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 ⁴I_9/2 → {⁴F_5/2, ²H_9/2}, and emitted at 1068 nm (transition ⁴F_3/2 → ⁴I_11/2). The RL performance was clearly enhanced for the sample with the highest crystallinity degree whose energy fluence excitation threshold (EFE_th) 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 EFE_th. This is the first time, for the best of the authors knowledge, that RL emission and RSB are reported for a glass–ceramic system.