Infrared to visible upconversion in Ho³+/Yb³+ co-doped Y₂ O₃ phosphor: effect of laser input power and external temperature

Power dependent photoacoustic and photoluminescence studies on a Ho3+/Yb3+ doped Y2O3 phosphor

The Ho³⁺/Yb³⁺ doped Y₂O₃ phosphor samples were synthesized through a combustion method and then were annealed at 800 °C, 1000 °C, and 1200 °C. The cubic phase of the synthesized samples was confirmed by XRD analysis. The upconversion (UC) & photoacoustic (PA) spectroscopic studies were done on prepared samples and both spectra are compared. The samples have shown intense green upconversion emission at 551 nm due to the ⁵S₂ → ⁵I₈ transition of Ho³⁺ ion along with other bands. The maximum emission intensity is obtained for the sample annealed at 1000 °C for 2 hours. The authors have also measured the lifetime corresponding to ⁵S₂ → ⁵I₈ transition and found that lifetime values follow the trend of upconversion intensity. The maximum lifetime of 224 μs is observed for the sample annealed at 1000 °C. A photoacoustic cell & a pre-amplifier was fabricated and optimized for maximum sensitivity of the system. The PA signal was found to increase with increase of excitation power within the studied range, while UC emission was found to saturate after a certain pump power. The increase in PA signal is due to the increase in non-radiative transitions in the sample. The wavelength-dependent photoacoustic spectrum of sample has shown absorption bands around 445, 536, 649 and 945 (970) nm with maximum absorption at 945 (970) nm. This indicates its potential for photo-thermal therapy using infrared excitation.

Demonstration of Temperature Dependent Energy Migration in Dual-Mode YVO4: Ho3+/Yb3+ Nanocrystals for Low Temperature Thermometry

A dual mode rare-earth based vanadate material (YVO₄: Ho³⁺/Yb³⁺), prepared through ethylene glycol assisted hydrothermal method, demonstrating both downconversion and upconversion, along with systematic investigation of the luminescence spectroscopy within 12–300 K is presented herein. The energy transfer processes have been explored via steady-state and time-resolved spectroscopic measurements and explained in terms of rate equation description and temporal evolution below room temperature. The maximum time for energy migration from host to rare earth (Ho³⁺) increases (0.157 μs to 0.514 μs) with the material’s temperature decreasing from 300 K to 12 K. The mechanism responsible for variation of the transients’ character is discussed through thermalization and non-radiative transitions in the system. More significantly, the temperature of the nanocrystals was determined using not only the thermally equilibrated radiative intra-4f transitions of Ho³⁺ but also the decay time and rise time of vanadate and Ho³⁺ energy levels. Our studies show that the material is highly suitable for temperature sensing below room temperature. The maximum relative sensor sensitivity using the rise time of Ho³⁺ energy level (⁵F₄/⁵S₂) is 1.35% K⁻¹, which is the highest among the known sensitivities for luminescence based thermal probes.

Probing a new approach for warm white light generation in lanthanide doped nanophosphors

Warm white light generation through modification of CCT by incorporation of the defect level induced emission of ZnO in Y_1.993Dy_0.001Tm_0.006O₃ nano-phosphors.

Upconverting/magnetic: Gd2O3:(Er3+,Yb3+,Zn2+) nanoparticles for biological applications: effect of Zn2+ doping

Upconverting/paramagnetic Gd₂O₃:1% Er³⁺, 18% Yb³⁺ with Zn²⁺ nanoparticles (NPs) permits one to perform optical imaging.

Improved luminescence and temperature sensing performance of Ho(3+)-Yb(3+)-Zn(2+):Y2O3 phosphor

The codoping effect of Zn(2+) ions on luminescence emission in visible and near infrared (NIR) regions of Y2O3:Ho(3+)-Yb(3+) phosphor prepared by low temperature combustion process have been investigated under 980 nm and 448 nm excitations. The phase and crystallite size of the prepared phosphor were determined by X-ray diffraction analysis and processes involved in the upconversion mechanism have been discussed in detail via pump power dependence, decay curve analysis and a suitable energy level diagram. The temperature sensing performance of the developed material has also been investigated by measuring the fluorescence intensity ratio of the blue upconversion emission bands centred at 465 nm and 491 nm up to 673 K. It is found that by using fluorescence intensity ratio technique, appreciable sensitivity for temperature measurement can be achieved from the present phosphor material, which indicates its applicability as a high temperature sensing probe. The fabrication of green LEDs using the developed phosphor material has also been suggested.