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Keywords:

  • upconversion;
  • oxygen sensors;
  • triplet-triplet annihilation;
  • luminescence;
  • porphyrin

Abstract

A novel concept for designing optical oxygen sensing materials is reported. Oxygen-sensitive anti-Stokes emission is generated via triplet–triplet annihilation-based upconversion and serves as an analytical parameter. Porous glass beads are used to incorporate the “sensing chemistry” including a sensitizer and an annihilator dissolved in a high boiling solvent. The beads are dispersed in silicone rubber or Teflon AF to produce solid state optodes. Inexpensive low power light sources (LEDs) are used for the excitation. The upconverted emission shows unmatched sensitivity both for the luminescence decay time and for the luminescence intensity. The latter features unusual quadratic Stern-Volmer plots. Much lower sensitivity of the residual NIR luminescence of the sensitizer allows determination of pO2 in the broad dynamic range from trace oxygen quantities to ≈40 kPa. Interrogation of the sensors in frequency domain is demonstrated. Influence of the excitation light power on the calibration, temperature effects, dynamic response to altering pO2, and photostability of the sensing materials are also investigated.