Thulium Doped Phosphors Under VUV Excitation
- PDF / 915,044 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 176 Views
1111-D08-04
Thulium doped phosphors under VUV excitation. Bernard Moine and Léna Beauzamy Laboratoire de Physico-Chimie des Matériaux Luminescents, CNRS, UMR5620, Université Lyon 1, Université de Lyon, 69622 Villeurbanne, France Richard S. Meltzer Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA ABSTRACT Development of highly efficient mercury free fluorescent lamps and plasma display panels has been a challenging task due to the need for a combination of phosphor properties that are difficult to obtain in a single material (high efficiency, short emission lifetime and weak sensitivity to aging process under VUV excitation). Quantum cutting mechanism is a way to improve the fluorescence efficacy. Here we describe quantum cutting involving pairs of Tm3+ ions in KY3F10. Efficient excitation in the vacuum UV is initiated to the 5d state of Tm3+. This is followed by a cross relaxation energy transfer (CRET) involving the excited ion in the 5d state and nearby Tm3+ in the ground state, producing a pair of Tm3+ in excited states of the 4f13 configuration. Both ions can then emit photons. The excitation and reflection spectra are studied as a function of Tm3+ concentration and temperature. An unusual enhancement of the reflectivity at excitation wavelengths corresponding to the Tm3+ 5d absorption peaks is shown to arise from strong 5d→4f emission which is confirmed from the VUV emission spectra. The strong reduction of the integrated 5d emission intensity and shortening of its lifetime with Tm3+ concentration indicates the effective presence of the desired CRET process that is required for the first step of the quantum cutting. High Tm3+ concentrations are required for efficient quantum cutting. Whereas the CRET from the 5d state is estimated to be quite efficient, the 4f13 states of Tm3+ also undergo a strong CRET and therefore, emission from the 4f13 excited states that are created from the first step are strongly quenched at high Tm3+ concentrations. As a result, quantum yields greater than unity are not achieved.
INTRODUCTION The use of xenon in plasma display panels and in new fluorescent lamps as a substitute for mercury necessitates phosphors capable of emitting more than one visible photon for each vacuum ultraviolet VUV photon absorbed. Such phosphors have a quantum yield greater than 1 and operate by a process called quantum cutting or down-conversion. This paper describes a
detailed study of a phosphor capable of emitting two blue photons for each VUV photon absorbed: KY3F10 (KYF): Tm3+. The quantum cutting occurs by a cross-relaxation energy transfer CRET in a pair of Tm3+ ions. The quantum cutting is characterized by emission, excitation, and reflectivity measurements in the visible, UV, and VUV ranges, and is studied as a function of concentration and temperature. In the first part a rationale is given for how Tm3+ as dopant ion and KY3F10 as host lattice where chosen. The second part describes the methods used to synthesize the materials and give some experimental de
Data Loading...
