Size dependent fluorescence spectroscopy of nanocolloids of ZnO

In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry–Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line with FWHM ∼0.4 nmwas observed at 576.5 nm.

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry–Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line with FWHM ∼0.4 nmwas observed at 576.5 nm.

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry–Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line with FWHM ∼0.4 nmwas observed at 576.5 nm.

Visible luminescence mechanism in nano ZnO under weak confinement regime

We describe the structure of luminescence spectrum in the visible region in nano-ZnO in colloidal and thin film forms under weak confinement regime by modeling the transition from excited state energy levels of excitons to their ground state. Measurements on nanocrystallites indicate the presence of luminescence due to excitonic emissions when excited with 255 nm. The relevant energy levels showing the transitions corresponding to the observed peaks in the emission spectrum of ZnO of particle size 18 nm are identified.

Spectral studies of naphthalocyanine (Nc) and rare earth phthalocyanine (RePc) molecules in an inorganic glassy borate matrix

Optical absorption and emission spectral studies of free and metal naphthalocyanine doped borate glass matrix are reported for the first time. Absorption spectra recorded in the UV- VIS-NIR region show the characteristic absorption bands, namely, the B-band and Q-band of the naphthalocyanine (Nc) molecule. Some of the important spectral parameters, namely, the optical absorption coefficient (α), molar extinction coefficient (ε) and absorption cross section (σa) of the principal absorption transitions are determined. Optical band gap (Eg) of the materials evaluated from the functional dependence of absorption coefficient on photon energy lies in the range 1.6 eV≤Eg≤2.1 eV. All fluorescence spectra except that of EuNc consist of an intense band in the 765 nm region corresponding to the excitation of Q-band. In EuNc the maximum fluorescence intensity band is observed at 824 nm. The intensity of the principal fluorescence band is maximum in ZnNc, whereas it is minimum in H2Nc. Radiative parameters of the principal fluorescence transitions corresponding to the Q-band excitation are also reported for the naphthalocyanine and phthalocyanine based matrices.

Optical properties of phthalocyanine molecules in cyano acrylate polymer matrix

Optical absorption and emission spectral studies of various phthalocyanine molecules, viz., LaPc, NdPc, SmPc, EuPc, CuPc and ZnPc in a polymer matrix of cyano acrylate are reported for the first time. All the absorption spectra show an intense B band (Soret) in the UV region followed by a weaker Q band in the visible region. The positions of the Q and B bands are found to have dependence on the metallic substitution. Values of the important spectral parameters, viz., molar extinction coefficient (ϵ), oscillator strength (f), radiative transition rate and decay time of the excited singlet state are also presented and compared with other solid matrices. The recorded fluorescence spectrum shows two broad emission bands in the case of NdPc, whereas for ZnPc only a very weak band is observed. The absence of emission bands for the other metallated phthalocyanines is attributed to increased spin orbit interaction and intersystem crossing.

Fluorescenec Emission of SrS:Eu2+ Phosphor-Energy Level Splitting of Eu2+

A method of preparation of strontium sulphide phosphors doped with europium is given. Nitrogen laser excited fluorescence emission spectra of these phosphors in the visible region are recorded. A band with line structure in the region 350-430 nm and a new broad band at 460 nm are observed. The splitting pattern for the 6p levels of Eu 2+ are given.

Effect of Ce3+ Ion on the X-Ray Induced Fluorescence Emission from CaS

The effect of Ce3+ on the fluorescence emission from CaS:Ce3+ phosphor is studied using X-ray excitation. Apart from the emission in the visible region, the phosphor also shows fluorescence emission in the ultraviolet region. Variation in wavelengths and intensities of these emissions due to change in dopant concentration is also analysed.

Enhanced UV emission from ZnO nanoflowers synthesized by the hydrothermal process

ZnO nanoflowers were synthesized by the hydrothermal process at an optimized growth temperature of 200 ◦C and a growth/reaction time of 3 h. As-prepared ZnO nanoflowers were characterized by x-ray diffraction, scanning electron microscopy, UV–visible and Raman spectroscopy. X-ray diffraction and Raman studies reveal that the as-synthesized flower-like ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase preferentially oriented along the (1 0 1 1) plane. The average length (234–347 nm) and diameter (77–106 nm) of the nanorods constituting the flower-like structure are estimated using scanning electron microscopy studies. The band gap of ZnO nanoflowers is estimated as 3.23 eV, the lowering of band gap is attributed to the flower-like surface morphology and microstructure of ZnO. Room temperature photoluminescence spectrum shows a strong UV emission peak at 392 nm, with a suppressed visible emission related to the defect states, indicating the defect free formation of ZnO nanoflowers that can be potentially used for UV light-emitting devices. The suppressed Raman bands at 541 and 583 cm−1 related to defect states in ZnO confirms that the ZnO nanoflowers here obtained have a reduced presence of defects