Dual luminophor pressure sensitive paint: II. Lifetime based measurement of pressure and temperature

Abstract

Two newly synthesized luminescent compounds provide a lifetime based dual pressure and temperature sensor when jointly dissolved in a polymer matrix. The temperature sensor is a tris(β-diketonate) phenanthroline europium complex, with a broad absorption peaked at 370 nm and a characteristic but relatively sharp 615 nm europium emission. The lifetime of this compound varies between 260 and 120 μs over the temperature range 5–45 °C for a derivative of −3.50 μs/°C. Our pressure sensor is a porphyrin compound called platinum tetra(pentafluorophenyl)porpholactone (PtTFPL) developed recently in our labs. This compound has a principal absorption band at 390 nm and a red-shifted phosphorescence at 730 μm. In silicone polycarbonate co-polymer, PtTFPL has a lifetime range of 42.7–6.6 μs in going from 0 to 1 atm at 1 atm. The two sensors have maximum absorption in the range 370–400 nm but non-overlapping emission spectra upon excitation with a broadband illumination at 400 nm. As a result, with appropriate band pass optical filters, the two emission lines can be detected separately. In addition to the high photostability of the dual system, our studies show that the luminescence properties of one sensor are independent of the presence of the other sensor. We note that measurement of decay rate is more robust than measuring intensity, since it is unaffected by changes in the light source, the index of refraction of the medium, optical geometry variations and fluctuations in film thickness and dye concentration. Hence the two compounds afford the possibility of a dual luminophor lifetime measurement of pressure and temperature.