Chromium-neodymium Energy Transfer in Yap

Yttrium aluminum perovskite (YAP) co-doped with CI3' and Nd3+ is of interest in laser applications because the chromium-neodymium energy transfer is more efficient in YAP than in YAG. Investigation of the energy transfer from the chromium R lines and pair states in the wavelength range 720-740 nm to the Nd3+ upper laser level shows that neither individual C? ions nor C?+-C? pairs are important energy donors in YAP. The results are consistent with a model of nonuniform distribution of donors. Single crystals of YAlO,, also known as yttrium aluminum perovskite (YAP), or yttrium orthoaluminate, are of interest as a laser host for specialized applications. The orthorhombic symmetry of YAP' causes anisotropy in the optical properties of substitutional, optically-active ions, and this anisotropy can be exploited in device desigm2 For applications in which the lasing ion is a rare earth and the pump source is broad-band, it is desirable to co-dope the crystal to improve the spectral overlap between the pump emission and the activator ion. One common combination of rare earth activator ion and co-doped sensitizer is Nd3+ and Cr3+. Recent detailed spectroscopic investigations of a similar material, Y3Al,0,, (yttrium aluminum garnet, or YAG)?B~ have shown that in this simpler cubic system both C? and Nd9 occupy several inequivalent sites. This work has also demonstrated that in YAG the main C?+ site does not transfer energy to the main Nd3+ site, thus limiting the usefulness of co-doping in increasing the efficiency of Nd:YAG lasers. It is thus important to investigate similar materials to search for one in which energy transfers by a more efficient connection between the main sites of activator and sensitizer ions. Previous studies5" have indicated that in YAP the energy transfer between Cr3+ and Nd3+ ions is more efficient than in YAG, and that the fluorescence dynamics of Nd3+ both alone and with Cr3+ may be unusually complex. In particular, multiple C? sites have been found in this host, and the Cr3+ fluorescence decay of co-doped Nd,Cr:YAP crystals cannot be explained by a model which assumes uniformly-distributed donors? Thus YAP is an interesting candidate material for more efficient Nd3+ lasers. Since the distance between adjacent Cr3+ sites is relatively small in YAP (3.8 A as compared to 5.2 A in YAG)," one possible source of the additional complexity of the fluorescence dynamics in co-doped Nd,Cr:YAP crystals is the existence of strong interactions between Nd3+ ions and Cx3+Cr3+ pairs. Thus, we have investigated the relationship between the lowest-lying C3' single-ion and cr3'-Cr3' pair states and emission from the Nd3+ 4F3, level, which is the usual upper level in Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1991798