  Infrared luminosities vLv(7.8 um) arising from dust reradiation are
determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4 < z < 5 using
detections at 22 um by the Wide-Field Infrared Survey Explorer. Infrared
luminosity does not show a maximum at any redshift z < 5, reaching a plateau
for z >~ 3 with maximum luminosity vLv(7.8 um) >~ 10^{47} erg per s; luminosity
functions show one quasar per cubic Gpc having vLv(7.8 um) > 10^{46.6} erg per
s for all 2 < z < 5. We conclude that the epoch when quasars first reached
their maximum luminosity has not yet been identified at any redshift below 5.
The most ultraviolet luminous quasars, defined by rest frame vLv(0.25 um), have
the largest values of the ratio vLv(0.25 um)/vLv(7.8 um) with a maximum ratio
at z = 2.9. From these results, we conclude that the quasars most luminous in
the ultraviolet have the smallest dust content and appear luminous primarily
because of lessened extinction. Observed ultraviolet/infrared luminosity ratios
are used to define "obscured" quasars as those having > 5 magnitudes of
ultraviolet extinction. We present a new summary of obscured quasars discovered
with the Spitzer Infrared Spectrograph and determine the infrared luminosity
function of these obscured quasars at z ~ 2.1. This is compared with infrared
luminosity functions of optically discovered, unobscured quasars in the SDSS
and in the AGN and Galaxy Evolution Survey. The comparison indicates comparable
numbers of obscured and unobscured quasars at z ~ 2.1 with a possible excess of
obscured quasars at fainter luminosities.
