In this work, we report the upconversion emission from Pr3+ and Nd3+ ions in potassium lead chloride crystal KPb2Cl5after excitation in the 4F5/2,3/2 levels of Nd3+ ions. We have observed violet, blue, green, orange, and red emissions at
room temperature. Blue emission from Pr3+ ions is induced by near infrared laser excitation of Nd3+ through energy
transfer from Nd3+ to Pr3+ ions. The mechanisms leading to the visible emissions have been investigated by studying the
dependence of the upconversion luminescence on the excitation wavelength and intensity of the IR pump light.
In the present work, we report on infrared thermography measurements in Nd-doped KPb2Cl5 crystal and
powder above and below the barycentre of the 4F3/2 level that were performed in order to assess the
relative weights of both the direct anti-Stokes absorption processes and those assisted by either excited
state absorption or energy transfer upconversion when cooling takes place in the material. As the laser
induced temperature changes are usually small, we used a special configuration of the samples that
allowed us to obtain differential measurements where an undoped sample acted as a temperature baseline.
This method allows us to ascertain whether the recorded temperature changes are optically induced or
they are due to some other effect.
The first experimental demonstration of local internal and bulk optical cooling in samples of Nd-doped
KPb2Cl5 crystals and Nd-doped KPb2Cl5 nanocrystalline powders upon laser excitation between the 4F3/2
and 4F5/2 manifolds is reported. The possibility of controlling the dynamics of the bulk optical cooling
process by adequately tuning the excitation wavelength is also demonstrated.
In this work, we report the optical properties of Tm3+, Er3+, and Tm3+-Er3+ codoped tellurite TeO2-WO3-PbO glasses for
different Er3+ and Tm3+ concentrations. Judd-Ofelt intensity parameters have been determined to calculate the radiative
transition probabilities and radiative lifetimes of excited states of Tm3+ and Er3+ ions. Luminescence spectra and
lifetimes were measured under 793 nm and 800 nm excitations. The infrared emission of Tm3+ at 1470 nm is broader by
around 30 nm and the stimulated emission cross section twice if compared to fluoride glasses used for S-band
amplifiers. Moreover, a broad emission from 1350 to 1600 nm with a full width at half-maximum of ~ 160 nm is
obtained by codoping the glass with Tm2O3 an Er2O3 which suggests these glasses could be promising materials as
broadband light sources and broadband amplifiers for wavelength-division-multiplexing (WDM) transmission systems.
In this work we report an experimental demonstration of broadband wavelength self-tuning in Rb5Nd(MoO4)4 laser crystal (RNM) together with a theoretical treatment of the system based on its birefringence properties. The experimental self-frequency tuning of the laser emission along the free spectral range of the RNM crystal (1060-1070 nm) was obtained by rotating the birefringent gain plate in its own plane. To investigate the tuning characteristics of the spectral filter, we have used the Jones-vector formalism. The calculated wavelength-selective tuning matches very precisely the experimental observations.
In this work we report infrared to visible upconversion luminescence in the low phonon-energy host material KPb2Cl5 doped with Er3+ ions. The low phonon energy strongly reduces multiphonon relaxation in this host. As a consequence, in addition to the strong green upconversion luminescence from 2H11/2,4S3/2) levels at room temperature, blue luminescence from 2H9/2 and 4F7/2 levels is also observed under near infrared excitation in the 4I9/2 (801 nm) and 4I11/2 (978 nm) multiplets respectively. The upconversion mechanisms are investigated by means of excitation and timeresolved luminescence spectroscopy.
In this work we report the upconversion luminescence of Pr3+ doped Kpb2Cl5 crystal upon excitation in the near infrared region inside the 1G4 level. Direct excitation in the visible region has been also carried out. A strong orange luminescence from the 1D2 leve, and a less intense blue, green, and red emission from the 3P0,1 levels have been observed under infrared excitation and compared with those obtained under one photon excitation. The upconverted fluorescence from the 1D2 level shows a quadratic dependence on the pump power indicating a two photon process, whereas the pump power dependence of the blue fluorescence from level 3P0 is nearly cubic (2.62), which indicates a three photon mechanism. Emission from levels 3P0,1 is also observed under pulsed excitation in the 1D2 state. The possible excitation mechanisms responsible for these upconversion processes are discussed.
Laser induced internal cooling has been investigated in a new fluorochloride glass (CNBZn) and a fluoride glass (BIG) doped with 2.1x1020 Yb3+ ions/cm3 and in a Kpb2Cl5 crystal doped with 5x1019 Yb3+ by using collinear photothermal deflection and conventional laser excitation spectroscopies under high photon irradiances. The cooling efficiency for CNBZn glass which is approximately 2% relative to the absorbed laser power at 1010 nm and 300 K falls about 20% at 77 K. The cooling efficiency for BIG glass was only approximately 6% at room temperature. For the Yb3+ doped Kpb2Cl5 crystal we have shown internal laser cooling with a cooling efficiency of about 0.2% at room temperature. This is the third ytterbium-doped crystal, after Kgd(WO4) (Ref.10) and YAG (Ref.11), in which anti-Stokes laser-induced internal cooling has been demonstrated. The observed temperature dependence of the cooling process can be explained by a simple model accounting for the photon-ion- photon interaction.
In this work we report the upconversion processes that produce blue, green, orange, and red emission in K5Nd(MoO4)4 stiochiometric crystal together with the dynamics and spectral properties of the laser emission. It was found that upconversion energy transfer processes reduce the energy storage capacity through the reduction of the fluorescence lifetimes of the metastable 4F3/2 level. The experiments were conducted in such a way that the dynamics of the IR and visible fluorescence was performed under lasing and nonlasing conditions. The dynamics of the unconverted emission shows that both upconversion energy transfer and excited state absorption of the laser emission occur.