Photophysical Characterization and Laser-Active Properties of (Dy,Ba)-Codoped ZrO ₂ Nanocrystals for Yellow Solid-State Laser and Optical Amplifier Applications

There is a growing need to find efficient phosphors and laser materials, minimizing cost and enhancing stability. Dysprosium-codoped Ba–ZrO2 nanocrystals are promising candidates for yellow solid-state laser and optical amplifier applications due to their tunable emission and phase-dependent luminescence. Varying concentrations (x = 0, 0.01, 0.02, ..., 0.08) of Dy3+ and a fixed concentration of Ba2+ (x = 0.03) were incorporated into ZrO2 nanocrystals using the chemical bath technique. Rietveld refinement results indicate a pure tetragonal phase for low Dy3+ concentrations (x = 0.01–0.04) and a mixture of tetragonal–cubic phases for higher Dy3+ concentrations (x = 0.05–0.08), suggesting that the structural phase of ZrO2 nanocrystals is critically dependent on both the synthesis technique and the concentration of the rare-earth ions. With increased Dy3+ doping, the energy band gap is observed to monotonically decrease for the tetragonal phase and increase for the mixed tetragonal–cubic phases. Judd–Ofelt analysis yielded high stimulated emission cross sections (25.8 × 10–20 cm2), branching ratios (0.98), gain bandwidth (46.0 × 10–28 cm3), optical bandwidth (15.3 × 10–25 cm2 s), and quantum efficiencies (97%) for the yellow transition. Diffuse-reflectance spectroscopy, fluorescence decay analysis, and CIE chromaticity mapping further support the suitability of these nanocrystals for low-temperature photonic devices. However, low thermal quenching temperatures limit their use in high-power light-emitting diodes.