Comparing Pr ³⁺ and Nd ³⁺ for deactivating the Er ³⁺ : ⁴ I _13/2 level in lanthanum titanate glass

Erbium lanthanum titanate glasses were prepared by levitation melting for the spectroscopic study of ways to promote the mid-infrared fluorescence. Two series of heavily erbium doped glasses (15 wt%) were prepared with the addition of either Pr ³⁺ or Nd ³⁺ in amounts relative to Er ³⁺ of 0.05, 0.1, and 0.2. Both ions quench the lower Er ³⁺ laser level with the Pr ³⁺ doing so more rapidly. Although high co-dopant concentrations result in higher energy transfer, as clearly evidenced in upconversion and downconversion fluorescence measurements, the mid-infrared lifetime also suffers a reduction and, therefore, a balance must be struck in the co-dopant concentration. Lifetime and spectral measurements indicate that, at a fixed relative co-dopant amount, Pr ³⁺ is more effective than Nd ³⁺ at removing the bottleneck of the Er ^{3+ 4} I _13/2 level. Moreover, consideration of the lifetimes alongside the absorption data of the individual ions indicates that despite the large absorption cross-section of Nd ³⁺ at 808 nm, the concentration needed to yield more absorbed power than utilizing direct 976 nm excitation of Er ³⁺ results in unfavorable lifetimes of the mid-infrared transition. In the end, Pr ³⁺ prevails as the superior co-dopant in terms of the effects on fluorescence lifetimes as well as potential laser system design considerations. In a unique self-doping approach, a reducing melt atmosphere of Ar instead of O ₂ creates a small fraction of Ti ³⁺ . In 5Er ₂ O ₃ -12La ₂ O ₃ -83TiO ₂ glass, the presence of Ti ³⁺ quenches the ⁴ I _13/2 emission about 2.6 times more than the ⁴ I _11/2 when lifetimes are compared to an O ₂ melt environment. As an additional means of increasing the mid-infrared emission, the effect of temperature on the mid- and near- infrared lifetimes of a lightly doped lanthanum titanate composition is investigated between 77-300 K. The mid-infrared lifetime increases by ∼30% while the near-infrared lifetime increases by ∼10%, which suggests in addition to co-doping, active cooling of the gain media will further enhance performance.