Photon Avalanche Process Research Articles

The mechanisms behind the extreme susceptibility of photon avalanche emission to quenching.

The photon avalanche (PA) process that emerges in lanthanide-doped crystals yields a threshold and highly nonlinear (of the power law order >5) optical response to photoexcitation. PA emission is the outcome of the excited-state absorption combined with a cross-relaxation process, which creates positive and efficient energy looping. In consequence, this combination of processes should be highly susceptible to small perturbations in energy distribution and can thus be hindered by other competitive "parasitic" processes such as energy transfer (ET) to quenching sites. Although luminescence quenching is a well-known phenomenon, exact mechanisms of the susceptibility of PA to resonant energy transfer (RET) remain poorly understood, limiting its practical applications. A deeper understanding of these mechanisms may pave the way to new areas of PA exploitation. This study focuses on the investigation of the LiYF4:3%Tm3+ PA system co-doped with Nd3+ acceptor ions, which are found to impact both the looping and emitting levels. This effectively disrupts the PA emission, causing an increase in the PA threshold (Ith) and a decrease in the PA nonlinearity (Smax). Our complementary modelling results reveal that ET from the looping level increases Ith and Smax, whereas ET from the emitting level diminishes Smax and the final emission intensity. Ultimately, significant PA emission quenching demonstrates a high relative sensitivity (SR) to infinitesimal amounts of Nd3+ acceptors, highlighting the potential for PA to be utilized as an ultra-sensitive, fluorescence-based reporting mechanism that is suitable for the detection and quantification of physical and biological phenomena or reactions.

Visible photon avalanche up-conversion of Yb3+ and Ho3+ doped NaBi(WO4)2 phosphors under excitation at 980nm.

Avalanche phenomenon uses critical pump power to produce extreme nonlinear behavior from small disturbances, and has gradually become known. Here, it is reported that the strong green up-conversion emission produced in NaBi(WO4)2 phosphor by the positive feedback enhancement of the energy transfer process. The power dependence indicates that the photon avalanche process has occurred. Contrary to other up-conversion mechanisms, photon avalanche (PA) is a bifurcation phenomenon: avalanches occur above the critical excitation power. The experimental results are analyzed using the rate equation model. The high-response photon avalanche process produced by Yb and Ho ions is discussed in detail. The results show that PA can not only improve the brightness and efficiency of up-conversion, but also has a wider range of applications than traditional up-conversion materials, especially in the detection material of temperature sensor plays an important role.

Intense green upconversion emission by photon avalanche process from Er3+/Yb3+ co-doped NaBi(WO4)2 phosphor

The Er3+/Yb3+ co-doped NaBi(WO4)2 (NBW) phosphor has been synthesized by conventional solid state reaction technique. The XRD analysis confirms the tetragonal crystal structure of NaBi(WO4)2. An intense green upconversion (UC) emission by photon avalanche (PA) process has been observed under excitation with 980 nm laser at room temperature. The observed green emission is due to 2H11/2, 4S3/2→4I15/2 (523, 548 nm) transitions of Er3+ ion. The green emission dominate because the intensities of other peaks are very small. The average number of photons involved in the UC process is 8.4 for 523 nm emission, the rise time of 2H11/2 level decreases with increasing the laser power and the power versus emission intensity plot is concave type. These are the characteristics of PA process. The PA process has been explained by looping energy transfer mechanism. In the present case, the PA appeared at very low power (<30 mW). This material may be applicable in intense green emission, finger printing, green component of white light and other optical devices.

Cooperative upconversion luminescence of Er3 + in Gd2O3 − xSx phosphor

Gd2O3−xSx:Er crystals were prepared through high-temperature solid-state reaction method in vacuum, with the vacuum synthesis mechanism determined by thermal analysis. The crystal structure and upconversion luminescence properties were investigated respectively by XRD, TEM and spectrophotometer. Well crystallized Gd2O2S:Er phosphors were prepared under 1000°C in vacuum with a certain excessive amount of sulfur content than stoichiometric. It is confirmed that with the increasing sulfur content the green emission was enhanced and red emission was weakened. The cooperative upconversion luminescence of Er3+ in non-stoichiometric Gd2O3−xSx crystals was interpreted as a result of two photon absorption and the photon avalanche process.

Synthesis and up-conversion luminescence of Er(3+) and Y b(3+) codoped nanocrystalline tetra- (KLaP4O12) and pentaphosphates (LaP5O14).

The up-converting nanocrystals of KLa0.95Er0.05Y bxP4O12 and La0.95-xEr0.05Y bxP5O14 were prepared using co-precipitation method. The spectroscopic properties of these materials were investigated in a function of Y b(3+) concentration. The up-conversion emission, power dependence of emission intensities, and the luminescence decay times were investigated. It was found that the green to red and (2)H11/2 → (4)I15/2 to (4)S3/2 → (4)I15/2 emission intensity ratio were strongly affected by the Y b(3+) concentration. Moreover, the order of up-conversion emission and threshold power rises up with Y b(3+) concentration for (4)S3/2 → (4)I15/2 transition. The luminescence decay time of the (4)S3/2 → (4)I15/2 emission increases with Y b(3+) concentration while the (4)F9/2 → (4)I15/2 emission is independent of dopant concentration. The influence of the Y b(3+) concentration on the up-conversion emission intensities was discussed in terms of concentration dependent hetero looped photon avalanche process. A comparison of the up-conversion properties of KLa0.95Er0.05Y bxP4O12 and La0.95-xEr0.05Y bxP5O14 nanocrystals was presented.

Photon avalanche upconversion in Ho3+-doped gallium nano-garnets

Lu3Ga5O12 and Y3Ga5O12 nano-garnets doped with 1.0mol% Ho3+ ions have been prepared by a citrate sol–gel method. Size distribution of the nano-garnets has been studied by dynamic light scattering technique. Intense green and weak red emissions have been observed in these nano-garnets under 751nm excitation. The observed green upconverted emission is due to photon avalanche process, characterized by a threshold pump-power density and a time of establishment of 331kW/cm2 and 33ms for the Lu3Ga5O12 nano-garnets and 238kW/cm2 and 18ms for the Y3Ga5O12 nano-garnets, respectively. The results indicate that the nano-garnets are suitable for green upconversion photonic applications.

Structural, thermal, and optical properties of Pr3+/Yb3+ co-doped oxyhalide tellurite glasses and its nano-crystalline parts

Nano-crystalized glass-ceramics and ceramics co-doped with Pr3+/Yb3+ have been successfully prepared by heat treatment of the precursor oxyhalide glass sample synthesized by melt-quench method. Thermal measurement of glass sample shows its glass transition temperature (Tg), and onset crystallization temperature (Tc). Formation of nano-crystals was verified by X-ray diffraction patterns and transmission electron microscopy (TEM) images. Values of optical band gap (Eopt) were found to be 2.85 eV and 1.54 eV for direct and indirect transitions, respectively. Up and downconversion emission spectra recorded with 976 and 532 nm laser wavelengths show emission from Pr3+ ions. Emission of Pr3+ enhances approximately thirty times when Yb3+ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase effectively when we approach to ceramic via glass-ceramic sample. Intense upconversion emission observed by naked eyes has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible takes place mainly via photon avalanche (PA) process. Upconversion mechanisms have been discussed in terms of excited state absorption (ESA) and energy transfer (ET) processes.

Structural, thermal, and optical properties of Er3+/Yb3+ co-doped oxyhalide tellurite glasses, glass-ceramics and ceramics

Glass-ceramics and ceramics containing nano-crystals of different phases doped with Er3+/Yb3+ ions have been successfully prepared by heat treatment of the precursor oxyhalide glasses synthesized by the melt-quench method. X-ray diffraction patterns and transmission electron microscopy (TEM) images verify the precipitation of nano-crystals. Emission of Er3+ enhances several times when Yb3+ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase to a great extent when we approach to ceramics from glasses via glass-ceramics. The intensity of the blue and green emission bands increases much faster than the red and NIR emission bands. Intense upconversion emission observed by the naked eye has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible radiation takes place mainly via photon avalanche (PA) process.

Optical avalanche in Ho:Yb:Gd2O3 nanocrystals

Intense green upconversion emission in Ho:Yb:Gd2O3 spherical nanoparticles is reported through hetrolooping enhanced energy transfer process. Different techniques used for structural characterization divulge the formation of spherical Ho:Yb:Gd2O3 crystals of diameter ∼100 nm. Efficient energy transfer from Yb3+ → Ho3+ ions set spherical nanocrystal to emit in the range of UV-NIR via three NIR photons absorption process. Power dependence and the temporal evolution of upconversion emission intensity suggest the occurrence of a photon avalanche process. The enhancement in emission intensity in nanophosphor sample has been explained and the photophysics involved is correlated with the unique structural properties of the crystallites formed and the time resolved spectroscopy.

Observation of avalanche upconversion emission in Pr:Y2O3 nanocrystals on excitation with 532 nm radiation

In this paper we report the two photon upconversion process in nanosize Pr:Y2O3 crystals on excitation with 532 nm photon at room temperature. Upconversion emission intensity shows an abrupt change at the critical pump threshold. On the basis of the temporal evolution of the intermediate state population and power-dependence studies, it is concluded that the significant variation in upconversion emission intensity is due to the photon avalanche process.

Up-conversion and photon avalanche in oxy-fluoride nano-structured glasses doped with Ho3+

Transparent nano-crystalline glass–ceramics (nano-structured glasses) were prepared from oxy-fluoride precursor glass doped with HoF3 and their luminescence properties were investigated. Visible blue, green and red emissions were observed, and the relative intensity of the green and red emission was strongly dependent on HoF3 concentration. Under 750 nm pumping, the intense green emission due to the photon avalanche process was observed at room temperature from nano-structured glass doped with high (0.5mol%) concentration of HoF3.

Ultraviolet and white photon avalanche upconversion in Ho3+-doped nanophase glass ceramics

Ho3+-doped fluoride nanophase glass ceramics have been synthesized from silica-based oxyfluoride glass. An intense white emission light is observed by the naked eye under near infrared excitation at 750nm. This visible upconversion is due to three strong emission bands in the primary color components, red, green, and blue. Besides, ultraviolet signals are also recorded upon the same excitation wavelength. The excitation mechanism of both the ultraviolet and the visible emissions is a photon avalanche process with a relatively low pump power threshold at about 20mW. The total upconverted emission intensity has been estimated to increase by about a factor of 20 in the glass ceramic compared to the precursor glass, in which an avalanche type mechanism is not generated.

Infrared-laser induced photon avalanche upconversion in Ho3+–Yb3+ codoped fluoroindate glasses

An intense green upconversion emission due to a photon avalanche mechanism has been observed in Ho3+–Yb3+ codoped fluroindate glasses, measured at 200 K, under excitation at around 750 nm. The influence of the Yb3+ concentration on the photon avalanche process has been studied. The pump power threshold of the avalanche mechanism decreases as the Yb3+ concentration is increased. A reduction by about a factor of 3 is observed from the 2.25 mol % Ho3+ single doped glass to the 2.25 mol % Ho3+–2.25 mol % Yb3+ codoped glass. This effect has been related to an extra feeding of the I47 intermediate level of Ho3+ ions via Ho3+→Yb3+ and Yb3+→Ho3+ energy transfer and back transfer processes, respectively.

Infrared detection scheme with the photon avalanche effect.

We present a new infrared (IR) detection scheme based on the infrared quantum counter (IRQC) detector and utilizing the photon avalanche process. At the time of its discovery, the phenomenon of photon avalanche was considered a limitation rather than an advantage for the development of IRQC. Both the experimental results and the numerical modeling presented demonstrate that the process responsible for photon avalanche can be used to enhance the detection of an IR signal. A new room-temperature IR detection scheme is proposed on the basis of the results of this research. The novel detection scheme presented demonstrates an increase in detectivity and a decrease in the noise-equivalent power when compared with the IRQC schemes previously discussed in the literature.

Photon avalanche upconversion inTm3+-doped fluoroindogallate glasses

In this work, a study of photon avalanche at 476 nm(1G4→3H6) in Tm-doped fluoroindogallate glasses is reported. TransientTm3+ emissions at 476, 450 nm (1D2→3F4) and transmission at the pumping wavelength (645 nm)were monitored as a function of excitation power and Tm3+concentration. We propose a theoretical treatment based on a set offive non-linear coupled rate equations, which include sequentialtwo-photon absorption (TPA), two cross-relaxations among Tm3+ions, and energy migration at the 3F4 metastable state. Itis demonstrated that energy migration in highly doped samples playsa fundamental role in the photon avalanche process, and may evensuppress it. Additionally, sequential TPA must be considered inorder to explain the transient behaviour of the 450 nm emission inthe photon avalanche regime.

Photon avalanche effect in doped quantum wells

A system of n-doped quantum wells is considered. The system is illuminated by IR radiation with frequency ω resonant to the transition between the second and third size-quantized subbands. At low light intensities j, the excitation does not induce any intersubband transitions. At higher j, however, a photon avalanche process can develop due to Auger-like transitions. The threshold light intensities for the effect, jth, are tens or hundreds of kW/cm 2. The equilibration times of the effect, τ eq, are extremely short: τ eq∼10–100 ps. The energy necessary for ultrafast switching between the states, when the second and third subbands are empty or populated, can be estimated at 10–100 fJ/μm 2.

Room temperature photon avalanche in Ho 3+ doped YAG, YAP, YLF and ZBLAN

Upconverted, green emission from the 5S 2 level of Ho 3+ ion in two oxides, YAG and YAP, and two fluorides, YLF and ZBLAN, was observed at room temperature under cw 580–590 nm excitation. Under these excitation wavelengths, which are off resonance with any ground state absorption, characteristic features of photon avalanche process are observed. A time-dependent rate equation model was employed to describe this behavior using experimentally determined parameters.

The up-conversion of near-infrared excitation radiation in Ho 3+-doped LiYF 4

The up-conversion processes due to the continuous wave excitation of the holmium 5 I 4 multiplet in LiYF 4 crystal are investigated. Despite a very low absorption cross-section for the transition from the holmium 5 I 8 ground state to the 5 I 4 multiplet, a bright green up-converted emission originating from the 5 S 2 multiplet is observed. The excitation and excited state absorption spectra indicate that the up-conversion process is based mainly on excited state absorption from the metastable 5 I 7 multiplet. Some features of the up-converted green emission are characteristic for the photon avalanche process.

Photon avalanche upconversion in YAIO3: Ho3+ crystals

We report room temperature upconverted emission in Ho3+-doped YAIO3 single crystals. Intense green fluorescene was observed under yellow, orange or red cw excitation. Under 580–590 nm excitation, where the characteristic features of a photon avalanche process are observed, the excitation power threshold is twice lower in the 5 at.% Ho3+-doped sample than in the 1 at.% Ho3+-doped one.

Photon avalanche up-conversion in Ho 3+ doped fluoride glasses

Photon avalanche-induced up-conversion green emission centered at 545 nm was observed in Ho 3+ doped, and Ho 3+, Tm 3+ co-doped ZrF 4-based heavy metal fluoride glasses, when excited near 585 nm, which is off resonance with any ground state absorption bands of either Ho 3+ or Tm 3+ ions. Analyses of spectral measurements suggest that the 545 nm emission occurs from the 5 S 2 and 5 F 4 states of Ho 3+ that are populated by excited-state absorption from the 5 I 7 state of Ho 3+. Multi-channel cross-relaxation processes that efficiently populate the 5 I 7 state make the photon avalanche process efficient in this system. The photon avalanche dynamics are discussed in detail by comparing the experimental results from the Ho 3+ doped and Ho 3+, Tm 3+ co-doped samples.