Effect of processing parameters on structural, morphological and optical Y2O3:Yb3+/Ho3+ powders characteristics

Color-tunable luminescence based on the efficient energy transfer of a Tm-Dy system for optical thermometry and white LED lighting

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10-3 K-1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields.

The effect of ion radius on luminescence for alkali ions doping in Y2O3: Yb3+/Ho3+ thin film

In this paper, alkali ion (Li⁺ Na⁺ K⁺ and Rb⁺)-doped Y₂O₃:Yb³⁺/Ho³⁺ up conversion films were prepared using the sol-gel method. The structures of the films were studied by using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. A series of high-quality thin films with good crystallization were prepared. For all samples, two emission bands were observed: green emission at 539 (550) nm and red emission at 664 nm, which can be attributed to ⁵F₄ (⁵S₂)→⁵I₇ and ⁵F₅→⁵I₈, respectively. The green emission is dominant, and the red emission is extremely weak. The effect of each alkali-ion dopant on the emission and color adjustment of samples was investigated. The green emission intensity is increased by a factor of 6.33 (Li), 2.03 (Na), 4.82 (K) and 1.92 (Rb) with increasing alkali-ion doping concentration, and red emission is increased by a factor of 7.80 (Li), 1.92 (Na), 4.78 (K) and 1.90 (Rb). The extreme value appears earlier with increasing ion radius. Li⁺ doping boosts luminescence in three ways, and the other alkali ions affect the light emission in two ways. Li⁺ doping and K⁺ doping can be used to adjust the color coordinates towards the 539 nm and 550 nm directions, respectively. Na⁺ and Rb⁺ doping can enhance emission with a stable color. This means that each alkali ion is a suitable choice as a color-regulating ion and can play a role in the regulation of luminescence.

Temperature dependence of up-conversion luminescence and sensing properties of LaNbO4: Nd3+/Yb3+/Ho3+ phosphor under 808 nm excitation

LaNbO₄: Nd³⁺/Yb³⁺/Ho³⁺ phosphor was prepared by a conventional high temperature solid-state reaction method. The temperature dependence of up-conversion (UC) luminescence property of LaNbO₄: Nd³⁺/Yb³⁺/Ho³⁺ phosphor under 808 nm excitation and the potential application of exploiting the red-to-green UC emission intensity ratio (I_R/I_G) of Ho³⁺ in temperature sensing were studied. Two-photon processes were confirmed to be responsible for both the green and the red UC emissions at different temperatures by analyzing the excitation power density dependent UC luminescence spectra measured at different temperatures. The energy level diagram was drawn to analyze the UC luminescence mechanism of Ho³⁺. In addition, it was found that the ratio I_R/I_G of Ho³⁺ was independent of the excitation power density of 808 nm laser under the current experimental condition, but it was sensitive to the temperature. And the temperature dependent UC luminescence spectra displayed that the ratio I_R/I_G exhibited a good linear increasing tendency with temperature rising. The obtained temperature sensing sensitivity was 2.04 × 10^-3 K^-1 in the temperature range of 303-693 K. The results suggest that LaNbO₄: Nd³⁺/Yb³⁺/Ho³⁺ phosphor may be a good candidate for application in optical temperature sensors.