Luminescence spectra (excitation and emission) and luminescence
decays curves have been recorded for KPb2Cl5:Er
3+
1% co-doped with
0%, 2%, 4%, 6% and 10% Yb
3+
to investigate the potential of the (Er
3+
,
Yb
3+
) couple in a chloride host material for downconversion. The
results show that the desired downconversion process from the
4
F7/2
level (the inverse of the efficient upconversion process) has very low
efficiencyduetofastmulti-phononrelaxationfromthe
4
F7/2tothe
4
S3/2
level via the intermediate
2
H11/2 level. Based on the energy gap
between the
4
F7/2 and the
2
H11/2 levels (1200 cm
1
)this was
unexpected, since thishost has aphononenergyof 200 cm
1
.Analysis
of luminescence decay curves shows that energy transfer from Er
3+
to
Yb
3+
is inefficient. In a host with even smaller phonon energies (viz.
bromide host materials) efficient emission from the
4
F7/2level, and
therefore downconversion, may be possible.
In the diffuse reflectance spectra a broad band of excitation to
the Yb
3+
–Cl
charge transfer band was observed between 300 and
400 nm. Excitation in this LMCTband results in twobroademission
bands centered around 430 and 700 nm at temperatures below
30 K. The emission is assigned to luminescence from the Cl
–Yb
3+
charge transfer state, which can also feed the Yb
3+ 2
F5/2 level,
followed by Yb
3+ 2
F5/2-2
F7/2emission around 980 nm
Luminescence spectra (excitation and emission) and luminescence
decays curves have been recorded for KPb2Cl5:Er
3+
1% co-doped with
0%, 2%, 4%, 6% and 10% Yb
3+
to investigate the potential of the (Er
3+
,
Yb
3+
) couple in a chloride host material for downconversion. The
results show that the desired downconversion process from the
4
F7/2
level (the inverse of the efficient upconversion process) has very low
efficiencyduetofastmulti-phononrelaxationfromthe
4
F7/2tothe
4
S3/2
level via the intermediate
2
H11/2 level. Based on the energy gap
between the
4
F7/2 and the
2
H11/2 levels (1200 cm
1
)this was
unexpected, since thishost has aphononenergyof 200 cm
1
.Analysis
of luminescence decay curves shows that energy transfer from Er
3+
to
Yb
3+
is inefficient. In a host with even smaller phonon energies (viz.
bromide host materials) efficient emission from the
4
F7/2level, and
therefore downconversion, may be possible.
In the diffuse reflectance spectra a broad band of excitation to
the Yb
3+
–Cl
charge transfer band was observed between 300 and
400 nm. Excitation in this LMCTband results in twobroademission
bands centered around 430 and 700 nm at temperatures below
30 K. The emission is assigned to luminescence from the Cl
–Yb
3+
charge transfer state, which can also feed the Yb
3+ 2
F5/2 level,
followed by Yb
3+ 2
F5/2-2
F7/2emission around 980 nm
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