Application of pressure to the nonemitting system Lu 2 O 3 :Ce 3ϩ leads to the generation of luminescence in the visible. The luminescence is assigned to the 5d→4 f transition of Ce 3ϩ , and is attributed to a pressureinduced electronic crossover of the excited 5d state of Ce 3ϩ and the conduction-band edge of Lu 2 O 3 . The results yield insight into the emission efficiency of 5d→4 f transitions, and provide a foundation for advancing new phosphors and tunable laser materials in the visible and ultraviolet based on the broad 5d→4 f emission of lanthanides.There is currently tremendous interest in the discovery of luminescent materials that emit at progressively shorter wavelengths. Short wavelength visible and ultraviolet ͑UV͒ emitting materials are desired for applications in imaging, lithography, optical data recording, tunable solid state lasers, scintillation, and displays. The challenges associated with obtaining efficient emission at short wavelengths has motivated work directed at creating materials systems with properties based on phenomena. Recent examples include the nitride semiconductors, 1 nanocrystalline materials, 2,3 and quantum cutting phosphors. 4 Lanthanide and transition-metal-doped insulators have enjoyed much success as luminescent materials, but have received relatively little attention for short-wavelength visible and UV-emitting applications. Because of efficient nonradiative decay from upper excited states, transition metals normally emit only from the first excited state. Since the first excited states of transition metals are located at energies corresponding to midvisible or near-infrared ͑NIR͒ wavelengths, the prospects for obtaining green, blue, or UV emission from transition-metal-activated materials appear to be limited. Short-wavelength visible and UV emission does occur from first or higher excited states in lanthanide ions. In most cases, lanthanide emission consists of narrow 4 f →4 f emission lines. As a result, lanthanide emission is oftentimes inconvenient to excite, and occurs at a limited number of discrete wavelengths, with little opportunity for achieving tunability.Most notable, Ce 3ϩ , Eu 2ϩ , and Sm 2ϩ lanthanide ions exhibit 5d→4 f emission. 5-10 5d→4 f emission is potentially advantageous for many applications because it combines the desirable broad absorption and emission features of transition metals with the high-energy emission properties of lanthanides. Although broad 5d→4 f emission has been observed in selected systems at wavelengths ranging from the NIR to the UV, its application has been limited and its potential for addressing current needs at short visible and UV wavelengths is only now becoming realized.The enigmatic nature of 5d→4 f transitions is one factor that has limited their application. Specifically, it has long been known that the emission efficiency of 5d→4 f transitions varies widely and randomly with the host lattice. Most studies have focused on Ce 3ϩ , and have shown that in some host lattices ͑e.g., Lu 2 SiO 5 ), Ce 3ϩ emits with high qu...

Many anaIytical methods have been used to identify the chemical composition of archaeological artefacts [1-4]. Museum CIRTA of the town of Constantine has a collection of more than 35000 coins and statuettes going back to Numide, Roman, Republican, Vandal and Byzantine times and is struck in the name of the cities, of the kingdoms and the empires. Surface analysis of these coins gives informations about the chemical composition and leads to recommendations for restoration and presevation. This work is a contribution of microchemical surface study of three coins with the effigy of the Numide King Massinissa (between 3rd and 2nd century before Jesus Christ). Scanning electron microscopy coupled with energy dispersive spectrometry (SEM + EDS) and energy dispersive fluorescence spectrometry (XRF) were used. The bulk of three coins is massif homogeneous metallic. Two coins are manufactured with lead (99.896% and 61.56%) and were probably conserved differently. The third one is from copper (92.28%). The optic microscopy (OMP) and SEM pictures of coins show heterogeneous surface with typical lead alteration products white patina of plumbonacrite, cerussite and hydrocerussite and red patina of cupric oxide on the cupric artefact. MS25 P09 Effects of Er 3+ and Yb 3+ doping on phase transitions of LiNH 4 SO 4 .