Red light-excitable dual lifetime referenced optical pH sensors with intrinsic temperature compensation.

Red light-excitable pH sensing materials are manufactured which rely on the use of a fluorescent seminaphthorhodafluor indicator and a luminescent inorganic phosphor as a reference. The phosphors, chromium(III)-activated lanthanide aluminium borates, benefit from chemical and photochemical robustness and are not affected by oxygen. Particularly, a dual lifetime referenced sensing material relies on Cr(III)-activated gadolinium aluminium borate which has low temperature dependence of the decay time. The second material is based on highly temperature-sensitive Cr(III)-doped yttrium aluminium borate and enables dual sensing of pH and temperature. Here, the phosphor simultaneously acts as a temperature probe and as a reference for the pH indicator. The adverse effects of temperature on the properties of the pH indicator are compensated for. The dynamic range of the sensors is optimized by varying the ratio of the components which makes the materials suitable for physiological measurements and for marine applications. The rather poor chemical and photochemical stability of the pH indicator at room temperature should be considered if prolonged measurements are performed.