VUV SPECTROSCOPY OF CRYSTALLINE EMITTERS BASED ON 5d–4f TRANSITIONS IN RARE EARTH IONS

Abstract

The spectroscopic properties of several fluoride crystals ( LiYF 4, KYF 4, K 2 YF 5, KLiYF 5, CsY 2 F 7, SrF 2) doped with Nd 3+, Er 3+ or Tm 3+ are analyzed from the viewpoint of their possible applications as active media for VUV solid state lasers. It has been found that in many crystals there exists very efficient nonradiative relaxation from higher-lying 5d states to the lowest 5d level responsible for the spin-forbidden luminescence. In fact, the energy level diagram of 5d–4f transitions for these two ions represents a typical four-level laser scheme with a considerably larger Stokes shift of 5d–4f luminescence from the edge of the strong spin-allowed 4f–5d absorption than for Nd 3+, which causes smaller reabsorption of emitted VUV radiation in the crystals doped with Er 3+ or Tm 3+. Two crystals LiYF 4: Nd 3+ and SrF 2: Er 3+ were tested for laser action under pumping by a pulsed F 2 laser operating at 157 nm. However, no indications of the appearance of stimulated emission have been detected for both crystals. The possible reasons for the absence of lasing are discussed.