J.P. Jouart

Site-selective upconversion excitation of Er3+:KYF4

A spectroscopic study of the green (4S3/2 4I15/2) and blue (2P3/2 4I11/2) emissions from Er3+:KYF4 induced by a red tunable laser excitation is realized at liquid nitrogen temperature, for two Er3+ concentrations: 0.1 and 5 at.%. The emission spectrum can only be accurately interpreted by considering that it is due to two sites, whose contributions are successfully isolated using a two-step absorption process via 4I13/2 for the green emission and a three-step absorption process via 4I13/2 and 4S3/2, for the blue emission. The excited-state energy transfer prevails over the excited-state absorption at high concentration (5 at.%).

Photoluminescence of Eu3+ in KYF4 and KLuF4

Abstract Using selective dye-laser excitation between 17250 and 17350 cm−1, the Stokes and anti-Stokes emission spectra arising from four Eu3+ centres have been isolated in KYF4 and KLuF4.Our results show that the Eu3+ ions occupy only four sites in KYF4, whereas the structural study foresees six sites. The Eu3+ sites of KLuF4 are very similar to those of KYF4.

Site selective laser spectroscopy of BaF2:Eu3+

Abstract The selective laser excitation of the flourescence of Eu3+ ions is used to investigate the defect sites in BaF2:Eu3+ for Eu3+ concentrations ranging from 0.03 to 2.43 mol%. We identified the fluorescence lines arising from the (Eu3+, F-i) dipole of C3v symmetry and established its energy level diagram. The compensating ion is an interstitial F-i ion located in the next-nearest-neighbour site, with respect to the Eu3+ ion. This (Eu3+, F-i) dipole dominates in BaF2. Fluorescence lines assignable to next-nearest-neighbour pairs of (Eu3+, F-i) dipoles have been found above 0.1 mol% dopant concentration.

UPCONVERSION FLUORESCENCE OF HO3+ IONS IN A BAF2 CRYSTAL

Abstract Efficient upconversion luminescence from the Ho3+ C3v centre in a BaF2 crystal is reported. The red-to-green and red-to-blue upconversion is observed upon pumping with a single cw red dye laser. The upconversion mechanism is assigned as a sequential two-photon excitation process in which the excitation wavelength is resonant with either ground state absorption (GSA) or excited state absorption transitions. The efficient green upconversion with excitation into GSA results from a double-resonant excitation between the 5I8→5F5 and 5I7→5F3 transitions.

Cubic Eu3+ centres in fluorite-type crystals

Abstract The laser excitation of the fluorescence of the Eu3+ ion is used to investigate the cubic Eu3+ sites of CdF2, CaF2, SrF2, PbF2 and BaF2. We identified the fluorescence lines arising from the cubic Eu3+ sites and established the energy level diagrams.

Three-photon upconversion in Er3+ doped Ca3Al2Ge3O12

Abstract Efficient upconversion fluorescence from an Er 3+ center in Ca 3 Al 2 Ge 3 O 12 has been observed, upon pumping with a single red dye laser. The mechanism for the blue upconversion is either a sequential three-photon absorption or an energy transfer process depending on the laser energy being tuned on either the excited state absorption or the ground state absorption transitions. Owing to a double resonant excited state absorption transition character, the three-photon blue upconversion efficiency is relatively high.

Red laser induced upconversion luminescence in Er-doped calcium aluminum germanate garnet

In this work, we have studied the spectroscopic and dynamic properties of the green (4S3/2→4I15/2) and blue (2P3/2→4I11/2) upconversions for a series of Er3+ doped Ca3Al2Ge3O12, induced by a red tunable laser excitation. The green emission is due to either an energy transfer involving two ions excited in the 4I11/2 multiplet or an excited state absorption from the 4I13/2 level, depending on whether the laser excitation wavelength is tuned on 4I15/2→4F9/2 or 4I13/2→4F5/2. The blue emission mainly results from a three-step absorption process through the 4I13/2 and 4S3/2 multiplets. The temperature and concentration effects have been analyzed for the green and blue upconversions.

Energy transfer up-conversion in CdF2:Er3+ and SrxCd1−xF2:Er3+

Abstract We study the influence of the site distribution on the up-conversion processes of Er3+ in CdF2 and SrxCd1−xF2 crystals. While the transfers efficiently occur in clusters despite large energy mismatches, they are closely dependent on an energy coincidence in the case of single centres. We show that the two-photon excitation spectra are essential tools to select the up-conversion sequences.

Anti-stokes emissions and determination of stark sub-level diagram of Er3+ ions in KY3F10

We are interested, in this work, in determining the Stark sub-level of Er3+ ions doping a KY3F10 single crystal with a molar concentration of 1%. We have used a new method of measurement of energies of the ground level and emitting levels from excitation and anti-Stokes emission spectra recorded at liquid nitrogen temperature. This technique is based on a spectral analysis of the anti-Stokes emissions recorded after selective excitation with a red dye tunable laser. Thus, we could determine the Stark sub-levels of the ground and the principal emitting levels in the infrared, visible and near-UV ranges with a very good precision.

Red-to-blue up-conversion spectroscopy of Tm3+ in SrF2, CaF2, BaF2 and CdF2

A spectroscopic study of the blue emission from different Tm 3+ centres of SrF 2 , CaF 2 , BaF 2 and CdF 2 crystals for CW red excitation by a single dye laser is presented. Our observations suggest that the cubic Tm 3+ centres are excited by an avalanche process rather than by a sequential two-photon process