Photon Avalanche Upconversion Research Articles

Lanthanide-Doped KMgF3 Upconversion Nanoparticles for Photon Avalanche Luminescence with Giant Nonlinearities.

Lanthanide (Ln3+)-doped photon avalanche (PA) upconversion nanoparticles (UCNPs) have great prospects in many advanced technologies; however, realizing efficient PA luminescence in Ln3+-doped UCNPs remains challenging due to the deleterious surface and lattice quenching effect. Herein, we report a unique strategy based on the pyrolysis of KHF2 for the controlled synthesis of aliovalent Ln3+-doped KMgF3 UCNPs, which can effectively protect Ln3+ from luminescence quenching by surface and internal OH- defects and thereby boost upconversion luminescence. This enables us to realize efficient PA luminescence from Tm3+ at 802 nm in KMgF3: Tm3+ UCNPs upon 1064 nm excitation, with a giant nonlinearity of ∼27, a PA response time of 281 ms, and an excitation threshold of 16.6 kW cm-2. This work may open up a new avenue for exploring highly nonlinear PA luminescence through aliovalent Ln3+ doping and crystal lattice engineering toward diverse emerging applications.

Low threshold photon avalanche upconversion emission for temperature sensing based on Yb(III)/Er(III) Co-doped NdVO4 with sphere 3D self-assembled structure microparticles

Upconversion luminescent microcrystals (UCMs) due to their optical characteristics have been applicated in temperature detecting fields. However, the accuracy of traditional temperature probes based on UCMs is limited by the low intensity of upconversion luminescence (UCL). Herein, Yb3+ and Er3+ ions co-doped NdVO4 (NdVO4:Yb/Er) UCMs with a 3D self-assembled structure were designed via a hydrothermal method. This innovative structure enables the realization of a photon avalanche (PA) emission process. The Yb3+ and Er3+ co-doping in NdVO4:Yb/Er UCMs significantly reduces the PA threshold compared to NdVO4:Er UCMs. Obvious PA process produced by Yb3+/Er3+ doping is observed at low excitation threshold (～13 mW) in NdVO4:Yb/Er UCMs, enhancing the whole UCL intensity. Additionally, the NdVO4:Yb/Er UCMs exhibit a high temperature sensitivity of 3.5% K−1 at low pump power, indicating that UCMs have the potential application in optical temperature sensor.

A Generalized Approach to Photon Avalanche Upconversion in Luminescent Nanocrystals.

Photon avalanching nanoparticles (ANPs) exhibit extremely nonlinear upconverted emission valuable for subdiffraction imaging, nanoscale sensing, and optical computing. Avalanching has been demonstrated with Tm3+-, Pr3+-, or Nd3+-doped nanocrystals, but their emission is limited to a few wavelengths and materials. Here, we utilize Gd3+-assisted energy migration to tune the emission wavelengths of Tm3+-sensitized ANPs and generate highly nonlinear emission from Eu3+, Tb3+, Ho3+, and Er3+ ions. The upconversion intensities of these spectrally discrete ANPs scale with nonlinearity factor s = 10-17 under 1064 nm excitation at power densities as low as 7 kW cm-2. This strategy for imprinting avalanche behavior on remote emitters can be extended to fluorophores adjacent to ANPs, as we demonstrate with CdS/CdSe/CdS core/shell/shell quantum dots. ANPs with rationally designed energy transfer networks provide the means to transform conventional linear emitters into a highly nonlinear ones, expanding the use of photon avalanching in biological, chemical, and photonic applications.

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.

Two distinct simultaneous NIR looping behaviours of Er3+ singly doped BiOBr: The underlying nature of the Er3+ ion photon avalanche emission induced by a layered structure

Traditional photon avalanche (PA) emission of rare earth (RE) ions is a consequence of the efficient cross-relaxation (CR) process between excited energy levels. Here, we report the simultaneous visible and near-infrared (NIR) PA emission of Er3+-doped BiOBr layered crystals showing a different construction mechanism. Over the threshold power point of a 980 nm laser, seven-photon PA upconversion (UC) behaviour and four-photon NIR emission of Er3+ ions are observed simultaneously, but only the latter significantly depends on the concentration. Compared to the reported BiOCl system, the great divergences in the Er3+-activated PA emission in BiOBr enable us to reconsider the basic mechanism underlying this emission and rediscover the special photo-physical nature of these layered crystals. According to the same power dependence of the PA emission and the host photocurrents, we show that the visible PA emission indeed is a deexcitation process of Er3+ ions from the NIR-excited band transition of BiOBr; but the NIR one retains traditional efficient CR between Er3+ ions, which demonstrates a new mechanism for PA emission different from the one previously reported. The results of this work not only offer new insight into the nature of PA emission but also promote potential applications of PA UC phosphors in solid-state lasers and optical switches.

Effect of Zn2+ dopant on photon avalanche upconversion behavior of BiOCl:Er3+ crystals

Effect of divalent dopants, Zn2+ ion, on the high-order photon avalanche (PA) upconversion (UC) emission of Er3+ doped BiOCl microcrystals was investigated. XRD results indicated that Zn2+ ion dopants would mostly enter into the lattice space at low and moderate doping concentration, and began to substitute Bi3+ ion gradually at heavily doping level. Under exaction at 980 nm, the PA UC of violet, green and red emission of Er3+ ions could be observed, and the UC emission intensity increased with increasing the Zn2+ addition below 8 mol.%, then decreased with further addition. Power dependence study showed that the dopant concentration of Zn2+ had no obviously negative effect on the occurrence of PA emission. On the bases of results investigated herein, we considered that the lattice distortion by Zn2+ doping could not directly change the special PA emission of BiOCl:Er3+, but would improve the emission intensity when used as lattice modifier.

High-Performance Simultaneous Two-Photon Absorption Upconverted Stimulated Single-Component Sr2V2O7 Phosphor for White LEDs

Notwithstanding the wide use of white light-emitting diodes (w-LEDs), conventionally consisting of multiple emitting components, some inevitable issues still exist nowadays, such as the intrinsic color balance, device complexity, and high cost associated with such multiple emitting components. We have synthesized simultaneous two-photon absorption upconverted stimulated single-component Sr2V2O7 phosphor for use in w-LEDs. Due to the photon avalanche upconversion, the as-grown phosphor exhibits an enhanced photoluminescence spectrum in the range of 400 nm to 650 nm for white light when excited by red light at 693 nm. Moreover, when evenly dispersed in polyethylene glycol dispersant, the as-grown phosphor simultaneously produced strong visible white light when using an excitation wavelength λex of 693 nm, suggesting a possible route to produce w-LEDs by using red chips as an excellent substitute for traditional w-LEDs with multiple emitting components based on rare-earth metals. Finally, density functional calculations were performed using the generalized gradient approximation to study the electronic structure of Sr2V2O7 crystal. A reasonable model is proposed to explain the two-photon absorption luminescence mechanism.

Photon avalanche upconversion in Ho3+–Yb3+ co-doped transparent oxyfluoride glass–ceramics

The Ho3+–Yb3+ co-doped transparent glass and glass–ceramics containing CaF2 nanocrystals have been prepared. Differential thermal analysis and X-ray diffraction measurements have been made to characterize thermal properties of glass and structural changes in glass–ceramics, respectively. Photon avalanche upconversion has been achieved by exciting the samples at 745nm at room temperature. An intense green and a weak red upconverted emissions corresponding to the 5S2:5F4→5I8 and 5F5→5I8 transitions, respectively, have been observed. The upconversion intensity has been found to increase with the increase in the size of the fluoride nanocrystals in glass–ceramics. Experimental evidences confirm that the mechanism of upconversion is photon avalanche.

Investigation of upconversion and near infrared emission properties in CeO_2: Er^3+, Yb^3+ inverse opals

The upconversion emission of rare earth ions can be modified in photonic crystals, however, the influence of upconversion emission modification of rare earths on near infrared emission has not been investigated yet in the photonic crystals. In the paper, CeO₂: Er³⁺, Yb³⁺ inverse opals with the photonic band gaps at 545, 680 and 450 nm were prepared by polystyrene colloidal crystal templates. The upconversion and the near infrared emission properties of Er³⁺ ions were systematically investigated in the CeO₂: Er³⁺, Yb³⁺ inverse opals. Comparing with the reference sample, significant suppression of both the green and red upconversion luminescence of Er³⁺ ions were observed in the inverse opals. It is interesting that the infrared emission located at 1,560 nm was enhanced due to inhibition of upconversion emission in the inverse opals. Additionally, mechanism of upconversion emission of the inverse opal was discussed. The photon avalanche upconversion process is observed.

PHOTON AVALANCHE UPCONVERSION EMISSION IN Ho:Gd2O3 NANOPHOSPHOR

This paper report, the structural and spectroscopic properties of Gd2O3 nano-phosphor activated with Ho3+ ions. XRD, SEM and TEM techniques have been used for the structural characterizations. The phosphor contains spherical nanocrystallites with uniform size of ~40 nm. Enhanced IR to green and red photon avalanche upconversion is reported under 976 nm laser excitations. Further, annealing shows a significant improvement in emission intensity. Temporal evolution of upconversion emission intensity were measured which suggests the photon-avalanche mechanism is responsible for the upconversion process. The enhancement of emission was explained and the photo-physics involved is correlated with the unique structural properties of the crystallites formed.

Photon avalanche upconversion and pump power studies in LaF3:Er3+/Yb3+ phosphor

Hexagonal LaF3:Er3+/Yb3+ phosphor material has been synthesized by chemical precipitation method to obtain high near-infrared to green upconversion (UC) efficiency. Its thermal, structural and fluorescence properties have been studied. UC emission bands have been observed up to 315 nm in UV region. The effect of input pump power on the intensities of various emission bands has been studied in detail and photon avalanche UC mechanism has been identified. On increasing the excitation power, some bands have shown saturation in intensity. Also, at higher pump intensities two new UC bands were observed and their origin has been discussed. The phosphor has also been tested for possible UC-based fingerprint detection.

Stimulated emission in the red, green, and blue in a nanostructured glass ceramics

Red, green, and blue stimulated emissions have been achieved in Ho3+ doped oxyfluoride glass ceramic at room temperature. The material shows three emission bands at the red (650 nm), green (545 nm), and blue (488 nm) regions under infrared excitation at 750 nm. These emission bands are caused by a photon avalanche upconversion process previously reported. A pump and probe experimental setup has been designed to show stimulated emissions at the three bands. The pump power threshold for positive gain in the 490 nm band has been estimated around 2.7 kW/cm2. Higher thresholds are expected for the other bands.

Photon-avalanche upconversion of Ho3+ in NaYF4 and enhancement of violet, blue and green emissions induced by sensitization of Tm3+

Abstract Ho 3+ singly doped and Ho 3+ /Tm 3+ co-doped hexagonal NaYF 4 powders have been synthesized by a solid-state reaction method. Under excitation of 671 nm diode laser, upconverted blue, green and red emission bands are observed in Ho 3+ singly doped sample. Temporal evolution and excitation power dependent behavior for the green emission are explored, indicating that a photon-avalanche mechanism is responsible for the upconversion processes in Ho 3+ singly doped hexagonal NaYF 4 sample. With the introduction of Tm 3+ , the intensities of both blue and green emissions of Ho 3+ are efficiently enhanced, which are attributed to two energy transfer processes from Tm 3+ to Ho 3+ , i.e., 3 F 4 (Tm 3+ ) + 5 I 8 (Ho 3+ ) → 3 H 6 (Tm 3+ ) + 5 I 7 (Ho 3+ ) and 1 G 4 (Tm 3+ ) + 5 I 8 (Ho 3+ ) → 3 H 6 (Tm 3+ ) + 5 F 3 (Ho 3+ ). The result offers a new sensitization approach to enhance the upconversion efficiency of Ho 3+ under 671 nm excitation.

Er3+掺杂Y2O3纳米晶粒的多光子上转换荧光

Visible upconversion emission intensities are investigated in Er3+-doped Y2O3 nanocrystals. We also find that the upconversion intensity varies nonlinearly with the excitation power with a threshold of 110 mW, which indicates that the green and red emissions would be photon avalanche upconversion when the excitation power exceeds the threshold.

Visible photon-avalanche upconversion in Ho^3+ singly doped β−Na(Y_15Na_05)F_6 under 980 nm excitation

Visible IR-to-green photon-avalanche upconversion is reported in an Ho3+ singly doped beta-Na(Y1.5Na0.5)F6 crystal under 980 nm excitation. Upconverted green, red, and IR emissions are observed at 540, 645, and 751 nm, respectively. Temporal evolution and excitation power dependent upconversion intensity are measured, suggesting that a photon-avalanche mechanism is responsible for the upconversion process. It is believed that an efficient cross relaxation (5S2,5I8)-->(5I6,5I6) mainly performs the population of 5I6 excited state, resulting in the intense photon-avalanche upconversion emission in the synthesized samples.

Laser-induced, Er3+ trace-sensitized red-to-blue photon-avalanche up-conversion in Tm3+:KY3F10

We report here the first results of a spectroscopic study of anti-Stokes emissions from a Tm3+-doped KY3F10 crystal demonstrating the sensitization effect of Er3+ ions, present as trace impurities, on the ESA (3F4→1G4) lines of Tm3+. We have also detected Ho3+ traces in Tm3+:KY3F10. Contrary to the Er3+ ion, the Ho3+ ion does not increase the possibilities of resonant transfer with the Tm3+ ion. The Tm3+→Ho3+→Tm3+ transfers are much less probable than the Tm3+→Er3+→Tm3+ transfers. The majority of the Tm3+ ions excited by sensitized photon-avalanche absorption are exclusively located in the immediate neighbourhood of Er3+ ions. Red-to-green up-conversion mechanism is, for Er3+ either a two-step absorption process or a photon-avalanche absorption process, depending on whether the excitation wavelength is tuned on the 4I13/2→4F5/2 or 3F4→1G4 transitions.

Laser-induced, Er3+ trace-sensitized red-to-blue photon avalanche up-conversion inTm3+-dopedLiKYF5 crystals

The results for a spectroscopic study demonstrating that the excited-state absorption (ESA) ofTm3+:LiKYF5 at648 nm is dependent on the purity of starting materials used for synthesizing the crystal are presented. TheEr3+-freeLiKYF5 crystaldoped with Tm3+ is transparent at 648 nm because the majority of theTm3+ ions are inthe ground 3H6 state whatever the selective excitation intensity, whereas theEr3+-contaminated crystal is semi-transparent. In the second case a small increase of theexcitation intensity above a certain threshold produces an abrupt enhancement of the ESAprocess at 648 nm as well as the blue and the green emissions that are detected. Allthree processes, namely ESA corresponding to the transition, the blue emission due to the transition and the green emission from the4S3/2 Er3+ level, are sensitized with the energy transfers which promote the conversion ofTm3+ ions fromthe 1G4 and the3H4 states to themetastable 3F4 state.

Infrared-to-visible photon avalanche upconversion dynamics in Ho3+-doped fluorozirconate glasses at room temperature

Abstract Blue, green and red emissions have been generated at room temperature by upconversion processes under infrared laser excitation at 750 and 840 nm in fluorozirconate glasses doped with Ho 3+ ions. The intense green emission, associated to the 5 S 2 , 5 F 4 → 5 I 8 transitions, has been carefully analysed in order to elucidate the mechanisms involved in the energy conversion process. The temporal dynamics of the emission intensities, the extremely weak ground state absorptions, the strong excited state absorptions and the different cross-relaxation processes indicate that two different photon avalanche mechanisms are responsible of the 750 and 840 nm laser-induced upconversion processes in the Ho 3+ -doped fluorozirconate glass.

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.

Theoretical analysis of the photon avalanche dynamics in Ho3+-Yb3+ codoped systems under near-infrared excitation

The photon avalanche upconversion mechanism in a ${\mathrm{Ho}}^{3+}\text{\ensuremath{-}}{\mathrm{Yb}}^{3+}$ system under near infrared excitation is discussed. Two looping cycles in the excitation process provide the necessary population of the $^{5}I_{7}$ intermediate level of ${\mathrm{Ho}}^{3+}$ ions to achieve the avalanche regime. The first one takes place between ${\mathrm{Ho}}^{3+}$ ions, while the second one occurs between ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Yb}}^{3+}$ ions. We present a simplified model of the process, which only takes into account the ground, intermediate and emitting levels of ${\mathrm{Ho}}^{3+}$ and the ground and excited levels of ${\mathrm{Yb}}^{3+}$ ions. The rate equations of the system have been solved, and the photon avalanche regime has been interpreted in terms of gain and loss of the population of the intermediate level. The model predicts a reduction of the avalanche pump power threshold when the ${\mathrm{Yb}}^{3+}$ concentration increases which is in good agreement with experimental data.