Vacuum ultraviolet spectra and crystal field analysis of YAlO
3
doped with Nd
3+
and Er
3+
Chang-kui Duan and Peter A. Tanner
Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong Special Administrative Region,
People’s Republic of China
Vladimir N. Makhov
Lebedev Physical Institute, Leninskii Prospect 53, 119991 Moscow, Russia and Institute of Physics, University of Tartu, Riia 142, 51014
Tartu, Estonia
Marco Kirm
Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
Received 19 January 2007; revised manuscript received 20 March 2007; published 25 May 2007
The synchrotron radiation excited emission and excitation spectra are reported at temperatures of 298 and
10 K for YAlO
3
YAP doped with 1 at. % Nd
3+
or Er
3+
. For both systems, no d- f emission is observed and
these results are rationalized and compared with other hosts. For YAP: Nd
3+
, excitation into the 4 f
2
5d elec-
tronic configuration of Nd
3+
gives intraconfigurational luminescence from
2
G2
9/2
and
4
F
3/2
and there is no
evidence for emission from other multiplet terms. Luminescence from
2
P
3/2
is observed for YAP:Er
3+
, with
additional transitions from
4
S
3/2
,
4
F
9/2
,
4
I
9/2
, and
4
I
11/2
. The emission spectra have been assigned in detail. The
literature energy level datasets are mostly consistent with the derived energy levels from the present study. The
f -d excitation spectra show that the lowest d-electron levels are energetically situated below the intrinsic
absorption of the host. Crystal field analyses have been performed by using 100 energy levels for each system
and the resulting standard deviations were 12.4 and 15.5 cm
-1
for Er
3+
and Nd
3+
, respectively. The multiplet
term barycenters are better fitted for the case of Nd
3+
, whereas crystal field splittings are better modeled for
Er
3+
. The fitted free ion parameters exhibit considerably less uncertainty for Nd
3+
.
DOI: 10.1103/PhysRevB.75.195130 PACS numbers: 78.55.-m, 32.30.Jc, 71.70.Ch, 32.50.+d
I. INTRODUCTION
The YAlO
3
YAP crystal is a widely used host for lasers,
scintillators, and optical recording media and it comprises
the substrate material for thin films of high-temperature su-
perconductors. The YAP crystal crystallizes in the orthor-
hombically distorted perovskite structure, belonging to the
D
2h
16
Pnma or No. 62 symmetry space group, and details
can be found in Refs. 1 and 2. Lanthanide ions replace Y
3+
ions with C
s
site symmetry and are surrounded by 12 O
2-
ligands with Y-O distances ranging from 0.2306 to
0.3010 nm. Detailed experimental investigations of absorp-
tion and reflection spectra of the pure compound in the en-
ergy range 6.5–42 eV have been presented in Refs. 3–5. Lu-
minescence excitation spectra of intrinsic emissions of pure
YAP at liquid helium temperature have been also investi-
gated in the vacuum ultraviolet VUV. According to the
literature the band-gap energy of YAP is 8.8 eV, the maxi-
mum of the excitonic absorption is at 8.0 eV, and the onset
of intrinsic absorption can be located at 7.6–7.7 eV.
6
The
energy band structure of YAP has been calculated recently by
Bercha et al.
7
The infrared and Raman spectra of YAlO
3
Ref. 8 and NdAlO
3
Ref. 9 have been reported.
The 4 f -4 f intraconfigurational spectra of Nd
3+
and Er
3+
in
YAlO
3
have received considerable attention. The detailed
scheme of the energy levels of these ions in YAlO
3
is de-
picted in Fig. 1. Antonov et al.
10
deduced the complete set of
levels for Er
3+
up to
4
G
11/2
26 500 cm
-1
from the 77 K
optical spectra. Donlan and Santiago
11
subsequently ex-
tended these studies and deduced 104 energy levels from
emission and absorption spectra at 4.2 K. The energy levels
have been tabulated by Kaminskii
12
and Morrison and
Leavitt.
13
The major interest in YAlO
3
:Er
3+
has resulted
from its laser action. At room temperature, laser action has
been observed at 550,
14,15
851,
16
1.66 m Refs. 17–19
from
4
S
3/2
, and 2.7–2.9 m Refs. 20–22from
4
I
11/2
.
The population dynamics and decay properties relevant to
these laser levels have been investigated.
23,24
The lumines-
cence from the higher multiplet term
2
P
3/2
is concentration
quenched.
25
Indeed, such cross-relaxation processes are
ubiquitous for Er
3+
in YAlO
3
and are effective in
upconversion
26,27
in addition to excited state absorption
28
and photon avalanche
29
processes. Pumping at 1500 nm can
provide green and red emission bands.
30
In fact, the first
upconversion laser emission reported was from YAlO
3
:Er
3+
,
which was produced by pumping between 785 and 840 nm
giving emission at 550 nm.
31,32
The infrared and red upcon-
versions are a continuing focus of research.
33,34
It is clear
that previous emphasis in experimental investigations has
been placed upon the structure of lower energy levels of
YAlO
3
:Er
3+
.
The optical spectra and intensities of Nd
3+
in YAlO
3
have
been reported by Weber and Varitimos
35
and the energy lev-
els up to
2
P
1/2
at 23 151 cm
-1
were assigned from studies at
300 and 85 K. The lowest
4
G
5/2
level was assigned at
16 849 cm
-1
but apparently this absorption band corresponds
to a hot transition from the first Stark level of
4
I
9/2
since it
disappears at 4.2 K.
36
Some luminescence transitions of
YAlO
3
:Nd
3+
have also been investigated by Basiev et al.
37
and by Rasuleva and Solomonov.
38
The luminescence from
higher energy levels of Nd
3+
in YAlO
3
was studied by pump-
PHYSICAL REVIEW B 75, 195130 2007
1098-0121/2007/7519/19513012 ©2007 The American Physical Society 195130-1