Phosphorescence light sources

In recent years luminescence nomenclature has become confusing within the literature and in practice. Luminescence involves both phosphorescence and fluorescence phenomena. While luminescence is the appropriate term when the specific photochemical mechanism is unknown, fluorescence is far more prevalent in practice. Moreover, the acronym LIE has historically inferred laser -induced fluorescence however, in recent years it has evolved to the more general term light -induced fluorescence due to the various light sources found within laboratory and real-time instruments. Within this chapter fluorescence and LIE are interchangeable terms. 

Fig. 7. Diagram of spectrophosphorimeter.28 L, light source Mi, Ms, Hilger D 247 quartz prism monochromators Di, D2, chopper discs driven by synchronous motors B, silica plat beam splitter F, 0.5-mm. silica optical cell containing fluorescent screen solution Pi, monitoring photomultiplier P2, fluorescence-phosphorescence photomultiplier Q, fused quartz dewar containing sample cell.

Fig. 9 Schematic representation of the time-domain DLR (f-DLR) scheme. The shortlived indicator fluorescence and the long-lived phosphorescence of the inert reference beads are simultaneously excited and measured in two time gates. The first (Aex) is in the excitation period where the light source is on and the signal obtained is composed of short-lived fluorescence and long-lived luminescence. The second gate (Aem) is opened in the emission period where the intensity is exclusively composed of the reference luminescence [18]...

Phosphorescence spectra are commonly weaker than fluorescence spectra, even when solid sample solutions are probed. For unperturbed detection of phosphorescence, the fluorescence must, therefore, be eliminated. This is readily achieved by surrounding the sample with a metal cylinder that is rotated at variable speed by a motor ( rotating can ). A hole in the cylinder exposes the sample to the excitation beam for a short period, during which the detector does not see the sample. Rotation of the can subsequently opens the sample to the detector, long after the fluorescence has decayed. The phosphorescence lifetime can then be determined from the intensity dependence of the phosphorescence on the rotational speed. In modem instalments, the elimination of fluorescence is commonly achieved by replacing the continuous light source with a pulsed source (a stroboscope or a pulsed laser) and the photomultiplier is electronically deactivated during and shortly after the excitation pulse. 

Figure 4.9 Schematic drawing of near-field optical probes. By pulling out an optical fiber and coating with aluminum, an optical probe with a very small aperture (<100 nm) is created. The probe can detect fluorescence or phosphorescence from objects in the near field close to the aperture, such as a thin film or flat surface (a) or from a labeled molecule (b). The probe is relatively insensitive to light in the medium in the far field further from the tip. The excitation light source can be transmitted through the probe or externally.

Phosphorescent (i.e., triplet) organic light-emitting diodes have very high EQEs/ and have been a subject of intense research and development activity worldwide. The realization of required luminous and power efficiencies, as well as long operafional lifetime, will enable phosphorescent OLED application in various displays for consumer electronics and as solid-state lighting sources. 

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