It is a recognised phenomenon that temperature affects the emission properties of phosphors. These properties include emission intensity, peak wavelength (emission and excitation), spectrum shape, decay and rise-time. By measuring one or more of these properties it is possible to determine the temperature of a phosphor. Phosphors used this way are referred to as thermographic phosphors and by incorporating them into a system, the temperature of the system may then be determined.
Changes in the peak wavelength are usually not large enough to be useful in measuring temperature. One exception is the excitation peak of Y2O3:Eu, which has been shown to shift up to 0.6nm/K.
All materials exhibit a reduction in emission intensity with an increase in temperature. Early efforts in luminescence thermometry looked at this but the difficulty in performing accurate enough measurements means that other techniques are now employed.
One common technique is to measure the ratio of two emission peaks. The material usually contains a single lanthanide activator with multiple emission peaks, or two different activators, each with their own emission peak. Increasing the temperature will alter this ratio. The emission intensity of the peak with the higher energy excitation state will increase relative to the peak with the lower energy excitation state.
Another common technique is to measure the decay time of the phosphor’s emission. A single emission band of the phosphor is measured for changes to the decay time. This and the previous technique are useful as they self-reference, limiting the effect of outside factors on the results.
As an alternative to decay time, rise time may be measured. Temperature will affect how quickly electrons will accumulate in the excited energy level. Increasing temperature will shorten the time taken. By measuring the time take for emission intensity to reach maximum the temperature can be determined.
These phosphors can be used in a number of different applications in the fields of engineering (thermal barrier coatings, surface temperature monitoring, fluid flow analysis, circuit boards, etc.) and biomedicine (cellular level temperature measurements, tumour monitoring, diagnosing ischemia, etc.). Below is a selection of thermographic phosphors that we supply.
The materials shown here that end with a ‘-X’ designation in their grade require their activator concentrations to be specified by the customer. The other materials each have a standard version, though the customer may specify activator concentrations for these as well. Other particle sizes can be supplied and may be specified by the customer.
Apart from the materials shown here, we can supply a wide range of materials according to our customers’ specifications. Please enquire if you have requirements for a thermographic phosphor not shown.