Specific spectral features of green to UV and violet up-conversion in Nd<sup>3+</sup>-doped fluorozirconate glass

Abstract

An increasing demand for new techniques of optical recording and processing of information motivates search for new, efficient sources of coherent radiation operating in the short-wavelength part of spectrum (both visible and ultraviolet). Apart from solutions based on wide energy gap semiconductors or frequency multiplication techniques, optical fiber solid state lasers based on low-phonon glasses doped with rare-earth ions continue to be considered as potential efficient short-wavelength sources utilizing optical properties of Nd3+, Ho3+, Er3+ or Tm3+ ions as active dopants [1]. Among these, the trivalent neodymium stands out with a rich energy level structure of the 4fn configuration with at least three high-energy levels known to have emitted UV-violet radiation: 2P 3/2 , 4D 3/2 and 2F(2) 5/2 [1–3]. Particularly, neodymium's highest energy level in the 4f 3 configuration, the 2F(2) 5/2 localized approximately 38600 cm−1 over the ground state, has been known for UV emission in Nd3+-doped silica oxide glasses [2] and fluoride as well as oxide crystals [3]. Still, knowledge of its spectroscopic properties in fluoride glasses, the only solid state medium to enable room temperature UV fiber laser [1 and ref. therein], remains largely incomplete. Because of a relatively weak ground state absorption, this level fails to fluoresce under direct excitation in a fluorozirconate glass, whereas most up-conversion pumping schemes yield dominantly 2P 3/2 and 4D 3/2 activity.