Temperature dependence of O2 singlet photoluminescence in silica nanoparticles

The near infrared singlet emission and photoluminescence lifetime of O2 molecules embedded in silicananoparticles are studied from room temperature down to 10 K. The area of the photoluminescence band underinfrared excitation decreases for temperature above 100 K and the lifetime is shortened. These observations provideevidence of a thermally activated relaxation channel with activation energy of about 40 meV. This relaxationmechanismadds to the already known temperature independent electronic-to-vibrational coupling involving highenergy vibrational modes of the host matrix or its impurities. The thermally activated process is suggested toconsist in the breakage of the O2moleculeweak bondswithwalls of thematrix interstices with ensuingmolecularmotion and collisional exchange of energy.