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The amplified spontaneous emission properties of a 2, 1, 3-benzothiadiazole attached polyfluorene semiconductor polymer were studied. The conjugated polymer shows a high photoluminescence quantum efficiency of 67% and emits a narrowed blue emissive spectrum with a full width at half-maximum of 3.6 nm when optically pumped, indicating better lasing action. A threshold energy as low as 0.22 mJ pulse −1 cm −2 , a net gain of 40.54 cm −1 and a loss of 7.8 cm −1 were obtained, demonstrating that this conjugated polymer could be a promising candidate as the gain medium for the fabrication of blue polymer lasers.

In ferri-and paramagnets in the optical region of the spectra a wavelength-independent Faraday effect OL has been discovered, determined by the nondiagonal component x of the magnetic permeability tensor at optical frequencies (1 to 3). XYIt has been shown in (1) that x of the ferrimagnetic garnets can be derived from the phenomenological equation of motion for the magnetic moment. A quantum-mechanical description of the effect in the paramagnet has been carried out in (3). (1) is valid only for paramagnets. In ferrimagnetic garnets exchange interactions between magnetic sublattices must be taken into account.Since the optical frequencies overwhelmingly exceed the frequencies of all intramultiplet transitions, over which we have taken the sum (1) , the result (1) can be extended to ferrimagnets. The relation (1) is the consequence of the universal sum rule (3). So, it is of interest to determine experimentally the frequency-independent Faraday effect in ferri-and paramagnetic garnets, to verify the validity of the expression (1). and to compare the magnetic permeabilities of the rare-earth ions in the optical frequency range for these materials.the Land6 factor of the j-th sublattice. The quantum- JjIn the paper (3) the Faraday effect in YbAlG was investigated and it was shown ion. 3+ that the approximation of J as a good quantum number is fulfilled for the Yb W e have accomplished measurements of the Faraday rotation in YbIG in a magnetic 7 physica (b)

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