Enhancing the 2.7 μm fluorescence emission intensity of Er3+-doped KBa0.94Ca0.06Y(MoO4)3 laser crystal via Nd3+ sensitization and deactivation mechanisms

Abstract

Mid-infrared laser exhibits significant application potential in fields such as national defense, communications, and healthcare. However, despite the fact that the ⁴I_11/2 → ⁴I_13/2 transition of Er³⁺ ions can achieve mid-infrared emission, the process is limited by two major factors: low absorption efficiency of 808 nm pump light and the "self-quenching effect" caused by the short lifetime of the ⁴I_11/2 energy level. These two factors jointly affect the luminescence efficiency of this wavelength band. To overcome this issue, this study reports a novel Nd³⁺/Er³⁺ co-doped KBa_0.94Ca_0.06Y(MoO₄)₃ crystal and the effects of different ion doping concentrations and their interactions on the spectral properties are investigated in detail. The emission competition mechanisms in the Vis, NIR, and MIR bands of crystals doped with different concentrations of Er³⁺ ions under excitation by 808 nm pump light were analyzed. Furthermore, the energy transfer mechanism between Nd³⁺ and Er³⁺ was thoroughly investigated. The experimental results indicate that Nd³⁺ can serve not only as a sensitizer to enhance the population of Er³⁺ ions at the ⁴I_11/2 energy level through an energy transfer mechanism, thereby increasing the emission intensity in the 2.7 μm band, but also as a desensitizer to suppress emissions in the visible and NIR bands and shorten the lifetime of the ⁴I_13/2 energy level, effectively mitigating the "self-quenching effect". When Er³⁺ and Nd³⁺ ions are co-doped at concentrations of 7 mol% and 5 mol%, respectively, the crystals exhibit the highest mid-infrared emission intensity and the lowest pumping threshold, indicating their potential as efficient laser gain media. This study not only delves into the spectral mechanisms of novel laser gain media but also lays a solid theoretical foundation and provides powerful experimental evidence for the practical application of all-solid-state laser gain media in the 2.7 μm wavelength band.