Transparent Er:(Y,La) 2 O 3 Ceramics With High La 3+ Concentration for Mid‐Infrared Laser Applications

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Exploration of mid‐infrared laser materials with broad emission spectra is crucial for the generation of ultrashort pulses, particularly in spectroscopic and material processing applications. The incorporation of La 3+ ions into Er:Y 2 O 3 , a representative mid‐infrared laser material, induces crystal lattice distortion and broadens its emission spectrum. However, the La 3+ doping concentration is typically limited to approximately 10 at.% owing to the formation of secondary phases. In this study, transparent (Er 0.05 Y 0.95‐ x La x ) 2 O 3 mixed sesquioxide ceramics with high La 3+ concentration of x = 0.2 was fabricated together with x = 0, 0.05, and 0.1 via co‐precipitation and low‐temperature spark plasma sintering (SPS) to investigate the effects of La 3+ concentration on mid‐infrared emission properties. Both the emission spectral width and luminescence lifetime at approximately 2700 nm increased with increasing La 3+ concentration. For x = 0.2, the values were approximately 17 nm and 3.8 ms, respectively, compared to approximately 4 nm and 3.3 ms for x = 0. Although the x = 0.2 sample achieved an in‐line transmittance above 80% at 2720 nm, it was still lower than those of samples with lower La 3+ content. Microstructural analysis revealed that La 3+ addition reduced the average grain size and formed residual pores, likely responsible for increased optical scattering. To eliminate the residual pores, post‐hot isostatic pressing (HIP) treatment was conducted at various temperatures, which resulted in improved optical transmittance. We believe that optimizing processing conditions could further enhance optical quality at high La 3+ concentrations, making it a promising candidate for mid‐infrared laser applications.