Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm³⁺ and Dy³⁺ ions incorporated in crystal structures of Yal YAl₃(BO₃)₄, LiNbO₃, Gd₃Ga₅O₁₂, Gd₂SiO₅, Lu₂SiO₅ and (Gd, Lu)₂SiO₅ are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions ⁴ G _5/2 → ⁶ H _7/2 of Sm³⁺ around 600 nm and ⁴ F _9/2 → ⁶ H _13/2 of Dy³⁺ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10^?20 cm² for Sm³⁺ in (Gd, Lu)₂SiO₅ to 1.17 × 10^?20 cm² for Sm³⁺ in LiNbO₃. Those for dysprosium-doped crystals range from 0.63 × 10^?20 cm² for LiNbO₃:Dy³⁺ to 2.0 × 10^?20 cm² for Yal YAl₃(BO₃)₄:Dy³⁺. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.