Energy transfer between Gd3+ and Tb3+ in phosphate glass
磷酸盐玻璃中Tb3+与Gb3+之间的能量转移
Abstract: The phosphate glass doped with Gd3+, Tb3+ and Gd3+/Tb3+ were prepared by high temperature melting. The photo-luminescence behavior of Gd3+ and Tb3+ in phosphate glass were investigated by absorption, excitation, and emission spectroscopy. Energy transfer between Gd3+ and Tb3+ in phosphate glass was studied, and it was found that there were two energy transfer mechanisms between Gd3+ and Tb3+ in
phosphate glass: one was from 4f7 level of Gd3+ to the 4f8 level of Tb3+, and the other was from 5d level of Tb3+ to 4f7 level of Gd3+. The new findings would be beneficial for the study of Tb3+-doped scintillating phosphate glass.
摘要：在这项工作中，我们利用高温融化技术来制备分别掺杂了Gb3+，Tb3+和Gd3+/Tb3+的磷酸盐玻璃。利用吸收，激发和发射光谱学，研究了磷酸盐玻璃中的Gb3+和Tb3+的光致发光行为。在此基础上研究了磷酸盐玻璃中Gb3+和Tb3+的能量转移。我们发现磷酸盐中哦那个的Gb3+和Tb3+的能量转移机制有两种：一种是由Gb3+的4f7能级向Tb3+的4f8能级转移，另外一种则是从Tb3+的5d能级向Gb3+的4f7能级转移。这个全新的发现对于研究掺杂了Tb3+的闪烁磷酸盐玻璃是非常有用的。
Keywords: energy transfer; gadolinium; terbium; phosphate glass; luminescence; rare earths
关键词：能量转移；钆；铽；磷酸盐玻璃；发光；稀土元素
Terbium-doped scintillating materials have been extensively
used in many applications such as thermal neutron
detection and radiography, because of their high luminescence
intensity around 550 nm which is convenient for direct coupling
with silicon detectors[1].铽掺杂的闪烁材料在很多应用中都被大量使用，例如热中子探测和射线照相术。这是由于它们的在550nm附近的高发光强度使得可以很方便得和硅探测器直接结合使用。 As an important part of scintillating
materials, Tb3+-doped glass and glass fiber have
been used in non-destructive testing[2] and high-resolution
medical X-ray imaging field such as mammography[3]. 作为闪烁材料的一个重要组成部分，铽掺杂玻璃与玻璃纤维已经用于无损探测和高分辨率医用X-射线成像领域，例如乳腺摄影术。For
the Tb3+-doped glass materials used in medical application,
the light yield is the most important parameter, because it
can reduce the radiative dose exposed to patients[4]. 医用的铽掺杂玻璃材料的最重要的参数是光输出，因为这可以减少患者受到的辐射剂量。 Many
researches have been done on increasing the luminescence
intensity of Tb3+ in many glass systems[5,6]. In these studied
Tb3+-doped glasses[7,8], Gd3+ was often used as sensitizer and
proved efficient for the energy transfer from 4f7 level of
Gd3+ to the 4f8 level of Tb3+. 许多研究致力于提升玻璃系统中Tb3+的发光强度。在这些研究过的铽掺杂的玻璃中，Gb往往用来作敏化剂，同时证明Gb3+的4f7能级向Tb3+的4f8能级的能量转移效率。
Due to the 4f8 orbital of Tb3+, it requires comparatively little
energy in UV region to excite the ground state to the 5d
state[9]. 由于Tb3+的4f8轨道，它由基态被激发到5d态只需要非常少的紫外波段的能量。 In addition, the 5d-4f transition of Tb3+ is an allowed
transition, so broad absorption bands in UV region can be
expected, which can effectively increase the luminescence
intensity of Tb3+ at 540 nm. 另外，铽的5d-4f转变是一个允许跃迁，所以可以期望它能在紫外波段具有非常宽的吸收带，这可以有效地提升铽在540nm的发光强度。Up to now, however, there
have been very few reports about the absorption bands of
Tb3+ in UV region because of the instinct absorption of
host glass. 然而，到目前为止很少有Tb3+在紫外波段的吸收带的报道，这是由于基质玻璃存在本征吸收。
As we know, phosphate glass has high transmittance in
UV/visible/NIR region (220–3 000 nm), high doping concentration
(>30 wt.%) of rare earth ions and good radiative
resistance properties[10,11], so it is a promising material for
studying the luminescence behavior of Tb3+. 众所周知，磷酸盐玻璃在紫外光/可见光/近红外光波段都具有高的透过率，高的稀土元素离子掺杂浓度和良好的辐射电阻性能，所以它是研究Tb3+的发光行为的很有前景的一种材料。In addition, due
to the high transmittance in the UV region and low covalency
of phosphate glass[12], the 5d level of Tb3+ was improved
close to the state 6DJ of Gd3+ in phosphate glass[9],
and the new energy transfer from 5d level of Tb3+ to 4f7 level
of Gd3+ maybe occur. 另外，由于磷酸盐玻璃在紫外波段的高透过率和弱共价，Tb3+的5d能级被修正到接近Gb3+的6DJ态能级的地步，这样Tb3+的5d能级向Gb3+的4f7能级的跃迁就变得可能。In this work, we studied the luminescence
behavior of Gd3+ and Tb3+ in phosphate glass and
the energy transfer between Gd3+ and Tb3+. It would be
beneficial for studying the Tb3+-doped scintillating phosphate
glass which could be used as bulk or fiber plate in
X-ray imaging. 在这项工作中，我们研究了磷酸盐中的Gb3+和Tb3+的发光性能和它们之间的能量转移。这对于研究能在X-射线成像中作为纤维片或光栅片的铽掺杂的闪烁磷酸盐玻璃是非常有益的。
1 Experimental 实验
Precursor glass with compositions, as listed in Table 1, of
oxides with commercial purity (usually 99.9%) and phosphate
was melted in aluminium crucibles. 前体玻璃，具有商业纯度的氧化物和磷酸盐按照表1中的配比在铝坩埚中溶化。Batches of about
200 g each of the well-mixed raw materials were melted at
1 400 ºC for 120 min in reducing atmosphere. 然后每份200g充分混合的原材料在还原性气氛，1400摄氏度下溶化120分钟。After melting,
the liquid was cast into a graphite mould and annealed for 2 h
below the glass transition temperature. The glass samples
obtained with a thickness of 2 mm were polished for optical
measurements. 溶化后，液体被倒入石墨模子中退火两个小时，期间温度在玻璃的转变温度以下。
The transmittance spectra of the samples were recorded
with a Perkin-Elmer-Lambda 900UV/VIS/NIR spectrophotometer in the range of 300–600 nm, and the tread speed is 0.5 nm. 样品的透射光谱是用一台Perkin-Elmer-Lambda 900紫外/可见光/近红外光分光光度计记录的，记录范围是300-600nm，胎面速度是0.5nm。 Photoluminescence (PL) spectra were recorded on a Perkin-Elmer luminescence spectrometer LS55 using a Xe
Table 1 Compositions of glass samples (mol.%) 表1：玻璃样品的组分
Glass P2O5 Al2O3 Li2O BaO La2O3 Gd2O3 Tb2O3
Gd2 50 15 10 5 18 2
Tb2 50 15 10 5 18 2
Gd2-Tb2 50 15 10 5 16 2 2
lamp as an excitation source. 光致发光谱使用Perkin-Elmer发光光谱仪LS55上记录的，其中氙灯用作激励电源。Radioluminescence (RL) spectra
were performed by an X-ray excited spectrometer, where
an F-30X-ray tube (W anticathode target) was the X-ray
source, and operated under 30 kV and 20 mA. 辐射发光谱在一个X-射线激励的分光计上得到，其中一台F-30 X-射线管（钨作为对阴极）作为X-射线源在30kV，20mA下工作。Luminescence
spectra were recorded with a 44 W plate grating monochromator
and a Hamamatsu R928-28 photomultiplier with the
date provided by a computer. 发光光谱是用44W光栅单色仪和一台Hamamatsu R928-28光电倍增管记录的。
2 Results and discussion 结果和讨论
2.1 Luminescence behavior of Gd3+ and Tb3+
Gb3+和Tb3+的发光行为
Fig. 1 gives the excitation (left, dot line) and emission
spectra (right, solid line) of Gd2 glass. 图1给出了Gd玻璃的激发（左边，虚线）和发射光谱（右边，实线）。
The excitation spectrum
comprises several narrow peaks located at 247, 253,
273 nm (the strongest), 276 and 279 nm, which are owing to
the transition from the ground state 8S7/2 to the excited states
6IJ and 6DJ. 激发光谱包含几个窄峰，分别位于247, 253,
273 nm (最强), 276 and 279 nm, 这些峰都源于从基态8S7/2到激发态6IJ，6DJ的跃迁。The emission spectrum of Gd3+, excited with 273 nm,
consists of a very narrow line at 312 nm and two shoulders
at 305 and 324 nm, which are all associated with the radiative
transition from the excited state 6PJ to the ground state
8S7/2. 被273nm的光激发的Gd3+的发射光谱包含一条位于312nm的非常窄的线和2个分别位于305nm和324nm的较低的峰，这些都是由从激发态6PJ向基态8S7/2的辐射跃迁产生的。From the energy level scheme showed in Fig. 1, energy
gaps between the states of 6DJ and 6IJ, 6IJ and 6PJ are about
4 000 cm–1, which is only about 3 times of the maximum phonon
of phosphate glass, so multi-phonons non-radiative relaxation
easily occurs from 6DJ and 6IJ states to the state of 6P7/2. 从图1所示的能级图可以知道，状态6DJ,6IJ,6LJ,6PJ之间的能量差大约为4000cm-1，只有磷酸盐玻璃最大声子能量的三倍，所以多声子的无辐射弛豫很容易发生，导致6DJ和6IJ态向6P7/2跃迁。
As the energy gap between the 8S7/2 and 6P7/2 is 32 000 cm–1,
Fig. 1 Excitation (left, dot line) and the emission spectra (right,
solid line) for Gd2 glass sample
图1：Gd2 玻璃样品的激发（左边，虚线）和辐射光谱（右边，实线）
much larger than the phonon of host, the population inversion
most occurs at 6PJ states of Gd3+ [13], and then the
strongest emission band of Gd3+ at 312 nm is observed,
which is associated with the transition from the 6PJ state to
the ground state 8S7/2. This is also illustrated by the lifetime
of the state 6P7/2 measured by time-resolved spectrum, which
is 4.8 ms. 由于8S7/2和6P7/2之间的能量差是32000cm-1，远大于基质的声子能量，粒子数反转大多发生在Gd3+的6PJ态，所以Gd3+的发射光谱带的最强处位于312nm，这个最强处来源于6PJ态向基态8S7/2的跃迁。这也可以由时间分辨光谱仪测得的6P7/2态的寿命（4.8ms）得到解释。
Fig. 2 (a) gives the absorption spectrum of Tb3+ in Tb2
glass.图2（a）给出了Tb3+在Tb2玻璃中的吸收光谱。
The absorption spectrum of Tb3+ includes two groups:
parity-forbidden f-f transitions within the 4f8 and allowed
4f8→4f75d transition. Tb3+的吸收光谱包括两族：4f8态内的宇称禁戒f-f跃迁和4f8态到4f5d态的允许跃迁。The weak absorption bands ranging
from 302 to 484 nm in phosphate glass are similar to those in
other glass systems such as silicate glass and borate glass[14],
because the 4f electrons are well shielded by completely
filled 5s and 5p orbital and the influence of composition is
expected to be small. 磷酸盐玻璃的从302nm到484nm的吸收带与其他的玻璃系统，比如硅酸盐玻璃和硼酸盐玻璃中的情况是非常相似的，这是因为4f壳层的电子被满占据的5s和5p轨道几乎完全屏蔽，所以化合物的影响应该是非常小的。However, the absorption band at 283 nm
is first seen due to the high transmittance of phosphate glass.
The strong and broad absorption bands at 230 and 250 nm allow
4f8→4f75d transition of Tb3+, which is more effected by
the surrounding[15]. 然而，位于283nm处的吸收带由于磷酸盐玻璃的高透射率而第一次看到。从230nm到250nm的强而宽的吸收带允许Tb3+发生4f8态到4f75d态的跃迁，这种情况受环境的影响更大一些。From these results, we can conclude that
the lowest 5d energy level of Tb3+ is 43 500 cm–1 in phosphate
glass, which is higher than the energy level 6DJ, 6IJ and 6PJ of
Gd3+.
根据这些结果，我们可以得出结论：磷酸盐玻璃中Tb3+ 5d态的最低能级是43500cm-1，高于Gd3+的6DJ，6IJ和6PJ能级。
Fig. 2 (b) exhibits the excitation and emission spectra of
Tb3+ in Tb2 glass. A number of excitation lines of Tb3+ ions
exist in UV range, such as 284, 302, 318, 351, 378, and 484 nm,
which are similar to the absorption spectrum of Tb3+. 图2(b)展示了Tb2玻璃中Tb3+的激发和发射光谱。在紫外波段存在Tb3+的一些激发谱线，比如84, 302, 318, 351, 378, 和 484 nm, 这和Tb3+的吸收光谱很相似。Due to
the allowed 4f-5d transition, the intensity of excitation band
at 257 nm is much stronger than the other excitation bands.
So in Tb3+-doped phosphate glass, the 4f-5d transition would
play an important role for the emission of Tb3+, which can
not be found in other glass. 由于4f-5d之间的跃迁是允许的，所以257nm处的激发带强度远大于其他激发带。所以在掺杂了Tb3+的磷酸盐玻璃中，4f-5d跃迁在Tb3+的发射中扮演了重要的角色，而在其他玻璃中并不是这样的。The emission spectrum of Tb3+
consists of several bands located at 487, 541, 548, 582 and
620 nm, which are all associated with the 5D4–7FJ (J=3–6)
transitions. Tb3+的发射光谱包含几条分别位于487, 541, 548, 582 和
620 nm的带，这些是由5D4–7FJ (J=3–6)跃迁产生的。Among them, the green emission at 541 nm related
with the transition 5D4–7F5 is the strongest, and the lifetime
of 5D4 state is measured to be 3.2 ms. 其中与5D4–7F5跃迁相联系的541nm绿光是最强的，测得5D4态的寿命为3.2 ms。
2.2 Energy transfer between Gd3+ and Tb3+
Gd3+ 和 Tb3+之间的能量转移
2.2.1 Energy transfer from 4f7 level of Gd3+ to the 4f8 level
of Tb3+
Gd3+的4f7能级到Tb3+的4f8能级之间的能量转移
Fig. 2 Absorption spectrum of Tb2 glass sample (a) and excitation (left, dot line) and the emission (right, solid line) spectra for Tb2 glass sample (b)
图2：Tb2玻璃样品(a)的吸收光谱和Tb2玻璃样品(b)的激发光谱（左边，虚线）以及发射光谱（右边，实线）。
It is clear that the strongest emission band of Gd3+ at
312 nm overlaps with the absorption bands of Tb3+ from 302
to 317 nm, which shows that the energy difference between
the 6PJ and 8S7/2 states of Gd3+ is almost equal with that of 7F6
and 5H6, 5H7 states of Tb3+. 可以很清楚得看到Gd3+位于312nm的最强的发射光谱带与Tb3+从302nm到317nm的吸收带重叠，这表明Gd3+ 的6PJ -8S7/2能量差和Tb3+的7F65-H6, 5H7能量差几乎相等。-So there could be sensitization
from the 6PJ state of Gd3+ to the 5HJ state of Tb3+ [16]. 所以可能存在从Gd3+的6PJ 态到Tb3+的5HJ 态的敏化作用。This
deduction has been proved in Fig. 3(a), which gives the excitation
spectrum of Tb2 and Gd-Tb2 with emission at 545 nm. 这个推断也能在图3（a）中得到证明，这张图给出了Tb2 和 Gd-Tb2的激发光谱在545nm处的发射谱线。
Compared with Tb2 glass, in Gd2-Tb2 glass, the new excitation
bands occur at 273, 276 and 312 nm, which are all attributed
to the absorption bands of Gd3+. This illustrates that
Gd3+ ions can absorb the energy at 273 and 312 nm, and then
transfer to Tb3+ ions. 与Tb2玻璃相比，在Gd2-Tb2玻璃中，新的激发带位于273, 276 和 312 nm处，这些都是由于Gd3+的吸收带导致的。这说明Gb3+粒子可以吸收273nm和312nm的能量，然后将这个能量传递给Tb3+离子。
The emission spectra of Gd2, Tb2 and Gd2-Tb2 glass are
shown in Fig. 3(b). It is obvious that energy transfer occurs
in Gd3+/Tb3+ co-doped glass. In Gd2-Tb2 glass, the intensity
of emission at 312 nm decreases remarkably compared with
Gd2 glass, indicating that the emission efficiency of Gd3+ is
reduced because of the energy transfer from Gd3+ to Tb3+. Gd2, Tb2 和Gd2-Tb2玻璃的发射光谱在图3(b)中，很显然在Gd3+/Tb3+共掺杂的玻璃中发生了能量转移。与Gd2玻璃相比，Gd2-Tb2玻璃312nm的发射强度明显降低，说明Gd3的发射效率因为能量从Gd3转移到Tb3+而降低。In
Tb2 and Gd-Tb2 glass, when excited with 273 nm, the new
characteristic emission bands of Tb3+ are observed and the
emission intensity of Tb3+ in Gd2-Tb2 glass is much stronger
than that of Tb2 glass. This indicates that in Gd2-Tb2 glass,
the Gd3+ ions can absorb the energy at 273 nm and transfer to
Tb3+ to increase the emission intensity of Tb3+. 当Tb2 和Gd-Tb2玻璃被273nm的光激发时，观察到新的Tb3+特征发射带，而且Gd2-Tb2玻璃中的Tb3+的发射强度远大于Tb2玻璃中的，这说明在Gd2-Tb2中，Gd3+离子能吸收273nm的光然后将能量转移到Tb3+，所以Tb3+的发射强度得到增强。 From the discussion
above, we can conclude that energy transfer occurs
from the 6PJ states of Gd3+ to the 7F6 and 5H6, 5H7 states of
Tb3+ in phosphate glass and the Gd3+ is a good sensitizer for
the emission of Tb3+ at 545 nm when excited with the absorption
bands of Gd3+ such as 273, 276 or 312 nm. 根据上述讨论，我们可以得出结论，当Gd3+吸收诸如273nm，276nm或者312nm能量的光被激发时，磷酸盐玻璃中Gd3+的6PJ态与Tb3+的7F6 和 5H6, 5H7之间发生能量转移，这时候Gd3+可以作为Tb3+发射545nm光的良好的敏化剂。
2.2.2 Energy transfer from 5d level of Tb3+ to 4f7 level of Gd3+
能量从Tb3+的 5d态向 Gd3+的4f7态转移
From the absorption spectra of Tb3+, as shown in Fig. 2(a),
the 5d energy level of Tb3+ in phosphate glass is calculated
as 43 500 cm–1, which is higher than the energy level 6DJ, 6IJ
and 6PJ of Gd3+, so energy transfer may occur from the 5d
state of Tb3+ to the 4f8 state of Gd3+. 根据图2（a）中Tb3+的吸收谱，磷酸盐玻璃中Tb3+的5d能级的能量被计算为43500cm-1,比Gd3+的6DJ, 6IJ
和 6PJ能级高，所以能量可能从Tb3+的5d态向Gd3+的4f8态转移。 Fig. 4(a) gives the excitation
spectrum of Gd3+ with emission at 312 nm in Gd2
glass and Gd2-Tb2 glass. In the region from 270 to 280 nm,
the sharp and narrow excitation bands are located at 273, 276
and 278 nm in Gd2 glass, which are typical characters associated
with 4f7 transitions of Gd3+. For Gd2-Tb2 glass, in
contrast, the excitation bands are broad, which belongs to the
4f→5d transitions of Tb3+. It means that Tb3+ can absorb the
energy by 4f→5d transitions and then transfers to 4f8 energy
level of Gd3+.图4（a）给出了Gd2和Gd2-Tb2玻璃中Gd3+的激发谱和在312nm处的发射谱。在270nm到280nm波段，Gd2玻璃中，窄而尖锐的激发带位于273, 276 和278 nm处，这是Gd3+的4f7态跃迁的典型特征。相比之下，在Gd2-Tb2中，激发带很宽，属于Tb3+的4f态到5d态之间的跃迁。说明Tb3+能够吸收4f->5d跃迁释放的能量然后转移给Gd3+的4f8能级。
This energy transfer from 5d level of Tb3+ to 4f7 level of
Gd3+ can also be proved by the emission intensity of Tb2 and
Gd2-Tb2 glass, as shown in Fig. 4(b). When excited with
260 nm, the 541 nm emission intensity of Tb3+ in Gd2-Tb2
glass decreases from 1.4×105 to 0.9×105, compared with that
in Tb2 glass. This suggests that part of energy absorbed by
Tb3+ can transfer to Gd3+ and reduce the efficiency of Tb3+
emission. 这种由Tb3+的5d能级到Gb3+的4f7能级的能量转移也能被图4(b)中所示的Tb2和Gd2-Tb2玻璃的发射强度证实。用260nm的光激励后，和Tb2玻璃相比，Gd2-Tb2玻璃中Tb3+的541nm的发射强度由1.4×105 降到 0.9×105。说明这部分被Tb3+吸收的能量被转移给了Gd3+从而降低了Tb3+的发射效率。The inset shows the emission of Gd2-Tb2 at the
range from 300 nm to 350 nm, and the characteristic emission
of Gd3+ at 312 nm appears. This also agrees well with
the excited spectrum of Tb2 and Gd2-Tb2 with emission at
545 nm, as shown in Fig. 3 (a). 这幅插图展示了Gd2-Tb2在300nm到350nm之间的发射谱，另外可以看到Gd3+在312nm处的特征发射出现了。这也是和Tb2的激发光谱以及Gd2-Tb2在545nm处的发射光谱吻合的很好的。Fig. 3 Excitation spectrum of Tb2 (solid line) and Gd2-Tb2 (dot line) with emission at 545 nm (a); the emission spectrum of Gd2 (dashed
line), Tb2 (solid line) and Gd2-Tb2 (dot line) excited with 273 nm (b)
图3. Tb2和Gd2-Tb2的激发光谱（实线），发射545nm的光（点线）(a)；Gd2和Gd2-Tb2的发射光谱（虚线），被273nm的光激发（点线）(b)。
Fig. 4 Excited spectrum of Gd2 and Gd2-Tb2 with the emission at 312 nm (a); the emission spectrum of Tb2 and Gd2-Tb2 glass excited with
260 nm (b)
图4. Gd2 和Gd2-Tb2的激发光谱，发射312nm的光（a）；Tb2 和 Gd2-Tb2的发射光谱，被260nm的光激发。
The intensity of excitation
band at 260 nm in Gd2-Tb2 glass is lower than that in Tb2
glass. From discussion above, we can conclude that energy
transfer from the 5d level of Tb3+ to the 4f8 level of Gd3+ occurs
in Gd3+/Tb3+codoped glass. Gd2-Tb2玻璃在260nm处的激发带的强度比Tb2玻璃低。根据以上讨论，我们可以得到结论：在Gd3+/Tb3+共掺杂的玻璃中，能量从Tb3+的5d能级转移到了Gd3+的4f8能级。As we know, X-ray luminescence
is host sensitization[13], the energy transferring to
the luminescent center is a spectra range, so incorporating
Gd3+ to Tb-doped phosphate scintillating glass may reduce
the efficiency of emission of Tb3+ at 545 nm due to the energy
transfer from Tb3+ to Gd3+. Fig. 5 gives the emission
spectra of Tb2 and Gd2-Tb2 glass excited with X-ray. For
Gd2-Tb2 glass, the emission band 312 nm of Gd3+ appears,
and the intensity of emission band at 541 nm decreases compared
with the Tb2 glass.
我们知道，X-射线荧光是一种敏化剂，传递到发光中心的是一个光谱范围，所以将Gd3+加到铽掺杂的磷酸盐闪烁玻璃可能可以降低Tb3+在545nm处的发射效率，因为能量可以从Tb3+转移到Gb3+。图5给出了Tb2玻璃和Gd2-Tb2玻璃被X-射线激发后的发射光谱。对于Gd2-Tb2玻璃而言，Gd3+的312nm的发射光谱出现了，而且跟Tb2玻璃相比，541nm的发射带的强度有所降低。
The energy transfer mechanism depicted in an energy
level diagram is given in Fig. 6. There are two energy transfer
mechanisms between Gd3+ and Tb3+ in phosphate glass.
When excited with 273 nm, the ground state of Gd3+ is promoted
to the excited states 6IJ, and non-radiative relaxation
occurs from the states 6IJ to 6PJ. Part of energy at 6PJ state of
Gd3+ transfers to the ground state with emission at 312 nm.
Another part of energy transfers to the 5D3, 5D4 state of Tb3+
and then radiative relaxation occurs from 5D3, 5D4 state to
ground state with emission at 378 and 484 nm. When excited
with 260 nm, the ground state of Tb3+ is promoted to the excited
5d state. Part of energy is transferred to 5D3, 5D4 states
by non-radiative delay and then emission at 378 and 484 nm
occurs with the transition from 5D3, 5D4 state to ground state.
Another part of energy transfers from 5d state of Tb3+ to the
states 6IJ, 6PJ of Gd3+, and then the emission at 312 nm occurs
with the transition from 6PJ state to ground state.
Fig. 5 Emission of Tb2 and Gd2-Tb2 glass excited with X-ray
图5. Tb2 和Gd2-Tb2玻璃受X-射线激励后的发射谱
Fig. 6 Energy transfer between Gd3+ and Tb3+ in phosphate glass
图6. 磷酸盐玻璃中Gd3+ 和 Tb3+之间的能量转移。
能量转移的机制在能级图：图6中画出来了。磷酸盐玻璃中Gb3+和Tb3+之间的能量转移具有两种机制。当被273nm的光激发时，Gd3+的基态被提升到激发态6IJ，然后无辐射弛豫发生在6IJ和6PJ之间。Gd3+的6PJ的部分能量被转移给基态并发射出312nm的光。另一部分能量转移给Tb3+的5D3, 5D4态，然后辐射弛豫发生在5D3, 5D4和基态之间，发射出378nm和484nm的光。当被260nm的光激励时，Tb3+的基态被提升到激发态5d，一部分能量通过无辐射弛豫转移给5D3, 5D4态，然后5D3, 5D4态回到基态，发射出378nm和484nm的光。另一部分能量从Tb3+的5d态被转移给Gd3+的6IJ, 6PJ态.，6PJ态跃迁到基态发射出312nm的光。
3 Conclusions
The luminescence behaviors of Gd3+, Tb3+ and Gd3+/Tb3+
excited with UV and X-ray in phosphate glass were studied.
The energy transfer from the 4f7 level Gd3+ to the 4f8 level of
Tb3+ was illustrated when excited with UV at absorption
bands of Gd3+, which was beneficial for the Tb3+-doped glass
used in UV field. The energy transfer from 5d level of Tb3+
to 4f7 level Gd3+ was also first found in phosphate glass,
which would deteriorate the sensitization of Gd3+ to the luminescence
behavior of Tb3+ in Tb-doped phosphate scintillating
glass.
我们研究了磷酸盐玻璃中的Gd3+, Tb3+ 和 Gd3+/Tb3+受紫外线和X-射线激励后的发光性质。我们也解释Gd3+的吸收带中吸收紫外光后4f7能级能量向Tb3+的4f8能级转移的过程，这对于研究在紫外光下利用三价铽粒子掺杂的玻璃是很有益处的。在磷酸盐玻璃中，我们首次发现了从Tb3+的5d能级向Gd3+的4f7能级的能量转移，这会破坏在铽掺杂的磷酸盐闪烁玻璃中Gd3+对于Tb3+发光性能的敏化作用。
