Broadband emission

The emerging analytical technique of laser-induced breakdown spectroscopy (LIBS) is a simple atomic emission spectroscopy technique that has the potential for real-time man-portable chemical analysis in the field. Because LIBS is simultaneously sensitive to all elements, a single laser shot can be used to record the broadband emission spectra, which provides a chemical fingerprint of a material. 

For comparison, steady-state cathodoluminescence spectra (Fig. 4.7) are presented from two scheelite samples with different rare-earth elements concentrations (Table 4.5). It is clearly seen that only broadband emissions are detected, while the narrow Unes of several rare-earth elements, mostly Sm + are extremely weak. 

Complexes of transition metal ions with a formally empty d shell often show intense broadband emission with a large Stokes shift of 10,000-20,000 cm k The most important examples for minerals are VO ", WO ", MoO " and TiOg . Atomic orbitals s,p, d of the central atom andp orbitals of oxygen form molecular orbitals of the complexes (Fig. 5.60). The excited state is considered to... 

The Srs(P04)3Cl crystals are hexagonal needles with lattice parameters ah = 9.953 A. and ch = 7.194 A. The needle axis corresponds to the crystallographic c axis. The europium(II) doped sample is a phosphor, readily excitable with electrons, x-rays, and both short and long ultraviolet light. It emits in the blue with a peak at 445 nm. Crystals of strontium chloride vanadate(V) are orthorhombic platelets with lattice constants a = 7.43 A., b = 11.36 A., and c = 6.54 A., with the b axis corresponding to the thin dimension of the flakes. Strontium chloride vanadate(V) is a self-activated phosphor giving broadband emission with a peak at 423 nm. when excited with 2537-A. radiation. All compounds are insulators, with resistivities >1012 ft-cm. 

Emission filters Broadband emission will produce a larger signal and should always be used except when there is crosstalk with the emission of another fluorophore in the same sample. For more details, please refer to http //www.chroma.com, http //www.omegafilters.com/ or http //www.semrock.com/Catalog/BrightlineCatalog.htm. 

The more or less isoelectronic systems CaW04 and CaMo04 show broadband emission with maxima at 410 nm and 530 nm, respectively. Whereas CaW04 is very efficient at room temperature, CaMo04 is partly quenched (96). 

Figure 18. CL emission spectra of fluorapatite from the Coldwell complex, Ontario. Top yellow-luminescent sample from a ferro-augite syenite in Center 1. This type of emission may closely resemble Mn broadband emission to the naked eye. Bottom yellow-red Inminescent sample from the same general region. Modified after Mitchell et al. (1997).

The combined effect of a large increase in the energy of the 2g shite and essentially no change in the energy of the Eg state with pressure is responsible for the observed electronic crossover. The change from a spin-allowed 2g emission to a spin-forbidden Eg A2g emission leads to the observed transformation from a smooth, broadband emission spectrum to a sharp, structured emission spectrum. The " T2g- Eg crossover was observed in many materials. The latest reviews on high-pressure spectroscopy of the Cr " -doped materials can be found in [81, 87]. A typical example is presented in Fig. 4.6a-e where the luminescence spectra and luminescence decays of the LiSc(W04)2 Cr system, obtained at different pressures between ambient and 260 kbar, are presented. As... 

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