Influence of BaCl₂ Nanocrystal Size on the Optical Properties of Nd³⁺ in Fluorozirconate Glass

Abstract

The optical properties of Nd 3+ ions embedded in fluorochlorozirconate glasses were studied, addressing in particular the effect of BaCl 2 nanocrystal growth in the matrix upon annealing. A Judd−Ofelt analysis for these glasses and for a Nd 3+ -doped fluorozirconate reference glass without nanocrystals yielded various radiative decay rates as a function of nanocrystal size. For the 4 F 3/2 to 4 I 9/2 transition, where multiphonon relaxation is negligible, the rates agree very well with experimental results. Further support for the validity of the Judd−Ofelt results was obtained using an alternative approach for the determination of radiative decay rates involving emission and absorption spectra and their connection through the McCumber theory and the Fuchtbauer−Ladenburg equation. The obtained variations of the Judd− Ofelt intensity parameters Ω λ reflect systematic changes in the local environment of the Nd 3+ ions as an effect of the BaCl 2 nanocrystal growth, indicating partial inclusion of Nd 3+ into the nanocrystals.

Light Management in Solar Modules

“…Currently however, although there are first promising up-conversion results under intense monochromatic illumination [20,21], the efficiency of the frequency conversion processes under normal solar illumination is far too low for any reasonable application. Therefore, research in that field is still mainly focused on understanding the fundamental processes determining the conversion efficiency (e.g., [22][23][24]). …”

Highly Efficient and Broadband Upconversion of NIR Sunlight with Neodymium‐Doped Glass Ceramics

“…A comprehensive rate equation model was set up covering the dynamics of the first 15 excited states in neodymium (up to 25 000 cm −1 ). Upon ground‐state absorption or ESA, processes like spontaneous emission, phonon emission or absorption as well as energy transfer and cross‐relaxation (CR) are modeled considering their spatial, time‐ and power‐dependence.…”

“…The influence of the latter with respect to phonon deexcitation channels was then modeled with an energy‐gap law for nanocrystals and the two contributions summed up. To practically assess the solutions of the glass and glass‐ceramic equation systems, the multiple overlaps of different transitions j → i within a single wavelength interval Δ λ were considered by summing up the individual spectral intensity contributions A SPE, j is the total radiative decay rate of level j , β ji is the branching ratio for the transition j → I , and N j is the occupation number density in j . Unlike the description of laser‐induced upconversion which included Gaussian beam shape and time dependence, the analysis of broadband solar excitation was made for spatially and temporally constant excitation light.…”

“…Neodymium though, does appear to benefit from the remarkably low maximum phonon energies of the nanocrystals, which lead to a huge increase of its (upconversion) emission intensity under excitation at 800 nm wavelength . For photo­voltaic upconversion in connection with silicon‐based solar cells, these findings however do not let neodymium appear as very attractive material, because its monochromatic upconversion step at 800 nm is already way beyond the silicon bandgap, with already very high quantum efficiency for direct (single photon) photovoltaic conversion.…”

“…The aim of this work is to give a prognosis on the feasibility of an upconverter device for broadband solar NIR radiation on the basis of ZBLAN‐based glasses and glass ceramics for an application in photovoltaics. The analysis is based on a comprehensive rate equation model that was established to describe time‐ and power‐dependent dynamics of neodymium embedded into these matrices …”