We have designed and synthesized NaGdF 4 :Nd 3+ , Yb 3+ , Tm 3+ magnetic nanophosphors with combined dual-mode downconversion (DC) and upconversion (UC) photoluminescence upon 800 nm excitation. Hexagonal-phase NaGdF 4 :Nd 3+ , Yb 3+ , Tm 3+ nanocrystals (NCs) with an average size of 21 nm were synthesized using a solvothermal approach. Nd 3+ , Yb 3+ , Tm 3+ triple-doped NaGdF 4 NCs exhibit a broad range of photoluminescence peaks covering a near infrared first/second window (860-900, 1,000, and 1,060 nm), and visible emission including blue (475 nm), green (520 and 542 nm) and yellow (587 nm) after excitation at 800 nm. A mechanism involving circulation of energy over Gd 3+ sublattices as bridge ions and final trapping by the initial activator ions (Nd 3+ ) has been proposed. Penetration depth studies indicate that NIR emission is easily detected even at a large tissue thickness of 10 mm. These paramagnetic nanophosphors demonstrate a large magnetization value of 1.88 emu/g at 20 kOe and longitudinal relaxivity value of 1.2537 mM -1 ·S -1 as a T 1 -weighted magnetic resonance imaging contrast agent. These NaGdF 4 :Nd 3+ , Yb 3+ , Tm 3+ NCs are promising for applications in biological and magnetic resonance imaging.
We report temperature-induced tuning of whispering gallery mode (WGM) laser emission from a Rhodamine-B-doped polymethylmethacrylate hollow optical fiber. Lasing studies on dye-doped hollow fibers with different radii were carried out with optical pumping using a Q-switched Nd:YAG laser. The observed lasing modes were confirmed as WGM emission with a high quality factor of 7.58×10. The diameter-dependent variation in lasing spectra of these hollow fibers was investigated. A tuning range of 0.44 nm with a sensitivity of 0.011 nm/°C was obtained for the lasing modes by varying the temperature from 25°C to 60°C from a dye-doped polymethylmethacrylate hollow fiber of diameter 305 μm.
Wavelength tuning of whispering gallery lasing modes has been observed from Rhodamine-B-doped polymer fibers under tensile strain. Good quality whispering gallery lasing modes are produced from both solid and hollow fibers by transverse optical pumping. The lasing modes are shifted linearly toward the shorter wavelength side when the fiber is elongated in the axial direction. Compared with solid fiber, the lasing modes of hollow fiber can be tuned over the entire gain spectrum with a tuning range of ∼5 nm. It is found that the tuning of the lasing modes of hollow fiber is reversible.
We report on the realization of a silver (Ag) nanoparticle doped polymer optical fiber random laser. Lasing characteristics and photostability of the system with varying concentration of Ag nanoparticles have been investigated. It was found that there is an enhanced spectral narrowing and emission intensity in rhodamine 6G–Ag nanoparticle doped polymer optical fiber compared to that of bare rhodamine 6G doped polymer optical fiber. In contrast with the latter, low-threshold coherent feedback random lasing with improved photostability was observed for an optimum concentration of Ag nanoparticles in the gain medium.
In this letter, we report random laser action in a system where optical amplification is provided by colloidal CdSe quantum dots (CQDs) triggered by the emission from Rhodamine 6G. The laser emission from CdSe QDs is optically excited by Rh-6G which in turn is photo-pumped by a frequency-doubled Q-switched Nd : YAG laser system at an excitation wavelength of 532 nm. At intensities greater than the threshold value, laser emission is characterized by narrowing peaks.
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