Thulium cross-relaxation in a low phonon energy crystalline host

Abstract

We report on the cross-relaxation of Tm 3ϩ in a low phonon energy chloride host. The temperature and concentration dependence for Tm 3ϩ cross-relaxation in the host YCl 3 was studied between 300 and 500 K, in crystals of YCl 3 with concentrations ranging from 0.7 to 7ϫ10 20 ions/cm 3 . Crystals were grown from melts of anhydrous YCl 3 and TmCl 3 powders under Cl 2 atmosphere using a self-seeded vertical Bridgeman technique. Fluorescence spectra and lifetimes resulting from quasi-cw pumping with a 0.5-W, 811-nm diode were collected and analyzed for the spectral region 1100-2000 nm versus temperature for three crystals with varying Tm 3ϩ densities. Each of the fluorescence spectra contain three broad features centered at 1200, 1490, and 1800 nm that reflect the populations of the first three excited levels of Tm 3ϩ . Rates for multiphonon relaxation and cross-relaxation were determined from the fluorescence lifetime data. An increase in 1200-nm fluorescence as the temperature rises is evidence of an endothermic cross-relaxation process. This suggests a fundamentally new mechanism for optical cooling. A macroscopic rate equation model with its temperature and concentration dependence given by theories for phonon-assisted energy transfer is fit to the spectral data.

Lanthanide upconversion luminescence at the nanoscale: fundamentals and optical properties

“…As a result, the energy transfer rate is linearly dependent with the activator concentration. This agrees well with experimental observations at low activator concentrations 30,77 . However, the UCL intensity reaches an optimum with increasing ion concentration, after which the UCL intensity decreases with further increasing ion concentration.…”

“…Among many nonradiative relaxation channels of an excited Ln 3+ ion, multiphonon relaxation has a special place due to the shielding of f electrons in Ln 3+ ions 77 . Miyakawa and Dexter developed a unified theoretical treatment to various multiphonon processes in the adiabatic approximation 85 .…”

“…Therefore, the concepts that explain resonance energy transfer can be generalised to describe cross-relaxation: the rate of cross-relaxation increases when two ions are in close proximity to each other. The cross-relaxation rates are related to the concentration of the relevant centres 30,77,90 :…”

Energy transfer up-conversion in Tm3+-doped silica fiber

“…The emission spectrum observed is characteristic of the 3 H 4 level. The large dip in the spectrum at ~ 795 nm, is assigned to the strong ground state absorption [15], in silica glass this energy gap can be bridged with the absorption of just one vibrational mode of the glass.…”

Rare-Earth-Doped Low Phonon Energy Halide Crystals for Mid-Infrared Laser Sources

“…Finally, another alternative could be found in the works performed on Tb 3+ and (Tb 3+ ,Tm 3+ )-doped KPb 2 Cl 5 , KPb 2 Br 5 and CsCdBr 3 single crystals, because of their potentially interesting MIR transitions 7 F 5  7 F 6 (4.6-5.5 m) and 7 F 4  7 F 5 (8 m) [Bluiett et al, 2011;Ganem et al, 2002;Lichkova et al, 2006;Okhrimchuk et al, 2002;Rademaker et al, 2004;Roy et al, 2005;Shakurov et al, 2004]. So far, no laser operation based on these systems could be demonstrated.…”