  In order to detect and characterise cold extended circumstellar dust
originating from collisions of planetesimal bodies in disks, belts, or rings at
Kuiper-Belt distances (30-50 AU or beyond) sensitive submillimetre observations
are essential. Measurements of the flux densities at these wavelengths will
extend existing IR photometry and permit more detailed modelling of the
Rayleigh-Jeans tail of the disks spectral energy distribution (SED),
effectively constraining dust properties and disk extensions. By observing
stars spanning from a few up to several hundred Myr, the evolution of debris
disks during crucial phases of planet formation can be studied. We have
performed 870-micron observations of 22 exo-Kuiper-Belt candidates, as part of
a Large Programme with the LABOCA bolometer at the APEX telescope. Dust masses
(or upper limits) were calculated from integrated 870-micron fluxes, and fits
to the SED of detected sources revealed the fractional dust luminosities
f_dust, dust temperatures T_dust, and power-law exponents beta of the opacity
law. A total of 10 detections with at least 3-sigma significance were made, out
of which five (HD 95086, HD 131835, HD 161868, HD 170773, and HD 207129) have
previously never been detected at submillimetre wavelengths. Three additional
sources are marginally detected with >2.5-sigma significance. The best-fit beta
parameters all lie between 0.1 and 0.8, in agreement with previous results
indicating the presence of grains that are significantly larger than those in
the ISM. From our relatively small sample we estimate f_dust proportional to
t^(-alpha), with alpha~0.8-2.0, and identify an evolution of the characteristic
radial dust distance R_dust that is consistent with the t^(1/3) increase
predicted from models of self-stirred collisions in debris disks.
