Structure and Upconversion Luminescence of Hydrothermal PbWO₄:Er³⁺, Yb³⁺Powders

Abstract

PbWO 4 : Er 3+ ,Yb 3+ nanocrystals (∼100 nm) were prepared by the hydrothermal method at different pH values (pH ) 4, 7, and 9). Their structure and luminescence properties under 978-nm laser-diode excitation were studied. The results indicate that the practical ratio of W to Pb in the nanocrystals and the doping concentration of Yb 3+ depended strongly on the pH value due to structure change. In upconversion, red ( 4 F 9/2 f 4 I 15/2 ) and green ( 2 H 11/2 , 4 S 3/2 f 4 I 15/2 ) emissions were observed, both of which occurred via a two-photon populating process. Biexponential upconversion dynamics were observed, which was attributed to luminescence centers surrounded by different local environments. The intensity ratio of 2 H 11/2 f 4 I 15/2 to 4 S 3/2 f 4 I 15/2 (R HS ) was explored to reveal the local thermal effect under the exposure of the laser diode, showing that the temperature at the exposed spot increased linearly with respect to excitation power density and Yb 3+ concentration.

Synthesis process and luminescence properties of Tm3+ in AWO4 (A=Ca, Sr, Ba) blue phosphors

“…It is suggested that the non-exponential dynamics are contributed by two different luminescent Tm 3+ centers. The process has also been observed in Yb 3+ , Er 3+ -codoped PbWO 4 powder [34], which is the same scheelite structure as AWO 4 . The decay curve for 1 D 2 → 3 F 4 (453 nm) of Tm 3+ ions can be well fitted into a double-exponential function as I = A 1 exp(−t/ 1 ) + A 2 exp(−t/ 2 ) ( 1 and 2 are fast and slow components of the luminescence lifetimes, respectively.…”

Large Upconversion Enhancement in the “Islands” Au–Ag Alloy/NaYF4: Yb3+, Tm3+/Er3+ Composite Films, and Fingerprint Identification

“…[ 38 ] The local thermal effect originates from the medium absorption and photothermal conversion to excitation light, which leads to the increase of the local temperature of the medium and luminescent quenching. [ 50 ] The energy gap from the starting level of the fi ve-photon populating state 1 I 6 to its nearest down level 3 P 1 is only 660 cm −1 , inducing the easily happening of the nonradiative relaxation of 1 I 6 -3 P 1 . In the existent of metal NPs, the local temperature of NaYF 4 : Yb 3+ , Tm 3+ can be largely improved in comparison to NaYF 4 : Yb 3+ , Tm 3+ due to large metal SPE at 980 nm and quick thermal transmission from the metal NPs to the UCNPs.…”

“…In the existent of metal NPs, the local excitation fi eld is greatly enlarged, resulting in the saturation effect as well as local thermal quenching of UCL and the corresponding suppression of EF with excitation power. [ 38,50 ] Figure 4 b,c display the double-logarithmic plots of the UCL intensity as a function of excitation power density, for the NaYF 4 fi lms, respectively (the size of UCNPs we used was 30 nm, for both NaYF 4 : Yb 3+ , Tm 3+ fi lm, and the composite fi lm). It should be noted that as the excitation power density is lower than 13 W cm −2 for the NaYF 4 : Yb 3+ , Tm 3+ fi lm and lower than 9 W cm −2 for the composite fi lm, the slopes of different transitions are near the same to the required photon numbers ( n = 2-5) to populate the corresponding levels for NaYF 4 : Yb 3+ , Tm 3+ and Au-Ag/NaYF 4 : Yb 3+ , Tm 3+ fi lms.…”

Structure and upconversion luminescence properties of BaYF5:Yb3+, Er3+ nanoparticles prepared by different methods

“…To investigate the fundamental UC mechanism of samples, the right presents the pumping power dependence of 2 H 11/2 ( 4 S 3/2 )-4 I 15/2 (green) and 4 F 9/2 -4 I 15/2 (red) transition emissions for as-prepared BYF samples. It is well known that the emission intensity (I f ) will be proportional to some power (n) of the infrared excitation power (P) [25]:…”