Luminescence instrumentation photomultipliers

T he luminescence instruments shown in I igures 15-10 and 15-11 both monitor the source intensity via a ret-crence photomultiplier. Most commonly, the ratio of the sample luminescence signal lo the signal from the reference detector is continuously obtained. This can compensate for source intensity fluctuations and drift. Both doubic-bcam-in space and doiihlc beam-in time designs are employed. 

The immense growth in the luminescence literature during the period between these two reviews had little to do with developments in fundamental theory. It was mainly due to the availability of new instrumentation, such as the photomultiplier (around 1950), the laser (around 1960), transistor and microcircuit electronics (around 1970), and ready access to laboratory computers (around 1975). All aspects of luminescence theory now being used to interpret luminescence measurements have been known since the early 1900 s and nearly all of the types of measurements now being made had been initiated with cruder techniques by 1930. We discuss here many of the latest techniques in luminescence analysis with selected highlights from the historical development of luminescence and a look at several recent developments in luminescence applications that appear likely to be important to future research. 

Phosphors for cathode-ray tubes, television screens, monitor screens, radar screens, and oscilloscopes are tested under electron excitation. Electron energy and density should be similar to the conditions of the tube in which the screen will be used. The phosphors are sedimented or brushed onto light-permeable screens and coated with an evaporated aluminum coating to dissipate charge. The luminescence brightness and color of the emitted light are measured with optical instruments such as photomultipliers or spectrophotometers. 

Luminescence decay curves may be observed by displaying the output of the photomultiplier on an oscilloscope. Precautions must be taken to correct for instrumental distortion of fast decay curves (D13). In multicomponent systems with differing decay times, electronic gating may be used to isolate the signal due to one component (time resolved phosphorimetry) (SI). A complete emission spectrum can be observed using a spectrograph with a photographic plate or television camera tube, but these systems are as yet only of specialist interest. 

We used a LB 9505 multidetector unit for the simultaneous and continuous recording of luminescence from six samples (Berthold and Maly 1987). This instrument is equipped with six rubidium-bialkali photomultiplier tubes placed in close proximity to the vials inside six independent counting chambers. Reflectors ensure optimum counting efficiency. Each measuring chamber has its own temperature control. Since the results from all six detectors should allow direct comparison, they were standardised by determination of its individual sensitivity constant (X-factor). 

Chemiluminescence is based on the catalysis or inhibition of the alkaline oxidation of a luminescent reagent by metal ions [319,320]. The required instrumentation is extremely simple, and may consist in a reaction vessel and a photomultiplier. The sample is mixed with the reagent (a buffered solution of luminol plus hydrogen peroxide and several additives) in an FIA system. Chemiluminescence presents lower detection limits than fluorometric techniques, but seems to be lesser precise than both fluorescence and phosphorescence [255,306]. 

Berkeley. In the simplest application of FDCD a photomultiplier tube is placed at 90° to the direction of emission detection in a modified commercial or custom-built CD instrument and the luminescence intensity in phase with the oscillating left and right circularly polarized absorption beam is monitored. For many applications, including recent uses of FDCD as detectors in HPLC, this type of experimental setup is sufficient. The major technical challenge in the construction of an FDCD instrument is associated with the fact that it is very difficult to produce pure circularly polarized excitation without any residual polarization. Furthermore, if this linear polarization varies in phase with the incident circular polarization, serious artefacts may result. To reduce this problem, a somewhat more complicated experimental setup is required. A schematic diagram of an FDCD instrument designed to deal with the linear polarization problem is shown in Figure 7. 

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