We have investigated the stimulated emission properties of Nd(3+) doped La(2)O(2)S powders at room temperature as a function of pumping energy density, excitation wavelength, and Nd(3+) ion concentration. The absolute stimulated emission energy has been measured. Expressions for the slope efficiencies and lasing thresholds as a function of rare earth concentration and pumping wavelengths, which qualitatively agree with experimental observations, are discussed.
We report internal laser cooling in Yb(3+) -doped KPb(2)Cl(5) . From the quantum efficiency values measured in the heating and cooling regions by use of the photothermal deflection technique, we have obtained a room-temperature cooling efficiency of 0.2% in a sample doped with ~5x10(19)ions/cm(3) . Excitation spectra obtained under high irradiation fluences show an excess of fluorescence with regard to those obtained at low fluences, which agrees with the prediction of a model based on photon-ion-phonon interaction.
In this work we report infrared-to-visible upconversion luminescence in the low-phonon-energy host material KPb 2 Cl 5 codoped with Pr 3ϩ and Yb 3ϩ ions. An orange luminescence from the 1 D 2 level, and less intense blue, green, and red emissions from the 3 P 0,1 levels of Pr 3ϩ have been observed under resonant excitation in the 1 G 4 level of Pr 3ϩ . As regards to Yb 3ϩ , when the 2 F 5/2 level is resonantly excited, the visible emissions are also present but the blue, green, and red emissions from 3 P 0,1 levels are enhanced if compared with the orange luminescence from level 1 D 2 . On the other hand, excitation at the high-energy wing of the 2 F 5/2 level originates emission only from 3 P 0,1 levels. The upconverted fluorescence from the 1 D 2 and 3 P 0,1 levels occurs by energy transfer upconversion and/or excited-state absorption processes depending on the excitation wavelength. The possible mechanisms which lead these processes are discussed.
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