A position sensitive detector based on red-shift in photoluminescence spectra

We propose to utilize spectral information of photoluminescence (PL) photons for position sensing. Suppose that a beam of radiation is incident at a certain point on a rectangular plate in which luminescent materials are uniformly dispersed. With an optical fiber attached to its edge surface, the PL photons are guided to a spectrometer. The spectrum of the PL photons is red-shifted due to self-absorption in the plate. The magnitude of the red-shift is enhanced as the PL photons propagate longer distance inside the plate. Hence, we can determine the distance by quantifying this spectral change. In experiment, we let a laser beam (wavelength 450nm) normally incident on an acrylic plate containing luminescent materials (40 mm × 40 mm × 2.9 mm). The incident position on the plate was varied and from each spectrum recorded we calculated chromaticity coordinates in the CIE1931-XYZ color space. With one sample plate, the coordinate x increased from 0.23 to 0.29 monotonically when we increased the horizontal distance on the plate from 2mm to 20mm. In another sample, the chromaticity coordinates behaved differently but the monotonic relation remained valid. We now have calibration curves for the position. This sensing technique might be suited for long-range position detection, usage in harsh environments and for insertion to narrow places.