PALS investigations of matrix Vycor glass doped with molecules of luminescent dye and silver nanoparticles. Discrepancies from the ETE model

Abstract

Abstract.A thermal stability of three materials: undoped reference Vycor glass, glass fi lled with ROT-305 red dye, and silver nanoparticles was investigated by positron annihilation lifetime spectroscopy (PALS) in a broad temperature range (from 93 to 473 K). The attempt of pore size calculations from the ortho-positronium lifetime data was performed using the extended Tao-Eldrup (ETE) model. Below room temperature, a signifi cant decrease in lifetime values of the longest-lived component was found for all the samples. This effect could not be explained by thermal shrinkage of the material and is probably caused by interaction of o-Ps with a Vycor glass matrix. The greatest discrepancy from the ETE model predictions was observed for the reference glass. Doping the base material with dye molecules and silver nanoparticles resulted in similar small decrease in this discrepancy. After reheating the samples to the room temperature, the PALS components returned to the initial values. In the temperature range of 293-473 K, quite good agreement between PALS results and the ETE model predictions was observed for the reference glass and the glass incorporated with dye molecules. The observed small discrepancy in this range could possibly be partly explained by thermal expansion of the material. For the glass doped with silver nanoparticles, a signifi cant change in PALS parameters was observed in the temperature range from 403 to 473 K.

Toward a European Network of Positron Laboratories

“…Recent measurements of the o-Ps lifetime in Vycor glasses [25] vs. temperature showed some persistent hysteresis: lifetimes change after cooling cycles and remain such until baking of the sample is applied. Measurements without the use of positron beams hardly explain this problem.…”