An absorption-type optical pH sensitive film based on immobilized
PCP in sol–gel film has been demonstrated. The PCP sensitive
film linearly responds over a broad dynamic pH range of 2–11
within 2 min and its reproducibility is less than 0.3%. The refractive
index nf and thickness df of the film is not changed with variation
of pH value. While the film extinction coefficient kf changes regularly
as pH increasing, tendency of which is in agreement with that
of the film absorbance at 633 nm. It is suggested that the sensing
model based on p-polarized reflectance method is reasonable and
this PCP-pH sensitive film is an absorption-type film. Our preliminary
results show that the natural indicator PCP is promising in
preparing pH sensitive film, and the PCP sensitive film has a great
application in fabricating absorption-type pH sensor.