We demonstrated the synthesis of LaPO 4 :Er:Yb-doped nanoparticles/nanorods and LaPO 4 :Er@Yb core-shell nanoparticles/nanorods by a solution-based technique. The mechanism related to morphology control of LaPO 4 : Er:Yb nanorods/nanoparticles is proposed and discussed. Bright-green (550 nm) and red (670 nm) emission were observed due to the transitions 2 H 11/2 + 4 S 3/2 f 4 I 15/2 and 4 F 9/2 f 4 I 15/2 , respectively. The experimental data for 550-and 670-nm emission bands of doped nanoparticle/nanorod and core-shell nanoparticles/nanorods have been fit with a straight line with a slope of ∼2, which confirms the two-photon absorption process. The enhancement of upconversion emission of LaPO 4 :Er:Yb-doped nanoparticles and LaPO 4 :Er@Yb core-shell nanoparticles/nanorods are mainly due to modifications of surface-related effects. It is found that the tensile strain increases from +1.0% to +1.9% with changing the shape from nanoparticle to nanorod and reversal of the lattice strain (compressive) is obtained for coated nanoparticle/ nanorod. It is worth mentioning that the lattice strain varies with changing the shape and surface coating on nanocrystals and the upconversion emission intensity increases with decreasing the tensile lattice strain and it increases with increasing compressive strain. Analysis suggests that the lattice strain plays an important role in modification of the upconversion properties of the rare-earth-doped nanocrystals.

Nitrogen-doped titanium dioxide (TiO 2 /N) nanoparticle thin films have been produced by a sol-gel method with hexamethylenetetramine (HMT) as the dopant source. The synthesized TiO 2 /N thin films have been sensitized with CdSe quantum dots (QDs) via a linking molecule, thioglycolic acid (TGA). Optical, morphological, structural, and photocurrent properties of the thin films with and without QD sensitization have been characterized by AFM, TEM, XPS, Raman spectroscopy, UV-visible spectroscopy, and photoelectrochemistry techniques. AFM measurements reveals that films with thicknesses of 150 and 1100 nm can be readily prepared, with an average TiO 2 particle size of 100 nm. TEM shows a uniform size distribution of CdSe QDs utilized in sensitizing the TiO 2 /N films. Doping of the TiO 2 crystal lattice by HMT was confirmed to be 0.6-0.8% by XPS. Differences in crystal phase caused by the precursors HMT, nitric acid, and poly(ethylene glycol) (PEG) are elucidated using XRD and Raman spectroscopy. The resultant crystal phase of TiO 2 /N varies but is a mixture of anatase, brookite, and rutile phases. UV-visible absorption spectra show that N doping of TiO 2 causes a red-shifted absorption into the visible region, with an onset around 600 nm. Nitrogen doping is also responsible for the enhanced photocurrent response of the TiO 2 /N nanoparticle films in the visible region relative to undoped TiO 2 films. In addition, CdSe QDs linked to TiO 2 /N nanoparticles using TGA were found to significantly increase the photocurrent and power conversion of the films compared to standard TiO 2 /N films without QD sensitization. The incident photon-to-current conversion efficiency (IPCE) is 6% at 400 nm for TiO 2 /N-TGA-CdSe solid-state solar cells and 95% for TiO 2 /N-TGA-CdSe films near 300 nm in a Na 2 S electrolyte, which is much higher than that of undoped TiO 2 with QD sensitization or TiO 2 /N without QD sensitization. The power conversion efficiency (η) was found to be 0.84% with a fill factor (FF%) of 27.7% with 1100 nm thick TiO 2 /N-TGA-CdSe thin films. The results show that combining nitrogen doping with the QD sensitization of TiO 2 thin films is an effective and promising way to enhance the photoresponse in the near-UV and visible region, which is important for potential photovoltaic (PV) and photoelectrochemical applications.

In this work, we synthesized ZnO nanorods by a wet chemical process. By varying different parameters of the synthesis process like precursor concentration, solvent used, surfactant, temperature, and reaction time, we were able to control the aspect ratio (l/d) and sharpness factor (S f ) h/b) of the rods. Rods with an aspect ratio of ∼20 and a sharpness factor of 10 were repeatedly obtained and characterized from scanning electron microscopy. High-resolution transmission electron microscopy and dark field analysis revealed that nanorods grow as a single crystal along the c axis [0001]. UV and visible emission was obtained in both flat-and sharp-terminated rods. According to the XPS analysis, rods present an excess of Zn 2+ of ∼4% that is responsible for the strong yellow emission band. Such defects were removed by annealing of the sample at 200 °C for 2 h. Possible mechanisms of changes in the morphology produced by changes in the synthesis process are also discussed.

A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer.