In this work we report a detailed spectroscopic study of the near-infrared to visible upconversion luminescence in Erdoped lanthanum oxysulfide crystal powders after excitation of level <sup>4</sup>I<sub>9/2</sub>. The analysis of the decay curves of the upconversion emission indicates that energy transfer upconversion is the main mechanism responsible for the green (<sup>4</sup>S<sub>3/2</sub>) and red (<sup>4</sup>F<sub>9/2</sub>) upconversion luminescence. The temperature dependence of the green upconverted emission from the two thermally coupled <sup>2</sup>H<sub>11/2</sub> and <sup>4</sup>S<sub>3/2</sub> levels has been analyzed in the 230 K- 300 K temperature range in order to check its availability as a temperature sensor.
We report the use of the low cost hot-pressing technique to produce ZnS for multispectral operation, from visible up to
12 μm. Considerable progress has been obtained by developing efficient precipitation and combustion powders synthesis
procedures. The main emphasis has been on the elaboration of ZnS precursor powders with controlled
morphology/chemical composition to reduce extrinsic scattering and impurities. We were able to produce ZnS parts with
visible transparency and transmission in the 8-12 μm range that is comparable to that of CVD ZnS. The correlation of
processing variables with powders sinterability and optical transmission of the HPed ceramics is discussed.
Gadolinium oxysulfide crystal is a wide-gap semiconductor material known as an excellent host for trivalent rare-earth ions. The present investigation explores the upconversion and thermal properties of Er<sup>3+</sup>-doped Gd<sub>2</sub>O<sub>2</sub>S crystal powders as well as their potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and temperature field for samples of various erbium concentrations is presented.
The present investigation explores the upconversion properties of Er<sup>3+</sup>- doped La<sub>2</sub>O<sub>2</sub>S crystal powder as well as its potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and of the temperature field of samples with various erbium concentrations is presented. The analysis of both spectroscopic and thermal measurements shows that after a transient heating induced by the background absorption, cooling can be attained by means of anti-Stokes processes.