Luminescence-center-mediated excitation as the dominant Er sensitization mechanism in Er-doped silicon-richSiO2films

Abstract

The structural and optical properties of erbium-doped silicon-rich silica samples containing 12 at. % of excess silicon and 0.63 at. % of erbium are studied as a function of annealing temperature in the range 600-1200°C. Indirect excitation of Er 3+ ions is shown to be present for all annealing temperatures, including annealing temperatures well below 1000°C for which no silicon nanocrystals are observed. Two distinct efficient ͑ tr Ͼ 60% ͒ transfer mechanisms responsible for Er 3+ excitation are identified: a fast transfer process ͑ tr Ͻ 80 ns͒ involving isolated luminescence centers ͑LCs͒, and a slow transfer process ͑ tr ϳ 4 -100 s͒ involving excitation by quantum confined excitons inside Si nanocrystals. The LC-mediated excitation is shown to be the dominant excitation mechanism for all annealing temperatures. The presence of a LC-mediated excitation process is deduced from the observation of an annealing-temperature-independent Er 3+ excitation rate, a strong similarity between the LC and Er 3+ excitation spectra, as well as an excellent correspondence between the observed LC-related emission intensity and the derived Er 3+ excitation density for annealing temperatures in the range of 600-1000°C. The proposed interpretation provides an alternative explanation for several observations existing in the literature.

Efficient energy transfer from Si-nanoclusters to Er ions in silica induced by substrate heating during deposition

“…3,25 The slight shift to higher energies, in spite of T d increase, reflects some lowering in the average size of Si-nc which is quite compatible with the above-commented decrease in Si excess. It is also worth noting that this visible emission was similarly observed and attributed to Si-nc by Savchyn et al 9,26,27 for their samples annealed at 1000°C during only 100 s. On the contrary, no contribution is detected in our samples of the so-called luminescent centers ͑LCs͒ emitting at around 500 nm. 9 The presence of a significant Er-PL in our as-deposited samples ͑for T d Ն 200°C͒ excited with a nonresonant wavelength reveals the occurrence of an efficient energy transfer from Si-nc to Er 3+ .…”

“…This is due to the lack of contrast between the amorphous Si-nc and the silica matrix, as stated by previous studies. 9,18 Moreover, the smallness of Si-nc in our as-deposited films makes difficult their observation by energy filtered TEM approach. 18 Nevertheless, a rough estimate of the Si excess content is possible from the analysis of the TO 3 -peak energy shift evolution in the FTIR spectra of our SRSO:Er film, as described elsewhere 19 and adopted in our previous work.…”

“…[4][5][6][7][8] It is then essential to nanoengineer the density and distribution of both Er 3+ ions and Si-based sensitizers within the silica matrix. In this regard, several groups have analyzed the influence of different annealing treatments on the optical performance of SRSO:Er layers [9][10][11][12][13] usually deposited at room temperature ͑RT͒ before being subsequently annealed at different temperatures. Such a process allowed the formation of Si-nc sensitizers and then the observation of Er photoluminescence ͑PL͒ under nonresonant optical excitation.…”

Si nanoparticle–Er3+ coupling through contact in as-deposited nanostructured films

“…[2][3][4] This limits the percentage of Er 3+ ions that are optically excited, usually to values of a few percent; and only recently has a value of 23% been achieved. 4 This is still far below the excitation fraction of 50% that is considered to be necessary to achieve gain, as has been proposed by recent reports, which suggest different routes to improve the excitation by achieving a longer excitation energy-transfer distance, 5 by using alternative excitation routes such as Si-related luminescent centers, 6,7 or by Er-doping of amorphous silicon-rich oxides. 8 The use of synthesis processes that allow control of the dopant location at the nanoscale is also a promising route.…”

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

“…13,14 In addition to the relatively slow ͑ s range͒ NC-mediated Er 3+ excitation, a much faster ͑100 ns range͒ and usually more dominating process has also been concluded. 15 Its physical origin has been considered recently 16 and participation of special luminescence centers in erbium excitation has been postulated in particular for low-temperature annealed samples. However, in spite of a considerable progress by both modeling and experiment, 4,17 many issues still lack sufficient explanation.…”