Population inversion of G14 excited state of Tm3+ investigated by means of numerical solutions of the rate equations system in Yb:Tm:Nd:LiYF4 crystal

Abstract

Energy transfer rates and population inversion of I 4 11 / 2 excited state of Er 3 + investigated by means of numerical solutions of the rate equations system in Er : LiYF 4 crystal In this work we present the spectroscopic properties of LiYF 4 ͑YLF͒ single crystals activated with thulium and codoped with ytterbium and neodymium ions. The most important processes that lead to the thulium upconversion emissions in the blue region were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the upconversion process that populates 1 G 4 ͑Tm 3+ ͒ excited state. Analysis of the energy transfer processes dynamics using selective pulsed laser excitations in Yb:Tm:Nd, Tm:Nd, and Tm:Yb YLF crystals shows that the energy transfer from Nd 3+ to Yb 3+ ions is the mechanism responsible for the enhancement in the blue upconversion efficiency in the Yb:Tm:Nd:YLF when compared with the Yb:Tm system. A study of the energy transfer processes in YLF:Yb:Tm:Nd crystal showed that the 1 G 4 excited level is mainly populated by a sequence of two nonradiative energy transfers that start well after the Nd 3+ and Tm 3+ excitations at 797 nm according to NdResults of numerical simulation of the rate equations system showed that a population inversion for 481.4 nm laser emission line is attained for a pumping rate threshold of 26 s −1 , which is equivalent to an intensity of 880 W cm −2 for a continuous laser pumping at 797 nm. On the other hand, a population inversion was not observed for the case of 960 nm ͑Yb 3+ ͒ pumping.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

“…The investigation into the timedependent PL behavior (or luminescence lifetime) of UC emissions is a good way to verify the validity of the proposed UC processes, and the rate constants could be extracted by fitting the measured time-dependent emission intensity with transient rate equations. [168][169][170] In a typical ETU process, energy transfer from the sensitizers (e.g., Yb 3+ ) will apparently lengthen the PL lifetimes of the activators (e.g., Er 3+ and Tm 3+ ), which are intrinsically orders of magnitude shorter than that of the sensitizers, due to slow population of the activator's excited state from the long-lived sensitizer's excited state. 171 As a result, the apparent UCL lifetime of the activators strongly depends on those of the sensitizers, which differs markedly from its downshifting PL lifetime upon direct excitation to the high-lying states.…”

Upconverting nanoparticles for pre‐clinical diffuse optical imaging, microscopy and sensing: Current trends and future challenges

“…The investigation on the time dependent behavior of UC emissions is a good way to verify the validity of the proposed UC pathways, and the rate constants could be extracted by fitting the measured time‐dependent emission intensity with time‐dependent rate equations . There are very few reports on the use of this approach on UCNPs in the literature and an interesting topic could be to correlate the microscopic rate constants and the reaction conditions in order to guide the synthesis of UCNPs.…”

Spectroscopic properties of ytterbium, praseodymium-codoped fluorozirconate glass for laser emission at 36 μm

“…11 was fitted using an empirical relation similar to Eq. (4) that has been used to fit upconversion luminescence transients with success in Er 3 and Yb 3 , Tm 3 -codoped fluoride crystals [13][14][15]. The upconversion transfer rate (W UP ) was obtained using…”