Tunable random lasing in dye-doped mesoporous silica SBA-15

Mesoporous silica, known as SBA-15, possesses a hexagonal pore structure, with 8-nm-diameter pores and high surface area $\left(\sim 700{\mathrm{m}}^2/\mathrm{g}\right)$. The mesoporosity of SBA-15 is excellent to be filled with luminescent chromophores aiming at optical and photonic applications. SBA-15 powder infiltrated with Rhodamine B (RB) was prepared with different RB loads. Using the second harmonic of a pulsed Nd:yttrium aluminum garnet (YAG) laser (8 ns, 10 Hz) as the excitation source, the light emission spectra of the samples were investigated. Typical incoherent feedback random laser behavior was observed. Tunable random laser emissions from 579 to 585 nm were obtained depending on the excitation laser spot diameter and the RB load. The results indicate that mesoporous SBA-15 infiltrated with RB is a promising material for the development of solid-state random lasers.

Figure 1

Experimental setup for luminescence and random laser measurements.

Figure 2

Pore-size distribution of SBA-15, SBA-RB1, and SBA-RB2 powders. Inset shows details of the pore-size distribution for pure and RB-doped SBA powders.

Figure 3

Thermogravimetric analyses of SBA-15 powders doped with two different RB dye concentrations. The inset shows a photography of the samples SBA-RB1 (left) and SBA-RB2 (right) with different loads of RB.

Figure 4

SEM images of the SBA-15 powder.

Figure 5

TEM image of the SBA-15 powder particle.

Figure 6

Emission spectra of SBA-RB1 and SBA-RB2 samples at low pump fluence of excitation ($0.5\mu \mathrm{J}/\mathrm{m}{\mathrm{m}}^2$, 532 nm, 8 ns). The inset shows a photograph of the SBA-RB1 powder under ambient light (top) and under excitation of a 405-nm laser spot (down).

Figure 7

RL emission spectra evolution as a function of the pump fluence. Laser excitation spot diameter equal to 1.9 mm: (a) SBA-RB1 and (b) SBA-RB2. (c) Normalized emission of both samples excited with $0.95\mathrm{mJ}/\mathrm{m}{\mathrm{m}}^2$.

Figure 8

Emission peak intensity vs pump fluence for SBA-RB1 (a) and SBA-RB2 (b). Emission linewidth vs pump fluence for SBA-RB1 (c) and SBA-RB2 (d). The solid lines are guides to the eyes. Excitation spot diameter equal to 1.9 mm.

Figure 9

RL threshold as a function of excitation spot diameter for SBA-RB1 (solid red circles) and SBA-RB2 (solid blue squares). The solid lines are guides to the eyes.

Figure 10

(a) Emission wavelength as a function of excitation spot diameter for SBA-RB1 (solid red circles) and SBA-RB2 (solid blue squares) samples. The solid lines are guides to the eyes. (b) Selected normalized emission spectra of both samples (SBA-RB1 and SBA-RB2) for distinct excitation spot diameters.