Efficient Enhancement of Bismuth NIR Luminescence by Aluminum and Its Mechanism in Bismuth‐Doped Germanate Laser Glass

Abstract

As a new member of laser glass family, bismuth‐doped glasses have received rising interests due to the application of fiber amplifiers and laser sources in the new spectral range for the next‐generation optical communication system. For practical application of the glasses, it must be considered on how to improve the luminescence efficiency. Here, we demonstrate that addition of aluminum can enhance the bismuth near‐infrared luminescence by more than 10 000 times, which is right followed by the discussion on the mechanism on why this can happen. We believe this work can be helpful for designing bismuth‐doped multiple component laser glasses with high efficiency. In addition, because of high susceptibility of bismuth to local field change, it can be used as probe ion to envision glass structures. Using bismuth as a luminescent structural probe, we can see the modifier ions of Bi+ are not completely randomly distributed inside germanate glass and they prefer the residence around tetrahedral AlO4 sites.

Predictable tendency of Bi NIR emission in Bi‐doped magnesium aluminosilicate laser glasses

“…22 Thus, we think what we observed in 3.2 correlates tightly to the glass structure changes as magnesium content is modulated. Because the absorptions and emissions of bismuth are from the 6p electrons which lie in the outmost orbitals, it can sense the tiny changes of local structure and therefore exhibit the tunable absorptions and emissions.…”

“…22 For glass samples containing lower content of magnesium, the integrity of glass network is basically better than those higher magnesium content doped samples. The initial increase in the peak means the increasing content of bismuth NIR emission center, and it implies that glass structure in the samples of 15%-30% should be beneficial to generation of bismuth NIR emission centers.…”

“…At the longer wavelength side of the peak at 700 nm, there is a weak absorption shoulder at 800 nm (see Figure 1). 21,22 If we examine the peak carefully, we notice that it is asymmetric at longer wavelength. 18,19 Once bismuth is introduced to glass network at higher temperature, different valent bismuth ions can be created and the conversion reaction between each other will soon reach an equilibrium.…”

“…Lower glass viscosity makes the release of the gases trapped in the melt more readily. 22 As a consequence, the distance between bismuth centers can be elongated, and the interaction between the centers can be weakened, and, therefore, the nonradiation processes can be suppressed. This has been evidenced by the enhanced vibration absorption at~700 cm À1 and formation of the new bridge bond of Si-O-Al (see Figure 4).…”

“…Traditional erbium fiber amplifier can work only in a narrow spectral range, [8][9][10][11] i.e., 36 nm in width around 1.53 lm, and it is physically impossible to fully utilize the low loss window of silica fiber such as 1000-1600 nm. 7,[16][17][18] Since bismuth NIR luminescence is known from the outmost 6p electrons, [19][20][21][22][23] it is highly sensitive to the changes of local crystal field bismuth resides. Bismuth [12][13][14][15] doped NIR glasses and fibers recently appeared as a new family of laser materials for this purpose, and they have aroused increasing interests since the beginning of 21st century due to its super broadband luminescence in 1000-1600 nm, and the success in tunable fiber lasers.…”