Confinement of electron–phonon interaction on luminescence dynamics in nanophosphors of Er 3+ :Y 2 O 2 S

Liu, G.K.; Chen, Xueyuan; Zhuang, Hua; Li, S.; Niedbala, R. Sam

doi:10.1016/s0022-4596(02)00195-0

Cited by 59 publications

(61 citation statements)

References 15 publications

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“…The quantum yield η is defined as (9) Combining eqns (2), (8) and (9), we have (10) Here L depends on the specific model. Thus, eqn (8) can be written as (11) τ rad relates to refractive index n eff through eqns (1) and (3)- (5), according to the specific model used to the study.…”

Section: Discussionmentioning

confidence: 99%

“…[3][4][5][6] Nanocrystalline materials have very different optical properties from that of counterpart bulk materials. [7][8][9][10] In a nanocrystal system, phonon density of states (PDOS) is modified due to confinement effects of nanocrystals, [11] and the surface effect becomes considerable. As a consequence, radiative and nonradiative relaxation rates become different.…”

Section: Introductionmentioning

confidence: 99%

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Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Zheng

Zhang

et al. 2009

Luminescence

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Tm(3+):LaF(3) nanocrystals were synthesized with hydrothermal technique. Local-field effect on the radiative relaxation rate was studied in the system of Tm(3+):LaF(3) nanocrystals immersed in several liquid media. The fluorescence lifetime was measured. It was found that the fluorescence decay presented the characteristics of second-order exponential decay, for which the contribution from the ions inside the nanocrystal and ions at the interface of the nanocrystal were distinguished. Investigating the experimental results with proposed models, we found that the surface effect had to be eliminated. For rare earth doped LaF(3) nanocrystals, real-cavity model well explains the influence of surrounding medium on the fluorescence relaxation rate.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Zheng

Zhang

et al. 2009

Luminescence

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“…The decrease in fluorescence efficiency is attributed to the lack of low-frequency phonon modes and restricted excitation migration in nanophosphors. [24][25][26] The decrease in up-conversion fluorescence is also attributed to the organic ligand on the surfaces, which quenched the ions for fluorescence. [18,21] The as-synthesized hexagonal nanocrystals in this work showed a high sensitivity of up-conversion fluorescence.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Hexagonal‐Phase NaYF₄:Yb,Er and NaYF₄:Yb,Tm Nanocrystals with Efficient Up‐Conversion Fluorescence

Chow

2006

Adv Funct Materials

755

574

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IR‐to‐visible up‐conversion fluorescent nanocrystals of hexagonal‐phase NaYF4:20 %Yb,2 %Er and NaYF4:20 %Yb,2 %Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF3COO)3Y, (CF3COO)3Yb, and (CF3COO)3Er/(CF3COO)3Tm in oleylamine at 330 °C. The average particle size is 10.5 ± 0.7 nm (from random measurements of 200 particles from five transmission electron microscopy images) and 11.1 ± 1.3 nm (from dynamic‐light‐scattering measurements). The up‐conversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic‐phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal‐phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes.

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“…Experimental evidence of this effect has been observed by G. Liu et al, 20,21 who conducted emission and excitation experiments on Er-doped Y 2 O 3 nanoparticles with radii ∼400 nm and 25 nm. Figure 8 shows an emission spectrum at 3 K of the 4 S 3/2 → 4 I 11/2 transition of Er in Y 2 O 3 following excitation with a pulsed laser into the 4 F 3/2 level.…”

Section: Effect Of the Phonon Dos On The Establishment Of Thermal Equmentioning

confidence: 76%

“…To express 13 in terms of the normal coordinates, recall that ih ∇ α = P α . The kinetic energy of the lattice in Cartesian coordinates and in normal coordinates is: [20] where the first sum is over all nuclei, the second and third sums are over all normal modes, and the M k are properly weighted masses. Using the term on the far right in 20, and re-deriving Equation 13, it is readily seen that the electron-phonon coupling operator of type B operating on the adiabatic wavefunction of the system is expressed as:…”

Section: Representation Of Eigenstates and Operatorsmentioning

confidence: 99%

Non-Radiative Processes in Crystals and in Nanocrystals

Collins

2015

ECS J. Solid State Sci. Technol.

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This paper discusses non-radiative processes that are relevant to the luminescence characteristics of optically active ions doped into insulators or large-gap semiconductors, with particular attention to how these processes are affected as the particle size is reduced from bulk single crystals to as small as a few nanometers. The non-radiative processes discussed in this article are thermal line broadening and thermal line shifting, relaxation via phonons between excited electronic states, vibronic emission and absorption, and phonon-assisted energy transfer. Given that one of the main effects of confinement in these particles is on the phonon density of states, we pay particular attention to how these non-radiative processes are altered due to the change in the phonon density of states as particle size decreases. Inorganic insulators doped with rare-earth ions and transition metal ions represent an important class of luminescent materials for many applications, including phosphors for lighting, scintillators, solid-state laser materials, bio-markers for imaging, and nanothermometry. Following excitation by radiation, the optical ions usually undergo some degree of non-radiative relaxation releasing a part or all of its energy to the lattice. During the non-radiative relaxation, all or part of the electronic energy initially stored in the optically active ion is converted into phonons.From the perspective of energy efficiency of luminescent materials, it may seem beneficial to attempt to eliminate non-radiative processes altogether. However, the conversion of electronic energy into heat energy following excitation is, in fact, desirable to many applications. Non-radiative processes play an important role in converting light from the blue LED into red and green light for white light generation in lamp phosphors, for efficient operation of many solid-state lasers, for energy transfer and multiphonon relaxation in bio-imaging, and also for the establishment of thermal equilibrium, the principle on which thermometry is based. For these technologies to be optimized, non-radiative processes must be controlled, or at least carefully considered. Thus, understanding these processes is of great interest to the luminescence community. The specific non-radiative processes addressed in this work are thermal line broadening, thermal line shifting, decay via a phonon from one electronic level to another, vibronic transitions, and phonon-assisted energy transfer.The main focus of this work is on how non-radiative processes are affected as the particle size decreases into the nano-regime. Generally speaking, the two main effects of going from the bulk to the nano are:(1) an increase in the surface to volume ratio, and (2) a reduction in the phonon density of states. Item (1) often leads to an increase in defect sites (mostly near the surface) and surface states, which in turn tends to decrease the luminescence efficiency as one goes from the bulk to the nano. This nonradiative process is outside the scope of this article. Item (...

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Confinement of electron–phonon interaction on luminescence dynamics in nanophosphors of Er 3+ :Y 2 O 2 S

Cited by 59 publications

References 15 publications

Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Synthesis of Hexagonal‐Phase NaYF₄:Yb,Er and NaYF₄:Yb,Tm Nanocrystals with Efficient Up‐Conversion Fluorescence

Non-Radiative Processes in Crystals and in Nanocrystals

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Confinement of electron–phonon interaction on luminescence dynamics in nanophosphors of Er 3+ :Y 2 O 2 S

Cited by 59 publications

References 15 publications

Local‐field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium

Local‐field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium

Synthesis of Hexagonal‐Phase NaYF4:Yb,Er and NaYF4:Yb,Tm Nanocrystals with Efficient Up‐Conversion Fluorescence

Non-Radiative Processes in Crystals and in Nanocrystals

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Product

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About

Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Local‐field effect on the fluorescence relaxation of Tm³⁺:LaF₃ nanocrystals immersed in liquid medium

Synthesis of Hexagonal‐Phase NaYF₄:Yb,Er and NaYF₄:Yb,Tm Nanocrystals with Efficient Up‐Conversion Fluorescence