Enhancement of Green Terbium-Related Photoluminescence from Highly Doped Microporous Alumina Xerogels in Mesoporous Anodic Alumina

Abstract

Strong enhancement of green photoluminescence ͑PL͒ from microporous alumina xerogels, highly doped with terbium ͑from 30 to 60 wt % as Tb 2 O 3 ͒, is reported. The regular structure of a 30 m thick, mesoporous anodic alumina layer was exploited for spin-on deposition of the alumina xerogel in a single step. The green PL, associated with predominant 5 D 4 → 7 F 5 transitions, along with 5 D 4 → 7 F j , j ϭ 3, 4, 5, 6 transitions of Tb 3ϩ , was found to increase with terbium concentration in the alumina xerogel. This effect is attributed to cross-relaxation. The thermal quenching of the green terbium-related emission does not exceed a factor of two within a temperature range from 10 to 300 K for any of the alumina xerogels confined in anodic alumina. Further, such quenching is much reduced with the rise of temperature compared with (i) Tb-doped titania xerogel, ͑ii͒ Tb-implanted thermally grown silicon dioxide film, and ͑iii͒ Tb-doped alumina xerogels fabricated onto monocrystalline silicon. Thus, the terbium-doped structure comprising alumina xerogel/anodic alumina is proposed as a basis for green room-temperature luminescent images. ver the last decade, the low-cost sol-gel method for fabricating luminescent structures containing incorporated optically active lanthanides has been investigated intensively. The sol-gel method allows diverse xerogel films, highly doped with lanthanides, to be produced. Spin-on deposition was usually employed in fabrication of films doped with optically active erbium, 1,2 neodymium, 3 terbium, 4 and other lanthanides. Unlike the dry processes, 5 the sol penetrates the mesopores of porous silicon, promoting synthesis of a xerogel film in the pore volume of a layer of several micrometers thickness. Strong 1.53 m photoemission from porous silicon, coated with a spin-on, erbium-doped silica gel film, has been shown. 1,6 Exploitation of the mesoporous layer avoids procedures involving numerous sequential spin-on depositions, which are needed to obtain strong room-temperature photoluminescence ͑PL͒ from lanthanide ions in a xerogel film of several micrometers thickness.Recently, we reported enhancement of terbium PL from a terbium-doped titania xerogel, mesoscopically confined in porous anodic alumina. 4 Porous anodic alumina exhibits a regular porous morphology, with pores at the centers of approximately hexagonally packed cells. 7 The regular morphology of porous anodic alumina, with pores passing normally to the macroscopic substrate surface, possesses some advantages over the irregular geometry of mesoporous silicon 8 for synthesis of sol-gel derived products. In addition, their regular mesoscale morphology can be extended to thicknesses of 100 m. Porous alumina has been demonstrated to be an excellent support for xerogel solids doped with the optically active lanthanides. 4,9,10 The combination of mesoporous layers and xerogels doped with optically active lanthanides enhances the lanthanide photoluminescence. This has already been confirmed for lanthanides incorporated within xerogel ...

Influence of porous anodic alumina matrix upon europium luminescence from sol–gel-derived films

“…It is seen in the insert that the xerogel layer processes also in the surface of PAA and the pores are still opened for further xerogel penetration inside. After 5-10 spin-on steps the full pore filling is approached [10] and planarization of PAA surface by xerogel occurs [11].…”

Luminescence of Lanthanides from Xerogels Embedded in Mesoporous Matrices

“…High-transparency of anodic alumina oxide on the one hand and strong optical anisotropy on the other hand may be the reasons of growing interest to exploit this material as a cage for light-emitting species. Filling the channels of the pores of anodic alumina films with silica [36][37][38], titania [23,[39][40][41][42], alumina [43][44][45] xerogels doped with lanthanide ions Er [37][38][39], Tb [23,38,44] and Eu [35,[40][41][42]45], organic dyes [46], semiconductor nanocrystals [47,48], polymers [ 49,50], quantum dots [51,52], and biological samples [53] was investigated, and strong luminescence of optically active species incorporated in voids of anodic alumina or, probably, in its walls [54,55] was reported.…”

Time-resolved photoluminescence analysis of distribution and migration of terbium ions in zeolites X

“…Concentration quenching is attributed to resonant ion-ion interactions located in close proximity. According to literature, terbium-terbium interactions in the 5 D 4 state are generally considered negligible [24][25][26][27].…”

“…Considering the structure of terbium energy levels (Scheme 1) and data on various terbium compounds including zeolites [12,[24][25][26][27] it is unlikely that the 200 ms based decay component is the result of the PL quenching of the 5 D 4 through ion-ion interactions. Further, assuming that terbium forms various complexes through coordination to zeolite oxygen atoms and OH groups, a lifetime shorter than E400 ms that is the lifetime of full hydrated terbium ion is not expected.…”