Frequency Upconversion in YF3:Yb3+,

Abstract

The stepwise conversion of infrared (=0.97 p) radiation to near infrared {0. 81 p) and visible (0.475 p) light in YF3 sensitized with Yb ' and activated with Tm ' has been studied in detail. The lifetimes and fluorescence intensities of the important manifolds (Yb I"&~2, Tm 3H4, Tm E4, and Tm G4), as we11 as the Yb-to-Tm transfer probability coefficients for the three steps of the process, have been measured as functions of concentration. A saturation effect previously observed in the Tm emission versus infrared excitation intensity has been shown to result from the rate of depopulation of Tm H4 by the second Yb-to-Tm transfer exceeding the Tm H4 decay rate. This was used to determine the second transfer probability coefficient.The first transfer probability coefficient was found to be 1.2&&10 ' cm sec independent of Tm concentration and for Yb concentration of the order of 10 at. /o and greater. The second transfer probability coefficient was found to be approximately 10 4 cm sec for Yb concentrations of 25 at. % and greater. The third transfer probability coefficient was found to be 2. 7x10 cm sec . The dependence on Yb concentration of the relative efficiency of conversion to 0.475p light agrees well with the values calculated from a rate-equation model using the measured lifetimes and transfer probability coefficients.

Energy transfer efficiency in YF3 nanocrystals: Quantifying the Yb3+ to Tm3+ infrared dynamics

“…The population dynamics and the emission of the different Yb 3þ and Tm 3þ levels in macroscopically sized YF 3 crystals have been described in a classical paper by Ostermayer et al 27 Nevertheless, it was demonstrated that while the first up-conversion step can be accurately characterized, the quantitative evaluation of the second and third ones is not so straightforward. 27,32 Considering all these facts, we will focus our attention in the quantification of the first energy transfer step probability.…”

“…As an example, in the inset of Figure 2 co-doped materials, the different energy levels of Tm 3þ ions are populated through a chain of at least three consecutive energy transfer processes from Yb 3þ ions. 27,28 These processes are schematically depicted in Figure 2(c).…”

“…27 After selective Yb 3þ excitation, the dynamics of the ytterbium excited state ( 2 F 5/2 ) can be expressed (applying the notation for the energy levels shown in Figure 2(c)) as…”

“…27,32 Considering all these facts, we will focus our attention in the quantification of the first energy transfer step probability.…”

Lanthanide upconversion luminescence at the nanoscale: fundamentals and optical properties

“…These transitions need to be selectively and individually excited 71,116,117 . A specific rate equations model is then proposed and its parameters adjusted to fit the experimental data.…”