
302 Nanosensors: Physical, Chemical, and Biological
made of nanocrystallites of different sizes and Er
3+
concentrations. How are
the measurements done? For the uorescence measurements, the samples were
placed on a hotplate and the temperature was monitored with TCs located
close to the samples. Frequency-upconverted emissions centered at 526 and
547 nm from two thermodynamically coupled excited states of Er
3+
doped in
BaTiO
3
nanocrystals were recorded (Figure 5.9). The samples were excited
with a low-power, continuous wave diode laser (wavelength: 980 nm; inten-
sity: 2.0 × 10
3
W cm
−2
) and the upconverted uorescence, easily visible to the