Vacuum ultraviolet 5d$^1$4f$^9$-4f$^{10}$ emission of Ho$^{3+}$ ions in alkaline-earth fluorides

TL;DR

This study investigates the emission properties of Ho$^{3+}$ ions in alkaline-earth fluorides, revealing specific spin-forbidden and allowed transitions with detailed decay characteristics relevant for optical applications.

Contribution

It provides new insights into the emission spectra and decay dynamics of Ho$^{3+}$ in CaF$_2$, SrF$_2$, and BaF$_2$, highlighting the nature of spin-forbidden and allowed transitions.

Findings

Long decay time emission near 168 nm from spin-forbidden transitions.

Weak emission at 158 nm observed only in CaF$_2$-Ho crystals.

Identification of excitation bands near 166 and 155 nm corresponding to allowed and forbidden transitions.

Abstract

Time-resolved emission, excitation as well as emission decay curves of CaF$_2$, SrF$_2$, BaF$_2$ doped with HoF$_3$ were investigated. Most intensive emission bands near 168 nm, having long decay time, belong to spin-forbidden transitions from 5d$^1$4f$^9$ high spin (HS) states to ground $^5$I$_8$ states of Ho$^{3+}$ ions. Weak spin allowed 5d$^1$4f$^9$(LS)-4f$^{10}$ emission band at 158 nm was observed only in CaF$_2$-Ho crystals. Spin allowed and spin-forbidden excitation bands were observed in all crystals near 166 and 155 nm respectively. Fast component of spin-forbidden emissions due to multiphonon relaxation to low-lying 4f$^{10}$ Ho$^{3+}$ level was observed for all crystals.