Low-cost thermoluminescence measurement using photodiode sensing
Many branches of scientific and industrial research require precise instrument(s) for control and measurement. Such instruments tend to be prohibitively expensive. In the current global economic climate the funding to procure research equipment is fast dwindling. One current interest that our institution has is the synthesis and thermoluminescence (TL) characterization of phosphors, polymers and nano-materials. TL measurement requires precise control and measurement of sample temperature as a function of output intensity. In the present research, we describe the design and construction of a low-cost TL instrument that allows automatic control of various steps of the experiment while logging instantaneous intensity output. This work started with two fundamental considerations. Firstly, whether a low-cost thermoluminescence equipment is feasible. Secondly and more importantly, whether a photodiode can form the intensity sensing apparatus. We answer these questions affirmatively by first putting together a course of research and assimilating the necessary tools needed. Using the the resulting demonstrable TL instrument, we demonstrate the versatility for temperature sequencing, range and heating control of the sample over the temperature range of 23 to 600 ± 0.5 ◦C. A comparable instrument in the institution operates at a maximum ceiling of 300 ◦C. Additional refinements to the prototype instrument enable the sample temperature to be held constant at any temperature within this range with the aid of software tuned Proportional-Integral-Derivative (PID) control. The intensity measurements are made using a temperature-compensated, large area photo-diode operated in photovoltaic mode and covering a wavelength range 400 to 1100 nm. The interfaces of the instrument that made the instrument easy to use were developed con-currently. For instance the Universal Serial Bus (USB) handler, the Visual BASIC.NET control program that also logs the temperature and intensity data, and the PIC18F2520 micro-controller firmware code that was written in the C-language. Several other tools, listed in the body of the dissertation were also used. Finally, we present various results of temperature control and measurement and a demonstration measurement on a ceramic sample.