Sol-gel synthesis of rare-earth-doped fluoride glass thin films

This paper describes ZBLA fluoride glass thin films produced via an inexpensive, low-temperature reactive atmosphere sol-gel approach. Luminescence from erbium at 1.55 mu m has been observed in x-ray-amorphous doped films deposited on calcium fluoride, polyimide, sapphire, and silicon substrates. Fluorescence studies of the erbium S-4(3/2) --> I-4(13/2) transition, a characteristic emission for a reduced phonon energy host, were conducted for both sol-gel-derived films and conventionally prepared glass rods. The peak intensity observed from the sol-gel films was blue-shifted by 16 nm with a FWHM value approximately half that measured for the melt-quenched rods. Excitation studies indicate that, unlike conventionally prepared glasses, sol-gel materials suffer from nonradiative relaxation of the S-4(3/2) excited state to the I-4(9/2) level, where subsequent radiative emission to the I-4(15/2) ground state occurs. The proposed source of the quenching mechanism are remnant species inherent to the sol-gel process. While this causes the luminescence behavior of rare-earth-doped sol-gel-derived fluoride materials to be similar to oxide hosts, these remnant species modify the branching ratios, resultantly leading to a novel 824 nn emission when excited at 488 nm.