High Temperature Oxygen Sensing Using K2Mo6Cl14 Luminescence

A reflection mode optical sensing system for monitoring oxygen in high temperature gas flows, 25-220degC and 500 sccm, is presented. The sensor is based on
³
O
₂
quenching of the red emission from K
₂
Mo
₆
Cl
₁₄
, one member of a family of hexanuclear molybdenum chloride clusters. One advantage of using inorganic Mo-clusters as the lumophore is the lack of sensitivity to gases typically present in a coal-fired boiler due to the triplet nature of the transition from the excited to ground state. The sensor is prepared by dip-coating fiber tip in a sol-gel solution containing K
₂
Mo
₆
Cl
₁₄
particle clusters. Drying and aging yields a composite film with K
₂
Mo
₆
Cl
₁₄
immobilized in a porous silica matrix. The composite film deposited on a planar substrate was characterized via in-situ spectroscopic measurement up to 200degC. The emission intensity is constant following 56 cumulative hours of heating at 200degC, demonstrating long-term stability at high temperature