Random lasing and replica symmetry breaking in GeO2-PbO-MgO glass–ceramics doped with neodymium

Abstract

We investigated the random lasing process and Replica Symmetry Breaking (RSB) phenomenon in neodymium ions (Nd3+) doped lead-germanate glass–ceramics (GCs) containing MgO. Glass samples were fabricated by conventional melt-quenching technique and the GCs were obtained by carefully devitrifying the parent glasses at 830 °C for different time intervals. The partial crystallization of the parent glasses was verified by X-ray diffraction. Photoluminescence (PL) enhancement of approx 500% relative to the parent glasses was observed for samples with a higher crystallinity degree (annealed during 5 h). Powders with grains having average size of 2 µm were prepared by griding the GCs samples. The Random Laser (RL) was excited at 808 nm, in resonance with the Nd3+ transition 4I9/2 → {4F5/2, 2H9/2}, and emitted at 1068 nm (transition 4F3/2 → 4I11/2). The RL performance was clearly enhanced for the sample with the highest crystallinity degree whose energy fluence excitation threshold (EFEth) was 0.25 mJ/mm2. The enhanced performance is attributed to the residence-time growth of photons inside the sample and the higher quantum efficiency of Nd3+ incorporated within the microcrystals, where radiative losses are reduced. Moreover, the phenomenon of Replica Symmetry Breaking (RSB), characteristic of a photonic-phase-transition, was detected by measuring the intensity fluctuations of the RL emission. The Parisi overlap parameter was determined for all samples, for excitation below and above the EFEth. This is the first time, for the best of the authors knowledge, that RL emission and RSB are reported for a glass–ceramic system.