Difference between revisions of "Measurement of Luminescence Decays: Methods and Instrumentation"

Revision as of 10:54, 9 September 2017

by Dr. Mark Sulkes

Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, USA.

Developments in electronics, PMT technology, and excitation light sources have contributed to improvements in luminescence decay detection. The result in recent years has been more precise determination of lifetimes, particularly in the sub-ns regime, at often drastically reduced costs. The most important factor in cost reduction, also affording some enhanced capabilities, has been the development of numerous LED and laser diodes, spanning a wide wavelength range, that can provide sub-ns pulses and can be driven even to GHz frequencies. The cost of these light sources is typically a small fraction of conventional laser systems. The result in the lowest cost regime (waveform digitizer combined with LED/laser diode excitation sources) is a rather good and potentially quite inexpensive system for determining strong emission luminescence lifetimes from multi-ns to µs. This review is particularly concerned with time and frequency domain methods that are capable of more precise lifetimes in the ns to the sub-ns regime. These capabilities have been available for several decades at fairly significant costs. The advent of LED/laser diode excitation sources has greatly lowered the cost of these capabilities and even afforded some performance enhancements, particularly in the frequency domain. Powerful commercial instrumentation is available at much-reduced cost. User implemented or improved, systems at a further reduced cost are increasingly feasible.

Introduction

The measurement of luminescence decays as a function of time provides fundamental information for an enormous range of applications and systems in chemistry and biology.[1-3] Continuing technical developments have made possible precise luminescence decay measurements, even on sub-ns timescales, at increasingly lower cost. Partly, this is due to the availability of faster electronics at a decreasing cost. However, the single most important factor has been the development of LEDs and laser diodes that can be driven with narrow pulses in time and at high frequencies - often replacing expensive laser systems. The result has been powerful commercial systems at lower cost. There are also growing opportunities for surplus, homemade, and home modified components with excellent performance at a far lower cost.[4] The other limiting factor is detector - photomultiplier (PMT) - performance. Ongoing PMT developments have brought about improved performance at lower prices. In addition, past technical publications have shown how to get greatly enhanced performance from common and inexpensive models. This review of instrumentation developments will mainly consider the time domain method of time correlated single photon counting (TCSPC)[1,2] and the frequency domain method of phase modulation fluorometry[1,2]; some other methods and equipment will be mentioned more briefly.