The multiphoton ultraviolet and visible upconversion luminescence of Tm3+Yb3+ codoped ZBLAN fluoride glass as
excited by a 975nm diode laser was studied. Two typical ultraviolet 290.6nm 1I6 → 3H6 and 362.0nm 1D2 → 3H6 upconversion luminescence lines were found. The careful measurement of the variation of upconversion luminescence intensity F as a function of the 975nm pumping laser power P has proven that the 290.6nm 1I6 → 3H6 and 362.0nm 1D2 → 3H6 upconversion luminescences are a six-photon and a five-photon upconversion luminescence respectively. Several visible upconversion luminescence lines at 450.5nm, 473.9nm, 648.5nm, (687.3nm, 696.2nm) and (793.5nm, 800.7nm)
were found also, which result from the fluorescence transitions of 1D2 → 3F4, 1G4 → 3H6, 1G4 → 3F4, 3F3 → 3H6 and 3H4 → 3H6 of Tm3+ ion respectively. It has been proved that the upconversion luminescence of 1G4 state is a three-photon upconversion process, while that of 3F3 or 3H4 state is a two-photon upconversion process. The theoretical analysis
suggests that the upconversion mechanism of the 362.0nm 1D2 → Tm3+ upconversion luminescence is the cross energy
transfer of {3H4(Tm3+) → 3F4(Tm3+), 1G4(Tm3+) → 1D2(Tm3+)} and {1G4(Tm3+) → 3F4(Tm3+), 3H4(Tm3+) → 1D2(Tm3+)} between Tm3+ ions, whereas the mechanism of the 290.6nm 1I6 → 3H6 upconversion luminescence is the sequential energy transfer of {2F5/2(Yb3+) → 2F7/2(Yb3+), 1D2(Tm3+) → 3P1(Tm3+)} and {2F5/2(Yb3+) → 2F7/2(Yb3+), 1D2(Tm3+) → 3P2(Tm3+)} from Yb3+ ions to Tm3+ ions. In addition, the upconversion luminescence of G4 and 3H4 state
also results from the sequential energy transfer {2F5/2(Yb3+) → 2F7/2(Yb3+), 3H4(Tm3+) → 1G4(Tm3+)} and {2F5/2(Yb3+) → 2F7/2(Yb3+), 3F4(Tm3+) → 3F2(Tm3+)} from Yb3+ ions to Tm3+ ions respectively.
A diode-laser pumped blue intracavity frequency-doubled self-Q-switched microchip laser of a chromium Cr4+ Neodymium Nd3+ codoped yttrium aluminum garnet crystal (Cr4+Nd3+:YAG) combined with a potassium niobate (KNbO3) crystal is developed. By coating the cavity mirrors with the films that suppress the 1064-nm operation and enhance the 946-nm laser, the 4F3/24I9/2 transition of the Nd3+ ion is facilitated to achieve the 946-nm laser oscillation. The 946-nm laser of the Cr4+Nd3+:YAG is self-Q-switched due to the saturable absorption of the Cr4+ ion. The full width at half maximum (FWHM) of the laser pulse at a 964-nm wavelength is about 5.07 ns. A self-Q-switched 473-nm laser pulse is sequentially obtained through intracavity frequency doubling of the 946-nm laser by the KNbO3 crystal, whose FWHM is about 4.30 ns. The 473-nm intracavity doubled laser has a good fundamental transverse TEM00 mode, because the self-Q-switched 946-nm laser has a good TEM00 mode that results from the absorption bleaching established by both the 808-nm pump laser and 946-nm oscillating laser. The constant FWHM results from both the response time of the self-Q-switching and the establishing time of the oscillating laser being much faster than the accumulated time of the pump laser energy. The constant peak power of the 946-nm self-Q-switched laser mainly depends on the modulation ability of the self-Q-switching.
Three-dimensional (3-d) volumetric display is urgently needed in the fields of air-transportation management, computer-assistant design, imaging application, biophysics, and congratulatory or entertaining art. Recently the growing í#information highwayí# has been accelerating the requirement for 3-d displays to show fast and complex pictures. Frequency up-conversion 3-d volumetric display, abstracting especially in its self-spatial vision, has the advantages of total-solidification, high reliability and speedy operation so that it has a broad range of application. Two-frequency up-conversion 3-d volumetric display was evaluated as the latest achievement of 1996 in physics. This paper careful investigates the one-beam pumping upconversion 3-d volumetric display , which is based on erbium Er doped glass. The bright-light facula length of one-beam pumping upconversion luminescence is studied by diode LD laser. The upconversion luminescence spectrum of Er doped glass is measured also. The physics basis of one-beam pumping upconversion 3-d volumetric display based on Er doped glass is discussed. This interesting result illustrates that the property of one-beam pumping 3-d volumetric display could be improved so much to achieve practical application greatly. As our best knowledge, similar result has not been reported.
Upconversion luminescence of Yb3+-doped and Yb3+ Ho3+-codoped oxyfluoride vitroceramics when excited by a diode laser operating at a wavelength of 960 nm is investigated. A strong 479-nm upconversion cooperative radiation luminescence, attributed to the coupled states of Yb3+Yb3+ clusters, is discovered. This result suggests an interesting and effective path to achieve compact blue upconversion luminescence. The presence of holmium in the Yb3+Ho3+-codoped oxyfluoride vitroceramics substantially reduces intensity of the cooperative upconversion luminescence.
This paper studies upconversion luminescence of oxyfluoride glass codoped with holmium and ytterbium. When the sample was excited in the infrared at a wavelength of 960 nm, several visible luminescence peaks were observed. The two strongest upconversion luminescence peaks are located at 544 and 658 nm, which are due to the 5S2 to 5I8 and 5F5 to 5I8 transitions of Ho3+, respectively. Additional upconversion luminescence peaks are present at 485, 751, and 799 nm. The upconversion luminescence process is initiated by excitation of the codoped Yb3+ ions, followed by a transfer of energy from the excited Yb3+ ions to the Ho3+ ions. The dependence of the upconversion luminescence intensity with the excitation laser power obeys a power law with fractional exponent. This unusual saturation phenomenon is likely a result of energy diffusion.
A diode-pumped microchip laser is developed and achieves self Q-switched operation, which produces nanosecond pulses at a wavelength of 946 nm. The laser medium is a crystal of yttrium aluminum garnet (YAG) doped with both neodymium and chromium. The two surfaces of the NdCr:YAG crystal are coated with dielectric layers, which serve as the mirrors of the laser cavity. The Nd3+ ions in the NdCr:YAG crystal function as the gain medium while the Cr4+ ions act as a saturable absorber. The presence of the saturable absorber leads to self Q-switching, which produces laser pulses of 3.7-ns duration and 946-nm wavelength at a peak power of 240 W. When the laser output is focused onto a KNbO3 crystal, nanosecond pulses of blue color at 473 nm are obtained. The blue laser output has a single frequency and TEM00 transverse mode at a peak power of approximately 18 W.
Rate equations describing the dynamic processes in Er3+ doped pentaphosphate crystals were built up. Using this rate equations the dynamic processes of the building up processes of the populations of the states of Er3+ ions in ErP5O14 crystal was gotten. The spontaneous radiative processes, multiphonon nonradiative processes, absorption of the pump photons and the possible energy transfer processes between all states of Er3+ ions were included in the rate equations, and the pump power was supposed to be unchanged with time. Considered that the equation n(t0+(Delta) t)=n(t0+dndivided bydt(Delta) t would be held if (Delta) t was small enough, and using the initial condition n1=1.0, ni=0(idoes not equal1), the time dependent populations of all states could be gotten from the rate equations. When the pump power was 103W, population of the ground state decreased rapidly with time and then tended to stable, at the same time, the population of 4F9/2, the state excited directly by the pump light, formed a peak-like structure and then tended to stable. The gradient of the decay side and the rising side of this structure was close, which believed to be the result of the large number of the energy transfer processes between 4F9/2 and other states and the great rate of these processes. Populations of the other excited states lower than 4F9/2 were all increase at first and then decrease with time while excited states higher than 4F9/2 were all increase with time and then tended to be stable. The system came to be stable at about 140 microsecond(s) .
Using the rate equations describing the dynamic processes of the system, how the strength of the upconversion luminescence change with the Er3+ ion concentration and the pump power was analyzed. The spontaneous radiative processes, multiphonon nonradiative processes, absorption of the pump photons and the possible energy transfer processes between all states of Er3+ ions were included in the rate equations, and the pump power was supposed to be unchanged with time. It came to the result that when x change from 0.1% to 100% in ErxLa1-xP5O14 crystal, lager x benefit the population of all states higher than 4F9/2 in the whole range of pump power we considered, except for a small range of pump power in which smaller concentration result in larger ion number of some high lying states. It can be interpreted as that the increasing of the concentration of Er3+ ions increases both energy transfer processes which populate the upper states of the upconversion luminescence and the cross relaxation processes which depopulate these states. Since the strength of upconversion luminescence is in proportion to the ion numbers of the upper states of the luminescence, the total result is that the upconversion luminescence from 4S3/2 would increase with the concentration of Er3+ ions, and the strength of this upconversion luminescence were most strong in ErP5O14 crystal; for a small range of pump power, the strength of upconversion luminescence from level (2G4F2H)9/2 and 4G11/12 of Er ions in Er0.8La(subscript 0.2P5O14 crystal was most strong, for all the other range of pump power, this luminescence was also strongest in ErP5O14 crystal.
Using the rate equations which describing the dynamic processes in Er3+ doped pentaphosphate crystals, the upconversion mechanism in this system under 650nm excitation was gotten, and the influence of the concentration of Er3+ ions on the dominant populate process of the upper state of the upconversion luminescence was analyzed. The spontaneous radiate processes, multiphonon nonradiative processes, stimulated transitions and the possible energy transfer processes between all states of Er3+ ions were included in the rate equations, and the pump power was supposed to be unchanged with time. It came to the result that under weak excitations, the main upconversion mechanism in ErP5O14 crystal was energy transfer upconversion, and contribution from excited state absorption was small. And some nonresonant energy transfer processes played an important role in building up of the population of the upper state of some upconversion luminescence. Such as nonresonant energy transfer process (3->1, 5->12), the energy mismatch of which is 1585cm-1;31.1% of the ions of 4G11/2, the upper state of 379nm upconversion luminescence, was populated through this processes. Since changed concentration of Er3+ ions would cause changed distance thus changed energy transfer rate between them, and then the contribution of all processes in the system would be different. The result showed in ErxLa1-xP5O14 crystal with different x, the upper states of the upconversion luminescence were populated from different process, with the concentration of ER3+ ions increased, the influence of energy transfer upconversion processes (Including some nonresonant energy transfer) became larger.
This paper has found for the first time that in the case of indirect up-conversion sensitization, the proportion of the up- conversion luminous intensity of (formula available in paper) under direct sensitization to 7.50 X 10-2 (or 1/13.3) under indirect sensitization. This paper has analyzed the physics understanding of the upconversion phenomenon penetratingly. It is found that spontaneous radiation A and multiphoton non-radiate relaxation Wn does act simultaneously.
Modulation lifetime inspections a new kind measurement mechanism in Frequency Domain. A CW tunable Xe lamp is used as a pumping source, which is modulated first and excites sample sequentially. The lifetime could be obtained by analyzing its demodulation (m) and phase shift ((phi) ). Because the excitation light power density is only about 1W/s, the lifetime of delicacy material could be inspected beautifully, accurately and nondestructively. Thus it is undoubted that Modulation Inspection is the best method for lifetime measurement of delicacy material.
Er3+ ion is such a kind of rare earth ions that has most splendid upconversion luminous phenomenon. It is very significant also to find some new mechanism, method and material to enhance the upconversion efficiency. This paper investigates the material and luminescence property of ErYb codoped oxyfluoride vitroceramics. In out experiment device, Optical Measurement could be proceeded very precisely, sensitively and nondestructively. Our research finds that oxyfluoride vitroceramics has good luminous property. The rare earth ions, which are within a same micro-crystallite, are easy to consist of couple-group. The intense cluster effects have emerged. It results in that the Er3+ ion's upconversion luminescence in oxyfluoride vitroceramics is ten times greater than that in oxyfluoride glass and ZBLAN fluoride glass.
Up-conversion three-dimensional volumetric display is a new application and hot-point of frequency up-conversion research. It is elected as one of the nicest international physics achievement in 1996. This paper reports the principle demonstrate works in up-conversion three-dimensional volumetric display. The used mechanism is di-frequency up-conversion sensitization proposed by authors firstly. The used material is Pr3+Yb3+:ZBLAN glass.
The transparent rare-earth ion doped oxyfluoride vitroceramics is a new kind of nanometer material, whose structure was thought comprised of fluoride microcrystals in an oxide glass matrix. It may have not only high up-conversion efficiency but also good material property. This paper studies the optical absorption and emission properties of the Tm3+-doped oxyfluoride vitroceramics (FOV) and glass (FOG). It is possible to be a good up-conversion 3D volumetric display material.
Upconversion study is imperative now to find good material that has high laser damage threshold, good physics and chemical property, easy in processing in order to develop various up- conversion applications. This paper studies the material property of oxyfluoride vitroceramics by Raman and x-ray diffraction spectroscopy. It reveals the physical reason why the Er3+ ion's upconversion luminescence in oxyfluoride vitroceramics is 101 times greater than that in oxyfluoride glass.
This paper reports a quite interesting 474 nm up-conversion fluorescence when ErYb co-doped oxyfluoride glass is excited by 966 nm-diode laser. It was found that the 474 nm fluorescence is two-photon fluorescence. It can be found also that 474 nm fluorescence is posited between 490.5 nm 4F7/2 yields 4I15/2 and 454.0 nm 4F5/2 yields 4I15/2 fluorescence transition, and cannot be the transition from high excited state to first excited state of Er3+ ion also. In brief, the 474 nm fluorescence must be an extraordinary up-conversion fluorescence of ErYb co-doped oxyfluoride glass. In fact, it is reasonable entirely to believe that this is cooperative radiation fluorescence oriented from a kind of Couple State of two Yb3+ ions' cluster. The up-conversion processes are as follows: First each isolating Yb3+ ion absorbs pumping photon energy and is excited to 2F5/2 state from 2F7/2 ground state. Then two Yb3+ ions, which are both in 2F5/2 excited state, form a kind of Couple State of cluster (formula available in paper). And then the 474 nm fluorescence would be radiated from excited state (formula available in paper) of cluster's Couple State to its ground state (formula available in paper). The similar mechanism has not been reported internationally up to now.
This paper reports an interesting `characteristic' saturation phenomenon of upconversion luminescence of TmYb co-doped ZBLAN glass when excited by 966 nm-diode laser. That is the log-log plot of upconversion fluorescence intensity upon laser power is a straight line basically, however the slope of the log-log curve of two-photon and three-photon upconversion fluorescence intensity upon laser power is smaller than 2 and 3 very evidently respectively in laser focus point. It is very interesting that the slope would be enlarge clearly if the facula of pumping laser was increased. It could be believed that this phenomenon is not a simple `typical' saturation phenomenon that is caused by population exhausting in ground state, which F-P log-log curve is gradually bending. The only reason is just the energy diffusion. That is said, because of the resonant energy transfer among Yb3+ ions, Yb3+ ions which are within the laser facula and absorbs photon energy of pumping laser would diffuse energy to those Yb3+ ions which are out the laser facula. This process would cause energy density waste. And the slope would reduce also. Especially the proportion of wasting energy density is independent to pumping laser power, so the slope would be a straight line basically. However if laser facula was bigger than energy diffusion length, the energy density waste caused by energy diffusion would have be zero basically. Under this case, the slopes of log-log variation F-P curve are quite near the normal multi-photon relation. The similar mechanism has not been reported internationally up to now.
3D display may be one of the most wonderful techniques attracting scientists to research on. But most of current approaches are fictitious ones. On the CLEO'94, E. A. Downing and L. Hesselink et al. reported a virtual 3D volumetric display using Pr doped fluoride glass upconversion luminescence which is evaluated as a new excellent physics achievement in 1996. The ZBLAN:Pr glass is proved by L. Hesselink to be a interesting material for 3D volumetric display based on upconversion. In the processes of upconverting near-infrared radiation to visible, the 1G4 level of Pr3+ locates at an important position. But the transition probability of 3H4- 1G4 proved to be one or two order of magnitude smaller than other strong transitions. So to improve the population on 1G4 has an practical significance. In this paper, we report a simple 3D volumetric display experiment which has used the upconversion sensitization method. A bulk ZBLAN:Pr,Yb and ZBLAN:pr glasses were selected as display medium. Just as the sensitized action of Yb3+ ion, the di-frequency upconversion luminescence intensity of Pr3+ ion is enhanced more than thirty times. So, the brightness of 3D display is better than the work of E. A. Downing and L. Hesselink. Some technique consideration is discussed. In addition a conception of multilayer 3D display device is also presented, which are thought having several advantages.
When excited into Tm33F4 level by a LD at approximately 798 nm, Tm3 and Yb3 codoped pentaphosphate noncrystalline samples emit blue light at 475 nm, which corresponds to transition 1G4 yields 3H6. Although laser is directly absorbed by Tm3+ ions, the upconversion process rely on the codoping of Yb3+ ions. One Tm3+ yields Yb3+ transfer process excites Yb3+ ions, then backward Yb3 yields Tm3 energy transfer excites Tm3 ions from 3H4 to 1G4 level.
Wide wavelength range of upconversion fluorescence at 360 nm, 450 nm, 475 nm, 647 nm, and 800 nm were observed in Tm3+ and Yb3+ codoped ZBLAN glass when pumped by a laser diode at approximately 970 nm. Those emissions are from three metastable states 1D2, 1G4 and 3F4, respectively. Three samples with varying Tm3+ and Yb3+ ion doping were investigated. It was shown that the luminescence intensity, as well as the dependence of intensity on laser power density, vary strongly with rare earth ion concentrations. And the mechanism for the population of 1D2 level is clarified further.
In the study of Rare-earth upconversion luminescence, it is always a key factor to efficiently increase the luminescence efficiency. Some exciting results have been achieved by the method of sensitization of codoped rare-earth ions. The high upconversion efficiency has been achieved by the very effective way of using the Yb3+ ions' 2F5/2 energy level as the intermediate level to transfer energy to many other rare-earth ions. Due to the strong absorption of Yb3+ ions between the wavelength of 900 nm to 1000 nm, the population can be accumulated largely on the 2F5/2 energy level and it becomes possible to transfer energy to higher levels. In recent years, the study of the upconversion luminescence of Ho3+, Er3+, Pr3+ sensitized by Yb3+ shows that Yb3+ can cause quench at the same time with sensitization. So the codoped system of Yb3+ + R E (rare-earth ions) has very complex luminescence mechanism and in most situation the upconversion channels are not single or single direction. The study of the sensitization and quench is very important just because these complexities. Since the diode laser in 900 nm to approximately 1000 nm has developed quite well, it becomes possible to use mono-frequency diode laser to pump upconversion laser and fiber laser. In this paper, the upconversion luminescence of Yb(0.3)Er(0.3):ZBLAN glass induced by 966 nm diode laser was studied. Base on the experiment data, these results are calculated by the rate equation: when the cross energy transfer P between Yb3+ and Er3+ ions is quite weak, the upconversion luminescence become saturated gradually by the increase of the pump laser power; when the P is quite strong, it will cause a steep uprising of the luminescence before the saturation. This is the phenomenon of second uprising by the laser power that observed in the experiment.
A new kind of spectral analytical instrument has been developed for measuring pulse time-resolved spectra. In this instrument, a special light beam modulator translates the time-distribution of optical spectra into the space- distribution of light intensity, and then the time-dependent spectra is detected by an ordinary 2D CCD device. The time resolution of 25 microsecond(s) and the wavelength range of 224-824 nm have been attained in the experiment of a Xe flash-lamp emission.
The absorption spectra and fluorescence spectra of a novel Er:Yb:phosphate glass were measured, and some emission parameters including the intensity parameters, integrated cross-section, emission cross-section, spontaneous emission probability were calculated by J-O theory. Green and red upconversion luminescence were obtained when excited with 966 nm LD, the mechanism of upconversion were analyzed in detail. Laser around 1.54 micrometers were obtained with the glass, the power is 5.2 mW.
Blue, even ultraviolet emissions and very strong green emissions have been observed in ZBLAN glasses codoped with Er3+ and Yb3+. The strong green emissions were demonstrated to be of sequential two-photon process, while the blue emissions be of multi-photon process, due to the strong sensitization of the Yb3+. The schemes of luminescence sensitization and quenching of Yb3+ to Er3+ were proposed.
Much strong blue emission has been observed in pentaphosphate non crystals at room temperature, highly doped with Yb3+ and Tm3+ when excited into the Yb3+2F7/2 state and the excited states of Tm3+ at 966 nm by laser diode. Energy transfer and back transfer between the two rare earth ions, participation of phonons, and pair induced quenching were demonstrated to be responsible for the upconversion process.
The basic spectroscopic properties of Cr3+:LaP5O14 glass have been investigated. Weak crystal field (Dq equals 2.12) and strong electron-phonon coupling lead to a broad 4A2 yield 4T2 luminescence in 720 - 1120 nm range. The measured and calculated results also show it has a rather large absorption and emission cross- sections. This kind of glass can be considered as a material for tunable infrared laser.
Stability of Ti:Sapphire laser is researched in the paper. The experimental results and theoretical analysis show that the instability of the output is contributed to the pump stability, the quality of the crystal, and the spontaneous emission photon numbers that enter into stimulated emission modes, which we believe is put forward for the first time.
In this paper, the temperature dependence of upconversion luminescence from Pr,Er,Yb codoped ZBLAN glass pumped by 960nm laser diode was studied. The temperature dependencies of upconversion luminescence for Pr3+ and Er3+ in ZBLAN glass were compared. The results showed that the temperature dependence of upconversion luminescence from Pr+ is different to that from Er+ in ZBLAN glass.
In this paper the first observation of up-conversion luminescence phenomenon of ErP5O14 and HoP5O14 noncrystalline is reported. It is found that the up-conversion mechanism for ErP5O14 noncrystalline is sequential two-photon absorption by a single Er3+ ion, however, for HoP5O14 noncrystalline its up-conversion mechanism is energy transfer between Ho3+ ions.
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