Energy transfer and upconversion of Nd3+ doped RbY2Cl7

Single crystals of Nd3+:RbY2Cl7 were grown by the Bridgman–Stockbarger method. The host crystal contains two slightly inequivalent Y3+ ions, each with an approximate C2v site symmetry. Anti-Stokes emission from the 4G7/2 and 4D3/2 levels was observed after laser excitation of the 4F3/2 and 4F9/2 multiplets. Laser excitation at 413 cm−1 or 453 cm−1 above the 4F3/2 multiplet resulted in emission from the 2P1/2 level. Laser site-selective upconverted emission spectra have been measured, as well as their emission transients and power dependence. Possible excited state absorption and energy-transfer upconversion (ETU) mechanisms are proposed and discussed. Due to the smaller crystal field and a somewhat different energy level structure for the Nd3+ ions in RbY2Cl7 as compared with those observed for Nd3+ in fluoride or oxide hosts, the 4G7/2 and 4D3/2 multiplets are populated under 4F3/2 excitation in a three and four step ETU process, respectively, instead of in a two and three step process as observed for the lighter hosts.