Luminescence spectroscopy of high-energy 4f¹¹levels of Er³⁺in fluorides

Abstract

The 4 f 11 energy levels of Er 3þ in LiYF 4 in the spectral region 39 000-65 000 cm À1 have been studied. The agreement between experimental energy levels, obtained from luminescence excitation spectra, and calculated energy levels is good. Luminescence originating from high-lying energy levels has been investigated. in LiYF 4 , where it lies in between the two lowest 4 f 10 5d states. IntroductionThe need for luminescent materials for excitation in the vacuum ultraviolet spectral region (VUV; E > 50 000 cm À1 , < 200 nm) has triggered an increase in research on the VUV spectroscopy of lanthanides. These materials (VUV phosphors) are required for application in mercury-free fluorescent lamps and in plasma display panels [1]. In these devices the VUV radiation generated by a noble gas discharge (e.g. Xe) has to be converted into visible light. In theory, the high energy of VUV photons is sufficient to generate two visible photons for each VUV photon absorbed by a phosphor. In other words, it is theoretically possible to obtain visible quantum efficiencies higher than 100%, which is called quantum cutting. In contrast, the quantum efficiencies of (UV) phosphors used in mercury discharge fluorescent tubes cannot exceed 100% due to the lower energy of the exciting photons. The use of VUV phosphors with quantum efficiencies above 100% can compensate for the lower number of photons generated per watt by the noble gas discharge relative to the mercury discharge.Because of their sharp-line emissions, trivalent lanthanide ions are optical centres for which quantum cutting, or photon-cascade emission, can possibly be obtained. Indeed, quantum cutting has been demonstrated for

Visible photon cascade emission from the high energy levels of Er3+

“…Contrary to what was suggested in [7] a visible quantum efficiency exceeding 100% is theoretically possible. For emission from the 2 F(2) 7/2 level the theoretical quantum efficiency is 112% if X 6 dominates (is much larger than X 2 and X 4 ).…”

“…The crystal field splitting has to be considered in order to find the energy gaps between energy levels for a lanthanide ion incorporated in a host-lattice. For Er 3+ we used the emitting levels that have been observed in previous investigations [7]. In LaF 3 :Er 3+ the highest energy levels from which emission is observed are the 2 F(2) 5/2 (63 110 cm À1 ), 2 F(2) 7/2 (54 390 cm À1 ), 4 D 1/2 (47 150 cm À1 ) and the 2 P 3/2 level (31 570 cm À1 ).…”

“…The recent investigations on the VUV energy levels of lanthanide ions has resulted in many new levels from which photon cascade emission is expected, possibly with quantum efficiencies in the visible above 100%. Recently, the VUV energy levels of Er 3+ were reported [7]. The erbium ion also has a energy level scheme suitable for photon cascade emission in the visible.…”

High-resolution measurements of the vacuum ultraviolet energy levels of trivalent gadolinium by excited state excitation

“…Nevertheless, the highest resolution excitation spectra in the VUV have been recorded using synchrotron radiation. [8][9][10][11] The use of excited state excitation, using tunable dye lasers with a resolution better than 1 cm −1 , offers the possibility to study the VUV levels of lanthanide ions with sufficient resolution to resolve all crystal field components.…”

Energy Level Structure of LiYF<SUB>4</SUB>:Dy<SUP>3+</SUP>: Crystal Field Analysis

“…To get the smoothed values of the B kq for all rare earth ions in the YLF, we used crystal field analysis of Nd 3þ and Er 3þ ions in the YLF, which had been performed in 21) and, 22) respectively. Obtained values of the smoothed crystal field parameters for the whole series of rare earth ions in the YLF crystal are shown in Table 2.…”