Spectrometer, photoluminescence

Absorption spectra were measured on spin-cast films using a Perkin-Elmer Lambda 19 UV/VIS/NIR spectrometer. Photoluminescence (PL) and EL were... 

In photoluminescence one measures physical and chemical properties of materials by using photons to induce excited electronic states in the material system and analyzing the optical emission as these states relax. Typically, light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distribution and time dependence of the emission are related to electronic transition probabilities within the sample, and can be used to provide qualitative and, sometimes, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. 

The photoluminescence measurements of Thewalt et al. (1985) were performed at 4.2 K with 200 mW of 514.5 nm excitation from an Ar-ion laser in a 4 mm-diameter spot. The spectrum was analyzed with a double-grating spectrometer using a cooled photomultiplier operating in the photon-counting mode. 

T. A. Louis, G. Ripamonti and A. Lacaita, Photoluminescence lifetime microscope spectrometer based on time-correlated single-photon counting with an avalanche diode detector, Rev. Sci Instrum. 61, 11-22(1990). 

Figure 3. Normalized to their integral intensities photoluminescence spectra of C6o single crystal at 5 K under excitation of light with energy of 2.84 eV a) pure fullerite C60 (b) helium-intercalated fullerite C6oi (c) differed spectrum. The (a) and (b) PL spectra were corrected for instrumental response. The recording spectrometer slit width was 2.6 nm.

Considerably more work is required before these techniques can he introduced in court, hut our studies and the work of others show that photoluminescence techniques have potential for wide application in forensic science. Indeed, because of the significant advances demonstrated in recent years, one can expect to see spectrophotofluorometers become as commonplace as infrared spectrometers in a crime laboratory. Although luminescence spectrometry is not, in general, as specific as infrared spectrometry, it is considerably more sensitive and convenient. 

Photoluminescence spectra were recorded with a Perkin-Elmer LS-55 spectrometer while the UV-vis absorption spectra were recorded with UV/VIS/NIR Perkin-Elmer spectrometer. Transmission electron microscope (TEM) images were obtained using a JOEL JEM 3010 instrument. Infrared spectra were recorded with a Bruker IFS-66v spectrometer. 

Luminous intensity-time curves and spectra of test samples stimulated thermally and photochemically were measured with a chemiluminescence spectrometer CLA-FSl. Colour photos of the photoluminescence of samples placed in a cell with a diameter of 50 mm were taken with the Cube-2DI, which is employing an ultra high sensitive colour CCD camera of Bitran Co., Japan. Both types of the apparatus are available from the Tohoku Electronic Industrial Co., Japan. The black light has power of 240 aW cm" and wavelength of 365 nm. In order to obtain a spectrum for steep decay photoluminescence curves, a sample was irradiated with the NUV light for 5 sec... 

Figure 1. (Left) Experimental setup for photoluminescence spectrometer equipped with NUV (375 nm)- and RGB-LED. (Right) Photo of anatase Ti02 irradiated with a NUV light in air.

This method is based on measuring the shift of the optical energy levels of fluorescent elements such as Cr3+ in response to a change of the stress state. This results in undergo as the result of altering the distance of ions within the strained crystal structure of the host lattice (Yu and Clarke, 2002). Equipment used to record photoluminescence spectra include confocal laser-Raman spectrometers equipped with a liquid nitrogen cooled CCD detector and a motorised X-Y microscope table to allow point-by-point mapping. 

Uniform 1.5 pm thick PS layers were formed by anodization of p-type Si wafers of 0.3 Ohm em resistivity in 48% HE. After anodization, the HE electrolyte was replaced by a O.IM FeS04+0.001M EifNOals solution and a Fe Er film was electrochemically deposited into PS. As SIMS analysis showed, both Er and Fe can be introduced deeply into PS by this electrochemical technique [5], The maximum Er and Fe concentrations were estimated to be 0.1 and 10 at. %. The samples were oxidized at 500°C for 360 min and then at 1100°C for 15 min in O2 atmosphere. This treatment has been shown to form 5-50 nm iron/erbium oxide clusters inside OPS [5]. As comparison reference, Er-doped OPS containing Si clusters (without Fe) samples were fabricated in a similar way by polarization of PS in an Er(N03)3 solution. Photoluminescence excitation (PLE) spectra were recorded at 77 K by a grating spectrometer MDR-23 equipped with a Ge Cu detector. A Xe lamp was used as the excitation source. 

Prior to spectroscopic measurements and photocatalytic reactions, the catalysts were degassed at 773 K for 2 h and calcined in O2 (> 20 Torr) at 773 K for 2 h, then degassed at 473 K for 2 h. The photoluminescence and lifetimes were measured at 77 K with a Shimadzu RF-501 spectrofluorophotometer and an apparatus for lifetime measurements, respectively. The ESR spectra were recorded with a JEOL-2X spectrometer (X band) at 77 K. XAFS (XANES and EXAFS) spectra were obtained at the BL-lOB facility of the High Energy Acceleration Research Organization (KEK) in Tsukuba. The XAFS spectra of the... 

In order to obtain quantitative information on the photoluminescence of the silicon nanoparticles as a function of their size, we have measured their light emission along a horizontal line with a calibrated PL spectrometer [11, 13]. A selected set of the PL curves that were measured in steps of... 

Figure 2 A schematic representation of the sample compartment of a photoluminescent spectrometer.

In the design of the detector system, the photoluminescence should be measured during enzymatic activity. This required the construction of a flow cell system that could be interfaced with both a UV-vis and fluorescence spectrometer. In addition, because ultimately the system will be handling very toxic materials, the complete system must be sealed to protect the operators. 

Figure 10.6 Schematic diagram of the setup for optically pumped photoluminescence measurements. The excitation polarization was varied by a half-wave plate. The emitted light was collected by the CCD spectrometer along the direction parallel to the sample surface. Reproduced from H. Yanagi, 5. Hotta, S. Kobayashi and F. Sas i, Low-dimensional jt-conjugating oligomer crystals - Raman laser action and pulse-shaped emission with time delay, Oyo Buturi, 75, 1471-1475 (2006) with permission of The Japanese Society of Applied Physics...

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