  The Planck catalogues of SZ sources, PSZ1 and PSZ2, are the largest
catalogues of galaxy clusters selected through their SZ signature in the full
sky. In 2013, we started a long-term observational program at Canary Island
observatories with the aim of validating about 500 unconfirmed SZ sources. In
this work we present results of the initial pre-screening of possible cluster
counterparts using photometric and spectroscopic data of the Sloan Digital Sky
Survey DR12. Our main aim is to identify previously unconfirmed PSZ2 cluster
candidates and to contribute in determination of the actual purity and
completeness of Planck SZ source sample. Using the latest version of the PSZ2
catalogue, we select all sources overlapping with the SDSS DR12 footprint and
without redshift information. We validate these cluster fields following
optical criteria (mainly distance with respect to the Planck pointing,
magnitude of the brightest cluster galaxy and cluster richness) and combining
them with the profiles of the Planck Compton y-maps. Together, this procedure
allows for a more robust identification of optical counterparts compared to
simply cross-matching with existing SDSS cluster catalogues that have been
constructed from earlier SDSS Data Releases. The sample contains new redshifts
for 37 Planck galaxy clusters that were not included in the original release of
PSZ2 Planck catalogue. We detect three cases as possible multiple counterparts.
We show that a combination of all available information (optical images and
profile of SZ signal) can provide correct associations between the observed
Planck SZ source and the optically identified cluster. We also show that Planck
SZ detection is very sensitive even to high-z (z>0.5) clusters. In addition, we
also present updated spectroscopic information for 34 Planck PSZ1 sources (33
previously photometrically confirmed and 1 new identification).
