Bi-Tm-codoped, and Tm-and Bi-singly doped germanate glasses were prepared, and their luminescent properties were investigated. Intense broadband near-IR emission with FWHM of 300 nm was observed in the Bi-Tm codoped glass. The emission intensity of Tm 3+ : 3 H 4 -13 F 4 and 3 F 4 -13 H 5 transitions in the BiTm-codoped glass was highly increased and reduced, respectively. The fluorescence lifetime of Tm 3+ at 1470 nm increased from 204 s to 301 s after codoping. These should be due to the efficient energy transfer from Bi-related centers to Tm 3+ ions. The highest energy transfer efficiency is estimated to be ϳ50%. OCIS codes: 160.2540, 300.6280, 250.5230. Owing to the rapid development of computer network and optical telecommunication, the wavelength division multiplexing (WDM) system demands fiber amplifiers with broader and more efficient gain bandwidth in the telecommunication windows. Although Er 3+ -doped fiber amplifier (EDFA) is available, its bandwidth is limited in silicate hosts to a maximum of 40 nm at the C band. Based on the bandwidth expansion of conventional EDFA at the C band by optical amplification at the S band of Tm 3+ -doped optical fibers (TDFA) [1], Er 3+ -Tm 3+ -codoped glasses were proposed for the broadband amplification in the S + C bands [2,3]. However, the bandwidth of all these rare-earth-doped glasses cannot cover the whole low-loss optical fiber transmission window ͑1270-1600 nm͒.
© 2009 Optical Society of AmericaRecently, Bi-doped glasses with broadband near-IR (NIR) luminescent properties have been extensively studied [4][5][6][7][8][9][10][11][12][13][14]. Among them, germanate glasses are particularly attractive because of their efficient luminescence [6]. Optical amplification in 1272-1348 nm and 1430-1495 nm wavelength ranges has been demonstrated in Bi-doped germanate glasses [11,12] and silicate fibers [13], respectively. Broadband optical amplification covering 1270-1600 nm wavelength region was also reported in Bi-doped germanate glasses, although rapidly decreased optical gain has to be accepted with the increment of signal wavelength, since there is a strong resemblance between the wavelength-dependent optical gain and fluorescence spectrum [14].For practical application in the WDM system, the materials with efficient and flat amplification characteristic are necessary, since gain excursion over the whole spectral width can be minimized. Based on our earlier studies, it is possible to obtain ultrabroadband emission through codoping bismuth with Tm 3+ .However, to our knowledge, there is no related report until now. In this Letter, we report on broadband NIR luminescence properties in Bi-Tm-codoped barium alumino-germanate glasses. The emission with an FWHM of 300 nm ͑1270-1570 nm͒ covering the whole O, E, S, C, and L bands was observed. The emission intensity of Tm 3+ : 3 H 4 -3 F 4 is highly increased by efficient energy transfer from bismuth ions to Tm 3+ . Glasses with an initial reagents ratio composition of 62GeO 2 -15.0Al 2 O 3 -11.8BaO -11.2Na 2 O -xTm 2 O 3...