Photon management with lanthanides

Abstract

Efficient conversion of photons from high energy radiation (e.g. ultraviolet or X-rays) to lower energies (visible) has been optimized by using luminescent materials based on the optical properties of lanthanide ions. Presently, luminescent materials with efficiencies close to the theoretical maximum are applied in e.g. fluorescent tubes, X-ray imaging and color television. Contrary to the mature status of luminescent materials in these fields, areas requiring new luminescent materials are emerging. There is great challenge in research on upand downconversion materials and lanthanide ions are the prime candidates to achieve efficient materials. Here downconversion processes will be discussed for VUV phosphors with Pr 3+ . The efficiency of resonant energy transfer of the 1 S 0 -1 I 6 energy from Pr 3+ to Eu 3+ and Mn 2+ is investigated. The aim is to convert the 405 nm photon of the first step of the well-known cascade emission of Pr 3+ into a more useful visible photon. For co-doping with Eu 3+ it is observed that the Pr 3+ emission is quenched, most probably through a metal-to-metal charge-transfer state. The energy transfer from Pr 3+ to Mn 2+ is found to be inefficient.An alternative for downconversion through resonant energy transfer is the non-resonant process of cooperative sensitization. For the Tb-Yb couple efficient cooperative energy transfer from the 5 D 4 level of Tb 3+ to two Yb 3+ neighbors is observed with a transfer rate of 0.26 ms À1 . This corresponds to an upper limit of 188% for the conversion efficiency of visible (490 nm) photons to infrared ($1000 nm) photons.

Effects of Ce3+ concentration, beam voltage and current on the cathodoluminescence intensity of SiO2:Pr3+–Ce3+ nanophosphor

“…Nie et al [16], on the other hand, reported the energy transfer between Pr 3+ and Cr 3+ in SrAl 12 O 19 . Vergeer et al [17] and Meijerink et al [18] found it difficult to find the efficient energy transfer from Pr 3+ to Eu 3+ irrespective of the fulfilment of an important condition for energy transfer which is the presence of resonance between Pr 3+ and Eu 3+ ions. The luminescence intensities were compared for different gels with and without Mg particles by varying the different concentrations of Mg [19].…”

Enhanced luminous efficiency in Pr3+ activated Ca0.5La(MoO4)2 red phosphor with blue excitation for WLED applications

“…-Mn 2? dual doped KMgF 3 [39], SrY 2 F 8 , YF 3 [40], SrBO 3 [41]. The visible emission spectra of dual doped phosphor shown in Fig.…”

“…and Mn 2? ions, no efficient energy transfer process occurs between them in Ca 0.5 La(MoO 4 ) 2 might be attributed to the selection rules, cross relaxation process, nearest neighboring pairs, total spin of the system change [9,[38][39][40]. By analyzing reflectance and excitation spectra it is recognized that the expected spectral overlaps between Pr 3?…”

Third‐Generation Solar Cells

“…The 3 P 2 , 1 I 0 and P 0 levels at between 440 and 490 nm can absorb blue photons that can then radiatively recombine via the 1 G 4 level at 1010 nm -at just greater than twice this wavelength -thus emitting two photons at just above the silicon bandgap, although nonradiative recombination via the other levels at longer wavelengths than 1 G 4 is also likely. Experiments indicating such photon cutting have been carried out on Pr 3 + embedded in various phosphors, [Meijerink et al, 2006], and also for other lanthanide-doped materials, [Wegh et al, 2002, Michels et al, 2002. Transition metals with their partially screened 'd' shell electrons also have partially discrete levels and work on photon cutting in transition-metal-doped materials has also been carried out, [Ilmas, 1970, Berkowitz andOlsen, 1991].…”