- It is possible to envisage that photoinduced reduction of Eu3+ to Eu2+ in Sr2SiO4 may be induced by....
envisage [ɪnˈvɪzɪdʒ] 想象; 设想; 展望;
- S is then often referred to as a sensitizer of the luminescence from A, although it may itself also act as activator.
be referred to as 被称作
the IBM tools referred to in this paper refer to xx中提到的
- In what follows I shall attempt to convey the reasons for these beliefs.
In what follows, 在下文中
- Research on these phosphors in particular has considerably advanced the understanding of characteristic luminescence, since the properties of these phosphors can be studied on simple model compounds.
- by the dissipation of the excitation energy in the form of heat
- Luminescent materials rely on electronic “traps” to store energy that is subsequently released in the form of light.
in the form of 以....的形式
- Rare earth ions, for example Eu3+ or Tb3+, are now substituted for a small proportion of the host lattice ions.
Substitute A for B 用A替换B A is substituted for B A(被用来)替换B
- virtually adv. 事实上，几乎；实质上 in a virtually random distribution.
- we will illustrate how the ideas presented in xxx work in the case of
- It may find technical applications in xx.
- The characteristic properties of the R ions are attributable to the presence in the ion of a deep-lying 4f shell which is not entirely filled. The electrons of this shell are screened by the outer electron shells, and as a result they give rise to a number of discrete energy levels. Since the presence of the crystal lattice scarcely affects the positions of these levels, there is a close resemblance between the energy-level diagram of the free ion and that of the incorporated ion.
- They are the representative of all the types encountered.
- The number of XXX is fairly large, except in.
- As the number of electrons increases, there is in general a rapid increase in the number of possible states.
- depend to a great extent on
- One electron is raised to the higher 5d level, strongly influenced by the lattice.
The answer to this question is bound up with the fact that a state with a completely or half-filled electron shell is very stable.
- Can readily accept an electron and thus xxx
- In the latter case, apart from xxx, xxx is nevertheless frequently observed.
- varies considerably from one lattice to another, so does xxxx
- decays stepwise from A state to B state
- returns to the ground state, thereby emitting radiation.
- The situation as far as the Ce3+ ion is concerned is entirely different.
As far as, adv 至于，直到，远到；就…而言
They may be there forever as far as any one of us is concerned.就我们任何一个人来说，它们也许会永远存在
- Contrary to the case of Tb3+
- Unlike XX, however, there is no no distinct splitting in xx
- In the emission process of the Eu3+ ion the charge-transfer level plays no part, since the ion decays from the charge-transfer level via a number of 4f levels to the 5D levels, from which the ground state is reached by the emission of radiation.
- More will be said about this in Section V
- Electric-dipole transitions between 4f levels of rare earth ions are strictly forbidden, because the parity does not change (Laporte's selection rule).
- Let us now consider the situation where the Eu3+ ion occupies a crystallographic site that does not coincide with a centre of symmetry.
- are similarly subject to selection rules
- a site which is not a centre of symmetry.
- This seemingly minor difference in structure has a considerable influence on the relative intensities of the Eu3+ emission lines.
- The relevant transitions occur because the ions of the host lattice vibrate. These vibrations can cause a deviation from pure inversion symmetry, which means that the electric-dipole transitions are no longer forbidden.
- This is approximately 1000 times longer than xx.
- Xxx can be well understood.
- The conversion efficiency of a phosphor can be numerically expressed in various ways.
Numerically, adv. 数字上；用数字表示 in number; with regard to numbers
- Various models have been proposed to explain the presence or absence of luminescence
- are based on what is termed the configurational-coordinate diagram
be termed XXX. 被称作XXX.
- it is too early for a full account of the long-term impact.现在详细说明长期影响还太早
a full account 详细说明
- She was granted a divorce on the grounds of unreasonable behavior by her husband.
on the grounds of 基于……理由，根据
- When drawing the configurational-coordinate diagram it is assumed (on not unreasonable grounds 基于合理的理由) that we need only take this symmetric valence vibration into account.
- Configurational-coordinate diagram of a luminescent centre. The potential energy E of the centre in the lattice is plotted as a function of the configurational coordinate r for the ground state and the first excited state. Vibrational states are represented schematically by horizontal lines in the parabola. In the region where the two parabola intersect, the curve is marked by dashes since the situation is actually more complicated than is indicated here.
parabola [pə‘ræb(ə)lə] 抛物线 horizontal line 水平线 Intersect vi. 相交，交叉
- In the symmetric vibrational mode the Mn+ ion remains stationary, while the O2- ions vibrate in phase along the M-O bonding axis.
- At absolute zero the luminescent centre will occupy the lowest vibrational level of the ground state. absolute zero 绝对零度
- The ions surrounding the central ion vibrate about their equilibrium positions situated at a distance r0 from the central ion.
situated at 位于….
- Since the equilibrium distance re of the excited state will not in general be equal to that of the ground stare, and since the centre may be at different vibrational levels, this transition will correspond to a fairly broad absorption band.
- is attributable to the rapid nature of electronic transitions as compared to vibrational movements,
- the system will relax towards the equilibrium state (of the excited level) by dissipating heat.
- Line emission is found in the case of small △r.
- The emission generally lies at a lower energy than the absorption.
- This displacement of emission with respect to absorption is known as the Stokes shift.displacement n. 位移，取代
- the centre will return non-radiatively to the equilibrium configuration of the ground state, dissipating heat in the process
- the luminescence decreases with rising temperature.
- the temperature dependence of the emission
- In the preceding parts of
preceding adj. 在前的；前述的
- As already mentioned
- We also pointed out that there is in fact no fundamental difference between these two kinds of centre.
- There are various methods that can be used to demonstrate the occurrence of energy transfer. One can, for example, measure xx
- This is illustrated in
- As a result τs will become shorter and so will the decay time of the luminescence from S.
- measure the decay time of the luminescence from S as a function of the concentration of A.
- This case is seldom of importance in the phosphors of interest to us.
- we need an interaction that can be of two essentially different types.
essentially, adv. 本质上；本来
- In the first place the transfer can be brought about by the Coulomb interaction between S and A. If S and A are so far apart that their charge clouds do not overlap, this form of energy transfer is the only one possible.
far apart 离得很远
- If the charge clouds of S and A do overlap, however, another transfer process is possible by exchange interaction between the electrons of S and A. The essential difference between the previous process and this one is that here electrons are exchanged between S and A, whereas in the Coulomb interaction process the electrons remain with their respective ions or ionic groups.
- we can disregard the contributions of the latter.
- It is possible to determine experimentally whether the levels involved are in resonance with one another by comparing the emission band of S with that of the relevant absorption band of A. The more these bands overlap, the better the resonance condition is fulfilled.
- an appreciable distance
An appreciable amount or effect is large enough to be important or clearly noticed.
appreciable adj. 可感知的；可评估的；相当可观的;
- Significant overlapping of the charge clouds of two cations in a crystal lattice is found only between cations that are nearest neighbours (separation 3 to 4 埃). Exchange interaction is therefore limited to neighbouring cations in the lattice. The critical distance for this transfer will never be much greater than 4 埃.
- We note that Psa(ex) does not comprise the optical properties of S and A (apart from the overlap integral). Exchange transfer, then, unlike transfer by Coulomb interaction, is not dependent on the oscillator strength or transition probability of the relevant transitions, and may even take place to a level from which a return to the ground state is strictly forbidden.
- The hopping time is the reciprocal of the transfer rate P mentioned above. reciprocal 互为倒数的 [rɪ'sɪprək(ə)l]
- In many cases, however, it is found that the emission efficiency decreases if the activator concentration exceeds a specific value known as the critical concentration.
- may be explained in a number of cases as follows.
- If the concentration of the activator becomes so high that the probability of energy transfer exceeds that from emission, the excitation energy starts migrating through the lattice. Now the host lattice is not perfect: it contains all kinds of sites where the excitation energy may, in some obscure way, be lost, such as at the surface, at dislocations, impurities, etc. The efficiency then decreases, in spite of the increase of the activator concentration.
- At room temperature the luminescence of the VO4 group in YVO4, for example, is concentration quenched. The vanadate emission can be observed by either Iowering the temperature, so that the energy migration through the lattice is stopped (Palilla et al., 1965) or by diluting the vanadate groups with phosphate groups (system YP1-xVxO4) so that the energy migration is stopped because of the increasing V-V distance.
- broad-band emitting R ions
For the sake of
be concerned with
a fairly constant emission
- Absorption is the process by which a photon is absorbed by the atom, causing an electron to jump from a lower energy level to a higher one.
- thermodynamic equilibrium will be valid universally.
- The above equation must hold at any temperature.
- The aim of xx is to distill this information, providing readers with xxx.
- The current attention to energy saving and reduction of CO2 emission in the atmosphere, should therefore give an additional boost to the development of LEDs for lighting.
- The present review is focused on six main performance requirements for state-of-art color conversion phosphors.
- XX remains unchanged at elevated temperature.
- This paper is reviewed as follows.
- However, we will specifically aim for white light only, as this is the type of light with the most universal applications.
- Xxxx is the highest xx that can ever be obtained.
- At very low light level, typically below 1 cd/m2, the rods of the retina, responsible for night vision, starts to play a role.
- Conversion losses with the use of phosphors are eliminated.
- XXX, as will be shown/discussed further on.
- This goes at the cost of efficiency, and vice versa.
- This choice is motivated by the fact that XX.
- It is therefore advisable to have a relatively flat excitation for the phosphor near the peak emission of the LED.
- There exists a trade-off between the increasing absorption and a decrease in the internal quantum efficiency.
- The failure in one aspect in principle renders the phosphors useless for commercial applications.
- This is of course very interesting from a fundamental point of view, care must be taken to asses these properties in conditions mimicking the pumping LED behavior.
- Xxx are related to the interplay between host and dopant.
- When looking at the data compiled in Table 1, it is clear that .
- Xxx makes them less suited as dopant for LED phosphors.
- Long decay time for Mn2+(typically being several to tens of millisecond)
- Especially the temperature dependency should be carefully investigated, to rule out temperature dependent color shifts.
- The peak wavelength of the red emission is situated beyond 650 nm.
- Depending on the emission spectrum aimed for.
- Resist the elevated temperature.
- Fulfill certain requiremnts.
- XX is shorthand for
- It is well established that BaFX materials are ubiquitously contaminated with oxygen impurities.33−35 This is corroborated by the fact that Tm2+ can be generated in nanocrystalline BaFCl:Tm3+ also by exposure to UV radiation at ∼200 nm (not illustrated here) where oxide impurities render strong absorbance.
- as time progresses
The approach used in this paper is easily transferable to other new persistent phosphors for better practical applications.
This model is not sustained by ab initio calculations.
sustain v. 维持，保持；维持……的生命；遭受，经受；(在体力或精神方面)支持，支撑；承受住……的重量；证实，证明；认可，赞成，确认；(演员)充分表演(角色，人物)，扮演
- which is in excellent agreement with the tabulated value in the literature.
Results for the test program haven't been tabulated. 试验的结果还没有制成表格。
- The elucidation of the Ba3MgSi2O8 structure has also been in the center of much discussion.
elucidation [ɪˌluːsɪˈdeɪʃn] n. 说明；阐明
- To circumvent this issue.
circumvent [ˌsɜːkəmˈvent] v. 设法回避; 规避; 绕过; 绕行; 绕道旅行;
- From the XRD data of pristine phosphor SrAl2O4:Eu2+.
- Similarly, it is a common misconception among laymen that radioactive compounds show glow-in-the-dark persistent luminescence.
- In the course of the years, several review papers, book chapters, and entire books have been published on persistent luminescence.
- Ultimately, some traps are not emptied at room temperature for months, making them useful for personal dosimetry, or for thousands of years, rendering them into excellent materials for geological dating.
- , this particle size reduction is is far from obvious.
is far from obvious 无从知晓
- While this kind of top-down approach to the synthesis of nanoparticles is successful in a number of cases, it is more obvious to opt for a bottom-up synthesis method, starting from liquid precursors.
opt for 选择
- In this fashion it was found that xxxx.
in this fashion 用这种方式; 以这种方式; 照这样;
- The quantum efficiency is a parameter which is used to indicate to which extent non-radiative pathways dominate the decay of the luminescence activator.
- This work helps to elucidate the mechanisms of the non-thermal excitation quenching process that has long been overlooked and most importantly explores the uncharted realms of the thermal-optical quenching of rare-earth doped phosphors.
uncharted 人迹罕至的; 无人涉足的; 陌生的; 地图上未绘出(或未标明)的;
- Hitherto, the discovery of phosphor materials has largely taken place through painstaking experiments.
hitherto [ˌhɪðəˈtuː] 今为止; 迄今; 直到某时;
- By virtue of the close correlation of the quantum yield with the rigidity of molecules, it seems rational to state that the rigidity of the host lattice could be viewed as an ideal indicator for efficient photoluminescence.
by virtue of 凭借，依靠，因为，由于;
- Considering that the Stokes shift varies from nearly zero to a value as large as 1.3 eV, the host effect on 5d-4f emission color through changes in Stokes shift also merits special consideration.
merit [ˈmerɪt] v. 值得，应受；应受赏(或罚)
- Self-healing phosphor: New paradigm for high-power LED lighting.
paradigm [ˈpærədaɪm] n. 典范，范例；样板，范式；词形变化表；纵聚合关系语言项
- Commercially used LED phosphors are often inorganic crystals doped with lanthanide ions, which still outcompete rapidly developing alternatives like quantum dots and perovskites.
outcompete vt. 超过；胜出
- The search for new materials and new mechanisms for hole burning is stimulated both by the desire to understand the breadth of the applicability of spectral hole burning as a powerful tool in high-resolution optical spectroscopy of solidsand by the need for materials with the properties required for frequency-domain optical storage.
- In a recent review article devoted exclusively to the coloration of WO3 films, Bange did an admirable job in compiling the vast amount of work that has been done in this field. It would be instructive at this point to recapitulate what we know about the coloration phenomena in WO3.
- displaying tailorable optical properties
- In particular, we show that, by rational control of different combinations of dopants and dopant concentration, a wealth of color output can be generated under single-wavelength excitation.
- Importantly, we demonstrate that an inert-shell coating provides the particles with stable emission against perturbation in surrounding environments, paving the way for their applications in the context of biological networks.
- The introduction of lanthanides into these solid materials laid the foundation for many modern applications, such as lighting, photonic communication, and battery devices.
- considerable interest had arisen in screening various dopant/host combinations for improved optical properties
- Although the optical transitions in lanthanide-doped nanoparticles essentially resemble those in bulk materials, the nanostructure amenable to surface modifications provides new opportunities for research.
- have enabled them to rival conventional luminescent probes in challenging tasks including
- one urgent task that confronts materials chemists lies in the synthesis of nanoparticles with tunable emissions
- lanthanide-doped nanoparticles are generally characterized by the emission of optical centers.
- exerts a strong influence on
- e control over doping concentration and host lattices.
- It is worth noting that although each lanthanide behaves differently and has different optical properties from all of the others, the lanthanides of different types can combine with one another to impart desired optical properties.
- This attribute, together with the lack of fully matched absorption bands between different lanthanide ions, impedes effective excitation of different lanthanide activators under a single wavelength.
- In a parallel effort, Wang demonstrated downshifting multicolor tuning in NaGdF4 particles doped with Tb3+, Eu3+, Dy3+, and Sm3+ as the activator, in conjunction with Ce3+ as the sensitizer.
- In search of dual emitters that do not cause deleterious cross relaxations
- The selection of dopants for multicolor tuning in conventional bulk materials needs to meet stringent criteria because the extensive dopant−dopant interactions in the host lattice may induce luminescence quenching.
- xxx is stable within the measurement error.
- Co-doping a material with several activators exhibiting emissions centered at specific wavelengths is a widely used approach to target the desired color of emission.
- It is highly desirable to understand and mitigate photodarkening to prevent the associated deterioration of laser performance and secure reliability over several years.
- Although some KSF:Mn4+-containing LED devices are on the market, it remains unclear to what extent the application potential of this phosphor is limited by its relatively poor saturation behavior.
- With the exception of YAG:Ce phosphor and some organic luminescent materials, however, there are no reports on yellow phosphor that has significant emission in the 450–470 nm excitation range.