Upconversion Effects in Resonantly Pumped Er3+ and Pr3+ Doped Low Phonon-Energy Crystals for Eye-Safe Laser Applications.

摘要

In this work, cw and pulsed a 1532 and a 1440 nm laser excitation of the 4I13/2 band of Er3+ and 3F3,3F4 band of Pr3+ was explored in low phonon-energy hosts KPb2Cl5 and KPb2Br5. Crystal growth along with upconversion and eye-safe emission (approximately 1.5-1.6 m) studies were conducted on both Er3+ and Pr3+ doped materials. Excitation spectra and emission decay transients of the infrared (4I9/2-->4I15/2) and green upconversion (2H11/2 + 4S3/2-->4I15/2) originating from Er3+ doped KPb2Cl5 and KPb2Br5 revealed that energy transfer upconversion (ETU) is the origin of the infrared and the green upconversion under 1532 nm excitation. Relative population calculations indicated that infrared upconversion is approximately two orders of magnitude stronger relative to the green upconversion. Interestingly, the upconversion microparameters for the infrared upconversion are very small having the values CDA approximately 3.5x10-42 cm6/s and CDA a 2.0x10- 42 cm6/s for Er: KPb2Cl5 and Er: KPb2Br5, respectively. Due to the strong spectral overlap of the 4I13/2-->4I15/2 emission and 4I15/2 -- >4I13/2 absorption bands Er-Er migration is believed to be assisting the energy transfer upconversion process in both Er: KPb2Cl5 and Er: KPb2Br5. Calculations indicated that the probability for energy migration is large yielding donor-donor critical radii of RDD approximately 16 and RDD ~ 17 for Er: KPb2Cl5 and Er: KPb2Br5, respectively, which are quite large but not unexpected due to the small stokes shifts between the 4I13/2-->4I15/2 emission band and 4I15/2-->4I13/2 absorption band of Er3+ in KPb2Cl5 and KPb2Br5. Visible upconversion was also observed in Pr3+ doped KPb2Cl5 and KPb2Br5 under 1440 nm excitation where the emission originates from the 3P0, 3P1, and 1D levels. Emission decay measurements imply that ETU is the basis of the upconversion in Pr3+.