The luminescent properties for the encapsulated complexes were systematically studied in contrast to the pure complexes, including excitation and emission spectra, fluorescence dynamics, photostability under UV exposure, and the temperature dependence of intensity and lifetime. The results indicate that the excitation bands assigned to the pi-pi* electron transition of the ligands for Tb complexes encapsulated in SBA-15 were split into different components due to decreased symmetry and disappeared at long wavelengths. Owing to suppressed vibration transitions, the outer quantum efficiency of the 5D4-7FJ (J = 0-5) emissions was enhanced largely in comparison to the pure complexes. In addition, the photostability and thermostability of the emissions were also improved considerably.

PbWO 4 : Er 3+ ,Yb 3+ nanocrystals (∼100 nm) were prepared by the hydrothermal method at different pH values (pH ) 4, 7, and 9). Their structure and luminescence properties under 978-nm laser-diode excitation were studied. The results indicate that the practical ratio of W to Pb in the nanocrystals and the doping concentration of Yb 3+ depended strongly on the pH value due to structure change. In upconversion, red ( 4 F 9/2 f 4 I 15/2 ) and green ( 2 H 11/2 , 4 S 3/2 f 4 I 15/2 ) emissions were observed, both of which occurred via a two-photon populating process. Biexponential upconversion dynamics were observed, which was attributed to luminescence centers surrounded by different local environments. The intensity ratio of 2 H 11/2 f 4 I 15/2 to 4 S 3/2 f 4 I 15/2 (R HS ) was explored to reveal the local thermal effect under the exposure of the laser diode, showing that the temperature at the exposed spot increased linearly with respect to excitation power density and Yb 3+ concentration.

A new type of bifunctional nanocomposites for biomedical applications, upconversion NaY F(4):Y b(3+), Tm(3+) nanoparticles coated with Ru(II) complex chemically doped SiO(2), has been developed by combining the useful functions of upconversion and oxygen-sensing properties into one nanoparticle. NaY F(4):Y b(3+), Tm(3+) nanoparticles were successfully coated with an Ru(II) complex doped SiO(2) shell with a thickness of approximately 30 nm, and the surface of the SiO(2) was functionalized with amines. The obtained nanocomposites exhibited bright blue upconversion emission, and the luminescent emission intensity of the Ru(II) complex in the nanocomposites was sensitive to oxygen. Compared with the simple mixture of Ru(II) complex and SiO(2), the core-shell nanocomposites showed better linearity between emission intensity of Ru(II) complex and oxygen concentrations. These bifunctional nanocomposites may find applications in biochemical and biomedical fields, such as biolabels and optical oxygen sensors, which can measure the oxygen concentrations in biological fluids.

Microstructure and spectroscopic properties of YV1−xPxO4:2 mol % Eu3+ (x=0, 0.05, 0.5, 0.95, and 1) powders derived from solid state reaction method were systematically reinvestigated by various spectroscopic techniques such as x-ray diffraction, Fourier transform infrared, excitation and emission spectra, and particularly by frequency-selective excitation techniques. The present results further show the evolutions of local environment surrounding both cations and anion groups with composition, which yielded systematic changes in spectroscopic properties. At least three symmetry sites were identified by laser-selective excitation to be present in the mixed yttrium vanadate/phosphate compounds due to chemical disorder in microstructure based on the random distribution of VO4 and PO4 tetrahedrons. Luminescence dynamics under site-selective excitation indicates that luminescence lifetime of D50 level of Eu3+ ions decreased in going from YPO4 to YVO4 host mainly due to the enhanced electronic dipole transitions. The Ω2 and Ω4 Judd–Ofelt intensity parameters for Eu3+ were determined from the emission spectra and also indicated different local environments experienced by Eu3+ due to the significant changes in ligand polarizability.

An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail.