[Paper Review] Multi-wavelength UV Upconversion in Lanthanides assisted by Photonic Crystals

Damien Rinnert, Drouard, Emmanuel+7 more|arXiv (Cornell University)|Jan 23, 2026

Luminescence Properties of Advanced Materials0 citations

TL;DR

The paper demonstrates 28-fold enhancement of UV upconversion from Yb3+-Tm3+ co-doped Y2O3 thin films using photonic crystal slabs that couple multi-wavelength (NIR and visible) excitation to UV emission via slow-light Bloch modes and enhanced ESA.

ABSTRACT

Upconversion luminescence consists of the absorption of low-energies photons followed by the emission of a higher energy photon. The process has mainly been studied in lanthanides to upconvert monochromatic near-infrared excitation to near-infrared or visible light, and has been exploited only to a limited extent to upconvert broad excitations to ultra-violet. In addition, upconverting near-infrared and visible light to ultra-violet is crucial for applications such as solar-to-fuel conversion or environmental remediation. However, upconversion luminescence is limited by the low absorption cross-sections of lanthanides. In this work, we engineered Bloch modes in a photonic crystal to assist a multi-wavelength upconversion mechanism and demonstrated a 28-fold enhancement of ultra-violet upconversion luminescence of Yb3+-Tm3+ doped thin films. Materials were selected and optimized to design nanostructures without parasitic absorption losses. The geometric parameters of the photonic crystals were scanned to match a slow-light resonance with an excited-state transition of Tm3+ and thus enhance incident visible light absorption. Ultra-violet light extraction was also enhanced by photonic crystal Bloch modes. Each of these two contributions were quantified and the measured photonic band structures were well reproduced by electromagnetic simulations.

Motivation & Objective

• Investigate multi-wavelength upconversion from NIR and visible excitation to UV in lanthanide-doped thin films.
• Engineer photonic crystal Bloch modes to enhance absorption and extraction without parasitic losses.
• Quantify the contributions of visible absorption and UV extraction to overall UV UCL enhancement.
• Demonstrate tunability of Bloch modes to align with specific lanthanide transitions.
• Validate experimental results with electromagnetic simulations and band-structure measurements.

Proposed method

• Fabricate a Y2O3:Yb3+,Tm3+ thin film on fused silica via pulsed laser deposition.
• Deposit a 144 nm SiNx top layer to form a square-lattice photonic crystal with p in the 240–280 nm range.
• Use RCWA to design PhC parameters that couple a slow-light Γ-point resonance to the 3F4→1D2 ESA in Tm3+.
• Pattern 22 PhC areas with lattice parameters around 259–267 nm and measure UV UCL under 995 nm NIR and 447 nm visible excitation.
• Characterize band structures and reflectance to identify TE0/TM0 slow-light resonances and their overlap with the Tm3+ absorption spectrum.
• Quantify enhancement factors (EF) by comparing to unpatterned references and extract contributions from visible absorption and UV extraction.

Figure 1: Multi-wavelength UV UCL mechanism in Yb 3+ -Tm 3+ . It involves 1 NIR photon absorption by Yb 3+ ( 7 F 7/2 $\rightarrow$ 7 F 5/2 ), whose energy is transferred to Tm 3+ ( 3 F 4 ), followed by 1 visible excited state absorption in Tm 3+ ( 3 F 4 $\rightarrow$ 1 D 2 ). UV emission is obtained

Experimental results

Research questions

• RQ1 Can multi-wavelength excitation (NIR + visible) enhance UV upconversion in Yb3+/Tm3+ co-doped systems?
• RQ2 Do photonic crystal Bloch modes at both excitation and emission wavelengths enhance UCL without parasitic losses?
• RQ3 What is the relative contribution of visible absorption versus UV extraction to the overall UV upconversion enhancement?
• RQ4 How does lattice parameter tuning affect slow-light resonances and the overlap with the Tm3+ 3F4→1D2 transition?
• RQ5 Is the observed enhancement consistent with a multi-photon power-law mechanism (nNIR = nvis = 1) for UV emission?

Key findings

• Achieved up to 28.1 ± 3.0 times higher UV emission than reference under NIR+visible excitation.
• Visible slow-light resonances enhance the ESA process by a factor of 10.4 ± 2.2, boosting UV upconversion.
• UV light extraction is enhanced by Bloch modes, contributing a factor of 2.71 ± 0.5.
• Measured UV upconversion follows a power law with nNIR = nvis = 1, confirming the multi-wavelength mechanism.
• Band-structure measurements align with RCWA simulations, validating the designed slow-light Bloch modes at the Γ-point.
• PhC design enables significant UV UCL enhancement while minimizing parasitic absorption.

Figure 2: Presentation of the PhC structure. (a) 3D scheme of the PhC design and operational principle: NIR and visible light absorption close to normal incidence and UV emission in a controlled direction. (b) SEM top view image of a fabricated PhC with the following parameters: period p = 267.3 $\p